Marine propulsion unit

Abstract

A marine propulsion unit (1000, 2000) with a motor air cooling system and a contra rotating electric motor (1) having an inner rotor (2) and an outer rotor (3), wherein the contra rotating motor comprises a perforated tube (4) with a plurality of radial openings (104, 105), the perforated tube being configured to transmit a torque of the outer rotor to a propeller unit and to support an outer rotor winding; the motor air cooling system comprises at least one ingoing air channel (31, 32) and at least one outgoing air channel (33); and the at least one ingoing air channel is connected to the at least one outgoing air channel via at least some of the plurality of radial openings of the perforated tube (FIG. 1)

Description

MARINE PROPULSION UNITTECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to a marine propulsion unit. Further embodiments relate to a method of cooling a contra rotating motor of a marine propulsion unit. Further embodiments relate to a method of maintaining a marine propulsion unit. Further embodiments relate to a method of maintaining a marine propulsion unit. Further embodiments relate to a bearing arrangement of a marine propulsion unit, and a bearing arrangement in a marine propulsion unit. Further embodiments relate to a method of supporting shafts in a marine propulsion unit. Further embodiments relate to a shaft design of the marine propulsion unit. Furthermore, the disclosure relates to methods for the assembly of the shafts of the marine propulsion unit. Embodiments of the present disclosure relate to a marine propulsion unit. Further embodiments relate to a marine vessel. Further embodiments relate to a method of installing a marine propulsion unit.BACKGROUND

[0002] To propel marine vessels, marine propulsion units with a high efficiency and maneuverability are desired. Different concepts for marine propulsion units are available, which typically prioritize specific operating properties of the marine propulsion system. Azimuthing propulsion units may generally provide marine propulsion units with a high efficiency and maneuverability. In azimuthing propulsion units, at least one marine propeller attached to a rotatable pod provides thrust. A direction of the thrust may be controlled via a rotation of the rotatable pod. In typical azimuthing propulsion units, at least one electric motor driving the at least one marine propeller is integrated in the pod. In some marine vessels, a shaft-line configuration of propulsion units may be preferred. In particular, the thrust may be provided by a motor arranged within the hull of the marine vessel and a propeller connected to the motor via a shaft-line.

[0003] For an efficient marine propulsion unit, contra rotating propellers may be employed. For driving a contra rotating propeller, a contra rotating electric motor can be suitable. However, reliable and efficient cooling systems for the contra rotating motor are required.

[0004] Marine propulsion units provide an efficient way to propel marine vessels. Different concepts for marine propulsion units are available, which typically prioritise specific operating properties of the marine propulsion system. In particular, azimuthing propulsion units provide anefficient manner to propel marine vessels. Further, azimuthing propulsion units allow for an improved maneuverability of marine vessels. In azimuthing propulsion units, at least one marine propeller attached to a rotatable pod provides thrust. A direction of the thrust may be controlled via a rotation of the rotatable pod. In typical azimuthing propulsion units, at least one electric motor driving the at least one marine propeller is integrated in the pod. In some marine vessels, a shaft-line configuration of propulsion units may be preferred. In particular, the thrust may be provided by a motor arranged within the hull of the marine vessel and a propeller connected to the motor via a shaft-line.

[0005] Maintaining marine propulsion units, particularly azimuthing propulsion units, commonly requires dry-docking, which is a time-consuming process. Thus, dry-docking a marine vessel to maintain the marine propulsion units requires for the marine vessel to be taken out of service in order for maintenance procedures, routine or not, to be undertaken. Therefore, marine propulsion units, particularly azimuthing propulsion units, that provide a high efficiency, durability and maintainability, in particular in view of the restricted amount of space available within a hull of the marine propulsion unit or the pod, are desired. Marine propulsion units, such as azimuthing propulsion units, with reduced maintenance efforts are desired.

[0006] Marine propulsion units provide an efficient way to propel marine vessels. Different concepts for marine propulsion units are available, which typically prioritise specific operating properties of the marine propulsion system. In particular, azimuthing propulsion units provide an efficient manner to propel marine vessels. Further, azimuthing propulsion units allow for an improved maneuverability of marine vessels. In azimuthing propulsion units, at least one marine propeller attached to a rotatable pod provides thrust. A direction of the thrust may be controlled via a rotation of the rotatable pod. In typical azimuthing propulsion units, at least one electric motor driving the at least one marine propeller is integrated in the pod. In some marine vessels, a shaft-line configuration of propulsion units may be preferred. In particular, the thrust may be provided by a motor arranged within the hull of the marine vessel and a propeller connected to the motor via a shaft-line.

[0007] Maintaining marine propulsion units, particularly azimuthing propulsion units, commonly requires dry-docking, which is a time-consuming process. Thus, dry-docking a marine vessel to maintain the marine propulsion units requires for the marine vessel to be taken out of service in order for maintenance procedures, routine or not, to be undertaken. Therefore, marine propulsion units, particularly azimuthing propulsion unit that provide a high efficiency, durability andmaintainability, in particular in view of the restricted amount of space available within the hull of the marine propulsion unit or the pod, are desired. Marine propulsion units such azimuthing propulsion units with reduced maintenance efforts are desired.

[0008] To propel marine vessels, marine propulsion units with a high efficiency and maneuverability are desired. Azimuthing propulsion units may generally provide marine propulsion units with a high efficiency and maneuverability. In azimuthing propulsion units, at least one marine propeller attached to a rotatable pod provides thrust. A direction of the thrust may be controlled via a rotation of the rotatable pod. In typical azimuthing propulsion units, at least one electric motor driving the at least one marine propeller is integrated in the pod. In some marine vessels, a shaft-line configuration of propulsion units may be preferred. In particular, the thrust may be provided by a motor arranged within the hull of the marine vessel and a propeller connected to the motor via a shaft-line.

[0009] For an efficient marine propulsion unit, contra rotating propellers may be employed. For driving a contra rotating propeller, a contra rotating electric motor or a motor and a gearbox can be suitable. This principle enables a high level of efficiency of the propulsion. To realize this principle more than one shaft is required to drive the contra rotating propeller. The layout and the construction of the shafts within the marine propulsion unit needs to fulfill several requirements. In some embodiments the shafts may at least partially run inside of each other. In some embodiments the shafts need to be supported by bearing units requiring a certain contact layout. In some embodiments, components must be mounted onto the shafts, for instance to ensure the power supply or seal at least parts of the unit.

[0010] Further embodiments of the present disclosure relate to a sealing unit for a marine propulsion unit, particularly for an azimuthing propulsion unit. Further embodiments relate to a method for servicing a sealing unit in a marine propulsion unit, particularly in an azimuthing propulsion unit.

[0011] For an efficient marine propulsion unit, contra rotating propellers may be employed. For driving a contra rotating propeller, a contra rotating electric motor can be suitable. An efficient, durable and maintainable sealing unit to seal an outside of the marine vessel, particularly the pod, from an inside of the marine vessel, particularly the pod, can be required. Embodiments of the present disclosure relate to such sealing units. Typically, embodiments of the present disclosure can fluidly connect an inner shaft sealing and an outer shaft sealing. Particularly, fluid can betransferred between the inner shaft sealing inside the outer shaft and the outer shaft sealing outside the outer shaft. To propel marine vessels, marine propulsion units with a high efficiency and good maintainability are desired. Particularly, for marine propulsion units, an adaptability to different marine vessels is desirable. To propel marine vessels, marine propulsion units with a high efficiency, good maintainability and a small footprint are desired. Further, improved methods for installing marine propulsion units in a marine vessel are desired.DISCLOSURE OF THE INVENTION

[0012] In the view of the foregoing, the present disclosure is directed to a marine propulsion unit and a method of cooling a contra rotating motor of a marine propulsion unit.

[0013] According to an aspect of the present disclosure, a marine propulsion unit with a motor air cooling system and a contra rotating motor having an inner rotor and an outer rotor is provided. The contra rotating motor comprises a perforated tube with a plurality of radial openings, the perforated tube being configured to transmit a torque of the outer rotor to a propeller unit and to support an outer rotor winding. The motor air cooling system comprises at least one ingoing air channel and at least one outgoing air channel. The ingoing air channel is connected to the outgoing air channel via at least some of the plurality of radial openings of the perforated tube.

[0014] According to another aspect of the present disclosure, the marine propulsion unit according to any of the embodiments described herein is an azimuthing propulsion unit.

[0015] According to another aspect of the present disclosure, a marine vessel comprising a marine propulsion unit according to any of the embodiments described herein is provided.

[0016] According to another aspect of the present disclosure, a method of cooling a contra rotating motor with an outer rotor and an inner rotor of a marine propulsion unit is provided. The contra rotating motor comprises a perforated tube configured to transmit a torque of the outer rotor to a propeller unit and configured to support an outer rotor winding. The method comprises providing cooling air to the contra rotating motor and drawing the cooling air from the contra rotating motor via the perforated tube.

[0017] According to some embodiments, the marine propulsion unit is configured to propel a marine vessel. In some embodiments, the marine propulsion unit comprises an azimuthingpropulsion unit. In some embodiments, the marine propulsion unit may comprise a shaft-line marine propulsion unit. In particular, the marine vessel may comprise at least one marine propulsion unit according to embodiments described herein. The marine vessel as described herein comprises seagoing or inland marine vessels. In particular, the marine vessel comprises ships and boats. In some embodiments, the marine vessel comprises merchant ships, in particular for transporting goods. In particular, the marine vessel may comprise a container vessel, a Ro-Ro or car carrier, a tanker or shuttle tanker, a liquid natural gas (LNG) carrier or a floating storage and regasification unit. In some embodiments, the marine vessel comprises ferries, in particular single-and double-ended ferries, cruise ships, water buses, yachts. In some embodiments, the marine vessel comprises offshore energy vessels, in particular service operation vessels (SOVs), cable laying vessels (CLVs), foundation installation vessels (FIVs), offshore construction (OCVs) and support vessels (OSVs), platform supply vessels (PSVs), and anchor-handling tug supply vessels (AHTS). In some embodiments, the marine vessel comprises research and survey vessels or other special purpose vessels, such as dredgers, heavy lift vessels or towboats. In some embodiments, the marine vessel comprises ice-going marine vessels, in particular icebreakers or marine vessels having an ice-class assigned by a classification society. In some embodiments, the marine vessel may comprise navy or coast guard vessels. In some embodiments, the marine vessel may comprise submarine vessels or unmanned remotely operated underwater vehicles (ROVs).

[0018] The marine vessel typically comprises a hull. In some embodiments, a pod of the marine propulsion unit, and particularly of the azimuthing propulsion unit, is attached to the hull of the marine vessel, in particular at the bottom of the hull. Typically, the hull defines a vessel interior and a vessel exterior. Space confined by the hull and configured to be isolated from sea water may be defined as the vessel interior. Space outside the hull, and in particular the sea, may be defined as the vessel exterior. Typically, the vessel interior is substantially free of sea water and substantially dry.

[0019] In some embodiments, the marine vessel may comprise a plurality of marine propulsion units. In particular, the marine vessel may comprise 2, 3, 4, or more marine propulsion units. Typically, each of the plurality of marine propulsion units may be controlled separately. In some embodiments, the marine vessel may comprise a single azimuthing propulsion unit with a single pod. In some embodiments, at least one azimuthing propulsion unit may be combined with one or more further marine propulsion unit on a single marine vessel. In other words, an azimuthing propulsion unit according to embodiments described herein may be combined with one or morenon-azimuthing marine propulsion units. The one or more non-azimuthing marine propulsion units may be built according to embodiments described herein.

[0020] Typically, the marine propulsion unit comprises a propeller unit. Typically, the marine propulsion unit, and particularly the azimuthing propulsion unit, comprises a pod with a pod hull. The pod is configured to be rotatably attached to the hull of the marine vessel, particularly at the bottom of the hull of the marine vessel. The pod may be rotated about a substantially vertical rotation axis of the marine propulsion unit. In particular, the pod may be rotated by at least 270°, at least 315° or at least 360° about the substantially vertical rotation axis of the azimuthing propulsion unit. In typical embodiments, the rotation of the pod about the substantially vertical rotation axis of the azimuthing propulsion unit is not restricted, in particular not mechanically restricted.

[0021] Typically, the pod comprises a hull cap at a first end of the pod and the propeller unit, in particular a pushing or pulling propeller unit, attached to a second end of the pod. The first end of the pod may also be described as non-driving end, NDE, and the second end of the pod may also be described as driving end, DE, of the pod. The propeller unit typically rotates about a rotation axis of the propeller unit. The rotation axis of the propeller unit may be substantially perpendicular to the vertical rotation axis of the azimuthing propulsion unit.

[0022] In some embodiments, the marine propulsion unit comprises at least one shaft-line marine propulsion unit. Typically, in the shaft-line marine propulsion unit, the electric motor, particularly the contra-rotating electric motor, is arranged within the hull of the marine vessel. The electric motor is connected to the propeller unit via a shaft-line. The propeller unit is typically arranged at a stern of the marine vessel. Particularly, the propeller unit is typically arranged at a skeg of the marine vessel. Typically, for a shaft-line marine propulsion unit, a stem-facing side of the marine propulsion unit may be described as driving end, DE, side of the marine propulsion unit. Typically, for a shaft-line marine propulsion unit, a vessel-center facing side of the marine propulsion unit may be described as non-driving end, NDE, side of the marine propulsion unit.

[0023] In typical embodiments, the propeller unit comprises an outer shaft propeller and an inner shaft propeller. Typically, the outer shaft propeller is arranged closer to the hull than the inner shaft propeller. In a pushing propeller unit, the outer shaft propeller may also be described as front propeller and the inner shaft propeller may be described as the rear propeller; and vice versa for a pulling propeller unit. In particular, for the azimuthing propulsion unit, the outer shaft propeller isarranged closer to the vertical rotation axis than the inner shaft propeller. Typically, the outer shaft propeller and the inner shaft propeller are arranged adjacent to each other. The outer shaft propeller and the inner shaft propeller rotate about the rotation axis of the propeller unit.

[0024] Typically, the propeller unit comprises a contra rotating propeller unit. In particular, the outer shaft propeller may be configured to rotate in a first direction, particularly about the rotation axis of the propeller unit, and the inner shaft propeller may be configured to rotate in a second direction opposite to the first direction, particularly about the rotation axis of the propeller unit. In other words, the outer shaft propeller may rotate clockwise and the inner shaft propeller may rotate counterclockwise, or vice versa, about the same rotation axis. In some embodiments, the outer shaft propeller and the inner shaft propeller of the contra rotating propeller unit are arranged adjacent to each other. In some embodiments, the outer shaft propeller and the inner shaft propeller of the contra rotating propeller unit are arranged at opposite ends of the marine propulsion unit or of a pod in which the marine propulsion unit is arranged. In other words, the contra rotating propeller unit may be arranged in a push-pull-configuration. A contra rotating propeller unit may advantageously allow for a higher hydrodynamic efficiency than other propeller concepts, in particular with respect to single propellers.

[0025] In some embodiments, the outer shaft propeller has a first diameter and the inner shaft propeller has a second diameter with the second diameter being different from the first diameter, particularly the first diameter being larger than the second diameter. Typically, the outer shaft propeller comprises a first number of first blades and the inner shaft propeller comprises a second number of second blades. Typically, the second number may be different from the first number. The outer shaft propeller may comprise 3, 4, 5, 6 or 8 first blades. The inner shaft propeller may comprise 3, 4, 5, 6 or 8 second blades. In some embodiments, the outer shaft propeller comprises one more first blade than the inner shaft propeller comprises second blades. Exemplarily, the outer shaft propeller comprises 6 first blades and the inner shaft propeller comprises 5 second blades. In some embodiments, the outer shaft propeller and the inner shaft propeller may comprise the same number of blades, in particular 3, 4, 5, 6 or 8 first and second blades, respectively. The outer shaft propeller and / or the inner shaft propeller may each be manufactured as a monoblock or in components, as a built-up propeller.

[0026] Typically, the propeller unit is driven by an electric motor. Typically, the electric motor has a power of at least 100 kW, at least 1 MW, at least 2 MW, at least 5 MW, at least 10 MW or at least 15 MW. The electric motor is typically arranged within the pod or within the hull of themarine vessel. Particularly, the electric motor is mechanically connected to the propeller gearlessly and / or without a clutch. Typically, a rotation axis of the electric motor is identical to a rotation axis of the propeller unit. In particular, an output shaft of the electric motor may be identical to the drive shaft of the propeller unit or may be gearlessly connected to a drive shaft of the propeller unit. The output shaft of the electric motor typically is coaxial to the drive shaft of the propeller unit. In typical embodiments, for a propeller unit comprising an outer shaft propeller and an inner shaft propeller, in particular for the contra rotating propeller unit, the outer shaft propeller and the inner shaft propeller may be driven by the same electric motor.

[0027] The electric motor typically comprises a contra rotating electric motor. In particular, the contra rotating electric motor comprises a dual rotor electric motor with an outer rotor and an inner rotor configured to rotate in opposite directions about a rotation axis of the electric motor. Typically, the rotation axis of the electric motor may be coaxially with the rotation axis of the propeller unit. Typically, the electric motor is a synchronous electric motor. Typically, the outer rotor comprises windings to be supplied with an electric current for the operation of the electric motor. The inner rotor may be a permanent magnet rotor or an externally excited synchronous rotor.

[0028] In some embodiments, the drive shaft of the propeller comprises an outer shaft and an inner shaft. Outer shaft and inner shaft are typically coaxially arranged. Typically, the outer rotor drives the outer shaft. The outer shaft is typically mechanically connected to the outer shaft propeller gearlessly. In some embodiments, the outer shaft and / or the inner shaft may comprise at least one shaft coupling. In particular, the outer shaft and / or the inner shaft comprising at least one shaft coupling advantageously allows to modularly adapt the marine propulsion unit to the marine vessel. Exemplarily a length of the shaft may be adapted dependent on a size of the marine vessel. Typically, the inner rotor drives the inner shaft. The inner shaft is typically mechanically connected to the inner shaft propeller gearlessly. Typically, the inner shaft is arranged inside the outer shaft; in other words, an inside radius of the outer shaft exceeds an outside radius of the inner shaft. The inner shaft and the outer shaft rotate about the same rotation axis, and in particular about the rotation axis of the electric motor.

[0029] Typically, the inner shaft is supported by a drive end, DE, inner bearing and a non-drive end, NDE, inner bearing. Typically, the outer shaft is supported by a drive end, DE, outer bearing and a non-drive end, NDE, outer bearing. For a push-pull-configuration, no non-drive end is present. Thus, in the push-pull-configuration a first bearing may be considered as a drive endbearing and a second bearing may be considered as non-drive end bearing. In other words, the terms non-drive end and drive end merely act to distinguish bearings by their bearing location. The NDE inner bearing and / or the NDE outer bearing may each comprise an axial bearing and a radial bearing, particularly within the same bearing housing. Employing a contra rotating electric motor may advantageously allow to drive the contra rotating propeller with a single electric motor gearlessly. Thereby, a more compact and efficient drive train may be provided.

[0030] In some embodiments, the marine propulsion unit, and particularly the contra-rotating motor, the drive shaft and the propeller unit, may form a single propulsion unit. Exemplarily, the single propulsion unit may be mounted into the pod or into the vessel hull as a single propulsion unit. In some embodiments, the drive shaft, the contra-rotating motor, the DE bearing and the NDE bearing, and a slip ring unit may be arranged within a frame structure, in other words arranged within a capsule structure. The capsule structure may advantageously allow to mount at least part of the marine propulsion unit as a single unit into the pod or the vessel hull. The capsule structure may advantageously reduce an assembly effort and / or assembly time during the building process of the marine vessel. Typically, the marine propulsion unit is connected to the vessel hull via the capsule structure. In some embodiments, the marine propulsion unit is connected to the pod via the capsule structure. Particularly, the capsule structure is configured to transmit at least 75% or at least 90% of a propulsion force of the marine propulsion unit to the marine vessel.

[0031] In some embodiments, the marine propulsion unit comprises a motor air cooling system, particularly for cooling the contra rotating motor. The motor air cooling system typically comprises at least one ingoing air channel and at least one outgoing air channel. In some embodiments, the motor air cooling system comprises one ingoing air channel or two ingoing air channels. In some embodiments, the number of ingoing air channels may be different from the number of outgoing air channels, and particularly the number of outgoing air channels may exceed the number of ingoing air channels. Typically, an ingoing air channel may be defined as an air channel through which the air of the motor cooling system passes prior to interacting with the motor, in particular prior to cooling the motor. Typically, an outgoing air channel may be defined as an air channel through which the air of the motor cooling system passes subsequent to interacting with the motor, in particular subsequent to cooling the motor. However, in some embodiments, a direction of the air flow may be reversible. Particularly, an air channel may be both an ingoing air channel and an outgoing air channel, depending on an operation of the motor air cooling system.

[0032] Typically, the contra rotating motor comprises a perforated tube. The perforated tube may substantially have a cylinder shape, particularly with a cage-like structure. In other words, the perforated tube may be described as a cage-like structure being configured to transmit a torque of the outer rotor to the propeller unit and to support the outer rotor winding. In some embodiments, the perforated tube may, at least in part, form an outer contour of the contra rotating motor. The perforated tube is configured to transmit a torque of the outer rotor to the propeller unit. The perforated tube supports an outer rotor winding of the outer rotor. Particularly, the outer rotor winding is connected to the perforated tube. In some embodiments, the outer rotor comprises a plurality of axial beams between a core of the outer rotor winding and the perforated tube. In particular, the outer rotor may comprise at least 3, at least 6, at least 12, or at least 24 axial beams. Typically, the axial beams are arranged parallel to an axis, particularly the rotating axis, of the perforated tube. Typically, the plurality of axial beams is arranged substantially parallel with respect to each other. The plurality of axial beams is typically configured to transmit a torque from the outer rotor core, which particularly accommodates the windings, to the perforated tube. The plurality of axial beams are configured to allow air to flow from an interior of the motor, particularly via radial slots in a core of the outer rotor winding of the outer rotor, towards the perforated tube, and particularly towards the radial openings in the perforated tube. The core of the outer rotor winding typically is a steel core.

[0033] The perforated tube typically comprises a plurality of radial openings. Exemplarily, the perforated tube may comprise at least 6, at least 12, at least 24, at least 50, at least 72, at least 100, or at least 200 radial openings. Typically, the plurality of radial openings are substantially quadratically with rounded corners. In some embodiments, the plurality of radial openings are substantially oval, and particularly round, or substantially triangular. Oval or triangular openings may advantageously alter the strength of the perorated tube. In some embodiments, the plurality of radial openings is arranged substantially symmetrical, particularly with respect to at least one axis of the perforated tube. In some embodiments, the plurality of radial openings may be arranged according to a pattern, particularly according to a quadratical or a triangular pattern. The plurality of radial openings may be arranged substantially rotational symmetrically about the rotational axis of the perforated tube. Rotational symmetry may particularly comprise a n-fold rotational symmetry with n being any natural number exceeding 1, and particularly exceeding 2. The plurality of radial openings may be arranged substantially mirror symmetrically, particularly with respect to a plane perpendicular to the rotational axis of the perforated tube.

[0034] In typical embodiments, the plurality of radial openings cover at least 10%, at least 20%, at least 25%, at least 35%, at least 50%, at least 70%, or at least 80% of a side surface of the perforated tube. Typically, the plurality of radial openings cover at most 90% of a side surface of the perforated tube. In particular, the plurality of radial openings cover at least 25% and at most 90 % of as side surface of the perforated tube. In some embodiments, the side surface of the perforated tube may comprise the area of the perforated tube in which the radial openings are arranged.

[0035] In some embodiments, the perforated tube, particularly when implemented as a cage-like structure, may be formed by axial beams or threaded bars, particularly by a plurality of axial beams or of threaded bars configured to transmit loads of the electric motor. The plurality of axial beams or of threaded bars may be arranged as extending through the outer rotor winding and may be configured to mechanically support the outer rotor winding. Typically, the plurality of axial beams or of threaded bars may be supported by rings in a radial direction, particularly to improve a stiffness of the perforated tube or cage-like structure. Typically, the plurality of axial beams or of threaded bars forms an outer contour generally resembling a perforated tube or a cage.

[0036] In typical embodiments, the plurality of openings is equally spaced with respect to each other in at least one dimension and particularly with respect to two dimensions. Exemplarily, the plurality of openings is equally spaced with respect to a radial and / or an axial dimension. In some embodiments, the plurality of openings may be equally spaced in a first direction and may be arranged with a decreasing distance in a second dimension, in particular towards the center of the perforated tube. The plurality of openings may be considered as equally spaced when neighboring openings have the same distance from each other in at least one dimension. A spacing of the plurality of openings may be advantageously adapted to a heat generation distribution of the electric motor and / or to an air flow within the electric motor. Particularly, the spacing of the plurality of openings may be adapted to ensure a substantially homogeneous cooling effect in the electric motor and / or to avoid hot spots.

[0037] The ingoing air channel is connected to the outgoing air channel via the perforated tube. Particularly, the ingoing air channel is connected to the outgoing air channel via at least some of the plurality of radial openings of the perforated tube. Typically, the plurality of radial openings comprises first openings connected to the at least one ingoing air channel and comprises second openings connected to the at least one outgoing air channel. The motor air cooling system is arranged such that at least part of the air from the at least one ingoing air channel enters the contrarotating motor via the first openings and exits the contra rotating motor via the second openings. Typically, the at least one outgoing air channel is connected to at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the plurality of radial openings. In other words, at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the plurality of radial openings are second openings. Particularly, air passing through the motor and exiting the motor may exit the perforated tube through at least 50%, at least 60%, at least 70%, at least 80% or at least 90% of the plurality of radial openings.

[0038] Typically, the at least one ingoing air channel is connected to at least 2%, at least 5%, at least 10%, at least 20% or at least 40% of the plurality of radial openings. In other words, at least 2%, at least 5%, at least 10%, at least 20% or at least 40% of the plurality of radial openings are first openings. The at least one ingoing air channel is typically connected to at most 50% or at most 60% of the plurality of radial openings. In other words, at most 50% or at most 60% of the plurality of radial openings are first openings. Particularly, air provided by the motor air cooling system and entering the motor may enter the motor via the perforated tube through at least 2%, at least 5% or at least 10%, at least 20% or at least 40% and / or at most 50% or at most 60% of the plurality of radial openings.

[0039] In typical embodiments, each of the plurality of radial openings is connected to either the at least one ingoing air channel or the at least one outgoing air channel. In other words, for each of the plurality of radial openings, cooling air provided by the motor air cooling system either enters the electric motor via the radial opening or exits the electric motor via the radial opening. Typically, each of the plurality of radial openings either is a first opening or a second opening.

[0040] Typically, the first openings and the second openings are separated by at least one air slot separating wall between the air slots and the perforated tube. The at least one air slot separating wall is configured to ensure that air entering via the first openings passes through the outer rotor, and particularly through the radial air slots in the outer rotor core, prior to exiting the outer rotor via the second openings. The at least one air slot separating wall is substantially perpendicular to the rotation axis of the perforated tube.

[0041] Typically, the motor propulsion unit comprises an outer rotor air sealing for sealing a gap between the outer rotor, which rotates in operation, and a stationary part, exemplarily a motor housing. The outer rotor air sealing may advantageously prevent air passing from the ingoing air channel to the outgoing air channel without passing the outer rotor. Particularly, the outer rotor airsealing may reduce an air fan power required to cool the motor. The outer rotor air sealing typically comprises a small gap, a labyrinth seal or a soft seal.

[0042] Typically, the outer rotor is connected to the outer shaft via at least one outer rotor end flange. The at least one outer rotor end flange typically comprises at least one flange opening. Particularly, the at least one outer rotor end flange comprises a plurality of flange openings, exemplarily at least 3 flange openings, at least 5 flange openings or at least 8 flange openings. Typically, the plurality of flange openings are arranged symmetrically, particularly according to an n-fold rotational symmetry with n being a natural number exceeding 1 or 2. The at least one flange opening typically extends substantially parallel to the rotational axis of the perforated tube. Typically, at least some of the at least one flange opening, particularly all of the at least one flange opening, are connected to the at least one ingoing air channel. Typically, at least part of the air entering the motor enters the motor through the at least one flange opening. Particularly, at least 2%, at least 5%, at least 10% or at least 20% of the air entering the motor enters the motor through the at least one flange opening.

[0043] Typically, the outer rotor is connected on both axial ends to the outer shaft via an outer rotor end flange. Particularly, the outer rotor is connected to the drive end (DE) outer shaft via a DE outer rotor end flange and is connected to the non-drive end (NDE) outer shaft via the NDE outer rotor end flange. In typical embodiments, the NDE outer rotor end flange and the DE outer rotor end flange both comprise at least one flange opening and are both connected to at least one ingoing air channel. Typically, an amount of air flowing into the motor via the at least one flange opening of the NDE outer rotor end flange and via the at least one flange opening of the DE outer rotor end flange varies by at most 5%, at most 10% or at most 20%. A similar air flow through the outer rotor end flange on both axial ends of the outer rotor may advantageously enable a homogenous air flow through the motor and a homogenous cooling of the motor.

[0044] In typical embodiments, a majority of the air passing through the at least one ingoing air channel enters the outgoing air channel via the perforated tube. In some embodiments, a part of the air passing thought the at least one ingoing air channel may be configured to cool other elements of the marine propulsion unit, exemplarily a slip ring unit. Typically, the air passing through the at least one ingoing air channel may be divided prior to reaching parts of the marine propulsion unit to be cooled. Exemplarily, the air passing through the at least one ingoing air channel may be divided prior to reaching the motor and the slip ring unit. In some embodiments, different parts of the motor air cooling system may be separated by one or more filters, in particularto reduce or to avoid contamination of different parts of the marine propulsion unit by the air passing through the motor air cooling system. In some embodiments, different parts of the motor air cooling system may be cooled subsequently. In other words, after cooling a first part of the marine propulsion unit, air is used to cool a second part of the marine propulsion unit, particularly prior to reaching an air cooling stage, such as a heat exchanger.

[0045] Typically, at least 80%, at least 90%, at least 95% or at least 99% of air passing through the at least one ingoing air channel enters the at least one outgoing air channel via the perforated tube. Ensuring a high fraction of the air, particularly of the volume of the air, passing through the perforated tube may advantageously allow an efficient cooling of the motor and may reduce a required air fan power.

[0046] In typical embodiments, the motor air cooling system is configured to first guide air along an axial direction of the perforated tube and subsequently in a radial direction of the perforated tube. In particular, air may enter the perforated tube via at least one flange opening and / or via radial openings of the plurality of radial openings adjacent to the outer rotor end flanges and may exit the perforated tube radially via radial openings of the plurality of radial openings, particularly arranged towards the center of the perforated tube.

[0047] Typically, the motor air cooling system is preferably configured such that the temperature of the air remains substantially identical in axial direction. Substantially identical may comprise a temperature difference in axial direction being at most 5%, at most 10% or at most 15% of the lowest temperature of air in the motor. In some embodiments, the motor air cooling system may comprise at least one temperature sensor, particularly a plurality of temperature sensors. Typically, the motor air cooling system may control an air flow, exemplarily by controlling an air fan setting or an air fan power, based upon at least one temperature signal of the at least one temperature sensor. In some embodiments, the motor air cooling system may comprise deflection or control shields to control an air flow within the motor to provide a substantially identical temperature of the air in axial direction. The flection or control shields may be fixed or controllable.

[0048] The at least one temperature sensor may comprise a physical temperature sensor, exemplarily a thermometer, or a virtual temperature sensor extrapolating a temperature from nontemperature sensor data, exemplarily motor performance data, being provided to a controller, exemplarily an air fan controller.

[0049] Typically, the motor air cooling system is arranged such that air from the ingoing air channel enters the perforated tube at a first axial position of the perforated tube and exits the perforated tube at a second axial position of the perforated tube, with the second axial position being closer to a center of the perforated tube than the first axial position. The center of the perforated tube may particularly be at an axial center, or at a middle axial length of the perforated tube. Particularly, within the perforated tube, air flows substantially axially from the first axial position to the second axial position. The first axial position may be associated with a position of the at least one outer rotor end flange and / or with radial openings of the plurality of radial openings being connected to the at least one ingoing air channel. The second axial position may be associated with radial openings of the plurality of radial openings being connected to the at least one outgoing air channel. The motor air cooling system being configured such that air enters the perforated tube at a first axial position and exits the perforated tube at a second axial position with the second axial position being closer to the center of the perforated tube than the first axial position may advantageously be associated with a balanced temperature distribution in the motor, and / or may advantageously be associated with sealings, bearings or flanges not being heated by the air already having passed though the motor. However, in some embodiments, the motor cooling system may be arranged in reverse, particularly such that the air enters the perforated tube at the second axial position and exits the perforated tube at the first axial position. For some embodiments, a heating of components of the marine propulsion unit may be desired and air exiting the perforated tube may be employed to achieve such a heating effect.

[0050] Typically, the motor air cooling system is configured to guide air along an axial direction of the perforated tube for ensuring an at least substantially equal convective heat transfer along the axial direction of the perforated tube from the inner rotor and / or the outer rotor to the air.

[0051] Typically, the motor air cooling system is arranged such that air from the at least one ingoing air channel enters the contra rotating motor via the at least one flange opening and exits the contra rotating motor via at least part of the plurality of radial openings, particularly through the second radial openings. In some embodiments, the direction of the air flow may be reversed. Thus, the air may enter the contra rotating motor via at least part of the plurality of radial openings and exits the contra rotating motor via the at least one flange opening.

[0052] Typically, the motor air cooling system is arranged such that a first part of the air entering the motor enters the motor via the at least one flange opening and a second part of the air enters the motor via at least part of the plurality of radial openings, particularly via the first radialopenings. In some embodiments, a majority of the air enters the motor via at least part of the plurality of radial openings, particularly via the first radial openings. Exemplarily, at least 60%, at least 70% or at least 80% of the air enters the motor via at least part of the plurality of radial openings, particularly via the first radial openings. In some embodiments, the ratio of the air entering via the at least one flange opening and via at least part of the plurality of radial openings may be variable, and particularly controllable.

[0053] In some embodiments, the marine propulsion unit comprises at least one air channel separating wall. The at least one air channel separating wall may separate the at least one ingoing air channel and the at least one outgoing air channel. Particularly, the at least one air channel separating wall ensures that the air passes through the components to be cooled, in particular through the motor and the perforated tube and / or the slip ring unit. In some embodiments, the at least one air channel separating wall may be configured to separate different streams of the ingoing air. Exemplarily, part of the ingoing air may be separated to cool the motor while another part of the ingoing air is separated to cool the slip ring unit. The at least one air channel separating wall may further avoid leaking of the closed loop air cooling system or contamination of the air within the closed loop air cooling system.

[0054] Typically, the motor air cooling system further comprises an air fan and a heat exchanger. The air fan is typically configured to propel air through the motor air cooling system. Particularly, the air fan may provide cooling air to the contra rotating motor and may draw the cooling air from the contra rotating motor via the perforated tube, particularly after cooling the contra rotating motor. Typically, the air fan is configured to generate an overpressure in the ingoing air channel and a negative pressure in the outgoing air channel.

[0055] Typically, the heat exchanger may be configured to cool the air of the motor air cooling system, particularly to remove heat received from the components of the marine propulsion unit, exemplarily from the motor. The heat exchanger may comprise a gas-to-liquid heat exchanger. In some embodiments, the air may be cooled using sea water, either directly or indirectly.

[0056] Typically, the air fan and / or the heat exchanger is arranged within a hull-integrated section of the marine propulsion unit, and particularly of the azimuthing propulsion unit. In other words, the air fan and / or the heat exchanger is typically arranged within the main contour of the hull of the marine vessel. Particularly, the air fan and / or the heat exchanger is not integrated in the pod of the azimuthing propulsion unit. In some embodiments, the heat exchanger may be integrated inthe pod of the azimuthing propulsion unit with the air fan not being integrated in the pod of the azimuthing propulsion unit.

[0057] Typically, the motor air cooling system is a closed loop air cooling system. Particularly, air within the motor air cooling system is cycled multiple times through the motor air cooling system. In some embodiments, the motor air cooling system is an open air cooling system. In some embodiments, the motor air cooling system may comprise a conditioning system for physical or chemical properties of the air, exemplarily for dehumidifying the air within the motor air cooling system. Typically, the motor air cooling system comprises a filter for filtering the air in the motor air cooling system. The filter may particularly be configured to filter dust or oil residues in the air.

[0058] The marine propulsions units described herein, and particularly the azimuthing propulsion units described herein, may be employed in a marine vessel. In particular, the marine vessel may comprise at least one marine propulsion unit according to embodiments described herein. Propelling a marine vessel using a marine propulsion unit according to embodiments described herein may improve maneuverability and efficiency of the marine vessel.

[0059] Typically, cooling a contra rotating motor with an outer rotor and an inner rotor of a marine propulsion unit, and in particular of an azimuthing marine propulsion unit, with the contra rotating motor comprising a perforated tube configured to transmit a torque of the outer rotor to a propeller unit and to support an outer rotor winding, comprises providing cooling air to the contra rotating motor and drawing the cooling air from the contra rotating motor via the perforated tube. Providing cooling air to the contra rotating motor and drawing the cooling air from the contra rotating motor typically comprises operating an air fan in a closed loop air cooling system.

[0060] Embodiments of the present disclosure provide marine propulsion units, particularly azimuthing propulsion units, with an improved cooling of the contra rotating motor and an improved efficiency. In particular, a homogeneous and efficient cooling of the contra rotating motor allows to operate the motor at higher power levels, with smaller motor dimensions and shields further components of the marine propulsion unit from heat. In particular, embodiments of the present disclosure ensure an effective cooling of both the inner rotor and the outer rotor.

[0061] In some embodiments, the marine propulsion unit can include an intake heat exchanger connected to the second position of the air channel arrangement, and optionally an air intake channel arrangement which is connected to the slip-ring housing and the intake heat exchanger, the intake heat exchanger is configured to provide an intake cooling airflow via the air intakechannel arrangement to the slip-ring housing. The air intake channel arrangement can provide an intake airflow from the intake heat exchanger to the slip-ring housing to cool the slip-ring unit. The intake heat exchanger may be configured to cool down the cooling airflow separately from the motor cooling airflow. The intake heat exchanger, the air intake channel arrangement, the slipring unit housing and the air channel arrangement may be configured as a closed-loop system. Providing the air intake channel arrangement can improve the air purity entering the slip-ring housing since it can help to avoid dust particles from the motor cooling airflow reentering the slipring housing. According to some embodiments the inflow filter unit may be provided between the air intake channel and the slip-ring housing.

[0062] In the view of the foregoing, the present invention is directed to a marine propulsion unit and a method of maintaining a marine propulsion unit. The marine propulsion unit is preferably an azimuthing propulsion unit.

[0063] According to an aspect of the present invention, marine propulsion unit is provided. The marine propulsion unit comprises a rotatable drive end (DE) inner shaft; a rotatable DE outer shaft, wherein the DE inner shaft runs at least partially within the DE outer shaft. The marine propulsion unit further comprises a DE inner bearing arranged between the DE outer shaft and the DE inner shaft. The DE outer shaft of the marine propulsion unit comprises a hatch.

[0064] According to another aspect, the marine propulsion unit according to any of the embodiments described herein is an azimuthing propulsion unit.

[0065] According to another aspect of the present invention, a method of maintaining of a marine propulsion unit according to any of the embodiments described herein is provided. The method comprises: opening a hatch of a DE outer shaft of the marine propulsion unit; and accessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft.

[0066] In some embodiments, the hull of the marine vessel comprises a hull of the marine propulsion unit. In some embodiments, the hull of the marine propulsion unit is a pod.

[0067] In some embodiments, the marine vessel may comprise a single marine propulsion unit, particularly a single azimuthing propulsion unit, and more particularly with a single pod. In some embodiments, at least one marine propulsion unit, such as the azimuthing propulsion unit, may be combined with one or more further marine propulsion unit on a single marine vessel. Where two or more marine propulsion units are present, the marine propulsion units may be the same ordifferent marine propulsion units. For example, the marine vessel can have two azimuthing propulsion units, two shaft-line marine propulsion units, or one azimuthing propulsion unit and one shaft-line marine propulsion unit.

[0068] Typically, the hull of the marine propulsion unit or the pod comprises a hull cap at a first end of the hull of the marine propulsion unit or pod and a propeller unit, in particular a pushing or pulling propeller unit, attached to a second end of the hull of the marine propulsion unit or pod. The first end of the hull of the marine propulsion unit or pod may also be described as a nondriving end (NDE), and the second end of the hull of the marine propulsion unit or pod may also be described as a driving end (DE), of the hull of the marine propulsion unit or pod. The propeller unit typically rotates about a rotation axis of the propeller unit. The rotation axis of the propeller unit may be substantially perpendicular to the vertical rotation axis of the azimuthing propulsion unit.

[0069] In some embodiments, the marine propulsion unit comprises a rotatable drive end (DE) inner shaft, a rotatable DE outer shaft, wherein the DE inner shaft runs at least partially within the DE outer shaft, and a DE inner bearing arranged between the DE outer shaft and the DE inner shaft, wherein the DE outer shaft comprises at least one hatch.

[0070] The marine propulsion unit described herein may permit the marine propulsion unit to be maintained without requiring the marine vessel to be dry-docked. Dry docking a marine vessel is a time and resource consuming process which ultimately adversely affects an efficiency of the marine vessel.

[0071] According to some embodiments, the at least one hatch may be, for example, configured to provide access to the DE inner bearing. According to some embodiments, the at least one hatch may be, for example, configured to be accessed by a user from within the marine propulsion unit. In order for the hatch to provide sufficient access to the DE inner bearing, the hatch may be of a defined shape and size. For example, the hatch may be any of the following shapes, but not limited to: a rectangle, a circle, a triangle, a rhombus, a pentagon, a hexagon, etc. For example, the hatch may be rectangular with a length of at least 0.2 m and / or up to 1.5 m, preferably at least 0.3 m or at least 0.4 m and / or up to 0.6 m or up to 0.5 m, and a width of at least 0.1 m and / or up to 0.8 m, preferably at least 0.3 m and / or up to 0.5 m or up to 0.4 m. In a further example, the hatch is circular with a diameter of at least 0.2 m and / or up to 1.5 m, preferably at least 0.3 m and / or up to 0.7 m.

[0072] The DE outer shaft may comprise, for example, two hatches, three hatches, four hatches, five hatches, etc. The marine propulsion unit comprising two or more hatches may comprise two or more of the same hatch, two or more different hatches, or a combination thereof. For example, wherein the marine propulsion unit comprises four hatches, each of the four hatches may be of a different shape and size, the same shape and size, or a combination thereof. In typical embodiments, the at least one hatch comprises at least one seal. In particular, the at least one seal is a hatch seal. The at least one hatch seal may prevent fluid, such as lubricating oil, from exiting a contained volume.

[0073] The at least one hatch may be configured to permit the user to access the DE inner shaft from within the marine propulsion unit. The hatch may be configured to permit the user to access a region between the DE inner shaft and the DE outer shaft. For example, the user may access the DE inner bearing from within the marine propulsion unit through the at least one hatch. The at least one hatch may be opened and / or removed to gain access to the region between the DE inner shaft and the DE outer shaft. For example, the at least one hatch may be opened through a push-to-unlock mechanism. For example, the at least one hatch may be opened by removing at least one fixing mechanism, such as a screw. The at least one hatch may be reused. For example, the at least one hatch may be opened and closed any number of times, for example, 20 times, 50 times, 100 times, 500 times, or more. In some embodiments, the at least one hatch is an opening through the DE outer shaft without a cover.

[0074] The at least one hatch may permit for maintenance to be done on the DE inner shaft and / or the DE outer shaft from within the marine propulsion unit. The maintenance may include checking, preparing, removing, replacing, adding, or any combination thereof of the components in the drive end of the marine propulsion unit.

[0075] According to some embodiments described herein, the DE inner bearing comprises inner bearing pads. According to some embodiments described herein, the DE inner bearing comprises an inner roller bearing. According to some embodiments described herein, the DE inner bearing comprises an inner bearing pad and / or an inner roller bearing. The DE inner bearing and / or the inner bearing pads may be arranged distally in relation to the at least one hatch. According to typical embodiments, the DE inner bearing is a segmented bearing. For example, the DE inner bearing comprises two or more inner bearing pads, for example 3 bearing pads, 5 bearing pads, 8 bearing pads, 12 bearing pads, or any predefined number of bearing pads. The inner bearing pads may be arranged around the DE inner shaft, and in particular around an entire circumference ofthe DE inner shaft. The inner bearing pads may be configured to be displaced along the DE inner shaft. The inner bearing pads may be slide bearing pads. The inner bearing pads may be configured to be slid along the DE inner shaft.

[0076] Typically, the DE inner bearing and / or inner bearing pads may be displaced proximally, and in particular, proximally towards the at least one hatch. The DE inner bearing and / or inner bearing pads may be displaced continuously or in intervals. The DE inner bearing and / or inner bearing pads may be displaced axially by a predetermined distance, for example, in line with the at least one hatch. The DE inner bearing and / or inner bearing pads may be displaced axially by a distance determined by the user, for example, 0.3 m. The DE inner bearing and / or inner bearing pads may be displaced according to the maintenance procedure taking place.

[0077] According to some embodiments described herein, the marine propulsion unit may further comprise a DE inner distal seal. The DE inner distal seal may be arranged between the DE inner shaft and the DE outer shaft. The DE inner distal seal may be arranged towards a drive end, and in particular the drive and of the marine propulsion unit. The DE inner distal seal may comprise at least one water seal and / or at least one lubricant seal. For example, the DE inner distal seal may prevent water from entering into the marine propulsion unit and / or may prevent lubricant, for example oil, from exiting the marine propulsion unit. The DE inner distal seal may prolong the lifespan of the marine propulsion unit and / or may prevent on environment from being contaminated.

[0078] Typically, the DE inner distal seal may be displaced proximally, and in particular, proximally towards the at least one hatch. The DE inner distal seal may be displaced continuously or in intervals. The DE inner distal seal may be displaced axially by a predetermined distance, for example, in line with the at least one hatch. The DE inner distal seal may be displaced axially by a distance determined by the user, for example, 0.3 m. The DE inner distal seal may be displaced according to the maintenance procedure taking place.

[0079] According to some embodiments described herein, the marine propulsion unit may further comprise a DE inner proximal seal. The DE inner proximal seal may be arranged between the DE inner shaft and the DE outer shaft. The DE inner proximal seal may be arranged towards the NDE. In typical embodiments, the DE inner proximal seal may be arranged distally to the at least one hatch. The DE inner proximal seal may comprise at least one seal. For example, the DE inner proximal seal comprises 2, 3, 4, 5, 6, 8, 10, or any number of seals. The DE inner proximal sealmay comprise at least one oil seal. For example, the DE inner proximal seal may prevent lubricant from leaving at least one desired region.

[0080] Typically, the DE inner proximal seal may be displaced distally, and in particular, distally towards the at least one hatch. The DE inner proximal seal may be displaced continuously or in intervals. The DE inner proximal seal may be displaced by a predetermined distance, for example, in line with the at least one hatch. The DE inner proximal seal may be displaced by a distance determined by the user, for example, 0.3 m. The DE inner proximal seal may be displaced according to the maintenance procedure taking place.

[0081] Typically, the DE inner distal seal and / or the DE inner proximal seal may comprise two or more seals. The DE inner distal seal and / or the DE inner proximal seal may be attached to at least the DE inner shaft. For example, the DE inner distal seal and / or the DE inner proximal seal may be attached to the DE inner shaft and the DE outer shaft.

[0082] According to some embodiments described herein, the marine propulsion unit may further comprise a hull of the marine propulsion unit or a pod, wherein the pod comprises a pod hull. The hull of the marine propulsion unit or the pod may permit for the DE inner bearing and / or the DE inner bearing pads and / or the DE inner distal seal and / or the DE inner proximal seal to be maintained from within the marine propulsion unit. This may be beneficial in that, for example, for the DE inner bearing and / or the DE inner bearing pads and / or the DE inner distal seal and / or the DE inner proximal seal to be maintained without requiring the marine propulsion unit and over the marine vessel to be dry-docked. This may for example, reduce time required for maintenance and / or permit for an increase in maintenance opportunities available. For example, the marine vessel may be docked at a port as part of its schedule and the DE inner bearing and / or the DE inner bearing pads and / or the DE inner distal seal and / or the DE inner proximal seal may be maintained during this time at the port. For example, the user may enter the marine propulsion unit through a vessel interior of the marine vessel, and may proceed to accessing any of the aforementioned components.

[0083] According to some embodiments described herein the marine propulsion unit may further comprise a DE outer bearing. In some embodiments, the DE outer bearing may comprise an outer bearing pad. According to some embodiments described herein, the DE outer bearing comprises an outer roller bearing. According to some embodiments described herein, the DE outer bearing comprises an outer bearing pad and / or an outer roller bearing. The DE outer bearing and / or theouter bearing pads may be arranged distally in relation to the at least one hatch. According to typical embodiments, the DE outer bearing is a segmented bearing. For example, the DE outer bearing comprises two or more outer bearing pads, for example 3 bearing pads, 5 bearing pads, 8 bearing pads, 12 bearing pads, or any predefined number of bearing pads. The outer bearing pads may be arranged around the DE outer shaft, and in particular around an entire circumference of the DE outer shaft. The outer bearing pads may be configured to be displaced along the DE outer shaft. The outer bearing pads may be slid. The outer bearing pads may be configured to be slid along the DE outer shaft. The DE outer bearing and / or outer bearing pads may be displaced radially from the DE outer shaft. In typical embodiments, the DE outer bearing and / or outer bearing pads may be slid and / or displaced radially.

[0084] The DE inner bearing and the DE outer bearing may be coupled. For example, the DE inner bearing and the DE outer bearing may be fluidly coupled. For example, the DE inner bearing may comprise a DE inner bearing chamber and the DE outer bearing may comprise a DE outer bearing chamber. In particular, the DE inner bearing chamber and the DE outer bearing chamber may be fluidly coupled. In typical embodiments, the DE outer shaft comprises at least one bore to fluidly couple the DE inner bearing and the DE outer bearing. The at least one bore may be through the DE outer shaft. Typically, the at least one bore is radially through the DE outer shaft. The fluid coupling may comprise a lubricant, such as grease and / or oil. The DE inner bearing and the DE outer bearing may be arranged coaxially to the rotation axis. The DE outer bearing may at least partially overlap the DE inner bearing. For example, the DE outer bearing and / or the outer bearing pads may be displaced proximally. In particular, the DE outer bearing and / or the outer bearing pads may be displaced axially. The DE outer bearing and / or the outer bearing pads may be displaced axially and proximally along the DE outer shaft. The outer bearing pads may comprise slide bearing pads.

[0085] The DE inner bearing and / or the inner bearing pads and / or the DE outer bearing and / or the outer bearing pads may be configured to be individually displaced and / or changed. The DE inner bearing may be rotated with respect to the DE inner shaft, the DE outer shaft, or both. For example, a gliding layer is between the DE inner bearing and the DE inner shaft, the DE outer shaft, or both. The DE inner bearing may be rotated along the DE inner shaft, the DE outer shaft, or both. The DE outer bearing may be rotated with respect to the DE outer shaft, the DE outer bearing housing, or both. For example, a gliding layer is between the DE outer bearing and the DE outer shaft, the DE outer bearing housing, or both. The DE outer bearing may be rotated along the DE outer shaft, the DE outer bearing housing, or both.

[0086] The marine propulsion unit described herein may enable inner bearing and seal change in a contra rotating propeller. For example, the marine propulsion unit described herein may enable maintenance without removing at least one propeller and / or driving conditions.

[0087] According to some embodiments described herein, a method of maintaining a marine propulsion unit is provided, particularly the marine propulsion unit described herein. In typical embodiments, the method of maintaining the marine propulsion unit comprises maintaining an azimuthing propulsion unit. The method of maintaining the marine propulsion unit described herein comprises opening a hatch of a DE outer shaft of the marine propulsion unit; and accessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft. Typically, the method of maintaining the marine propulsion unit may be performed within the marine propulsion unit described herein. In particular, the method of maintaining the marine propulsion unit may be performed without requiring for the marine propulsion unit and / or a marine vessel to be drydocked.

[0088] According to some embodiments described herein, the method of maintaining the marine propulsion unit may further comprise, after accessing the DE inner bearing to the hatch, displacing the DE inner bearing. The method may comprise releasing the DE inner bearing. In particular, releasing the DE inner bearing may occur prior to displacing the DE inner bearing. For example, the DE inner bearing may be secured between the DE inner shaft and the DE outer shaft. Releasing of the DE inner bearing may enable the displacing of the DE inner bearing. For example, the method comprises displacing the DE inner bearing towards the motor, preferably without removing a portion through the hatch. For example, the method comprises displacing the DE inner bearing at least partially through the hatch. For example, the method comprises displacing the entire DE inner bearing through the hatch.

[0089] Typically, displacing the DE inner bearing may comprise removing the DE inner bearing through the hatch. For example, removing the DE inner bearing may comprise proximally displacing the DE inner bearing to a position in line with the hatch. Upon displacing the DE inner bearing to the position in line with the hatch, the method may comprise extracting the DE inner bearing, in particular extracting the DE inner bearing through the hatch. Typically, displacing the DE inner bearing comprises displacing the DE inner bearing to a service position. When the DE inner bearing is at the service position, the method of maintaining the marine propulsion unit typically comprises servicing the DE inner bearing. For example, servicing the DE inner bearing may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular,servicing the DE inner bearing may be for the entire DE inner bearing or at least a portion thereof. For example, servicing the DE inner bearing comprises servicing at least one wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE inner bearing is through the hatch. Typically, servicing the DE inner bearing is performed within the hatch. Typically, servicing the DE inner bearing is performed outside the hatch.

[0090] Typically, displacing the DE inner bearing may comprise axially displacing the DE inner bearing a distance of at least 0.1 m, 0.2 m, 0.3 m, up to 1.5 m, or any distance therebetween. For example, displacing the DE inner bearing may comprise displacing the DE inner bearing within a region between the DE inner shaft and the DE outer shaft.

[0091] Typically, the method of maintaining the marine propulsion unit may further comprise installing the DE inner bearing and / or replacing the DE inner bearing, and in particular with a new DE inner bearing and / or at least a new portion thereof.

[0092] According to some embodiments described herein, the method of maintaining the marine propulsion unit may further comprise, after displacing the DE inner bearing, accessing a DE inner distal seal through the hatch, and displacing the DE inner distal seal. Typically, displacing the DE inner bearing comprises displacing the DE inner distal seal to a service position. The service position may be proximal to the at least one hatch. Typically, displacing the DE inner bearing comprises partly or completely displacing the DE inner bearing through the at least one hatch. Typically, displacing the DE inner bearing comprises displacing the DE inner distal seal to a service position and partly or completely displacing the DE inner bearing through the at least one hatch. The method may comprise releasing the DE inner distal seal. In particular, releasing the DE inner distal seal may occur prior to displacing the DE inner distal seal. For example, the DE inner distal seal may be secured between the DE inner shaft and the DE outer shaft. Releasing of the DE inner distal seal may enable the displacing of the DE inner distal seal.

[0093] Typically, displacing the DE inner distal seal may comprise removing the DE inner distal seal through the hatch. For example, removing the DE inner distal seal may comprise proximally displacing the DE inner distal seal to a position in line with the hatch. Upon displacing the DE inner distal seal to the position in line with the hatch, the method may comprise extracting the DE inner distal seal, in particular extracting the DE inner distal seal through the hatch. Typically, displacing the DE inner distal seal comprises displacing the DE inner distal seal to a serviceposition. When the DE inner distal seal is at the service position, the method of maintaining the marine propulsion unit typically comprises servicing the DE inner distal seal. For example, servicing the DE inner distal seal may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular, servicing the DE inner distal seal may be for the entire DE inner distal seal or at least a portion thereof. For example, servicing the DE inner distal seal comprises servicing at least one wearable part. Typically, a seal, such as a lip seal, is a wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE inner distal seal is through the hatch. Typically, servicing the DE inner distal seal is within the hatch. Typically, servicing the DE inner distal seal is outside the hatch.

[0094] Typically, displacing the DE inner distal seal may comprise axially displacing the DE inner distal seal a distance of at least 0.1 m, 0.2 m, 0.3 m, up to 3 m, or any distance therebetween. For example, displacing the DE inner distal seal may comprise displacing the DE inner distal seal within a region between the DE inner shaft and the DE outer shaft.

[0095] Typically, the method of maintaining the marine propulsion unit may further comprise installing the DE inner distal seal and / or replacing the DE inner distal seal, and in particular with a new DE inner distal seal and / or at least a new portion thereof.

[0096] According to some embodiments described herein, the method of maintaining the marine propulsion unit may further comprise accessing a DE inner proximal seal through the hatch, and displacing the DE inner proximal seal. The method may comprise releasing the DE inner proximal seal. In particular, releasing the DE inner proximal seal may occur prior to displacing the DE inner proximal seal. For example, the DE inner proximal seal may be secured between the DE inner shaft and the DE outer shaft. Releasing of the DE inner proximal seal may enable the displacing of the DE inner proximal seal.

[0097] Typically, displacing the DE inner proximal seal may comprise removing the DE inner proximal seal through the hatch. For example, removing the DE inner proximal seal may comprise distally displacing the DE inner proximal seal to a position in line with the hatch. Upon displacing the DE inner proximal seal to the position in line with the hatch, the method may comprise extracting the DE inner proximal seal, in particular extracting the DE inner proximal seal through the hatch. Typically, displacing the DE inner proximal seal comprises displacing the DE inner proximal seal to a service position. When the DE inner proximal seal is at the service position, themethod of maintaining the marine propulsion unit typically comprises servicing the DE inner proximal seal. For example, servicing the DE inner proximal seal may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular, servicing the DE inner proximal seal may be for the entire DE inner proximal seal or at least a portion thereof. For example, servicing the DE inner proximal seal comprises servicing at least one wearable part. Typically, a seal, such as a lip seal, is a wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE inner proximal seal is performed through the hatch. Typically, servicing the DE inner proximal seal is within the hatch. Typically, servicing the DE inner proximal seal is performed outside the hatch.

[0098] Typically, displacing the DE inner proximal seal may comprise axially displacing the DE inner proximal seal a distance of at least 0.1 m, 0.2 m, 0.3 m, up to 3 m, or any distance therebetween. For example, displacing the DE inner proximal seal may comprise displacing the DE inner proximal seal within a region between the DE inner shaft and the DE outer shaft.

[0099] Typically, the method of maintaining the marine propulsion unit may further comprise installing the DE inner proximal seal and / or replacing the DE inner proximal seal, and in particular with a new DE inner proximal seal and / or at least a new portion thereof.

[0100] According to some embodiments described herein, the method of maintaining the marine propulsion unit, displacing any of the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, or any combination thereof, may comprise axially displacing along the DE inner shaft. For example, displacing any of the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, or any combination thereof, may comprise sliding, in particular axially, along the DE inner shaft. For example, displacing any of the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, or any combination thereof, may comprise rotating, preferably rotating to displace the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, the DE outer shaft, the DE inner shaft, or any combination thereof.

[0101] According to some embodiments described herein, the method of maintaining the marine propulsion unit, comprises an marine propulsion unit which comprises: a DE outer proximal seal, a DE outer bearing, a DE outer distal seal, or any combination thereof. The method typically further comprises displacing any of a DE outer proximal seal, a DE outer bearing, a DE outer distal seal, or any combination thereof. For example, displacing the DE outer proximal seal, the DE outerbearing, the DE outer distal seal, or any combination thereof, may comprise axially displacing along the DE outer shaft and / or sliding along the DE outer shaft and / or radially displacing from the DE outer shaft. Typically, displacing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof, comprises displacing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof to a service position. When the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is at the service position, the method of maintaining the marine propulsion unit typically comprises servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof. For example, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof may be for the entire DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof, or at least a portion thereof. For example, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof comprises servicing at least one wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is through the hatch. Typically, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is within the hatch. Typically, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is outside the hatch.

[0102] The method of maintaining the marine propulsion unit may comprise servicing the DE inner proximal seal and / or the DE inner distal seal. The method of maintaining the marine propulsion unit may comprise repairing and / or replacing the DE inner proximal seal and / or the DE inner distal seal. Repairing and / or replacing the DE inner proximal seal and / or the DE inner distal seal may occur after accessing the DE inner proximal seal and / or the DE inner distal seal, and in particular, after releasing and displacing the DE inner proximal seal and / or the DE inner distal seal.

[0103] Typically, the DE inner distal seal and / or the DE inner proximal seal comprise sealing elements. Sealing elements may comprise sealing lips. Typically, the sealing elements the DE inner distal seal and / or the DE inner proximal seal is replaced, displaced and / or serviced with the respective seal staying in place, after moving the respective seal to a service position or without removing the respective seal from the DE inner shaft. Typically, sealing elements are handled asdescribed without necessarily displacing and / or servicing the entire DE inner distal seal and / or the entire DE inner proximal seal.

[0104] In typical embodiments, the method comprises displacing the DE inner distal seal and / or the DE inner proximal seal. In typical embodiments, the method comprises servicing the DE inner distal seal and / or the DE inner proximal seal. In typical embodiments, the method comprises displacing the sealing elements of the DE inner distal seal and / or the DE inner proximal seal. In typical embodiments, the method comprises servicing the sealing elements of the DE inner distal seal and / or the DE inner proximal seal. For example, the DE inner distal seal and / or the DE inner proximal seal comprises a seal ring. For example, the DE inner distal seal and / or the DE inner proximal seal comprises a seal housing. The seal housing may comprise housing rings. The seal housing is typically configured to hold the sealing elements. Typically, servicing comprises cutting the seal rings.

[0105] In typical embodiments, the method comprises proximally and / or distally displacing the seal housing. The method typically comprises proximally and / or distally displacing with respect to the DE inner bearing housing. The method typically comprises displacing the seal housing to the hatch. In particular, the method comprises displacing the seal housing to the hatch on the DE outer shaft. The method typically comprises servicing the seal housing. Servicing the seal housing typically comprises dismantling the housing rings. Typically, the housing rings are not removed through the hatch. Dismantling the housing rings typically comprises detaching from one another. Typically, the method comprises displacing sealing lips. Typically, the method comprises removing the sealing lips. Typically, displacing and / or removing the sealing lips is after dismantling the housing rings. In typical embodiments, the method comprises replacing the sealing lips. In typical embodiments, the method comprises repairing the sealing lips. In typical embodiments, the method comprises installing new sealing lips. In typical embodiments, the method comprises bonding and / or joining the sealing lips. In typical embodiments, the method comprises bonding to one another. Typically, bonding is done through the at least one hatch. Typically, in case of elastomer seals, chemicals such as glue, compression, and heat are used in bonding. In typical embodiments, the method comprises joining the sealing lips on the DE shaft. Typically, in case of polyurethane seals, bonding and / or joining comprises heating two ends of the seal ring and pressing the two ends together. In typical embodiments, the method comprises assembling the seal housing. In typical embodiments, the method comprises re-assembling the seal housing. In typical embodiments, the method comprises assembling the housing rings.

[0106] Typically, the DE inner shaft and / or the DE outer shaft may be supported. Supporting the DE inner shaft and / or the DE outer shaft may provide more room to manipulate the remaining components in the marine propulsion unit.

[0107] Typically, a user may perform the method of maintaining the marine propulsion unit described herein. For example, the user may open the hatch and may access the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal. The user may further perform the displacing of the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal. For example, the user may reach into the region accessible through the at least one hatch, and may displace any of the aforementioned components and / or subsidies thereof. The user may perform the opening of the hatch and / or the displacing of the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal using their labour and / or tools. For example, the user may employ at least one rod, threaded bar, grappling tool, and / or any tool suitable for releasing and displacing the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal.

[0108] For example, the user may access the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal. The user may further perform the displacing of the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal. The user may perform the displacing of the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal using their labour and / or tools. For example, the user may employ at least one rod, threaded bar, grappling tool, and / or any tool suitable for releasing and displacing the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal.

[0109] Embodiments of the present invention provide marine propulsion units, in particular marine propulsion units with an improved drive end shaft structure enabling inner bearing and seal change. With exemplary embodiments, the bearings and / or the seals might undergo maintenance and / or might be changed without it being mandatory to bring the vessel into a dry dock. For example, before removing the seals, shafts might be sealed against the water with some temporary seals applied from the waterside of the hull of the marine vessel to allow a seal change whilst the vessel is in a swimming condition.

[0110] In the view of the foregoing, the present invention is directed to a marine propulsion unit and a method of maintaining a marine propulsion unit.

[0111] According to an aspect of the present invention, a marine propulsion unit is provided. The marine propulsion unit comprises a rotatable drive end (DE) shaft, a DE outer bearing arrangedbetween the DE shaft and the DE outer bearing housing, wherein the DE outer bearing is configured to be displaced, and wherein the DE outer bearing comprises outer bearing pads. The marine propulsion unit further comprises a DE outer distal seal, wherein the DE outer distal seal is configured to be accessed from within the marine propulsion unit, is provided.

[0112] According to another aspect of the present disclosure, the marine propulsion unit according to any of the embodiments described herein is an azimuthing propulsion unit.

[0113] According to another aspect of the present invention, a method of maintaining of a marine propulsion unit according to any of the embodiments described herein is provided. The method comprises: accessing a DE shaft from an interior of a hull of the marine propulsion unit; accessing a DE outer bearing arranged between a DE shaft and a DE outer bearing housing; and accessing a DE outer distal seal.

[0114] In some embodiments, the hull of the marine vessel comprises a hull of the marine propulsion unit. In some embodiments, the hull of the marine propulsion unit is a pod.

[0115] In some embodiments, the marine vessel may comprise a single marine propulsion unit, particularly a single azimuthing propulsion unit, and more particularly with a single pod. In some embodiments, one typical marine propulsion unit, such as the azimuthing propulsion unit, may be combined with one or more further marine propulsion unit, e.g. one or more further marine propulsion unit or other propulsion mechanisms, in a single marine vessel. Where two or more marine propulsion units are present, the marine propulsion units may be the same or different marine propulsion units. For example, the marine vessel can have two azimuthing propulsion units, two shaft-line marine propulsion units, or one azimuthing propulsion unit and one shaft-line marine propulsion unit.

[0116] Typically, the hull of the marine propulsion unit or the pod comprises a hull cap at a first end of the hull of the marine propulsion unit or the pod and a propeller unit, in particular a pushing or pulling propeller unit, attached to a second end of the hull of the marine propulsion unit or the pod. The first end of the hull of the marine propulsion unit or the pod may also be described as a non-driving end (NDE), and the second end of the hull of the marine propulsion unit or the pod may also be described as a driving end (DE), of the hull of the marine propulsion unit or the pod. The propeller unit typically rotates about a rotation axis of the propeller unit. The rotation axis of the propeller unit may be substantially perpendicular to the vertical rotation axis of the azimuthing propulsion unit.

[0117] In some embodiments, the marine propulsion unit for a vessel comprises a rotatable drive end (DE) shaft. The DE shaft is typically hollow. Some embodiments comprise a solid DE shaft. Typically, the marine propulsion unit comprises a DE outer bearing arranged between the DE shaft and the DE outer bearing housing. The DE outer bearing is typically configured to be displaced. The DE outer bearing may comprise outer bearing pads. Typically, the marine propulsion unit comprises a DE outer distal seal, the DE outer distal seal is typically configured to be accessed from within the marine propulsion unit. The DE outer distal seal is typically arranged distally with respect to the DE outer bearing. The DE outer distal seal is typically arranged in contact with the DE shaft, the DE outer bearing housing, or a combination thereof. The DE outer distal seal may, for example, prevent water from entering the marine propulsion unit, prevent lubricant such as oil or grease from exiting the marine propulsion unit, or a combination thereof. The DE outer distal seal is typically a water and / or lubricant seal. The DE outer distal seal is typically arranged between an inner portion of the DE outer bearing housing and an outer portion of the DE shaft. The DE outer distal seal is typically arranged in contact with the inner portion of the DE outer bearing housing and the DE shaft, in particular, the outer portion of the DE shaft.

[0118] The outer bearing pads are typically configured to be displaced axially and / or radially, and / or the DE outer distal seal is configured to be displaced axially and / or radially.

[0119] For example, the outer bearing pads are configured to be displaced axially along the DE outer shaft. In particular, the outer bearing pads are configured to be displaced proximally. The outer bearing pads are typically configured to slide. In particular, the outer bearing pads are configured to be slid by a user. For example, the outer bearing pads are slid proximally by the user along the DE outer shaft. Typically, the outer bearing pads are configured to be displaced axially. In particular, the outer bearing pads are configured to be displaced axially, and not along the DE outer shaft. For example, a gap is between the outer bearing pads and the DE outer shaft. For example, a film such as a protective film and / or sliding film is between the outer bearing pads and the DE outer shaft.

[0120] For example, the DE outer distal seal is configured to be displaced axially along the DE outer shaft. In particular, the DE outer distal seal is configured to be displaced proximally. The DE outer distal seal is typically configured to slide. In particular, the DE outer distal seal is configured to be slid by a user. For example, the DE outer distal seal is slid proximally by the user along the DE outer shaft. Typically, the DE outer distal seal is configured to be displaced axially. In particular, the DE outer distal seal is configured to be displaced axially, and not along the DE outershaft. For example, a gap is between the DE outer distal seal and the DE outer shaft. For example, a film such as a protective film and / or sliding film is between the DE outer distal seal and the DE outer shaft.

[0121] The outer bearing pads are typically configured to be displaced radially and / or the DE outer distal seal is configured to be displaced radially. For example, the outer bearing pads are configured to be displaced radially from the DE outer shaft. In particular, the outer bearing pads are configured to be displaced radially outwards. The outer bearing pads are typically configured to be extracted from the DE outer bearing housing. In particular, the outer bearing pads are configured to be displaced and / or extracted by a user. For example, the outer bearing pads are displaced and / or extracted radially outwards from the DE outer bearing housing by the user. In particular, the outer bearing pads may be displaced and / or extracted from the DE outer bearing housing through at least one hatch in the DE outer bearing housing.

[0122] For example, the DE outer distal seal is configured to be displaced radially from the DE outer shaft. In particular, the DE outer distal seal is configured to be displaced radially outwards. The DE outer distal seal is typically configured to be extracted from the DE outer bearing housing. In particular, the DE outer distal seal is configured to be displaced and / or extracted by a user. For example, the DE outer distal seal is displaced and / or extracted radially outwards from the DE outer bearing housing by the user. In particular, the DE outer distal seal is may be displaced and / or extracted from the DE outer bearing housing through the at least one hatch in the DE outer bearing housing.

[0123] Typically, the DE outer distal seal is arranged between the DE shaft and the DE outer bearing housing. The DE outer distal seal is typically arranged towards a propeller mounted on the DE shaft, i.e. more distal with respect to the motor. The DE outer distal seal may be in contact with an enclosed environment within the marine propulsion unit and / or an outside environment, such as water. The DE outer bearing housing may be a single unit or comprising any number of units. The DE outer bearing housing may comprise 2, 3, 4, 5, 6, 8, or any number of housing units.

[0124] In some embodiments, the marine propulsion unit comprises a DE outer proximal seal. The DE outer proximal seal is typically arranged between the DE shaft and the DE outer bearing housing. The DE outer proximal seal is typically more proximal to the motor compared to the DE outer distal seal. The DE outer proximal seal is typically arranged on the DE shaft, the DE outerbearing housing, or a combination thereof. The DE outer proximal seal is typically arranged between a proximal portion of the DE outer bearing housing and an outer portion of the DE shaft. The DE outer proximal seal is typically arranged in contact with the proximal portion of the DE outer bearing housing, the outer portion of the DE shaft, or a combination thereof.

[0125] Typically, the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal are replaceable from within a hull of the marine propulsion unit or a pod hull of the pod of the marine propulsion unit. For example, the DE outer distal seal, and / or the DE outer proximal seal are configured to be replaced from within the marine propulsion unit. In particular, the DE outer distal seal, and / or the DE outer proximal seal are configured to be replaced from within the hull of the marine propulsion unit or the pod hull. For example, the DE outer distal seal, and / or the DE outer proximal seal are replaceable from a proximal region. For example, the proximal region is towards the motor of the marine propulsion unit. For example, the user may access the proximal region to maintain the DE outer distal seal, and / or the DE outer proximal seal. This may be beneficial in reducing the time required for a maintenance procedure as the user may access the DE outer distal seal, and / or the DE outer proximal seal in less time than having to access these components from outside the marine propulsion unit.

[0126] Typical embodiments of the marine propulsion unit described herein may permitthe marine propulsion unit to be maintained without requiring the marine vessel to be dry-docked. Dry docking a marine vessel is a time and resource consuming process which ultimately adversely affects an efficiency of the marine vessel. Typical marine propulsion units as described herein may be maintained from within the respective marine propulsion unit. The marine propulsion unit described herein may provide the benefit of not requiring accessing, for example, the DE outer distal seal mandatorily from outside the marine propulsion unit. It should be understood, that an access from the outside is still possible with typical embodiments as described herein.

[0127] Typically, the marine propulsion unit is a contra rotating propeller azimuthing propulsion unit. For example, the DE shaft is a DE outer shaft. In particular, the rotatable DE shaft is a rotatable DE outer shaft.

[0128] In typical embodiments, the marine propulsion unit comprises a rotatable drive end (DE) inner shaft, a rotatable DE outer shaft, wherein the DE inner shaft runs at least partially within the DE outer shaft. Typically, the DE outer shaft comprises one or more hatches. Typically, the marinepropulsion unit comprises a DE inner bearing. The DE inner bearing is typically arranged between the DE outer shaft and the DE inner shaft.

[0129] According to some embodiments, the at least one hatch may be, for example, configured to provide access to the DE inner bearing. Typically, the DE inner bearing is accessible through the at least one hatch. According to typical embodiments, the at least one hatch may be, for example, configured to be accessed by a user from within the marine propulsion unit. In order for the hatch to provide sufficient access to the DE inner bearing, the hatch may be of a defined shape and size. For example, the hatch may be any of the following shapes, but not limited to: a rectangle, a circle, a triangle, a rhombus, a pentagon, a hexagon, etc. For example, the hatch may be rectangular with a length of at least 0.2 m and / or up to 1.5 m, preferably at least 0.3 m and / or up to 0.6 m, and a width of at least 0.1 m and / or up to 0.8 m, preferably at least 0.3 m and / or up to 0.5 m. In a further example, the hatch 302 is circular with a diameter of at least 0.2 m and / or up to 1.5 m, preferably at least 0.3 m and / or up to 0.7 m.

[0130] The DE outer shaft may comprise, for example, two hatches, three hatches, four hatches, five hatches, etc. The marine propulsion unit comprising two or more hatches may comprise two or more of the same hatch, two or more different hatches, or a combination thereof. For example, wherein the marine propulsion unit comprises four hatches, each of the four hatches may be of a different shape and size, the same shape and size, or a combination thereof. In typical embodiments, the at least one hatch comprises at least one seal. In particular, the at least one seal is a hatch seal. The at least one hatch seal may prevent fluid, such as lubricating oil, from exiting a contained volume.

[0131] The at least one hatch may be configured to permit the user to access the DE inner shaft from within the marine propulsion unit. The hatch may be configured to permit the user to access a region between the DE inner shaft and the DE outer shaft. For example, the user may access the DE inner bearing from within the marine propulsion unit through the at least one hatch. The at least one hatch might be a hatch including a cover. For example, the hatch may be opened and / or removed to gain access to the region between the DE inner shaft and the DE outer shaft. For example, the at least one hatch may be opened through a push-to-unlock mechanism. For example, the at least one hatch may be opened by removing at least one fixing mechanism, such as a screw. The at least one hatch may be reused. For example, the at least one hatch may be opened and closed any number of times, for example, 20 times, 50 times, 100 times, 500 times, or more. Insome embodiments, the at least one hatch is an opening through the DE outer shaft without a cover.

[0132] The at least one hatch may permit for maintenance to be done on the DE inner shaft and / or the DE outer shaft from within the marine propulsion unit. The maintenance may include checking, preparing, removing, replacing, adding, or any combination thereof of the components in the drive end of the marine propulsion unit.

[0133] According to some embodiments described herein, the DE inner bearing comprises inner bearing pads. According to some embodiments described herein, the DE outer bearing comprises generally a bearing. For example, the DE outer bearing comprises an outer roller bearing. According to some embodiments described herein, the DE outer bearing comprises outer bearing pads and / or outer roller bearings. The DE inner bearing and / or the inner bearing pads may be arranged distally in relation to the at least one hatch. According to typical embodiments, the DE inner bearing is a segmented bearing. For example, the DE inner bearing comprises two or more inner bearing pads, for example 3 bearing pads, 5 bearing pads, 8 bearing pads, 12 bearing pads, or any predefined number of bearing pads. The inner bearing pads may be arranged around the DE inner shaft, and in particular around an entire circumference of the DE inner shaft. The inner bearing pads may be configured to be displaced along the DE inner shaft. The inner bearing pads may be slide bearing pads. The inner bearing pads may be configured to be slid along the DE inner shaft.

[0134] Typically, the DE inner bearing and / or inner bearing pads may be displaced proximally, and in particular, proximally towards the at least one hatch. The DE inner bearing and / or inner bearing pads may be displaced continuously or in intervals. The DE inner bearing and / or inner bearing pads may be displaced axially by a predetermined distance, for example, in line with the at least one hatch. The DE inner bearing and / or inner bearing pads may be displaced axially by a distance determined by the user, for example, 0.3 m. The DE inner bearing and / or inner bearing pads may be displaced according to the maintenance procedure taking place.

[0135] According to some embodiments described herein, the marine propulsion unit may further comprise a DE inner distal seal. The DE inner distal seal may be arranged between the DE inner shaft and the DE outer shaft. The DE inner distal seal may be arranged towards a drive end, and in particular the drive and of the marine propulsion unit. The DE inner distal seal may comprise at least one water seal and / or at least one lubricant seal. For example, the DE inner distal seal mayprevent water from entering into the marine propulsion unit and / or may prevent lubricant, for example oil, from exiting the marine propulsion unit. The DE inner distal seal may prolong the lifespan of the marine propulsion unit and / or may prevent on environment from being contaminated.

[0136] Typically, the DE inner distal seal may be displaced proximally, and in particular, proximally towards the at least one hatch. The DE inner distal seal may be displaced continuously or in intervals. The DE inner distal seal may be displaced axially by a predetermined distance, for example, in line with the at least one hatch. The DE inner distal seal may be displaced axially by a distance determined by the user, for example, 0.3 m. The DE inner distal seal may be displaced according to the maintenance procedure taking place.

[0137] According to some embodiments described herein, the marine propulsion unit may further comprise a DE inner proximal seal. The DE inner proximal seal may be arranged between the DE inner shaft and the DE outer shaft. The DE inner proximal seal may be arranged towards the NDE. In typical embodiments, the DE inner proximal seal may be arranged distally to the at least one hatch. The DE inner proximal seal may comprise at least one seal. For example, the DE inner proximal seal comprises 2, 3, 4, 5, 6, 8, 10, or any number of seals. The DE inner proximal seal may comprise at least one oil seal. For example, the DE inner proximal seal may prevent lubricant from leaving at least one desired region.

[0138] Typically, the DE inner proximal seal may be displaced distally, and in particular, distally towards the at least one hatch. The DE inner proximal seal may be displaced continuously or in intervals. The DE inner proximal seal may be displaced by a predetermined distance, for example, in line with the at least one hatch. The DE inner proximal seal may be displaced by a distance determined by the user, for example, 0.3 m. The DE inner proximal seal may be displaced according to the maintenance procedure taking place.

[0139] Typically, the DE inner distal seal and / or the DE inner proximal seal may comprise two or more seals. The DE inner distal seal and / or the DE inner proximal seal may be attached to at least the DE inner shaft. For example, the DE inner distal seal and / or the DE inner proximal seal may be attached to the DE inner shaft and the DE outer shaft.

[0140] According to some embodiments described herein, the marine propulsion unit may further comprise a hull of the marine propulsion unit or a pod, wherein the pod comprises a pod hull. The hull of the marine propulsion unit or the pod may permit for the DE inner bearing and / or the DEinner bearing pads and / or the DE inner distal seal and / or the DE inner proximal seal to be maintained from within the marine propulsion unit. This may be beneficial in that, for example, for the DE inner bearing and / or the DE inner bearing pads and / or the DE inner distal seal and / or the DE inner proximal seal to be maintained without requiring the marine propulsion unit and over the marine vessel to be dry-docked. This may for example, reduce time required for maintenance and / or permit for an increase in maintenance opportunities available. For example, the marine vessel may be docked at a port as part of its schedule and the DE inner bearing and / or the DE inner bearing pads and / or the DE inner distal seal and / or the DE inner proximal seal may be maintained during this time at the port. For example, the user may enter the marine propulsion unit through a vessel interior of the marine vessel, and may proceed to accessing any of the aforementioned components.

[0141] According to some embodiments described herein the marine propulsion unit may further comprise a DE outer bearing. The DE outer bearing may comprise outer bearing pads. The DE outer bearing and / or the outer bearing pads may be arranged distally in relation to the at least one hatch. According to typical embodiments, the DE outer bearing is a segmented bearing. For example, the DE outer bearing comprises two or more outer bearing pads, for example 3 bearing pads, 5 bearing pads, 8 bearing pads, 12 bearing pads, or any predefined number of bearing pads. The outer bearing pads may be arranged around the DE outer shaft, and in particular around an entire circumference of the DE outer shaft. The outer bearing pads may be configured to be displaced along the DE outer shaft. The outer bearing pads may be slide bearing pads. The outer bearing pads may be configured to be slid along the DE outer shaft. The DE outer bearing and / or outer bearing pads may be displaced radially from the DE outer shaft. In typical embodiments, the DE outer bearing and / or outer bearing pads may be slid and / or displaced radially.

[0142] The DE inner bearing and the DE outer bearing may be coupled. For example, the DE inner bearing and the DE outer bearing may be fluidly coupled. For example, the DE inner bearing may comprise a DE inner bearing chamber and the DE outer bearing may comprise a DE outer bearing chamber. In particular, the DE inner bearing chamber and the DE outer bearing chamber may be fluidly coupled. In typical embodiments, the DE outer shaft comprises at least one bore to fluidly couple the DE inner bearing and the DE outer bearing. The at least one bore may be through the DE outer shaft. Typically, the at least one bore is radially through the DE outer shaft. The fluid coupling may comprise a lubricant, such as grease and / or oil. The DE inner bearing and the DE outer bearing may be arranged coaxially on the rotation axis. The DE outer bearing may at least partially overlap the DE inner bearing. For example, the DE outer bearing and / or the outer bearingpads may be displaced proximally. In particular, the DE outer bearing and / or the outer bearing pads may be displaced axially. The DE outer bearing and / or the outer bearing pads may be displaced axially and proximally along the DE outer shaft. The outer bearing pads may comprise slide bearing pads.

[0143] The DE inner distal seal and the DE outer distal seal may be coupled. For example, the DE inner distal seal and the DE outer distal seal may be fluidly coupled. For example, the DE inner distal seal may comprise a DE inner distal seal chamber and the DE outer distal seal may comprise a DE outer distal seal chamber. In particular, the DE inner distal seal chamber and the DE outer distal seal chamber may be fluidly coupled. The fluid coupling may comprise a lubricant, such as grease and / or oil, and / or water.

[0144] The DE inner bearing and / or the inner bearing pads and / or the DE outer bearing and / or the outer bearing pads may be configured to be individually displaced and / or changed. The DE inner bearing may be rotated with respect to the DE inner shaft, the DE outer shaft, or both. For example, a gliding layer is between the DE inner bearing and the DE inner shaft, the DE outer shaft, or both. The DE inner bearing may be rotated along the DE inner shaft, the DE outer shaft, or both. The DE outer bearing may be rotated with respect to the DE outer shaft, the DE outer bearing housing, or both. For example, a gliding layer is between the DE outer bearing and the DE outer shaft, the DE outer bearing housing, or both. The DE outer bearing may be rotated along the DE outer shaft, the DE outer bearing housing, or both.

[0145] The marine propulsion unit described herein may enable inner bearing and seal change in a contra rotating propeller. For example, the marine propulsion unit described herein may enable maintenance without removing at least one propeller and / or driving conditions.

[0146] According to some embodiments described herein, a method of maintaining a marine propulsion unit is provided. In typical embodiments, the method of maintaining the marine propulsion unit comprises maintaining an azimuthing propulsion unit. The method of maintaining a marine propulsion unit may concern any of the embodiments described herein. The method of maintaining the marine propulsion unit comprise accessing a DE shaft from an interior of a hull of the marine propulsion unit or for example a pod hull of a pod of the marine propulsion unit; and accessing a DE outer bearing arranged between the DE shaft and a DE outer bearing housing; displacing the DE outer bearing; and accessing a DE outer distal seal from within the hull of the marine propulsion unit or the pod hull.

[0147] Accessing the DE outer distal seal typically comprises accessing the DE outer distal seal arranged between the DE shaft and the DE outer bearing housing. The DE outer distal seal is typically accessed upon accessing the DE outer bearing. For example, a user accessing the DE outer distal seal is accessing the DE outer bearing prior to accessing the DE outer distal seal. Typically, the user accessing the DE outer distal seal is accessing the DE shaft prior to accessing the DE outer bearing. Accessing the DE outer distal seal may comprise accessing a distal region with respect to the DE outer bearing.

[0148] Typically, the method of maintaining the marine propulsion unit comprises releasing and displacing a DE outer proximal seal prior to accessing the DE outer bearing. For example, releasing the DE outer proximal seal comprises loosening and / or removing at least one joining mechanism such as a screw and / or nut and bolt, overcoming at least one tolerance fit, and / or releasing at least one joining point. Displacing the DE outer proximal seal typically comprises axially displacing in a typically proximal direction. For example, displacing the DE outer proximal seal comprises axially displacing the DE outer proximal seal along the DE shaft, typically towards a motor of the marine propulsion unit, which is typically the proximal direction. In particular, displacing the DE outer proximal seal comprises axially displacing the DE outer proximal seal proximally along the DE shaft. The DE outer proximal seal may be displaced partly or completely. The method of maintaining the marine propulsion unit may comprise repairing and / or replacing the DE outer proximal seal. Repairing and / or replacing the DE outer proximal seal may occur after accessing the DE outer proximal seal, and in particular, after releasing and displacing the DE outer proximal seal. In typical embodiments, at least one seal is present to prevent water from entering the marine propulsion unit.

[0149] Typically, the DE outer distal seal and / or the DE outer proximal seal comprise sealing elements. Sealing elements may comprise sealing lips. Typically, the sealing elements the DE outer distal seal and / or the DE outer proximal seal is replaced, displaced and / or serviced with the respective seal staying in place, after moving the respective seal to a service position or without removing the respective seal from the DE outer shaft. Typically, sealing elements are handled as described without necessarily displacing and / or servicing the entire DE outer distal seal and / or the entire DE outer proximal seal.

[0150] In typical embodiments, the method comprises displacing the DE outer distal seal and / or the DE outer proximal seal. In typical embodiments, the method comprises servicing the DE outer distal seal and / or the DE outer proximal seal. In typical embodiments, the method comprisesdisplacing the sealing elements of the DE outer distal seal and / or the DE outer proximal seal. In typical embodiments, the method comprises servicing the sealing elements of the DE outer distal seal and / or the DE outer proximal seal. For example, the DE outer distal seal and / or the DE outer proximal seal comprises a seal ring. For example, the DE outer distal seal and / or the DE outer proximal seal comprises a seal housing. The seal housing may comprise housing rings. The seal housing is typically configured to hold the sealing elements.

[0151] In typical embodiments, the method comprises proximally displacing the seal housing. The method typically comprises proximally displacing with respect to the DE outer bearing housing. The method typically comprises displacing the seal housing to the hatch. In particular, the method comprises displacing the seal housing to the hatch on the DE shaft. The method typically comprises servicing the seal housing. Servicing the seal housing typically comprises dismantling the housing rings. Typically, the housing rings are not removed through the hatch. Dismantling the housing rings typically comprises detaching from one another. Typically, the method comprises displacing sealing lips. Typically, the method comprises removing the sealing lips. Typically, displacing and / or removing the sealing lips is after dismantling the housing rings. In typical embodiments, the method comprises replacing the sealing lips. In typical embodiments, the method comprises repairing the sealing lips. In typical embodiments, the method comprises installing new sealing lips. In typical embodiments, the method comprises bonding and / or joining the sealing lips. In typical embodiments, the method comprises bonding to one another. In typical embodiments, the method comprises joining the sealing lips on the DE shaft. In typical embodiments, the method comprises assembling the seal housing. In typical embodiments, the method comprises reassembling the seal housing. In typical embodiments, the method comprises assembling the housing rings.

[0152] Methods of maintaining the marine propulsion unit may comprise displacing the DE outer bearing after accessing the DE outer bearing, and displacing the DE outer distal seal after accessing the DE outer distal seal. For example, displacing the DE outer bearing comprises releasing the DE outer bearing. Displacing the DE outer distal seal typically comprises releasing the DE outer distal seal. The method of maintaining the marine propulsion unit permits for maintaining the marine propulsion unit from within the marine propulsion unit.

[0153] In some embodiments, displacing any of the DE outer bearing, the DE outer distal seal, the DE outer proximal seal, or any combination thereof, comprises axially displacing along the DE shaft and / or radially displacing from the DE shaft. For example, axially displacing the DE outerbearing, the DE outer distal seal, the DE outer proximal seal, or any combination thereof, comprises displacing in a proximal direction. For example, radially displacing the DE outer bearing, the DE outer distal seal, the DE outer proximal seal, or any combination thereof, comprises displacing through at least one hatch in the DE outer bearing housing. For example, radially displacing the DE outer proximal seal allows for axially displacing the DE outer bearing. For example, radially displacing the DE outer bearing allows for axially and / or radially displacing the DE outer distal seal.

[0154] Typically, axially moving or displacing the DE outer bearing, the DE outer distal seal, the DE outer proximal seal, or any combination thereof, comprises, axially moving or displacing the DE outer bearing, the DE outer distal seal, or the DE outer proximal seal to a service position. For example, the service position may be in a proximal location with respect to the DE outer bearing housing. For example, the service position may be between the DE outer bearing housing and a motor of the marine propulsion unit. In typical embodiments, the service position is in a location between the DE outer bearing housing and a motor of the marine propulsion unit, and in particular, the location is proximal to the DE outer bearing housing and distal to the motor. For example, the service position for the DE outer bearing, the DE outer distal seal, or the DE outer proximal seal may be the same for each, different for each, or a combination thereof. The service position might also be a removal position or might be named as a removal position.

[0155] Typically, methods of maintaining a typical CRP marine propulsion unit as described herein comprises displacing any of: a DE inner proximal seal arranged proximally between the DE inner shaft and the DE outer shaft, a DE inner bearing arranged between the DE inner shaft and the DE outer shaft, a DE inner distal seal arranged distally between the DE inner shaft and the DE outer shaft, or any combination thereof, through a hatch in the DE outer shaft.

[0156] Typical methods comprise removing any of a DE inner proximal seal, a DE inner bearing, a DE inner distal seal, or any combination thereof, through at least one hatch. The at least one hatch may be on the DE shaft.

[0157] Typically, the method of maintaining the marine propulsion unit may further comprise installing and / or replacing any of: the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, the DE inner distal seal, the DE inner bearing, the DE inner distal seal, and in particular with a new component and / or at least a new portion thereof.

[0158] Typically, a user may perform the method of maintaining the marine propulsion unit described herein. For example, the user is accessing the DE shaft from the vessel interior or pod hull of the marine propulsion unit. For example, the user is releasing and / or displacing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof, using at least one hand and / or at least one tool. The user may perform the method of maintaining the marine propulsion unit described herein by accessing the marine propulsion unit through a vessel interior.

[0159] According to some embodiments described herein, a method of maintaining an marine propulsion unit is provided, particularly the marine propulsion unit described herein. In typical embodiments, the method of maintaining the marine propulsion unit comprises maintaining an azimuthing propulsion unit. The method of maintaining the marine propulsion unit described herein comprises opening a hatch of a DE outer shaft of the marine propulsion unit; and accessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft. Typically, the method of maintaining the marine propulsion unit may be performed within the marine propulsion unit described herein. In particular, the method of maintaining the marine propulsion unit may be performed without requiring for the marine propulsion unit and / or a marine vessel to be drydocked.

[0160] According to some embodiments described herein, the method of maintaining the marine propulsion unit may further comprise, after accessing the DE inner bearing to the hatch, displacing the DE inner bearing. The method may comprise releasing the DE inner bearing. In particular, releasing the DE inner bearing may occur prior to displacing the DE inner bearing. For example, the DE inner bearing may be secured between the DE inner shaft and the DE outer shaft. Releasing of the DE inner bearing may enable the displacing of the DE inner bearing. For example, the method comprises displacing the DE inner bearing towards the motor, preferably without removing a portion through the hatch. For example, the method comprises displacing the DE inner bearing at least partially through the hatch. For example, the method comprises displacing the entire DE inner bearing through the hatch.

[0161] Typically, displacing the DE inner bearing may comprise removing the DE inner bearing through the hatch. For example, removing the DE inner bearing may comprise proximally displacing the DE inner bearing to a position in line with the hatch. Upon displacing the DE inner bearing to the position in line with the hatch, the method may comprise extracting the DE inner bearing, in particular extracting the DE inner bearing through the hatch. Typically, displacing theDE inner bearing comprises displacing the DE inner bearing to a service position. When the DE inner bearing is at the service position, the method of maintaining the marine propulsion unit typically comprises servicing the DE inner bearing. For example, servicing the DE inner bearing may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular, servicing the DE inner bearing may be for the entire DE inner bearing or at least a portion thereof. For example, servicing the DE inner bearing comprises servicing at least one wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE inner bearing is through the hatch. Typically, servicing the DE inner bearing is within the hatch. Typically, servicing the DE inner bearing is outside the hatch.

[0162] Typically, displacing the DE inner bearing may comprise axially displacing the DE inner bearing a distance of at least 0.1 m, 0.2 m, 0.3 m, up to 1.5 m, or any distance therebetween. For example, displacing the DE inner bearing may comprise displacing the DE inner bearing within a region between the DE inner shaft and the DE outer shaft.

[0163] Typically, the method of maintaining the marine propulsion unit further comprises installing the DE inner bearing and / or replacing the DE inner bearing, and in particular with a new DE inner bearing and / or at least a new portion thereof.

[0164] According to some embodiments described herein, the method of maintaining the marine propulsion unit may further comprise, after displacing the DE inner bearing, accessing a DE inner distal seal through the hatch, and displacing the DE inner distal seal. Typically, displacing the DE inner bearing comprises displacing the DE inner distal seal to a service position. The service position may be proximal to the at least one hatch. Typically, displacing the DE inner bearing comprises partly or completely displacing the DE inner bearing through the at least one hatch. Typically, displacing the DE inner bearing comprises displacing the DE inner distal seal to a service position and partly or completely displacing the DE inner bearing through the at least one hatch. The method may comprise releasing the DE inner distal seal. In particular, releasing the DE inner distal seal may occur prior to displacing the DE inner distal seal. For example, the DE inner distal seal may be secured between the DE inner shaft and the DE outer shaft. Releasing of the DE inner distal seal may enable the displacing of the DE inner distal seal.

[0165] Typically, displacing the DE inner distal seal may comprise removing the DE inner distal seal through the hatch. For example, removing the DE inner distal seal may comprise proximallydisplacing the DE inner distal seal to a position in line with the hatch. Upon displacing the DE inner distal seal to the position in line with the hatch, the method may comprise extracting the DE inner distal seal, in particular extracting the DE inner distal seal through the hatch. Typically, displacing the DE inner distal seal comprises displacing the DE inner distal seal to a service position. When the DE inner distal seal is at the service position, the method of maintaining the marine propulsion unit typically comprises servicing the DE inner distal seal. For example, servicing the DE inner distal seal may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular, servicing the DE inner distal seal may be for the entire DE inner distal seal or at least a portion thereof. For example, servicing the DE inner distal seal comprises servicing at least one wearable part. Typically, a seal, such as a lip seal, is a wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE inner distal seal is through the hatch. Typically, servicing the DE inner distal seal is within the hatch. Typically, servicing the DE inner distal seal is outside the hatch.

[0166] Typically, displacing the DE inner distal seal may comprise axially displacing the DE inner distal seal a distance of at least 0.1 m, 0.2 m, 0.3 m, up to 3 m, or any distance therebetween. For example, displacing the DE inner distal seal may comprise displacing the DE inner distal seal within a region between the DE inner shaft and the DE outer shaft.

[0167] Typically, the method of maintaining the marine propulsion unit may further comprise installing the DE inner distal seal and / or replacing the DE inner distal seal, and in particular with a new DE inner distal seal and / or at least a new portion thereof.

[0168] According to some embodiments described herein, the method of maintaining the marine propulsion unit may further comprise accessing a DE inner proximal seal through the hatch, and displacing the DE inner proximal seal. The method may comprise releasing the DE inner proximal seal. In particular, releasing the DE inner proximal seal may occur prior to displacing the DE inner proximal seal. For example, the DE inner proximal seal may be secured between the DE inner shaft and the DE outer shaft. Releasing of the DE inner proximal seal may enable the displacing of the DE inner proximal seal.

[0169] Typically, displacing the DE inner proximal seal may comprise removing the DE inner proximal seal through the hatch. For example, removing the DE inner proximal seal may comprise distally displacing the DE inner proximal seal to a position in line with the hatch. Upon displacingthe DE inner proximal seal to the position in line with the hatch, the method may comprise extracting the DE inner proximal seal, in particular extracting the DE inner proximal seal through the hatch. Typically, displacing the DE inner proximal seal comprises displacing the DE inner proximal seal to a service position. When the DE inner proximal seal is at the service position, the method of maintaining the marine propulsion unit typically comprises servicing the DE inner proximal seal. For example, servicing the DE inner proximal seal may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular, servicing the DE inner proximal seal may be for the entire DE inner proximal seal or at least a portion thereof. For example, servicing the DE inner proximal seal comprises servicing at least one wearable part. Typically, a seal, such as a lip seal, is a wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE inner proximal seal is through the hatch. Typically, servicing the DE inner proximal seal is within the hatch. Typically, servicing the DE inner proximal seal is outside the hatch.

[0170] Typically, displacing the DE inner proximal seal may comprise axially displacing the DE inner proximal seal a distance of at least 0.1 m, 0.2 m, 0.3 m, up to 3 m, or any distance therebetween. For example, displacing the DE inner proximal seal may comprise displacing the DE inner proximal seal within a region between the DE inner shaft and the DE outer shaft.

[0171] Typically, the method of maintaining the marine propulsion unit may further comprise installing the DE inner proximal seal and / or replacing the DE inner proximal seal, and in particular with a new DE inner proximal seal and / or at least a new portion thereof.

[0172] According to some embodiments described herein, the method of maintaining the marine propulsion unit, displacing any of the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, or any combination thereof, may comprise axially displacing along the DE inner shaft. For example, displacing any of the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, or any combination thereof, may comprise sliding, in particular axially, along the DE inner shaft. For example, displacing any of the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, or any combination thereof, may comprise rotating, preferably rotating to displace the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, the DE outer shaft, the DE inner shaft, or any combination thereof.

[0173] According to some embodiments described herein, the method of maintaining the marine propulsion unit, comprises a marine propulsion unit which comprises: a DE outer proximal seal, aDE outer bearing, a DE outer distal seal, or any combination thereof. The method typically further comprises displacing any of a DE outer proximal seal, a DE outer bearing, a DE outer distal seal, or any combination thereof. For example, displacing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof, may comprise axially displacing along the DE outer shaft and / or sliding along the DE outer shaft and / or radially displacing from the DE outer shaft. Typically, displacing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof, comprises displacing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof to a service position. When the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is at the service position, the method of maintaining the marine propulsion unit typically comprises servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof. For example, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof may comprise: repairing, replacing, installing, removing, or any combination thereof. In particular, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof may be for the entire DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof, or at least a portion thereof. For example, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof comprises servicing at least one wearable part. The at least one wearable part may be defined as any part which needs to be serviced, and / or is due for service. Typically, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is through the hatch. Typically, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is within the hatch. Typically, servicing the DE outer proximal seal, the DE outer bearing, the DE outer distal seal, or any combination thereof is outside the hatch.

[0174] The method of maintaining the marine propulsion unit may comprise servicing the DE inner proximal seal and / or the DE inner distal seal. The method of maintaining the marine propulsion unit may comprise repairing and / or replacing the DE inner proximal seal and / or the DE inner distal seal. Repairing and / or replacing the DE inner proximal seal and / or the DE inner distal seal may occur after accessing the DE inner proximal seal and / or the DE inner distal seal, and in particular, after releasing and displacing the DE inner proximal seal and / or the DE inner distal seal.

[0175] Typically, the DE inner distal seal and / or the DE inner proximal seal comprise sealing elements. Sealing elements may comprise sealing lips. Typically, the sealing elements the DEinner distal seal and / or the DE inner proximal seal is replaced, displaced and / or serviced with the respective seal staying in place, after moving the respective seal to a service position or without removing the respective seal from the DE inner shaft. Typically, sealing elements are handled as described without necessarily displacing and / or servicing the entire DE inner distal seal and / or the entire DE inner proximal seal.

[0176] In typical embodiments, the method comprises displacing the DE inner distal seal and / or the DE inner proximal seal. In typical embodiments, the method comprises servicing the DE inner distal seal and / or the DE inner proximal seal. In typical embodiments, the method comprises displacing the sealing elements of the DE inner distal seal and / or the DE inner proximal seal. In typical embodiments, the method comprises servicing the sealing elements of the DE inner distal seal and / or the DE inner proximal seal. For example, the DE inner distal seal and / or the DE inner proximal seal comprises a seal ring. For example, the DE inner distal seal and / or the DE inner proximal seal comprises a seal housing. The seal housing may comprise housing rings. The seal housing is typically configured to hold the sealing elements. Typically, servicing comprises cutting the seal rings.

[0177] In typical embodiments, the method comprises proximally and / or distally displacing the seal housing. The method typically comprises proximally and / or distally displacing with respect to the DE inner bearing housing. The method typically comprises displacing the seal housing to the hatch. In particular, the method comprises displacing the seal housing to the hatch on the DE shaft. The method typically comprises servicing the seal housing. Servicing the seal housing typically comprises dismantling the housing rings. Typically, the housing rings are not removed through the hatch. Dismantling the housing rings typically comprises detaching from one another. Typically, the method comprises displacing sealing lips. Typically, the method comprises removing the sealing lips. Typically, displacing and / or removing the sealing lips is after dismantling the housing rings. In typical embodiments, the method comprises replacing the sealing lips. In typical embodiments, the method comprises repairing the sealing lips. In typical embodiments, the method comprises installing new sealing lips. In typical embodiments, the method comprises bonding and / or joining the sealing lips. In typical embodiments, the method comprises bonding to one another. Typically, bonding is done through the at least one hatch. Typically, in case of elastomer seals, chemicals such as glue, compression, and heat are used in bonding. In typical embodiments, the method comprises joining the sealing lips on the DE shaft. Typically, in case of polyurethane seals, bonding and / or joining comprises heating two ends of the seal ring and pressing the two ends together. In typical embodiments, the method comprisesassembling the seal housing. In typical embodiments, the method comprises re-assembling the seal housing. In typical embodiments, the method comprises assembling the housing rings.

[0178] Typically, the DE inner shaft and / or the DE shaft may be supported. Supporting the DE inner shaft and / or the DE shaft may provide more room to manipulate the remaining components in the marine propulsion unit.

[0179] Typically, a user may perform the method of maintaining the azimuthing propulsion unit described herein. For example, the user may open the hatch and may access the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal. The user may further perform the displacing of the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal. For example, the user may reach into the region accessible through the at least one hatch, and may displace any of the aforementioned components and / or subsidies thereof. The user may perform the opening of the hatch and / or the displacing of the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal using their labour and / or tools. For example, the user may employ at least one rod, threaded bar, grappling tool, and / or any tool suitable for releasing and displacing the DE inner bearing, the DE inner distal seal, and / or the DE inner proximal seal.

[0180] For example, the user may access the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal. The user may further perform the displacing of the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal. The user may perform the displacing of the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal using their labour and / or tools. For example, the user may employ at least one rod, threaded bar, grappling tool, and / or any tool suitable for releasing and displacing the DE outer bearing, the DE outer distal seal, and / or the DE outer proximal seal.

[0181] Embodiments of the present invention provide marine propulsion units, in particular marine propulsion units with an improved drive end shaft structure enabling inner bearing and seal change. With exemplary embodiments, the bearings and / or the seals might undergo maintenance and / or might be changed without it being mandatory to bring the vessel into a dry dock. For example, before removing the seals, shafts might be sealed against the water with at least one temporary seal applied from the waterside of the hull of the marine vessel to allow a seal change whilst the vessel is in a swimming condition. For example, the marine propulsion unit comprises at least one temporary seal. In particular, the at least one temporary seal is configured to be activated on demand.

[0182] In the view of the foregoing, the present disclosure is directed to a bearing unit for a marine propulsion unit, a marine propulsion unit comprising a bearing unit and a method of supporting an inner shaft and an outer shaft in a marine propulsion unit.

[0183] According to an aspect of the present disclosure, a bearing unit for a marine propulsion unit is provided. The marine propulsion unit includes a rotatable inner shaft and a rotatable outer shaft, wherein the inner shaft runs at least partially within the outer shaft. The bearing unit includes: a bearing arrangement including at least one axial bearing (especially axial bearings) for the inner shaft and the outer shaft, wherein the bearing arrangement is configured for supporting at least a part of the inner shaft and the outer shaft; and a bearing housing for housing the bearing arrangement and the part of the inner shaft and the outer shaft to be supported by the bearing arrangement. The bearing arrangement is configured for allowing a transfer of axial forces between the outer shaft and the inner shaft. According to embodiments described herein, a marine propulsion unit including a bearing unit as described herein is provided.

[0184] With the bearing unit according to embodiments described herein, the shafts of the marine propulsion unit can be supported in a space-saving arrangement and, at the same time, the maintenance, repair and replacement of parts of the bearing arrangement, or parts of / at the bearing housing is facilitated.

[0185] Typically, the bearing arrangement includes a first axial bearing between the inner shaft and the outer shaft for allowing the transfer of axial forces between the inner shaft and the outer shaft. In some embodiments, the bearing arrangement includes the first axial bearing between the inner shaft and the outer shaft, a second axial bearing arranged between a bearing housing wall and the inner shaft, and a third axial bearing arranged between a bearing housing wall and the outer shaft. The arrangement of the axial bearings between the shafts as well as a common placement of the axial bearing(s) for both shafts allows for an efficient, space-saving, and compact arrangement of the bearings used for the shafts of the marine propulsion unit.

[0186] In some embodiments, the bearing housing includes at least one hatch or opening for reaching into the inside of the bearing housing. Especially, the at least one hatch is configured for allowing access to the axial bearing(s), maintenance of the axial bearing(s) and replacement of the axial bearing(s) of the bearing arrangement for the inner shaft and the outer shaft. Additionally, or alternatively, the at least one hatch allows for access to the housing for allowing maintenance, repair or replacement of the radial bearing(s) and / or other elements within, at or near the bearinghousing (such as seals and the like). This facilitates the maintenance, repair and replacement of elements of the marine propulsion unit, and saves time and costs.

[0187] According to some embodiments, the bearing unit may inlcude an oil seal. In particular, the oil seal may be located between the inner shaft and the outer shaft, especially between a flange of the inner shaft and a flange of the outer shaft. In some embodiments, the oil seal may be located under (inside) the first bearing. Especially, the oil seal may be removable throug the at least one hatch. More specifically, the first bearing may be removed at least partly to open up a maintenance route / space for maintenance, repair or exchange of the oil seal, especially via hatch. In some embodiments, the oil seal may include an oil seal housing. According to some embodiments, the oil seal housing part can be fastened to one of the inner shaft and the outer shaft, or both (or the respective flanges of the shafts). Typically, the oil seal may contain elastic lips seals against liner.

[0188] According to some embodiments described herein, at least one of the axial bearings (and / or, optionally, at least one of the radial bearings) of the bearing arrangement is a pad bearing. A pad bearing provides a reliable function with a simple design. In some embodiments, the pad bearing can easily be removed from the bearing housing due to its simple design and uncomplicated montage possibilities.

[0189] According to embodiments described herein, a marine propulsion unit, especially an azimuthing propulsion unit, is provided including a bearing unit according to embodiments described herein. Especially, the marine propulsion unit is configured for allowing access of a person to a hatch of the bearing housing of the bearing unit. The marine propulsion unit with the bearing unit according to embodiments described herein, enables an easy access to the complete bearings of the shafts of the NDE side of the marine propulsion unit.

[0190] According to another aspect of the present disclosure, a method of supporting an inner shaft and an outer shaft in a marine propulsion unit according to any of the embodiments described herein is provided, wherein the marine propulsion unit includes the inner shaft and the outer shaft and wherein the inner shaft runs at least partially within the outer shaft. The method includes providing a bearing arrangement and a bearing housing for housing the bearing arrangement, the bearing arrangement including at least one axial bearing for the inner shaft and the outer shaft; and arranging the axial bearing of the bearing arrangement for allowing a transfer of axial forces between the outer shaft and the inner shaft.

[0191] According to some embodiments described herein, arranging the axial bearings for a transfer of axial forces between the outer shaft and the inner shaft includes arranging a first axial bearing between the inner shaft and the outer shaft. In some embodiments, which may be combined with other embodiments described herein, arranging the first axial bearing between the inner shaft and the outer shaft includes utilizing a bearing pad mounted between the inner shaft and the outer shaft. This may provide a compact, reliable, and cost-efficient solution for supporting both shafts of the marine propulsion unit. Furthermore, the transfer of axial forces between the inner shaft and the outer shaft is enabled by the one axial bearing between the two shafts.

[0192] Typically, the method according to some embodiments described herein may include accessing the bearing arrangement (or other elements, such as oil seals, and the like) within the bearing housing through a hatch or opening. In particular, the method according to embodiments described herein, may include performing repair, maintenance, and / or replacement of the bearing arrangement through the at least one hatch or opening. Accessing the inside of the bearing housing through a hatch (which is in some embodiments accessible from the inside of the pod of the azimuthing propulsion unit) facilitates maintenance and repair, and safes time and costs for the maintenance and repair. In some embodiments, the bearing unit may include an oil seal, which may especially be located between the inner shaft and the outer shaft, or their flanges. Typically, the method may include removing the oil seal from the bearing unit through the at least one hatch. According to some embodiments, which may be combined with other embodiments described herien, the method may inlcude removing the first bearing (being e.g. designed as a pad bearing) at least partly to open up a maintenance route / space for maintenance, repair or exchange of the oil seal, especially via hatch. In some embodiments, the oil seal may include an oil seal housing. According to some embodiments, the oil seal housing part can be fastened on the inner and / or outer shaft, or on or into one (or both) of the flanges of the inner shaft and the outer shaft.

[0193] Further advantages, features, aspects and details that can be combined with embodiments described herein are evident from the dependent claims, the description and the drawings.

[0194] In the view of the foregoing, the present disclosure is directed to a marine propulsion unit and a method for construction and assembly of a plurality of shafts of the of a marine propulsion unit.

[0195] According to an aspect of the present disclosure, a marine propulsion unit comprising a motor, the marine propulsion unit further comprising a rotatable inner shaft coupled to the motor,and a rotatable outer shaft coupled to the motor, wherein the inner shaft runs at least partially within the outer shaft, and wherein the inner shaft comprises a distal inner segment and a proximal inner segment is provided.

[0196] According to another aspect of the present disclosure, a method for mounting an marine propulsion unit, comprising providing an outer shaft with a hollow cross section, and providing an inner shaft, wherein the inner shaft comprises a distal inner segment and a proximal inner segment, wherein the method further comprises inserting at least one of or both of the distal inner segment and the proximal inner segment into the outer shaft, and coupling the distal inner segment to the proximal inner segment is provided.

[0197] The propeller unit is driven by a motor. In some embodiments, the motor is an internal combustion engine. The motor may by a diesel engine, preferably a two-stroke diesel engine. The motor may be a marine LNG engine. The motor may by a steam turbine or a gas-turbine engine. Typically, the motor is mechanically connected to the propeller via a gearbox.

[0198] Typically, the motor is an electric motor. Typically, the electric motor has a power of at least 100 kW, at least 1 MW, at least 2 MW, at least 5 MW, at least 10 MW or at least 15 MW. The electric motor is typically arranged within the pod or within the hull of the marine vessel. Particularly, the electric motor is mechanically connected to the propeller gearlessly and / or without a clutch. Typically, a rotation axis of the electric motor is identical to a rotation axis of the propeller unit. In particular, an output shaft of the electric motor may be identical to the drive shaft of the propeller unit or may be gearlessly connected to a drive shaft of the propeller unit. The output shaft of the electric motor typically is coaxial to the drive shaft of the propeller unit. In typical embodiments, for a propeller unit comprising an outer shaft propeller and an inner shaft propeller, in particular for the contra rotating propeller unit, the outer shaft propeller and the inner shaft propeller may be driven by the same electric motor.

[0199] The marine propulsion unit includes a motor, an inner shaft and an outer shaft. The inner shaft is coupled to the motor. The outer shaft is coupled to the motor. The inner shaft runs at least partially within the outer shaft. The inner shaft includes a distal inner segment and a proximal inner segment.

[0200] In typical embodiments, the motor is a dual rotor electric motor. The dual rotor electric motor may include an outer rotor and an inner rotor. The inner rotor is typically arranged coaxiallywithin the outer rotor. In such embodiments, the inner shaft is typically coupled to the inner rotor of the motor and the outer shaft is typically coupled to the outer rotor of the motor.

[0201] In some embodiments, the outer shaft includes an NDE outer shaft and the inner shaft includes an NDE inner shaft. In some embodiments, wherein the marine propulsion unit is an azimuthing propulsion unit, the NDE outer shaft and NDE inner shaft are both located on the NDE and within a pod of the azimuthing propulsion unit. In some embodiments, the NDE outer shaft and NDE inner shaft are both located on the NDE and within a hull. The NDE outer shaft and NDE inner shaft are located on the opposite side of the electric motor as the propeller or the propellers of the marine propulsion unit.

[0202] In typical embodiments, the NDE outer shaft and NDE inner shaft both rotate along the same rotation axis. Typically, the rotation axis is the rotation axis of the electric motor.

[0203] Typically, the NDE inner shaft runs at least partially within the NDE outer shaft. In some embodiments, the NDE inner shaft is longer than the NDE outer shaft or runs within the whole elongation of the NDE outer shaft. Typically, the NDE inner shaft runs within the whole elongation of the NDE outer shaft and comprises sections of shaft to both sides, regarding the direction of the rotation axis, of the NDE outer shaft. Typically, the NDE inner shaft runs within the whole elongation of the NDE outer shaft and comprises a section of shaft to one side, regarding the direction of the rotation axis, of the NDE outer shaft.

[0204] In typical embodiments, the NDE inner shaft is longer regarding the elongation in direction of the rotation axis than the NDE outer shaft. Typically, the length of NDE inner shaft is 1.1, 1.2, 1.3, 1.5 or 2.0 times longer than the NDE outer shaft. In typical embodiments, the length of NDE inner shaft is 1.45 times longer than the NDE outer shaft. Typically, the NDE inner shaft and NDE outer shaft are exactly or nearly the same length. In typical embodiments, the NDE outer shaft is longer regarding the elongation in direction of the rotation axis than the NDE inner shaft.

[0205] In typical embodiments, the NDE outer shaft comprises a hollow cross section in at least one elongated section of the NDE outer shaft. Typically, the NDE outer shaft comprises a hollow cross section regarding its whole elongation. The elongation of NDE inner shaft and the NDE outer shaft are considered in the orientation of the rotation axis.

[0206] In typical embodiments, the NDE inner shaft is coupled to the inner rotor of the electric motor. In typical embodiments, the NDE inner shaft is coupled to the inner rotor by an inner rotorconnection. The inner rotor connection may be an inner rotor screw connection. The inner rotor screw connection may comprise a plurality of screws, fasteners or bolts, wherein the screws, fasteners or bolts may be of identical dimensions and type or may differentiate from each other. Typically, the inner rotor screw connection comprises a plurality of screws, fasteners or bolts. The screws, fasteners or bolts of the inner rotor screw connection are typically arranged along the circumference of the inner rotor. The screws, fasteners or bolts of the inner rotor screw connection are typically arranged on a bolt circle of the inner rotor screw connection. The screws, fasteners or bolts of the inner rotor screw connection may be arranged on more than one bolt circle.

[0207] In some embodiments, the NDE inner shaft or at least a section, especially the proximal inner segment of the NDE inner shaft is an integral part of the inner rotor. In exemplary embodiments, the proximal inner segment of the NDE inner shaft might be the proximal flange, which might form the NDE side cap of the inner rotor.

[0208] In typical embodiments, the NDE outer shaft is coupled to the outer rotor of the electric motor. In typical embodiments the NDE outer shaft is coupled to the outer rotor by an outer rotor connection. The outer rotor connection may be an outer rotor screw connection. The outer rotor screw connection may comprise a plurality of screws, fasteners or bolts, wherein the screws, fasteners or bolts may be of identical dimensions and type or may differentiate from each other. Typically, the outer rotor screw connection comprises a plurality of screws, fasteners or bolts. The screws, fasteners or bolts of the outer rotor screw connection are typically arranged along the circumference of the outer rotor. The screws, fasteners or bolts of the outer rotor screw connection are typically arranged on a bolt circle of the outer rotor screw connection. The screws, fasteners or bolts of the outer rotor screw connection may be arranged on more than one bolt circle.

[0209] In some embodiments, the NDE outer shaft or at least a section, especially the proximal outer segment of the NDE outer shaft is an integral part of the outer rotor. In exemplary embodiments, the proximal outer segment of the NDE outer shaft might be the proximal flange, which might form the NDE side cap of the outer rotor.

[0210] Typically, the threads of the inner rotor screw connection and the outer rotor screw connection are manufactured into the respective rotor and the through bores of the screw connections are part of the respective shaft or the flange of the respective shaft. In some embodiments, the threads of the inner rotor screw connection and the outer rotor screw connectionare manufactured into the respective shaft and the through bores of the screw connections are part of the respective rotor.

[0211] The outer rotor connection and the inner rotor connection may be realized using other types of connections. The outer rotor connection and the inner rotor connection may be of the same type of connection or may be of different types of connection. Typical types of connections for the outer rotor connection and the inner rotor connection include rivet connections, any type of welded connections, adhesive connections, soldered connections, shrink-fit connections, tapered joint connections, bolt connections or any combination of connection types.

[0212] In typical embodiments, the proximal inner segment of the NDE inner shaft is elongated and runs through the inner rotor and comprises a section of the NDE inner shaft on the drive end side. Typically, the section of NDE inner shaft on the drive end side is coupled to the inner shaft propeller. In some embodiments, the inner rotor is coupled to the section of NDE inner shaft on the drive end side. Typically, the inner rotor or the inner shaft propeller are coupled to the section of NDE inner shaft on the drive end side by means of a shrink fit or a tapered joint.

[0213] The outer rotor connection and the inner rotor connection may be centered by a centering collar. The centering collar may be located on the respective rotor or the respective shaft. The centering enables the respective rotor and the respective shaft to align to the rotation axis of each other and therefore reduces potential unbalances.

[0214] In typical embodiments, the NDE inner shaft or the NDE outer shaft comprises a plurality of segments. Typical embodiments of the NDE inner shaft is composed of 2 or 3 segments. Typically, the NDE inner shaft comprises or is composed of a distal inner segment and a proximal inner segment. Typical embodiments of the NDE outer shaft is composed of 2 or 3 segments. Typically, the NDE outer shaft comprises or is composed of a distal outer segment and a proximal outer segment. Typically, the segments being arranged next to each other regarding the direction of the rotation axis. Typically, the segments of the respective shaft are coupled together to form the respective shaft.

[0215] Within this document the terms of location are related to the electric motor of the marine propulsion unit. Therefore, in the case of the NDE inner shaft and the NDE outer shaft the terms distal and proximal may be understood related to the location of the electric motor.

[0216] Typically, the distal inner segment, the distal outer segment, the proximal inner segment or the proximal outer segment are monolithic. In some embodiments, at least some of the distal inner segment, the distal outer segment, the proximal inner segment or the proximal outer segment are monolithic and comprise one or more parts being mounted thereto. Typical parts include flanges, washers, retaining rings, lock or shaft nuts, sleeves, distance rings, liners, or bearing rings.

[0217] In typical embodiments, at least one of the NDE inner shaft and the NDE outer shaft comprises a dismountable flange. The dismountable flange forms one of the segments of the respective shaft. In some embodiments, the dismountable flange forms the proximal inner segment or the distal inner segment. In some embodiments, the dismountable flange forms the proximal outer segment or the distal outer segment. Typically, the dismountable flange is located to one end of the respective shaft regarding the elongation of the respective shaft.

[0218] Due to the possibility to dismount the dismountable flange from the respective shaft, mounting of components onto the outer surface of the respective shaft may be enabled. In some embodiments, this enables the mounting of an integral component, which otherwise could only be mounted if the component is of a split design.

[0219] Typically, the distal outer segment and the proximal outer segment are coupled with an outer shaft connection. The distal inner segment and the proximal inner segment are coupled with an inner shaft connection in typical embodiments.

[0220] In some embodiments, the outer shaft connection is an outer shaft screw connection. Typically, the inner shaft connection is an inner shaft screw connection. In typical embodiments, shaft segments can be disassembled in a non-destructive way. Especially during maintenance this enables the at least partial disassembly of the respective shaft even in constraint spatial conditions.

[0221] Typically, the inner shaft screw connection comprises a plurality of screws, fasteners or bolts. Typically, the outer shaft screw connection comprises a plurality of screws, fasteners or bolts. In some embodiments, the screws, fasteners or bolts of one respective connection are of the same type. In some embodiments, the screws, fasteners or bolts of one respective connection are of more than one type.

[0222] In typical embodiments, the threads of the inner shaft screw connection or the outer shaft screw connection are manufactured within the proximal inner segment or the proximal outersegment respectively. The through bores of the respective screw, fastener or bolt connection are within the distal inner segment or the distal outer segment respectively. With other words, the screws, fasteners or bolts are run through the respective bore within the respective distal segment, before the screws, fasteners or bolts are screwed into the respective threads of the respective proximal segment.

[0223] In some embodiments, the outer shaft connection or the inner shaft connection are realized using other types of connections. The outer shaft connection and the inner shaft connection may be of the same connection type or may be of different connection types. Typical types of connections for the outer shaft connection and the inner shaft connection include rivet connections, any type of welded connections, adhesive connections, soldered connections, shrink-fit connections, tapered joint connections, bolt connections or any combination of connection types.

[0224] The outer shaft connection and the inner shaft connection may be centered by a centering collar. The centering collar may be located on each of the respective segments of the respective connection. The centering enables the respective segments to align to the rotation axis of each other and therefore reduces potential unbalances.

[0225] In typical embodiments, the NDE inner shaft and the NDE outer shaft are manufactured out of the same material. Typically, the NDE inner shaft and the NDE outer shaft are manufactured out of the different materials. Typically, all respective segments of a respective shaft are manufactured out of the same material. The segments of a respective shaft may be manufactured out of different materials. Typical materials include ferrous materials, aluminum alloys, composite materials like fiberglass-reinforced materials or carbon fiber-reinforced materials. Typically, the shafts are manufactured by steel casting or forging. At least parts of the manufacturing may include machining. The shafts or at least parts or segments of the shafts may be manufactured by additive manufacturing.

[0226] In typical embodiments, the NDE inner shaft comprises a proximal inner flange. Typically, the proximal inner flange is part of the proximal inner segment. In typical embodiments, the NDE inner shaft comprises a distal inner flange. Typically, the distal inner flange is part of the distal inner segment.

[0227] Typically, the proximal inner flange is located on the proximal end of the proximal inner segment. In some embodiments, the proximal inner segment comprises a section proximal to theproximal inner flange. In some embodiments, the NDE inner shaft comprises more than two flanges.

[0228] Typically, a flange of a shaft is characterized by a difference in diameter compared to the surrounding section of shaft. In typical embodiments, a flange comprises a wider diameter compared to the adjoining section of shaft. Typically, a flange is located on the end of a shaft regarding the rotation axis. A flange can be advantageous because due to the change in diameter it is possible to arrange more than one connection on one shaft, wherein a potential spatial interference of the connections is reduced or prevented.

[0229] Within this document a flange is typically defined regarding the design of the whole shaft in its mounted stage. A flange might exemplarily be formed by one of the segments of the respective shaft having a wider diameter than one or two of the segments of this shaft with a smaller diameter and neighboring the segment with the wider diameter. The surrounding section of a respective flange, defining the flange due to a difference in diameter can be located on another segment or part of the shaft than the flange itself. In other words, a segment of a shaft without change of diameter itself may form a flange of the shaft it is part of, if the surrounding sections of shaft or the adjoining section of shaft comprises a different diameter. In typical embodiments, a flange is formed by an outer segment of a shaft, which is located to one end of the shaft, wherein the segment comprises a constant outer diameter, wherein the constant outer diameter is wider than the outer diameter of the section of shaft next to the outer segment of the shaft. This description of a flange typically refers to both shafts, the NDE inner shaft and the NDE outer shaft, and their segments, respectively.

[0230] In some embodiments, a flange of a shaft may be formed by a part of the shaft, wherein the part of the shaft and the rest of the shaft comprise a contact in radial direction of the shaft. In other word, a part of a shaft forming a flange and the rest of the shaft overlap regarding the elongation of the shaft at least partially, wherein the cross section of the part of the shaft forming the flange surrounds the cross section of the rest of shaft.

[0231] In typical embodiments, the NDE outer shaft comprises a proximal outer flange. Typically, the proximal outer flange is part of the proximal outer segment. In typical embodiments, the NDE outer shaft comprises a distal outer flange. Typically, the distal outer flange is part of the distal outer segment.

[0232] Typically, the proximal outer flange is located on the proximal end of the proximal outer segment. In some embodiments, the proximal outer segment comprises a section proximal to the proximal outer flange. In some embodiments, the NDE outer shaft comprises more than two flanges.

[0233] Typically, the outer rotor connection is realized at the proximal outer flange. Typically, the inner rotor connection is realized at the proximal inner flange.

[0234] In typical embodiments, the respective rotor connection of the NDE inner shaft or the NDE outer shaft is located on a wider diameter around the rotation axis than the respective shaft connection. Typically, the diameter of the rotor connection is approximately 1.5, 2.0, 3.0, 4.0 or 5.0 times wider than the diameter of the respective shaft connection. Typical embodiments enable sufficient access and space for the mounting and dismounting of the fasteners of the respective connection.

[0235] Typically, the NDE inner shaft or the NDE outer shaft is in a first step of manufacturing at least partially manufactured as an integral shaft. In a second step of manufacturing the shaft is then dived up into segments. In typical embodiments, a manufacturing sequence of the NDE inner shaft or the NDE outer shaft might be preformed as follows: in a first task, distal and proximal segments might be manufactured separately. Thereby, a connection interface area is manufactured precisely to final dimensions. Then, the connection between distal and proximal segments might be fastened, typically with bolts. Final machining is done with shafts connected together, e.g. to get tolerances precise). Afterwards, parts are again detached and pod building can be started. Typical processes as described herein enable, that the required manufacturing tolerances of the respective distal and proximal flange of the respective shaft are achieved.

[0236] In typical embodiments, the NDE inner shaft comprises a hollow cross section in at least one elongated section of the NDE inner shaft. Typically, the NDE inner shaft comprises a hollow cross section regarding its whole elongation. The hollow cross section of the NDE inner shaft may comprise one inner diameter. The hollow cross section of the NDE inner shaft may comprise more than one inner diameter.

[0237] The hollow cross section of the NDE inner shaft enables the installation of components inside of the NDE inner shaft. In typical embodiments, a cable, a wire, a pipe or a line runs at least partially inside of at least a section of the NDE inner shaft.

[0238] Typically, the NDE inner shaft comprises an opening. In some embodiments, the opening is oriented in a radial direction of the NDE inner shaft. A radial direction of the NDE inner shaft runs vertical to the direction of the rotation axis of the NDE inner shaft. Typically, the opening is oriented approximately in a radial direction of the NDE inner shaft. Typically, the NDE inner shaft comprises a plurality of openings, wherein the openings may be located on one circumferential circle of the NDE inner shaft or on different circumferential circles of the NDE inner shaft.

[0239] Typically, the opening is located within a section of the NDE inner shaft comprising a hollow cross section. The opening may run through the whole cross section of the NDE inner shaft. In other words, the opening may create a connection between an inner surface of the NDE inner shaft and an outer surface of the NDE inner shaft.

[0240] Typically, the opening is a bore. In some embodiments, the cross section of the opening is of round form or of elliptical form. Typically, the cross section of the opening is of the shape of a polygon. In typical embodiments, the opening is manufactured by drilling through the cross section of the NDE inner shaft. Typically, the opening is manufactured during the casting or machining process of the NDE inner shaft.

[0241] The opening enables the running of a component from the inside of the NDE inner shaft to the outside of the NDE inner shaft. Typically, a cable, a wire, a line or a pipe is run through the hollow cross section of the NDE inner shaft and run through the opening of the NDE inner shaft to reach the outside of the NDE inner shaft. Such a routing of a cable may be used to run an electric wire or cable to the inner rotor. In the case of an externally excited rotor the electric wire can provide electric power to the inner rotor.

[0242] Typically, the NDE outer shaft comprises an opening. In some embodiments, the opening is oriented in a radial direction of the NDE outer shaft. A radial direction of the NDE outer shaft runs vertical to the direction of the rotation axis of the NDE outer shaft. Typically, the opening is oriented approximately in a radial direction of the NDE outer shaft. Typically, the NDE outer shaft comprises a plurality of openings, wherein the openings may be located on one circumferential circle of the NDE outer shaft or on different circumferential circles of the NDE outer shaft.

[0243] In typical embodiments, the proximal inner flange or the proximal outer flange comprise at least one axial opening. There might be more than one opening in some embodiments, e.g. for cable route and / or maintenance access. The opening runs through the respective flange in exactlyor nearly the orientation of the rotation axis. Typically, the axial opening is located closer to the rotation axis than the outer rotor connection or the inner rotor connection respectively.

[0244] The at least one axial opening may be applied to run a cable or wire from one side of the respective flange to the other side of the respective flange. In some embodiments, such a cable may provide electrical power to the electric motor.

[0245] In some embodiments, the NDE outer shaft is supported by an NDE outer bearing. In some embodiments, the NDE inner shaft is supported by an NDE inner bearing. The NDE outer bearing and the NDE inner bearing may support the respective shaft in axial or radial direction. Typically, the NDE outer bearing is in contact with the distal outer flange. Typically, the NDE inner bearing is in contact with the distal inner flange. In typical embodiments the distal outer flange or the distal inner flange are part of a respective thrust bearing supporting the respective shaft in axial direction.

[0246] Typically, the distal outer flange is located on the proximal end of the distal outer segment. In some embodiments, the distal outer segment comprises a section proximal to the distal outer flange. Typically, the distal inner flange is located on the proximal end of the distal inner segment. In some embodiments, the distal inner segment comprises a section proximal to the distal inner flange.

[0247] In typical embodiments, the section of the NDE inner shaft on the proximal side of the distal inner flange has a smaller outer diameter than the distal inner flange. This section is typically located on the proximal inner segment. In typical embodiments, the section of the NDE outer shaft on the proximal side of the distal outer flange has a smaller outer diameter than the distal outer flange. This section is typically located on the proximal outer segment.

[0248] This profile of the NDE inner shaft and NDE outer shaft respectively may enable the sufficient design of the NDE inner bearing and NDE outer bearing respectively. Due to the elevation of the respective outer flange the respective bearing unit may contact the flange from both sides regarding the direction of the rotation axis. This may enable the support of the respective shaft in direction of the rotation axis.

[0249] In typical embodiments, at least a section of the NDE outer shaft is, regarding the direction of the rotation axis, located in between the distal inner flange and the proximal inner flange. In typical embodiments, the whole NDE outer shaft is, regarding the direction of the rotation axis, located in between the distal inner flange and the proximal inner flange.

[0250] In typical embodiments, the smallest inner diameter of the section of NDE outer shaft in between the distal inner flange and the proximal inner flange is smaller than the outer diameter of the distal inner flange. Typically, the smallest inner diameter of the section of NDE outer shaft in between the distal inner flange and the proximal inner flange is smaller than the outer diameter of the proximal inner flange.

[0251] Typically, due to the design of the NDE inner shaft the mounting of the NDE inner shaft is enabled. Typically, when the coupling between the distal inner segment and the proximal inner segment is open, the NDE inner shaft can be mounted into position.

[0252] In typical embodiments, an integral ring shaped component is mounted onto the outer surface of the NDE outer shaft. Typically, the integral ring shaped component is located in between the proximal outer flange and the distal outer flange. In some embodiments, the NDE outer shaft comprises a waisted outer surface located in between the proximal outer flange and the distal outer flange, wherein the diameter of the waisted outer surface is smaller than the diameter of the proximal outer flange and the distal outer flange. Typically, the integral ring shaped component is mounted onto the waisted outer surface. In typical embodiments, the integral ring shaped component comprises a inner diameter, wherein the inner diameter is smaller than the diameter of the proximal outer flange and the distal outer flange.

[0253] In typical embodiments, the integral ring shaped component is a slip ring unit. Typically, the slip ring unit is part of a system for the transfer of electrical power to the electric motor. Typically, the integral ring shaped component is a seal, for example a non-splitting oil seal. In typical embodiments the integral ring shaped component is a bearing, sensor ring or a washer. In typical embodiments, mounting of the ring shaped component is enabled, when the coupling between the distal outer segment and the proximal outer segment is open, even if the inner diameter is smaller than the diameter of the proximal outer flange and the distal outer flange.

[0254] In typical embodiments, an enclosed volume is defined in between the bearing housing, the NDE inner shaft and the NDE outer shaft. In some embodiments, the enclosed volume is sealed. Typically, the enclosed volume is sealed from the surrounding volume. In some embodiments, the sealing of the enclosed volume is realized with a distal seal, a proximal inner seal and a proximal outer seal.

[0255] Typically, the distal seal is located on the outer surface of NDE inner shaft. In some embodiments, the distal seal is located on the outer surface of the distal inner segment. The distalseal is placed in between the NDE inner shaft and the bearing housing. In typical embodiments, the proximal inner seal is located in between the NDE inner shaft and the NDE outer shaft. In some embodiments, the proximal inner seal is located in between the proximal outer segment and the proximal inner segment. In typical embodiments, the proximal outer seal is located on the outer surface of NDE outer shaft. In some embodiments, the proximal outer seal is located on the outer surface of proximal outer segment. The proximal outer seal is placed in between the NDE outer shaft and the bearing housing.

[0256] Typically, the distal seal, the proximal inner seal or the proximal outer seal are a radial shaft seal. The distal seal, the proximal inner seal or the proximal outer seal may comprise more than one seal. Typically, the distal seal, the proximal inner seal or the proximal outer seal function in one direction or in both directions. Typically, the distal seal, the proximal inner seal or the proximal outer seal prevent a fluid from entering or exiting the enclosed volume.

[0257] In typical embodiments, the proximal inner seal comprises a seal housing and a seal liner. Typically, the seal housing is placed in contact with the NDE outer shaft and the seal liner is placed in contact with the NDE inner shaft. Typically, the seal housing is placed in contact with the NDE inner shaft and the seal liner is placed in contact with the NDE outer shaft.

[0258] In some embodiments, the proximal inner seal is accessible through a proximal service opening. Typically, the proximal service opening is a hatch. In typical embodiments, the proximal service opening is an opening in axial direction within the proximal outer flange. In typical embodiments, the proximal service opening is an opening in radial direction within the outer rotor. Due to the proximal service opening the mounting, maintenance or replacement of the proximal inner seal is typically enabled without the requirement of dismounting parts of the shafts.

[0259] In some embodiments, the proximal inner seal is accessible through a distal service opening. Typically, the distal service opening is a hatch. In typical embodiments, the distal service opening is an opening in radial direction within the NDE outer shaft. Due to the distal service opening the mounting, maintenance or replacement of the proximal inner seal is typically enabled without the requirement of dismounting parts of the shafts. For example, components of the proximal inner seal, like e.g. a lip of the proximal inner seal, may be slid axially to bring them into a service position, e.g. a position accessible through the opening or the hatch. Wear parts of the proximal inner seal, for example lips may be changed or a bonding tool may be used via theopening or the hatch. The hatch may have an openable cover or may be without any cover. There might be one or more hatches present.

[0260] Typically, a method for mounting a marine propulsion unit comprises providing an outer shaft. Further, an inner shaft is provided, wherein the inner shaft comprises a distal inner segment and a proximal inner segment. The method typically includes the insertion of at least one of the distal inner segment and the proximal inner segment into a hollow cross section of the outer shaft. Typically, only the proximal inner segment is inserted into the hollow cross section of the outer shaft. Typically, the proximal inner segment is inserted into the hollow cross section of the outer shaft from a first direction and the distal inner segment is inserted into the hollow cross section of the outer shaft from a second direction, wherein the second direction is opposite of the first direction. Afterward an inner shaft connection is closed and the distal inner segment and the proximal inner segment are coupled together.

[0261] Typically, the outer shaft is a NDE outer shaft and the inner shaft is a NDE inner shaft.

[0262] This method enables the mounting of the NDE inner shaft even if the diameter of a distal inner flange and a diameter of the proximal inner flange are wider than the inner diameter of a section of NDE outer shaft located in between the distal inner flange and the diameter of the proximal inner flange.

[0263] Typically, the providing of the NDE outer shaft of the method for mounting the marine propulsion unit comprises providing a proximal outer segment and a distal outer segment. The proximal outer segment and the distal outer segment are coupled together by closing an outer shaft connection.

[0264] Typically, the method comprises mounting an integral ring shaped component onto an waisted outer surface of the NDE outer shaft. This is typically done before the proximal outer segment and the distal outer segment are coupled together.

[0265] With typical embodiments, the integral ring shaped component can be mounted onto the waisted outer surface of the NDE outer shaft, even if an inner diameter of the integral ring shaped component is smaller than the outer diameter of the distal outer flange and the proximal outer flange. Moreover, during maintenance typical embodiments enable the disassembly or renewal of parts mounted onto the shafts without the total disassembly of the respective shaft.

[0266] Typically, the method for mounting the marine propulsion unit further comprises the closing of an outer rotor connection and the closing of an inner rotor connection.

[0267] In the view of the foregoing, the present disclosure is directed to a sealing unit for a marine propulsion unit, particularly an azimuthing propulsion unit, and a method for servicing a sealing unit in a marine propulsion unit, particularly an azimuthing propulsion unit.

[0268] According to an aspect of the present disclosure, a sealing unit for a marine propulsion unit, particularly for an azimuthing propulsion unit, is provided.

[0269] According to another aspect of the present disclosure, a method for servicing of a sealing unit in a marine propulsion unit, particularly in an azimuthing propulsion unit, according to any of the embodiments described herein is provided.

[0270] In some embodiments, a marine propulsion unit, particularly an azimuthing propulsion unit, comprises a rotatable inner shaft and a rotatable outer shaft. The inner shaft runs at least partially within the outer shaft. The outer shaft runs at least partially within a sealing housing of a marine vessel, particularly a pod. A sealing unit for such a marine propulsion unit, particularly an azimuthing propulsion unit, comprises a plurality of chamber systems, an inner shaft sealing and an outer shaft sealing. Each chamber system of the plurality of chamber systems comprises an inner shaft seal chamber, an outer shaft seal chamber and a passage through the outer shaft fluidly connecting the inner shaft seal chamber and the outer shaft seal chamber. The inner shaft sealing seals the inner shaft seal chambers of the plurality of chamber systems. The outer shaft sealing seals the outer shaft seal chambers of the plurality of chamber systems.

[0271] Typically, a plurality can be understood as at least one, particularly one or more. For example, a plurality of chamber systems can be understood as at least one chamber system, particularly one or more chamber systems.

[0272] In some embodiments, the outer shaft can be a DE outer shaft and the inner shaft can be a DE inner shaft.

[0273] Typically, the fluid connection of the inner chamber and the outer chamber of a chamber system enables fluid transportation between the inner chamber and the outer chamber. Particularly, fluid can be transported through the outer shaft to the inner chamber of each chamber system.

[0274] In some embodiments, the inner shaft sealing can seal an inside of the outer shaft from an outside of the marine vessel, particularly the pod. The outer shaft sealing can seal an inside of the marine vessel, particularly the pod from the outside of the marine vessel, particularly the pod. Particularly, outside of the marine vessel can be understood as outside the exterior of the marine vessel, outside the exterior of the pod, particularly outside the pod hull, outside the hull of the vessel and / or the vessel exterior. Particularly, inside of the outer shaft can be understood as the space inside the outer shaft and / or the space between the outer shaft and the inner shaft.

[0275] In some embodiments, the inner shaft sealing can comprise an inner composure, an outer composure and a plurality of inner sealing elements. Typically, the inner composure, the outer composure and the inner sealing elements can be serviced and / or replaced separately from each other.

[0276] In some embodiments, the inner composure of the inner shaft sealing can be a seal liner and the outer composure of the inner shaft sealing can be a seal housing. The seal liner can rotate with the inner shaft. An inner static sealing between the seal liner and the inner shaft can seal the inside of the outer shaft from the outside of the marine vessel, particularly the pod. The seal housing can rotate with the outer shaft. An outer static sealing between the seal housing and the outer shaft can seal the inside of the outer shaft from the outside of the marine vessel, particularly the pod.

[0277] In some embodiments, the outer composure of the inner shaft sealing can be a seal liner and the inner composure of the inner shaft sealing can be a seal housing. The seal liner can rotate with the outer shaft. An outer static sealing between the seal liner and the outer shaft can seal the inside of the outer shaft from the outside of the marine vessel, particularly the pod. The seal housing can rotate with the inner shaft. An inner static sealing between the seal housing and the inner shaft can seal the inside of the outer shaft from the outside of the marine vessel, particularly the pod.

[0278] Typically, the inner composure of the inner shaft sealing and the outer composure of the inner shaft sealing and / or the inner sealing elements can be serviced individually, e.g. replaced individually. For example, the inner sealing elements and / or the seal liner may experience larger wear in comparison to the seal housing.

[0279] In some embodiments, the outer shaft sealing can comprise an inner composure, an outer composure and a plurality of outer sealing elements. Typically, the inner composure, the outercomposure and the outer sealing elements can be serviced and / or replaced separately from each other.

[0280] In some embodiments, the inner composure of the outer shaft sealing can be a seal liner and the outer composure of the outer shaft sealing can be a seal housing. The seal liner can rotate with the outer shaft. An inner static sealing between the seal liner and the outer shaft can seal the inside of the marine vessel, particularly the pod from the outside of the marine vessel, particularly the pod. The seal housing can be comprised by the sealing housing. An outer static sealing between the seal housing and the sealing housing can seal the inside of the marine vessel, particularly the pod from the outside of the marine vessel, particularly the pod.

[0281] In some embodiments, the outer composure of the outer shaft sealing can be a seal liner and the inner composure of the outer shaft sealing can be a seal housing. The seal liner can be comprised by the sealing housing. An outer static sealing between the seal liner and the sealing housing can seal the inside of the marine vessel, particularly the pod from the outside of the marine vessel, particularly the pod. The seal housing can rotate with the outer shaft. An inner static sealing between the seal housing and the outer shaft can seal the inside of the marine vessel, particularly the pod from the outside of the marine vessel, particularly the pod.

[0282] Typically, the inner composure of the outer shaft sealing and the outer composure of the outer shaft sealing and / or the outer sealing elements can be serviced individually, e.g. replaced individually. For example, the outer sealing elements and / or the seal liner may experience larger wear in comparison to the seal housing.

[0283] Typically, the plurality of inner sealing elements seals the plurality of inner shaft seal chambers and the plurality of outer sealing elements seals the plurality of outer shaft seal chambers. The inner sealing elements and / or the outer sealing elements can be sealing lips.

[0284] In some embodiments, a least one passage, particularly each passage, through the outer shaft can comprise an inner groove. The inner groove can be in at least one of: the inside of the outer shaft; and / or the inner shaft sealing. Particularly, the inner groove can be in an outer composure of the inner shaft sealing.

[0285] Typically, the inner groove of a chamber system provides a constant fluid connection between the inner shaft seal chamber of the chamber system and the outer shaft seal chamber of the chamber system. Particularly, the inner groove of the chamber system provides a constant fluidconnection between the inner shaft seal chamber of the chamber system and the channels of the chamber system through the outer shaft.

[0286] In some embodiments, an inner groove can be sealed by at least one inner groove sealing element. The inner groove sealing element(s) can typically prevent leakage between the inner grooves. Particularly, each inner groove sealing element can be a static ring and / or a sealing ring.

[0287] In some embodiments, at least one passage, particularly each passage, through the outer shaft can comprise an outer groove. The outer groove can be in at least one of: the outside of the outer shaft; and / or the outer shaft sealing. Particularly, the outer groove can be in the inner composure of the outer shaft sealing.

[0288] Typically, the outer groove of a chamber system provides a constant fluid connection between the inner shaft seal chamber of the chamber system and the outer shaft seal chamber of the chamber system. Particularly, the outer groove of the chamber system provides a constant fluid connection between the outer shaft seal chamber of the chamber system and the channels of the chamber system through the outer shaft.

[0289] In some embodiments, an outer groove can be sealed by at least one outer groove sealing element. The outer groove sealing element(s) can typically prevent leakage between the outer grooves. Particularly, each outer groove sealing element can be a static ring and / or a sealing ring.

[0290] In some embodiments, at least one passage, particularly each passage, through the outer shaft can comprise a plurality of channels through the outer shaft fluidly connecting the inner shaft seal chamber and the outer shaft seal chamber, particularly the inner shaft seal chamber and the outer shaft seal chamber of one chamber system.

[0291] In some embodiments, at least one passage, particularly each passage, through the outer shaft can comprise a plurality of channels through the outer shaft fluidly connecting the inner groove and the outer groove.

[0292] In some embodiments, a plurality of channels through the outer shaft can typically provide an improved fluid connection between the inner shaft seal chamber of a chamber system and the outer shaft seal chamber of the chamber system. Particularly, a plurality of channels through the outer shaft can typically provide an improved fluid connection between the inner groove of a chamber system and the outer groove of the chamber system.

[0293] In some embodiments, at least one passage, particularly each passage, through the outer shaft can comprise at least one hole, drilled through the outer shaft. Particularly, each channel of the plurality of channels of each passage through the outer shaft can comprise a hole, drilled through the outer shaft.

[0294] In some embodiments, drilling a hole through the outer shaft provides a simple method to create a channel, a plurality of channels and / or a passage through the outer shaft of an appropriate size and / or at an appropriate location.

[0295] In some embodiments, the plurality of chamber systems can comprise a proximate chamber system. The proximate chamber system can be fluidly connected to an oil reservoir. Particularly, oil can be transferred from the oil reservoir to the proximate chamber system.

[0296] Typically, oil can be transferred from the oil reservoir to the inner shaft seal chamber through the outer shaft seal chamber and the passage through the outer shaft. Particularly, oil can be transferred from the proximate chamber system to the oil reservoir. Typically, oil can be transferred from the inner shaft seal chamber to the oil reservoir through the outer shaft seal chamber and / or the passage through the outer shaft.

[0297] Typically, the pressure inside the proximate chamber system is adjustable. Particularly the pressure inside the proximate chamber system is adjustable by adjusting the pressure inside the oil reservoir. Particularly, the sealing properties of the sealing unit can be improved by optimizing the pressure inside the proximate chamber system.

[0298] In some embodiments, the plurality of chamber systems can comprise a distant chamber system. Particularly, the distant chamber system can be free from oil. Typically, oil contamination of water leaking in the distant chamber system can be avoided.

[0299] In some embodiments, the plurality of chamber systems can comprise an intermediate chamber system. The intermediate chamber system can be fluidly connected to an air reservoir, particularly to a pressurized air reservoir.

[0300] Particularly, air can be transferred from the air reservoir, particularly the pressurized air reservoir, to the intermediate chamber system. Typically, air can be transferred from the air reservoir, particularly the pressurized air reservoir, to the inner shaft seal chamber through the outer shaft seal chamber and the passage through the outer shaft.

[0301] Particularly, air, leakage oil and / or leakage water can be transferred from the intermediate chamber system to the air reservoir, particularly the pressurized air reservoir. Typically, air, leakage oil and / or leakage water can be transferred from the inner shaft seal chamber to the air reservoir, particularly the pressurized air reservoir, through the outer shaft seal chamber and / or the passage through the outer shaft. Typically, air, leakage oil and / or leakage water can be transferred from the inner shaft seal chamber to an outlet reservoir, particularly an outlet reservoir of the air reservoir, particularly of the pressurized air reservoir, through the outer shaft seal chamber and / or the passage through the outer shaft.

[0302] Typically, the pressure inside the intermediate chamber system is adjustable. Particularly the pressure inside the intermediate chamber system is adjustable by adjusting the pressure inside the air reservoir, particularly the pressurized air reservoir. Typically, the sealing properties of the sealing unit can be improved by adjusting the pressure inside the intermediate chamber system.

[0303] Typically, leakage oil and / or leakage water can be removed from the intermediate chamber system. Typically, oil contamination of the distant chamber system can be avoided and / or water contamination of the proximate chamber system can be avoided. Particularly, the intermediate chamber system can seal the proximate chamber system from the distant chamber system.

[0304] In some embodiments, the air reservoir, particularly the pressurized air reservoir, can be fluidly connected to a compressor. In some embodiments, the air reservoir, particularly the pressurized air reservoir, can be a compressor. In some embodiments, the air reservoir, particularly the pressurized air reservoir, can be a pressurized air network, particularly a pressurized air network of a vessel.

[0305] In some embodiments, the proximate chamber system can be the chamber system of the plurality of chamber systems closest to a motor. The motor can be configured to drive the inner shaft and / or the outer shaft. The motor can be a dual rotor electric motor. The distant chamber system can be the chamber system of the plurality of chamber systems farthest from the motor. The intermediate chamber system can be a chamber system of the plurality of chamber systems between the proximate chamber system and the distant chamber system.

[0306] In some embodiments, the plurality of chamber systems can comprise a proximate chamber system, a distant chamber system and an intermediate chamber system. The proximate chamber system can be fluidly connected to an oil reservoir and the intermediate chamber system can be fluidly connected to an air reservoir, particularly a pressurized air reservoir.

[0307] Particularly, water from outside of the marine vessel, particularly the pod may leak inside the distant chamber system. The intermediate chamber system may seal the distant chamber system from the proximate chamber system. Typically, contamination of the distant chamber system with oil can be avoided. Typically, contamination of the proximate chamber system with water can be avoided.

[0308] In some embodiments, the plurality of chamber systems can comprise at least four chamber systems. At least two chamber systems of the plurality of chamber systems can be fluidly connected to an oil reservoir and / or at least one chamber system of the plurality of chamber systems can be fluidly connected to an air reservoir, particularly a pressurized air reservoir.

[0309] In some embodiments, each chamber system of the plurality of chamber systems can contain at least one of: (a) oil; (b) air; and / or (c) leakage fluid. Typically, the air can be pressurized air. Typically, the leakage fluid can be oil leaked from a neighboring chamber system and / or water leaked from outside the marine vessel, particularly the pod.

[0310] In some embodiments, each fluid connection of a chamber system of the plurality of chamber systems with a reservoir can comprise a supply groove. The supply groove can be in at least one of: the sealing housing; and / or the outer shaft sealing.

[0311] In some embodiments, each fluid connection of a chamber system of the plurality of chamber systems with a reservoir can comprise at least one supply channel. Each supply channel can fluidly connect the chamber system with the reservoir. Typically, at least one supply channel can be an inlet supply channel and at least one supply channel can be an outlet supply channel. Typically, fluid can be transferred from the reservoir to the chamber system through the inlet supply channel. Typically, fluid can be transferred from the chamber system to the reservoir through the outlet supply channel.

[0312] In some embodiments, a reservoir can comprise an inlet reservoir. Typically, fluid can be transferred from the inlet reservoir to a chamber system of the plurality of chamber systems through at least one inlet supply channel. Typically, the inlet reservoir can provide fresh / ready-to-use fluid to a chamber system.

[0313] In some embodiments, a reservoir can comprise an outlet reservoir. Typically, fluid can be transferred from a chamber system of the plurality of chamber systems to the outlet reservoir through at least one outlet supply channel. Typically, the outlet reservoir can receive used fluid,e.g. contaminated fluid such as oil-contaminated water, water-contaminated oil, oil-contaminated air and / or water-contaminated air.

[0314] In some embodiments, a supply groove can be sealed by at least one supply groove sealing element. Particularly, each outer groove sealing element can be a static ring and / or a sealing ring. Typically, the supply groove(s) provide(s) a constant fluid connection between the outer shaft seal chamber(s) and the supply channel(s).

[0315] In some embodiments, the propulsion unit can further comprise an inner bearing and an outer bearing. The inner bearing can be inside an inner bearing chamber between the inner shaft and the outer shaft. The outer bearing can be inside an outer bearing chamber between the outer shaft and the bearing housing. The sealing unit can further comprise an inner bearing sealing and an outer bearing sealing. The inner bearing sealing can seal the inside of the marine vessel, particularly the pod from the inner bearing chamber. The outer bearing sealing can seal the inside of the marine vessel, particularly the pod from the outer bearing chamber.

[0316] In some embodiments, the inner bearing can be a DE inner bearing and the outer bearing can be a DE outer bearing.

[0317] In some embodiments, the inner bearing chamber and / or the outer bearing chamber can be filled with oil.

[0318] In some embodiments, the bearing housing and the sealing housing can be connected. Particularly, the bearing housing and the sealing housing can be provided in a combined bearing and sealing housing.

[0319] Typically, oil from inside the inner bearing chamber can be prevented from leaking inside the marine vessel, particularly the pod by the inner bearing sealing. Typically, oil from inside the outer bearing chamber can be prevented from leaking inside the marine vessel, particularly the pod by the outer bearing sealing.

[0320] In some embodiments, the inner bearing chamber and the outer bearing chamber can be fluidly connected. Typically, oil can be supplied from an oil reservoir to the inner bearing chamber through the outer bearing chamber.

[0321] In some embodiments, the inner shaft sealing can seal the outside of the marine vessel, particularly the pod from the inner bearing chamber. The outer shaft sealing can seal the outsideof the marine vessel, particularly the pod from the outer bearing chamber. Typically, oil from inside the inner bearing chamber and / or from inside the outer bearing chamber can be prevented from leaking to the outside of the marine vessel, particularly the pod. Typically, water from the outside of the marine vessel, particularly the pod can be prevented from leaking inside the inner bearing chamber and / or the outer bearing chamber.

[0322] An embodiment describes a method for servicing a sealing unit in a marine propulsion unit, particularly an azimuthing propulsion unit. The propulsion unit comprises a rotatable inner shaft and a rotatable outer shaft, wherein the inner shaft runs at least partially within the outer shaft and wherein the outer shaft runs at least partially within a sealing housing of a marine vessel, particularly the pod. The sealing unit is a sealing unit according to any embodiment described herein. The method for servicing the sealing unit comprises: providing a service sealing arrangement, wherein the service sealing arrangement seals the inner shaft sealing from the outside of the marine vessel, particularly the pod; dismounting, at least partially, through a hatch provided in the outer shaft, an inner bearing between the inner shaft and the outer shaft; dismounting, at least partially, the inner shaft sealing through the hatch; servicing the inner shaft sealing; mounting the serviced inner shaft sealing through the hatch; and mounting the inner bearing through the hatch.

[0323] In some embodiments, the service sealing arrangement can be a pneumostop sealing arrangement.

[0324] In some embodiments, dismounting, at least partially, the inner bearing can comprise moving, at least partially, the inner bearing along a rotation axis of the inner shaft to provide access to the inner shaft sealing through the hatch.

[0325] In some embodiments, servicing the inner shaft sealing can comprise: replacing at least one inner sealing element of the inner shaft sealing; and bonding the new inner sealing element(s). Typically, bonding the new inner sealing element can provide a continuous sealing element around the entire circumference of the inner shaft.

[0326] Typically, the inner shaft sealing of the sealing unit in the marine propulsion unit, particularly the azimuthing propulsion unit, can be serviced without removing the marine propulsion unit, particularly the azimuthing propulsion unit, from the water. Particularly, the inner shaft sealing of the sealing unit in the marine propulsion unit, particularly the azimuthingpropulsion unit, can be serviced without the use of a dry dock and / or without removing the vessel from the water.

[0327] In some embodiments, the service sealing arrangement can seal the outer shaft sealing from the outside of the marine vessel, particularly the pod. The method can further comprise: dismounting, at least partially, an outer bearing between the outer shaft and the bearing housing; dismounting, at least partially, the outer shaft sealing; servicing the outer shaft sealing; mounting the serviced outer shaft sealing; and mounting the outer bearing.

[0328] In some embodiments, the service sealing arrangement can comprise a service sealing to seal the inner shaft sealing and the outer shaft sealing from the outside of the marine vessel, particularly the pod. In some embodiment, the service sealing arrangement can comprise an inner service sealing to seal the inner shaft sealing from the outside of the marine vessel, particularly the pod. In some embodiments, the service sealing arrangement can comprise an outer service sealing to seal the outer shaft sealing from the outside of the marine vessel, particularly the pod. In some embodiments, the service sealing arrangement can comprise the inner service sealing and the outer service sealing. Typically, the inner service sealing and the outer service sealing may be activated and / or deactivated at the same time, particularly through the same mechanism.

[0329] In some embodiments, servicing the outer shaft sealing can comprise: replacing at least one outer sealing element of the outer shaft sealing; and bonding the new outer sealing element(s). Typically, bonding the new outer sealing element can provide a continuous sealing element around the entire circumference of the outer shaft.

[0330] In some embodiments, the method can further comprise: dismounting, at least partially, an outer bearing sealing, wherein the outer bearing sealing seals the inside of the marine vessel, particularly the pod, from the outer bearing chamber; and mounting the outer bearing sealing. Typically, dismounting the outer bearing sealing provides access to the outer bearing.

[0331] Typically, the outer shaft sealing of the sealing unit in the marine propulsion unit, particularly the azimuthing propulsion unit, can be serviced without removing the marine propulsion unit, particularly the azimuthing propulsion unit, from the water. Particularly, the outer shaft sealing of the sealing unit in the marine propulsion unit, particularly the azimuthing propulsion unit, can be serviced without the use of a dry dock and / or without removing the vessel from the water.

[0332] In some embodiments, the method can further comprise: mounting an inner spacer ring arrangement between the inner shaft and the outer shaft. The inner spacer ring arrangement can define the location of the inner shaft sealing, particularly of the inner sealing elements, the outer composure of the inner shaft sealing and / or the inner composure of the inner shaft sealing, along the rotation axis of the inner shaft.

[0333] The inner spacer ring arrangement can comprise a first inner spacer ring and / or a second inner spacer ring. The first inner spacer ring can engage with the inner shaft, particularly with a shaft shoulder of the inner shaft, and the inner shaft sealing, particularly the inner composure of the inner shaft sealing. The second inner spacer ring can engage with the outer shaft, particularly with a shaft shoulder of the outer shaft, and the inner shaft sealing, particularly the outer composure of the inner shaft sealing.

[0334] Typically, the location of the inner shaft sealing, the inner composure of the inner shaft sealing, the outer composure of the inner shaft sealing and / or the inner sealing elements along the rotation axis of the inner shaft can be changed be replacing a mounted inner spacer ring arrangement with a replacement inner spacer ring arrangement. The mounted inner spacer ring arrangement, particularly the first inner spacer ring and / or the second inner spacer ring of the mounted inner spacer ring arrangement, can have a different thickness, particularly a thickness in the direction of the rotation axis of the inner shaft and the outer shaft, compared to the thickness, particularly a thickness in the direction of the rotation axis of the inner shaft and the outer shaft, of the replacement inner spacer ring arrangement, particularly the first inner spacer ring and / or the second inner spacer ring of the replacement inner spacer ring arrangement.

[0335] Typically, by changing the location of the inner shaft sealing, of the inner composure of the inner shaft sealing, of the outer composure of the inner shaft sealing and / or of the inner sealing elements along the rotation axis of the inner shaft, the inner shaft sealing, the inner composure of the inner shaft sealing, the outer composure of the inner shaft sealing and / or the inner sealing elements can be relocated to a location on the inner shaft with less wear. Typically, by changing the location of the inner composure of the inner shaft sealing and / or the location of the outer composure of the inner shaft sealing the inner composure of the inner shaft sealing can be relocated compared to the outer composure of the inner shaft sealing (or vice versa). Particularly, the inner sealing elements can be relocated relative to the inner composure of the inner shaft sealing or the outer composure of the inner shaft sealing to a location with less wear on the inner composure of the inner shaft sealing or the outer composure of the inner shaft sealing.

[0336] In some embodiments, the method can further comprise: mounting an outer spacer ring arrangement between the outer shaft and the sealing housing. The outer spacer ring arrangement can define the location of the outer shaft sealing, particularly of the outer sealing elements, the outer composure of the outer shaft sealing and / or the inner composure of the outer shaft sealing, along the rotation axis of the outer shaft.

[0337] The outer spacer ring arrangement can comprise a first outer spacer ring and / or a second outer spacer ring. The first outer spacer ring can engage with the outer shaft, particularly with a shaft shoulder of the outer shaft, and the outer shaft sealing, particularly the inner composure of the outer shaft sealing. The second outer spacer ring can engage with the sealing housing, particularly with a shoulder of the sealing housing, and the outer shaft sealing, particularly the outer composure of the outer shaft sealing.

[0338] Typically, the location of the outer shaft sealing, of the inner composure of the outer shaft sealing, of the outer composure of the outer shaft sealing and / or of the outer sealing elements on the outer shaft can be changed be replacing a mounted outer spacer ring arrangement with a replacement outer spacer ring arrangement. The mounted outer spacer ring arrangement, particularly the first outer spacer ring and / or the second outer spacer ring of the mounted outer spacer ring arrangement, can have a different thickness, particularly a thickness in the direction of the rotation axis of the inner shaft and the outer shaft, compared to the thickness, particularly a thickness in the direction of the rotation axis of the inner shaft and the outer shaft, of the replacement outer spacer ring arrangement, particularly the first outer spacer ring and / or the second outer spacer ring of the replacement outer spacer ring arrangement.

[0339] Typically, by changing the location of the outer shaft sealing, of the inner composure of the outer shaft sealing, of the outer composure of the outer shaft sealing and / or of the outer sealing elements along the rotation axis of the outer shaft, the outer shaft sealing, the inner composure of the outer shaft sealing, the outer composure of the outer shaft sealing and / or the outer sealing elements can be relocated to a location on the outer shaft with less wear. Typically, by changing the location of the inner composure of the outer shaft sealing and / or the outer composure of the outer shaft sealing the inner composure of the outer shaft sealing can be relocated compared to the outer composure of the outer shaft sealing (or vice versa). Particularly, the outer sealing elements can be relocated relative to the inner composure of the outer shaft sealing or the outer composure of the outer shaft sealing to a location with less wear on the inner composure of the outer shaft sealing or the outer composure of the outer shaft sealing. In view of the foregoing, the presentdisclosure is directed to a marine propulsion unit, a marine vessel and to methods of installing a marine propulsion unit.According to an aspect of the present disclosure, a marine propulsion unit is provided. The marine propulsion unit comprises a dual rotor electric motor having an inner rotor and an outer rotor; a contra rotating propeller having an inner shaft propeller and an outer shaft propeller; a drive shaft having an inner shaft connecting the inner rotor to the inner shaft propeller and an outer shaft connecting the outer rotor to the outer shaft propeller; and a slip ring unit for transmitting an electric current to the dual rotor electric motor.According to another aspect of the present disclosure, a marine vessel comprising a marine propulsion unit according to any of the embodiments described herein is provided.According to an aspect of the present disclosure, a marine propulsion unit is provided. The marine propulsion unit comprises a dual rotor electric motor having an inner rotor and an outer rotor and a contra rotating propeller having an inner shaft propeller and an outer shaft propeller. An axial distance of a motor-facing end of the contra rotating propeller to a propeller-facing end of the dual rotor electric motor is at most, three times an axial length of the dual rotor electric motor.According to another aspect of the present disclosure, a marine vessel comprising a marine propulsion unit according to any of the embodiments described herein is described.According to another aspect of the present disclosure, a method of installing a marine propulsion unit according to embodiments described herein is provided. The method comprises assembling the marine propulsion unit in the marine propulsion unit assembly structure outside the marine vessel; inserting the marine propulsion unit assembly structure into the marine vessel, particularly via an opening in the stern of the marine vessel; and mechanically connecting the marine propulsion unit assembly structure with the marine vessel.According to another aspect of the present disclosure, a method of installing a marine propulsion unit according to embodiments described herein is provided. The method comprises assembling the marine propulsion unit in the marine propulsion unit assembly structure outside the marine vessel; constructing a hull of the marine vessel with an omission of a skeg of the hull; attaching the marine propulsion unit assembly structure to the hull of the marine vessel at the omission, particularly wherein the marine propulsion unit assembly structure acts as the skeg of the hull; and mechanically connecting the marine propulsion unit assembly structure with the marine vessel.According to some embodiments, the marine propulsion unit is configured to propel a marine vessel. In some embodiments, the marine propulsion unit comprises a shaft-line marine propulsion unit. In particular, the marine vessel may comprise at least one marine propulsion unit according to embodiments described herein. The marine vessel as described herein comprises seagoing or inland marine vessels. In particular, the marine vessel comprises ships and boats. In some embodiments, the marine vessel comprises merchant ships, in particular for transporting goods. In particular, the marine vessel may comprise a container vessel, a Ro-Ro or car carrier, a tanker or shuttle tanker, a liquid natural gas (LNG) carrier or a floating storage and regasification unit. In some embodiments, the marine vessel comprises ferries, in particular single and double-ended ferries, cruise ships, water buses, yachts. In some embodiments, the marine vessel comprises offshore energy vessels, in particular service operation vessels (SOVs), cable laying vessels (CLVs), foundation installation vessels (FIVs), offshore construction (OCVs) and support vessels (OSVs), platform supply vessels (PSVs), and anchor-handling tug supply vessels (AHTS). In some embodiments, the marine vessel comprises research and survey vessels or other special purpose vessels, such as dredgers, heavy lift vessels or towboats. In some embodiments, the marine vessel comprises ice-going marine vessels, in particular icebreakers or marine vessels having an ice-class assigned by a classification society. In some embodiments, the marine vessel may comprise navy or coast guard vessels. In some embodiments, the marine vessel may comprise submarine vessels or unmanned remotely operated underwater vehicles (ROVs).The marine vessel typically comprises a hull. Typically, the hull defines a vessel interior and a vessel exterior. Space confined by the hull and configured to be isolated from sea water may be defined as the vessel interior. Space outside the hull, and in particular the sea, may be defined as the vessel exterior. Typically, the vessel interior is substantially free of sea water and substantially dry. In some embodiments, the vessel interior is configured to transport cargo and / or persons.In some embodiments, the marine vessel may comprise a plurality of marine propulsion units. In particular, the marine vessel may comprise 2, 3, 4, or more marine propulsion units. Typically, each of the plurality of marine propulsion units may be controlled separately.The marine propulsion unit typically comprises at least one shaft-line marine propulsion unit. Typically, in the shaft-line marine propulsion unit, the electric motor, particularly a dual rotor electric motor, which may also be described as contra-rotating electric motor, is arranged within the hull of the marine vessel. The electric motor is connected to a propeller unit via a shaft-line or drive shaft. The propeller unit is typically arranged at a stern of the marine vessel. Particularly, thepropeller unit is typically arranged at a skeg of the marine vessel. Typically, for a shaft-line marine propulsion unit, a stern-facing side of the marine propulsion unit may be described as the driving end (DE) side of the marine propulsion unit. Typically, for a shaft-line marine propulsion unit, a vessel-center facing side of the marine propulsion unit may be described as the non-driving end (NDE) side of the marine propulsion unit.In typical embodiments, the propeller unit comprises an outer shaft propeller and an inner shaft propeller. In other words, the propeller unit may be named a contra rotating propeller. Typically, the outer shaft propeller is arranged closer to the hull than the inner shaft propeller. In a pushing propeller unit, the outer shaft propeller may also be described as the front propeller and the inner shaft propeller may be described as the rear propeller; and vice versa for a pulling propeller unit. Typically, the outer shaft propeller and the inner shaft propeller are arranged adjacent to each other. The contra rotating propeller has a motor-facing end, particularly a motor-facing axial end, facing the motor. The outer shaft propeller and the inner shaft propeller rotate about the rotation axis of the propeller unit. In other words, the outer shaft propeller and the inner shaft propeller rotate about the same rotation axis.Typically, the propeller unit comprises a contra rotating propeller unit. In particular, the outer shaft propeller may be configured to rotate in a first direction, particularly about the rotation axis of the propeller unit, and the inner shaft propeller may be configured to rotate in a second direction opposite to the first direction, particularly about the rotation axis of the propeller unit. In other words, the outer shaft propeller may rotate clockwise and the inner shaft propeller may rotate counterclockwise, or vice versa, about the same rotation axis. A contra rotating propeller unit may advantageously allow for a higher hydrodynamic efficiency than other propeller concepts, in particular with respect to single propellers.In some embodiments, the outer shaft propeller has a first diameter and the inner shaft propeller has a second diameter, with the second diameter being different from the first diameter, particularly the first diameter being larger than the second diameter. Typically, the outer shaft propeller comprises a first number of first blades and the inner shaft propeller comprises a second number of second blades. Typically, the second number may be different from the first number. The outer shaft propeller may comprise 3, 4, 5, 6 or 8 first blades. The inner shaft propeller may comprise 3, 4, 5, 6 or 8 second blades. In some embodiments, the outer shaft propeller comprises one first blade more than the inner shaft propeller comprises second blades. Exemplarily, the outer shaft propeller comprises 6 first blades and the inner shaft propeller comprises 5 second blades. Insome embodiments, the outer shaft propeller and the inner shaft propeller may comprise the same number of blades, in particular 3, 4, 5, 6 or 8 first and second blades, respectively. The outer shaft propeller and / or the inner shaft propeller may each be manufactured as a monoblock or in components, as a built-up propeller.The propeller unit is driven by an electric motor. The electric motor is typically a dual rotor electric motor. The dual rotor electric motor may also be described as a contra-rotating motor. Typically, the electric motor has a power, particularly a rated electric power, of at least 100 kW, at least 200 kW, at least 1 MW, at least 2 MW, at least 5 MW, at least 10 MW or at least 15 MW. The electric motor is typically arranged within the hull of the marine vessel. Particularly, the electric motor is mechanically connected to the propeller gearlessly and / or without a clutch. Typically, a rotation axis of the electric motor is identical to a rotation axis of the propeller unit. In particular, an output shaft of the electric motor may be identical to the drive shaft of the propeller unit or may be gearlessly connected to a drive shaft of the propeller unit. The output shaft of the electric motor is typically coaxial to the drive shaft of the propeller unit. In typical embodiments, for a propeller unit comprising an outer shaft propeller and an inner shaft propeller, in particular for the contra rotating propeller unit, the outer shaft propeller and the inner shaft propeller may be driven by the same electric motor.The electric motor comprises a dual rotor electric motor with an outer rotor and an inner rotor configured to rotate in opposite directions about a rotation axis of the electric motor. Typically, the rotation axis of the electric motor may be coaxially with the rotation axis of the propeller unit. Typically, the electric motor is a synchronous electric motor. Typically, the outer rotor comprises windings to be supplied with an electric current for the operation of the electric motor. The inner rotor may be a permanent magnet rotor or an externally excited synchronous rotor.Typically, the dual rotor electric motor comprises a perforated tube. The perforated tube may substantially have a cylinder shape, particularly with a cage-like structure. In some embodiments, the perforated tube may, at least in part, form an outer contour of the dual rotor electric motor. The perforated tube is configured to transmit a torque of the outer rotor to the propeller unit. The perforated tube supports an outer rotor winding of the outer rotor. Particularly, the outer rotor winding is connected to the perforated tube. In some embodiments, the outer rotor comprises a plurality of axial beams between a core of the outer rotor winding and the perforated tube. In particular, the outer rotor may comprise at least 3, at least 6, at least 12, or at least 24 axial beams. Typically, the axial beams are arranged parallel to an axis, particularly the rotating axis, of theperforated tube. Typically, the plurality of axial beams is arranged substantially parallel with respect to each other. The plurality of axial beams is typically configured to transmit a torque from the outer rotor core, which particularly accommodates the windings, to the perforated tube. The plurality of axial beams are configured to allow air to flow from an interior of the motor, particularly via radial slots in a core of the outer rotor winding of the outer rotor, towards the perforated tube, and particularly towards the radial openings in the perforated tube. The core of the outer rotor winding is typically a steel core.In some embodiments, the drive shaft of the propeller comprises an outer shaft and an inner shaft. The outer shaft and inner shaft are typically coaxially arranged. Typically, the outer rotor drives the outer shaft. In some embodiments, the outer shaft, in particular a drive end outer shaft, comprises at least one hatch. Typically, the at least one hatch can be configured to provide access to a bearing supporting the inner shaft in the outer shaft. The at least one hatch may permit maintenance to be done on the inner shaft and / or on the outer shaft from within the marine propulsion unit. Particularly, disassembling of the marine propulsion unit may advantageously be avoided.In some embodiments, the outer shaft and / or the inner shaft may comprise at least one shaft coupling. In particular, the outer shaft and / or the inner shaft comprising at least one shaft coupling advantageously allows to modularly adapt the marine propulsion unit to the marine vessel. Exemplarily a length of the shaft may be adapted dependent on a size of the marine vessel. Typically, the inner rotor drives the inner shaft. Typically, the inner shaft is arranged inside the outer shaft; in other words, an inside radius of the outer shaft exceeds an outside radius of the inner shaft. The inner shaft and the outer shaft rotate about the same rotation axis, and in particular about the rotation axis of the electric motor.Typically, the at least one shaft coupling is arranged for removably separating the drive shaft between the rotating propeller and the dual rotor electric motor. The at least one shaft coupling typically allows for separating the inner shaft and the outer shaft. In typical embodiments, the marine propulsion unit comprises exactly one shaft coupling, exactly two shaft couplings or exactly three shaft couplings. A shaft coupling, particularly a first shaft coupling, may typically be arranged in the proximity of the rotating propeller or the dual rotor electric motor. A shaft coupling, particularly a second shaft coupling, may typically be arranged in the proximity of the rotating propeller or the dual rotor electric motor, particularly for the first shaft coupling being arranged at the respective opposite end of the drive shaft. In other words, with the first shaftcoupling being arranged at the proximity of the rotating propeller, the second shaft coupling would be arranged at the proximity of the dual rotor electric motor, and vice versa. A shaft coupling being arranged in the proximity of the rotating propeller or of the dual rotor electric motor may be described as being arranged at a distance not exceeding 10% of a total length of the drive shaft. A shaft coupling, particularly a third shaft coupling, may typically be arranged in an intermediate position along the drive shaft. Particularly, the shaft coupling may be arranged between 20% and 80% of an overall length of the drive shaft or between 30% and 70% of an overall length of the drive shaft.The at least one shaft coupling can advantageously allow to adapt a length of the drive shaft variably based upon modular components of the marine propulsion unit. Similarly, a maintenance of the marine propulsion unit may be facilitated. Exemplarily, the same dual rotor electric motor and / or the same contra rotating motor may be used for drive shafts with different lengths, particularly for marine vessels with different preferred arrangements of the marine propulsion unit.Typically, the inner shaft is supported by at least one drive end (DE) inner bearing and a non-drive end (NDE) inner bearing. Typically, the outer shaft is supported by at least one DE outer bearing and an NDE outer bearing. The NDE inner bearing and / or the NDE outer bearing may each comprise an axial bearing and a radial bearing, particularly within the same bearing housing. The NDE inner bearing and the NDE outer bearing may form an NDE bearing unit.With the NDE bearing unit, the shafts of the marine propulsion unit can be supported in a spaceefficient arrangement and, at the same time, the maintenance, repair and replacement of parts of the bearing arrangement, or parts of / at a bearing housing is facilitated.Typically, the bearing arrangement includes a first axial bearing between the inner shaft and the outer shaft for allowing the transfer of axial forces between the inner shaft and the outer shaft. In some embodiments, the bearing arrangement includes the first axial bearing between the inner shaft and the outer shaft, a second axial bearing arranged between a bearing housing wall and the inner shaft, and a third axial bearing arranged between a bearing housing wall and the outer shaft. The arrangement of the axial bearings between the shafts as well as a common placement of the axial bearing(s) for both shafts allows for an efficient, space-saving, and compact arrangement of the bearings used for the drive shaft of the marine propulsion unit.According to some embodiments, the bearing unit may include an oil seal. In particular, the oil seal may be located between the inner shaft and the outer shaft, especially between a flange of theinner shaft and a flange of the outer shaft. In some embodiments, the oil seal may be located under (inside) the first bearing. Especially, the oil seal may be removable through the at least one hatch. More specifically, the first bearing may be removed at least partly to open up a maintenance route / space for maintenance, repair or exchange of the oil seal, especially via the hatch. In some embodiments, the oil seal may include an oil seal housing. According to some embodiments, the oil seal housing part can be fastened to one of the inner shaft and the outer shaft, or both (or the respective flanges of the shafts). Typically, the oil seal may contain elastic lip seals against a liner.According to some embodiments described herein, at least one of the axial bearings (and / or, optionally, at least one of the radial bearings) of the bearing arrangement is a pad bearing. A pad bearing provides a reliable function with a simple design. In some embodiments, the pad bearing can easily be removed from the bearing housing due to its simple design and uncomplicated mounting possibilities.Employing a contra rotating electric motor may advantageously allow to drive the contra rotating propeller with a single electric motor gearlessly. In other words, a torque of the dual rotor electric motor is transmitted to the contra rotating propeller without a gearbox. Thereby, a more compact and efficient drive train may be provided.Typically, the drive shaft is supported by a non-drive end (NDE) thrust bearing. The NDE thrust bearing is typically arranged separately from the dual rotor electric motor and / or from the slip-ring unit. Typically, the NDE thrust bearing comprises a slide bearing, particularly a hydrodynamic bearing. In some embodiments, the NDE thrust bearing comprises a roller bearing. Typically, employing a slide bearing as the NDE thrust bearing may be preferred. Particularly, additional pumps may be avoided for a hydrodynamic bearing. Having a slide bearing as NDE thrust bearing may advantageously reduce a maintenance effort.In some embodiments, the marine propulsion unit comprises at least one support bearing. The at least one support bearing is typically configured to support the drive shaft between a propeller bearing and a drive end bearing. Typically, the at least one support bearing is arranged between 20% and 80%, particularly between 30% and 70%, of an overall between a propeller bearing and a drive end bearing. Particularly for a long drive shaft, exemplarily in twin screw marine vessels, the at least one support bearing may advantageously provide an additional mechanical support and may be associated with an improved performance and reduced wear-and-tear. In someembodiments, particularly for an exposed shaft, at least one of the at least one support bearing may be arranged outside the ship hull.In some embodiments, the marine propulsion unit comprises a slip-ring unit. The slip-ring unit is configured to transmit an electric current to the dual rotor electric motor, particularly to the outer rotor of the dual rotor electric motor. The slip-ring unit is typically arranged on a vessel center facing side of the dual rotor electric motor. The slip-ring unit typically comprises a slip-ring housing and a slip-ring assembly arranged within the housing. Typically, the slip-ring assembly comprises at least one slip-ring element which is in contact with the outer rotor.Typically, the slip-ring housing can be understood as a casing which is configured to accommodate the slip-ring assembly separately in the marine vessel. The slip-ring housing is configured to prevent dust, in particular carbon dust, from entering the interior of the vessel, which advantageously allows for avoiding contamination. Typically, the slip-ring housing is arranged separately from the dual rotor electric motor. In some embodiments, the slip-ring unit includes a set of seals at both ends of the slip-ring assembly, at the slip-ring housing and the outer rotor to seal the slip-ring housing against the outside. In particular, the set of seals are configured to seal the slip-ring housing in an area between the slip-ring housing and an outer surface of the outer rotor.The slip-ring unit is typically cooled by a slip-ring unit cooling system. Typically, the slip-ring unit cooling system is based on cooling air being circulated and / or is cooling liquid based. Typically, the slip-ring cooling system is connectable to a low temperature liquid cooling medium vessel cooling system. Typically, the low temperature liquid cooling medium vessel cooling system is a low temperature water vessel cooling system. The low temperature water of the low temperature water vessel cooling system may particularly be cooled by sea water. In some embodiments, the slip-ring unit may be cooled using an oil, exemplarily a transformer oil.In some embodiments, the marine propulsion unit further includes an inflow filter unit at the slipring housing for the slip-ring assembly. The inflow filter unit is configured to filter air entering the slip-ring housing. The inflow filter unit may be integrated in the slip-ring housing. The inflow filter unit may also be arranged at an opening in the slip-ring housing. According to embodiments, more than one inflow filter units can be provided. Typically, the inflow filter unit is an air filter configured to filter out dirt particles from a motor cooling airflow entering the slip-ring housing. Thereby, a contamination of the slip-ring unit can be adventurously avoided or reduced.Typically, the slip-ring element includes a sliding contact, in particular brushing means fixed in the slip-ring housing which are configured to transfer electrical power, signal or data to a corresponding slip-ring arranged on the outer surface of the outer rotor by contacting the corresponding slip-ring element. In some embodiments, the slip-ring unit comprises an excitation slip-ring for providing an electric current to the inner rotor of the dual rotor electric motor. Typically, a rotating part of the slip-ring unit is connected to the outer rotor of dual rotor electric motor with a dismountable connection. The dismountable connection may exemplarily comprise a flanged joint, a keyed joint, a tapered joint or a shrink fitted joint. Particularly, the rotating part of the slip-ring unit may be replaced and / or mounted without dismounting the outer rotor. Having the rotating part of the slip-ring unit connected to the outer rotor of the dual rotor electric motor with a dismountable connection may advantageously allow for a more modular and scalable marine propulsion unit, and may improve the maintainability and / or the assemblage of the marine propulsion unit.In some embodiments, the marine propulsion unit comprises an excitation slip-ring unit, particularly for providing an electric current to the inner rotor. The excitation slip-ring unit may be distinct and / or separated from the motor slip-ring unit or may be integrated into the motor slipring unit.In some embodiments, the marine propulsion unit comprises a cooling air system for providing cooling air to the dual rotor electric motor. In some embodiments, the cooling air system comprises a cooling air unit which integrates at least some parts of the cooling air system in a single unit. In some embodiments, the cooling air system is formed by a plurality of distinct sub-systems. The cooling air system typically comprises an air fan and a heat exchanger. The air fan is typically configured to propel air through the cooling air system. Particularly, the air fan may provide cooling air to the dual rotor electric motor and may draw the cooling air from the dual rotor electric motor, particularly after cooling the contra rotating motor. Typically, the air fan is configured to generate an overpressure in an ingoing air channel and a negative pressure in an outgoing air channel. In some embodiments, the cooling air system is an annular cooling air system with at least a part, and particularly all of the cooling air entering and / or exiting the dual rotor electric motor annularly. An annular cooling air system may be particularly favorable for compact marine propulsion units with a compact dual rotor electric motor. In some embodiments, the cooling air system is an annular cooling air system with at least a part of the cooling air entering and / or exiting the dual rotor electric motor axially. An axial cooling air system may be particularly favorable for an electric motor with a larger diameter.In some embodiments, the slip-ring unit cooling system is distinct from the cooling air system. In particular, the slip-ring unit cooling system may have a distinct cooling air circuit separated from an air circuit of the cooling air system of the dual rotor electric motor. In other words, the slip ring unit is cooled using a slip ring cooling system independent of the cooling air system for cooling the dual rotor electric motor.An axial distance of the motor-facing end of the contra rotating propeller to a propeller-facing end of the dual rotor electric motor is at least two times, at least three times, at least four times, preferably at least two times, an axial length of the dual rotor electric motor. In some embodiments, the drive shaft of the marine propulsion unit has a length of at least 10 meters, at least 20 meters or at least 30 meters. Having an extensive drive shaft may advantageously allow to position the dual rotor electric motor and the contra rotating propeller at positions in the vessel most suitable for each of the components of the marine propulsion unit. Exemplarily, the dual rotor may be arranged at a particularly accessible position. In some embodiments, earthing of the drive shaft and / or of bearings is facilitated, particularly by an improved accessibility.Typically, the motor-facing end of the contra-rotating propeller is a motor-facing end of the outer shaft propeller. Particularly, the motor-facing end of the contra-rotating propeller may be a most motor-facing edge of a propeller blade of the contra rotating propeller. In some embodiments, the motor-facing end of the contra-rotating propeller may be a most motor-facing connection of a propeller blade of the contra rotating propeller with the drive shaft, and particularly with the outer shaft. Typically, the propeller-facing end of the dual rotor electric motor is a propeller-facing end of the inner rotor and / or of the outer rotor. In some embodiments, the propeller-facing end of the dual rotor electric motor is a propeller-facing end of an electric motor housing or a propeller-facing end of windings of the dual rotor electric motor. The axial distance of the motor-facing end of the contra rotating propeller to the propeller-facing end of the dual rotor electric motor is typically defined along the rotation axis of the drive shaft or along the rotation axis of the dual rotor electric motor or along the rotation axis of the contra rotating propeller. Typically, the rotation axis of the drive shaft, the rotation axis of the dual rotor electric motor and the rotation axis of the contra rotating propeller are at least parallel and typically identical.Typically, the marine propulsion unit according to embodiments described herein is part of a marine vessel. Particularly, the marine propulsion unit propels the marine vessel. The marine propulsion unit is typically installed in a ship yard. Maintaining the marine propulsion unit may comprise disassembling at least part of the marine propulsion unit. Particularly, maintaining themarine propulsion unit may comprise disassembling the at least one shaft coupling, maintaining or replacing a part of the marine propulsion unit, and reassembling the drive shaft at the at least one shaft coupling.Embodiments of the present disclosure provide marine propulsion units with an improved performance and a good maintainability. The marine propulsion units described herein allow for modular marine propulsion units well adaptable to marine vessel requirements. Particularly, having a long drive shaft may advantageously allow to increase a dimension of the dual rotor electric motor, particularly a diameter of the dual rotor electric motor to increase a torque of the electric motor. A larger distance between the propeller and the electric motor typically improves the accessibility and maintainability of the marine propulsion unit advantageously.In some embodiments, the drive shaft of the propeller comprises an outer shaft and an inner shaft. Outer shaft and inner shaft are typically coaxially arranged. Typically, the outer rotor drives the outer shaft. The outer shaft is typically mechanically connected to the outer shaft propeller gearlessly. In some embodiments, the outer shaft and / or the inner shaft may comprise at least one shaft coupling. In particular, the outer shaft and / or the inner shaft comprising at least one shaft coupling advantageously allows to modularly adapt the marine propulsion unit to the marine vessel. Exemplarily a length of the shaft may be adapted dependent on a size of the marine vessel. Typically, the inner rotor drives the inner shaft. The inner shaft is typically mechanically connected to the inner shaft propeller gearlessly. Typically, the inner shaft is arranged inside the outer shaft; in other words, an inside radius of the outer shaft exceeds an outside radius of the inner shaft. The inner shaft and the outer shaft rotate about the same rotation axis, and in particular about the rotation axis of the electric motor.Typically, the inner shaft is supported by a drive end (DE) inner bearing and a non-drive end (NDE) inner bearing. Typically, the outer shaft is supported by a DE outer bearing and an NDE outer bearing. The NDE inner bearing and / or the NDE outer bearing may each comprise an axial bearing and a radial bearing, particularly within the same bearing housing. In some embodiments, the axial bearing may be arranged in an axial bearing housing and the radial bearing may be arranged in a, particularly separate, radial bearing housing. In other words, each of the bearings may be arranged in a sperate housing. Employing a contra rotating electric motor may advantageously allow to drive the contra rotating propeller with a single electric motor gearlessly. Thereby, a more compact and efficient drive train may be provided.An axial distance of the motor-facing end of the contra rotating propeller to a propeller-facing end of the dual rotor electric motor is at most five times, at most four times, at most two times, preferably at most three times, an axial length of the dual rotor electric motor. Typically, the motorfacing end of the contra-rotating propeller is a motor-facing end of the outer shaft propeller. Particularly, the motor-facing end of the contra-rotating propeller may be a most motor-facing edge of a propeller blade of the contra rotating propeller. In some embodiments, the motor-facing end of the contra-rotating propeller may be a most motor-facing connection of a propeller blade of the contra rotating propeller with the drive shaft, and particularly with the outer shaft. Typically, the propeller-facing end of the dual rotor electric motor is a propeller-facing end of the inner rotor or of the outer rotor. In some embodiments, the propeller-facing end of the dual rotor electric motor is a propeller-facing end of an electric motor housing or a propeller-facing end of windings of the dual rotor electric motor. The axial distance of the motor-facing end of the contra rotating propeller to the propeller-facing end of the dual rotor electric motor is typically defined along the rotation axis of the drive shaft or along the rotation axis of the dual rotor electric motor or along the rotation axis of the contra rotating propeller. Typically, the rotation axis of the drive shaft, the rotation axis of the dual rotor electric motor and the rotation axis of the contra rotating propeller are at least parallel and typically identical.In some embodiments, the marine propulsion unit comprises a slip-ring unit. The slip-ring unit is configured to transmit an electric current to the dual rotor electric motor, particularly to the outer rotor of the dual rotor electric motor. The slip-ring unit is typically arranged on a vessel center facing side of the dual rotor electric motor. The slip-ring unit typically comprises a slip-ring housing and a slip-ring assembly arranged within the housing. Typically, the slip-ring assembly comprises at least one slip-ring element which is in contact to the outer rotor. Typically, the slipring housing can be understood as a casing which is configured to accommodate the slip-ring assembly separately in the pod. The slip-ring housing is configured to prevent dust, in particular carbon dust from entering the interior of the vessel, which advantageously allows for avoiding contamination. Typically, the slip-ring element includes a sliding contact, in particular brushing means fixed in the slip-ring housing which are configured to transfer electrical power, signal or data to a corresponding slip-ring arranged on the outer surface of the outer rotor by contacting the corresponding slip-ring element. In some embodiments, the slip-ring unit comprises an excitation slip-ring for providing an electric current to the inner rotor of the dual rotor electric motor.In some embodiments, the marine propulsion unit comprises a slip-ring unit cooling system for cooling the slip-ring unit. Typically, the slip-ring unit cooling system is based on cooling air beingcirculated and / or is based on a cooling liquid. In some embodiments, the slip-ring cooling system is connectable to a low temperature liquid cooling medium vessel cooling system. Typically, the low temperature liquid cooling medium vessel cooling system is a low temperature water vessel cooling system. The low temperature water of the low temperature water vessel cooling system may particularly be cooled by sea water. In some embodiments, the slip-ring unit may be cooled using an oil, exemplarily a transformer oil.In some embodiments, the slip-ring unit cooling system may be a closed air cooling loop system. Typically, the slip-ring unit cooling system comprises an air-to-air heat exchanger for cooling the closed air cooling loop system. Having a closed air cooling loop system advantageously reduces a risk of dust exiting the slip-ring unit and particularly of dust contaminating other components of the marine propulsion unit. The closed air cooling loop system may advantageously improve a performance of the slip-ring unit cooling system.In some embodiments, the marine propulsion unit comprises a cooling air system for providing cooling air to the dual rotor electric motor. In some embodiments, the cooling air system comprises a cooling air unit which integrates at least some parts of the cooling air system in a single unit. In some embodiments, the cooling air system is formed by a plurality of distinct sub-systems. The cooling air system typically comprises an air fan and a heat exchanger. The air fan is typically configured to propel air through the cooling air system. Particularly, the air fan may provide cooling air to the dual rotor electric motor and may draw the cooling air from the dual rotor electric motor, particularly after cooling the contra rotating motor. Typically, the air fan is configured to generate an overpressure in an ingoing air channel and a negative pressure in an outgoing air channel. In some embodiments, the slip-ring unit cooling system may be cooled by cooling air of the cooling air system. Particularly the cooling air of the cooling air system may cool the closed air cooling loop system via the air-to-air heat exchanger.In some embodiments, the cooling air system is an annular cooling air system with at least a part of the cooling air entering and / or exiting the dual rotor electric motor annularly. An annular cooling air system may be particularly favorable for compact marine propulsion units with a compact dual rotor electric motor. In some embodiments, the cooling air system is an annular cooling air system with at least a part of the cooling air entering and / or exiting the dual rotor electric motor axially. An axial cooling air system may be particularly favorable for an electric motor with a larger diameter.According to some embodiments, the marine propulsion unit comprises a marine propulsion unit assembly structure. The marine propulsion unit assembly structure may comprise a marine propulsion unit housing, a cage structure or a frame structure. The marine propulsion unit assembly structure may be described as a capsule arrangement in which at least some components of the marine propulsion unit are arranged. The dual rotor electric motor and the drive shaft are typically arranged inside the marine propulsion unit assembly structure and are mechanically connected to the marine propulsion unit assembly structure. Particularly, the marine propulsion unit assembly structure typically physically supports the dual rotor electric motor and the drive shaft. Typically, the marine propulsion unit assembly structure further comprises an installation interface for installing the marine propulsion unit to a marine vessel via the marine propulsion unit assembly structure. The installation interface particularly provides a mechanical connection between the marine propulsion unit assembly structure and the marine vessel. In other words, physical forces are typically substantially transmitted from the dual rotor electric motor, from the drive shaft and / or from the contra rotating propeller to the marine vessel via the marine propulsion unit assembly structure and the installation interface. In some embodiments, the installation interface comprises mechanical interfaces for transmitting mechanical forces. Typically, the installation interface comprises at least two mechanical interfaces, particularly a drive end interface and a nondrive end interface. Typically, the dual rotor electric motor is arranged between the drive end interface and a non-drive end interface after installation. In some embodiments, the installation interface comprises electrical interfaces for transmitting electricity or electric signals, exemplarily for powering or controlling the marine propulsion unit. In some embodiments, the installation interface comprises interfaces for liquids for transmitting liquids, exemplarily for providing a cooling liquid or a lubricant to the marine propulsion unit. In some embodiments, the installation interface comprises cooling air interfaces, or at least one air passage, for connecting the dual rotor electric motor to a cooling air system, particularly to a cooling air system outside of the marine propulsion unit assembly structure.In some embodiments, the marine propulsion unit assembly structure comprises at least one cooling air channel for guiding air from an interface of the marine propulsion unit assembly structure with the cooling air unit to the dual rotor electric motor. Particularly, the marine propulsion unit assembly structure may comprise the ingoing air channel and the outgoing air channel.Typically, at least one of a drive shaft bearing or the slip-ring unit are arranged inside the marine propulsion unit assembly structure and are mechanically connected to the marine propulsion unitassembly structure. In some embodiments, the cooling air unit is arranged inside the marine propulsion unit assembly structure. In some embodiments, substantially all components of the marine propulsion unit are arranged inside the marine propulsion unit assembly structure. Having substantially all components of the marine propulsion unit arranged inside the marine propulsion unit assembly structure may advantageously allow to reduce an installation effort or a maintenance effort for the marine propulsion unit in a marine vessel. Particularly, the marine propulsion unit may be assembled and / or maintained independent of the further marine vessel, particularly independent of the vessel hull. A modular marine vessel assembly or maintenance process may be facilitated. The marine propulsion unit assembly structure may advantageously protect at least parts of the marine propulsion unit from damage during the installation and / or maintenance.In some embodiments, the marine propulsion unit comprises an auxiliary unit. The auxiliary unit comprises auxiliary devices of the marine propulsion unit, exemplarily a controller unit or a sensor unit, or a unit for providing a lubricant. The auxiliary unit is typically movable and / or flexibly attachable to the marine propulsion unit assembly structure. A movable auxiliary unit may advantageously improve an access and allow for an easy installation of the auxiliary unit.The marine propulsion unit assembly structure typically substantially extends along a rotation axis of the marine propulsion unit. Typically, the marine propulsion unit assembly structure substantially extends from a shaft seal towards the slip-ring unit. Typically, an extension of the marine propulsion unit assembly structure along a longitudinal axis of the marine vessel exceeds an extension of the marine propulsion unit assembly structure along a transverse and / or vertical axis of the marine vessel.In some embodiments, a smallest dimension of the marine propulsion unit assembly structure is at most 3 times, at most 2 times or at most 1.5 times a diameter of the dual rotor electric motor. Typically, the smallest dimension of the marine propulsion unit assembly structure is a diameter of the marine propulsion unit assembly structure. The diameter of the marine propulsion unit assembly structure typically is a largest extension of the marine propulsion unit assembly structure perpendicular to the rotation axis of the marine propulsion unit, of the dual rotor electric motor or of the drive shaft. In some embodiments, the diameter of the marine propulsion unit assembly structure is an average extension of the marine propulsion unit assembly structure perpendicular to the rotation axis of the marine propulsion unit. The diameter of the marine propulsion unit assembly structure being at most 3 times, at most 2 times or at most 1.5 times the diameter of the dual rotor electric motor is typically associated with a compact marine propulsion unit und mayallow a favorable handling of the marine propulsion unit, particularly during assembling, mounting, disassembling or maintaining the marine propulsion unit.Typically, the marine propulsion unit assembly structure has an n-fold symmetry along an axis of the marine propulsion unit. Typically, n is a natural number of at least 4. In some embodiments, the marine propulsion unit assembly structure is substantially rotational symmetric. Particularly, the marine propulsion unit assembly structure substantially follows a shape of a cylinder.Typically, the marine propulsion unit assembly structure is configured to transmit at least 60%, at least 75%, at least 85%, at least 90%, or at least 95% of a propulsion force of the marine propulsion unit to the marine vessel. In other words, the propulsion force of the marine propulsion unit, and particularly of the contra rotating propeller, is transmitted to the marine vessel via the marine propulsion unit assembly structure. Typically, the propulsion force is transmitted via the installation interface, and particularly via at least one of the mechanical interfaces.In some embodiments, the marine propulsion unit comprises part of a hull of a marine vessel. Particularly, the marine propulsion unit comprises part of a skeg of the marine propulsion unit. The marine propulsion unit is connectable to the hull of the marine vessel via interfaces, exemplarily by welding. Typically, the marine propulsion unit, and particularly the part of the hull, is specifically adapted for a specific marine vessel or for a specific marine vessel design. Exemplarily, the part of the hull is configured to ensure a smooth transition of the hull of the marine vessel to the part of the hull of the marine propulsion unit. In other words, the hull of the marine propulsion unit is configured to ensure an optimal flow of water along the hull and the transition of the hull of the marine vessel to the hull of the marine propulsion unit. The marine propulsion unit with the part of the hull of the marine vessel may also be described as a motor block. Typically, the part of the hull of the marine propulsion unit has a largest dimension exceeding a diameter of the dual rotor electric motor by at least a factor of 3 or at least a factor of 5. Particularly, an extension along a vertical axis of the marine propulsion unit may exceed a diameter of the dual rotor electric motor by at least a factor of 3 or at least a factor of 5.A marine vessel may comprise a marine propulsion unit according to any of the embodiments described herein. Particularly, the marine vessel may be provided with propulsion by at least one marine propulsion unit according to any of the embodiments described herein. Typically, the marine vessel comprises a hull with a receiving interface for receiving the marine propulsion unit.The marine propulsion unit may be integrated into the marine vessel as a modular unit. Exemplarily, the marine propulsion unit may be integrated into the marine vessel as a whole.In typical embodiments, the marine vessel comprises a receiving structure for receiving the marine propulsion unit, and particularly for receiving the marine propulsion unit assembly structure. Typically, the receiving structure defines a position of the marine propulsion unit in the marine vessel. According to some embodiments, the receiving structure may also act to define the ingoing air channel and the outgoing air channel. The receiving structure may be part of a bulkhead of the marine vessel. Exemplarily, the receiving structure may comprise openings in the bulkhead fitted for receiving the marine propulsion unit and particularly for receiving the marine propulsion unit assembly structure.Typically, an electric power supply from the marine vessel, in other words from the motor and the electric generator of the marine vessel, to the dual rotor electric motor may be provided along a vertical axis. Exemplarily, the electric power supply may be provided from a lower deck or from a higher deck.A marine propulsion unit according to any of the embodiments described herein, particularly a marine propulsion unit in a capsule arrangement, may be installed in a marine vessel as described herein. The method of installing the marine propulsion unit comprises assembling the marine propulsion unit in the marine propulsion unit assembly structure outside the marine vessel. In other words, the marine propulsion unit may be assembled independent of the marine vessel assembly process, particularly independent of the location and / or a progress of assembly of the marine vessel. Accordingly, in some embodiments, the marine propulsion unit may be assembled at a different location from the marine vessel and may be transported to the marine vessel, or the ship yard, as a whole. Assembling the marine propulsion unit outside the marine vessel may advantageously allow for economy of scale effects and may improve a cash flow during the vessel building process.The method of installing the marine propulsion unit comprises inserting the marine propulsion unit assembly structure into the marine vessel. Typically, the marine propulsion unit is inserted into the marine vessel from outside the hull of the marine vessel. Particularly, the marine propulsion unit is inserted via an opening in the stem of the marine vessel. Typically, after inserting the marine propulsion unit into the hull of the marine vessel, the marine propulsion unit substantially closesthe opening of the marine vessel. In other words, the marine propulsion unit substantially matches the opening of the marine vessel.The method of installing the marine propulsion unit comprises mechanically connecting the marine propulsion unit assembly structure with the marine vessel. Mechanically connecting the marine propulsion unit assembly structure with the marine vessel typically comprises at least one of welding or bolt mounting. In particular, the opening in the skeg may be closed and sealed and a mechanical connection may be established. The marine propulsion unit may be connected to the marine vessel via the installation interface and / or the receiving interface. In some embodiments, the method of installing the marine propulsion unit further comprises establishing electric and / or air passage connections.A marine vessel with a marine propulsion unit according to any of the embodiments described herein, particularly a marine propulsion unit in a capsule arrangement, may be maintained. A method of maintaining the marine propulsion unit may comprise removing a connection, particularly a bolted connection between the marine vessel and the marine propulsion unit. The method may further comprise removing the marine propulsion unit through an opening in the stern of the marine vessel. Typically, removing the marine propulsion unit through an opening in the stern of the marine vessel comprises moving the marine propulsion unit substantially parallel to a longitudinal axis of the marine vessel. The method comprises maintaining the marine propulsion unit outside the hull of the marine vessel. Subsequently, the marine propulsion unit assembly structure is inserted into the marine vessel, particularly via an opening in the stem of the marine vessel, and the marine propulsion unit assembly structure is mechanically connected with the marine vessel.A marine propulsion unit according to any of the embodiments described herein, particularly a marine propulsion unit in a motor block arrangement, may be installed in a marine vessel as described herein. The method of installing the marine propulsion unit comprises assembling the marine propulsion unit in the marine propulsion unit assembly structure outside the marine vessel. In other words, the marine propulsion unit may be assembled independently of the marine vessel assembly process, particularly independently of a location and / or a progress of assembly of the marine vessel.The method of installing the marine propulsion unit comprises constructing a hull of the marine vessel with an omission of a skeg of the hull. Particularly, the hull is constructed such that themarine propulsion unit may be attached to the hull at the omission or opening. Exemplarily, constructing the hull may comprise constructing the receiving interface for receiving the installation interface of the marine propulsion unit assembly structure.The method of installing the marine propulsion unit comprises attaching the marine propulsion unit assembly structure to the hull of the marine vessel at the omission. Particularly, the marine propulsion unit assembly structure acts as the skeg of the hull. Typically, there is a smooth transition from the hull to the marine propulsion unit assembly structure acting as the skeg of the hull, particularly to avoid unnecessary turbulences.Subsequently, the marine propulsion unit assembly structure is mechanically connected with the marine vessel. Typically, mechanically connecting the marine propulsion unit assembly structure with the marine vessel comprises welding and or bolt-mounting. In some embodiments, the method further comprises establishing electric and / or air passage connections.Embodiments of the present disclosure provide marine propulsion units with an improved performance and a small footprint. The marine propulsion units described herein allow for easy and independent assemblage and for good maintainability.BRIEF DESCRIPTION OF THE DRAWINGS

[0340] The accompanying drawings relate to embodiments of the disclosure and are described in the following:FIG. 1 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 2 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 3 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 4 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 5 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 6 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 7 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 8 schematically illustrates a marine propulsion unit with a slip-ring cooling system according to embodiments described herein;FIG. 9 schematically illustrates a marine propulsion unit with a slip-ring cooling system according to a further embodiment described herein;FIG. 10 schematically illustrates a cross-sectional view of a dual rotor electric motor of a marine propulsion unit according to the embodiments described herein;FIG. 11 schematically illustrates a detail of a marine propulsion unit according to the embodiments described herein;FIG. 12 schematically illustrates a detail of a marine propulsion unit according to the embodiments described herein;FIG. 13 schematically illustrates a method of cooling a contra rotating motor of a marine propulsion unit according to embodiments described herein.FIG. 14 schematically illustrates a cross-section of an isometric view of a marine propulsion unit according to the embodiments described herein;FIG. 15 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein;FIG. 16 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein;FIG. 17 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein;FIG. 18 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein; andFIG. 19 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein.FIG. 20 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG. 21 schematically illustrates a cross-section of an isometric view of a marine propulsion unit according to the embodiments described herein;FIG. 22 schematically illustrates a cross-section of an isometric view of a marine propulsion unit according to the embodiments described herein;FIG. 23 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein;FIG. 24 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein;FIG. 25 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein; andFIG. 26 illustrates a flow chart of a method of maintaining a marine propulsion unit according to the embodiments described herein.FIG. 27 schematically shows an NDE side of the marine propulsion unit with a bearing unit according to some embodiments described herein;FIG. 28 schematically shows a bearing unit for a marine propulsion unit according to some embodiments described herein;FIG. 29 schematically shows a bearing unit for a marine propulsion unit according to some embodiments described herein and the transfer of forces therein;FIG. 30 schematically shows a perspective view of a bearing unit at the NDE side of a marine propulsion unit according to some embodiments described herein;FIG. 31 schematically shows an enlarged view of Fig. 27; and,FIG. 32 schematically shows a flow chart of a method for supporting shafts in a marine propulsion unit according to some embodiments described herein.FIG. 33 schematically illustrates embodiments according to the present disclosure;FIG. 34 schematically illustrates embodiments according to the present disclosure;FIG. 35 schematically illustrates embodiments according to the present disclosure;FIG. 36 schematically illustrates embodiments according to the present disclosure;FIG. 37 schematically illustrates a method for the assembly of a marine propulsion unit;FIG. 38 schematically illustrates embodiments of a method according to the present disclosure;FIG. 39 schematically illustrates embodiments of a method according to the present disclosure.FIG. 40 schematically illustrates a sealing unit inside a marine propulsion unit according to the embodiments described herein;FIG. 41 schematically illustrates a sealing unit inside a marine propulsion unit according to the embodiments described hereinFIG. 42 schematically illustrates a method for servicing a sealing unit inside a marine propulsion unit according to the embodiments described herein.FIG 43 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG 44 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG 45 schematically illustrates a dual rotor electric motor according to embodiments described herein;FIG 46 schematically illustrates a slip-ring unit according to embodiments described herein; andFIG 47 schematically illustrates an NDE bearing according to embodiments described herein.FIG 48 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG 49 schematically illustrates a marine propulsion unit according to the embodiments described herein;FIG 50 schematically illustrates installing a marine propulsion unit according to the embodiments described herein;FIG 51 schematically illustrates the marine propulsion unit of Fig. 50 in an installed state;FIG 52 schematically illustrates a method of installing a marine propulsion unit according to the embodiments described herein;FIG 53 schematically illustrates a method of installing a marine propulsion unit according to the embodiments described herein.DETAILED DESCRIPTION OF EMBODIMENTS

[0341] Reference will now be made in detail to the various embodiments of the disclosure, one or more examples of which are illustrated in the figures. Generally, only the differences with respect to individual embodiments are described. Each example is provided by way of explanation of the disclosure and is not meant as a limitation of the disclosure. Further, features illustrated or described as part of one embodiment can be used on or in conjunction with other embodiments to yield a further embodiment. It is intended that the description includes such modifications and variations. In the figures, elements may be depicted with exaggerated dimensions to improve the comprehensibility of the detailed description of embodiments. In particular, relations of lengths and widths of components shown may be distorted. Further, some elements may be depicted with enlarged dimensions while other elements in the same figure are depicted, relatively, with reduced dimensions.

[0342] Fig. 1 schematically illustrates a marine propulsion unit, particularly in the embodiments of Fig. 1 - 4 an azimuthing propulsion unit 1000, according to typical embodiments described herein. In Fig. 5 - 7, a shaft-line marine propulsion unit 2000 is schematically illustrated. The azimuthing propulsion unit 1000 of Fig. 1 comprises a dual rotor electric motor 1. The dual rotor electric motor 1 may also be described as contra rotating electric motor. The dual rotor electric motor 1 is typically arranged substantially horizontally centrally within the azimuthing propulsionunit 1000. Particularly, the dual rotor electric motor 1 is arranged within a pod of the azimuthing propulsion unit 1000.

[0343] The dual rotor electric motor 1 comprises an inner rotor 2 and an outer rotor 3. The inner rotor 2 is arranged within the outer rotor 3. Inner rotor 2 and outer rotor 3 are arranged coaxially with respect to each other. The inner rotor 2 and the outer rotor 3 are configured to rotate about a rotation axis 50. The rotation axis 50 is a longitudinal axis of the azimuthing propulsion unit 1000. The inner rotor 2 drives an inner shaft propeller 10 and the outer rotor 3 drives an outer shaft propeller 9. The outer shaft propeller 9 and the inner shaft propeller 10 are arranged coaxially and rotate about the rotation axis 50. The outer shaft propeller 9 and the inner shaft propeller 10 form a contra rotating propeller unit. In the embodiment of Fig. 1, the outer shaft propeller 9 and the inner shaft propeller 10 substantially have the same diameter. In embodiments not shown in Fig.1 the outer shaft propeller 9 may have a diameter different from the diameter of the inner shaft propeller 10. Exemplarily, the outer shaft propeller 9 may have a diameter of at least 6 m, exemplarily of 6.1 m, and the inner shaft propeller 10 may have a diameter of at most 6 m, exemplarily of 5.575 m.

[0344] The outer rotor 3 of the dual rotor electric motor 1 typically comprises a perforated tube 4, as shown in the typical embodiment of Fig. 1. The perforated tube 4 mechanically supports the outer rotor winding and comprises a plurality of openings. The plurality of openings of the perforated tube 4 are configured to pass air from an exterior of the dual rotor electric motor 1 into an interior of the dual rotor electric motor 1, and vice versa. Warm air, particularly heated by the dual rotor electric motor 1, may pass from an air gap 23 between the inner rotor 2 and the outer rotor 3 through the perforated tube 4 to an annular air channel 14.

[0345] The perforated tube 4 transmits a torque of the outer rotor 3 to outer rotor end flanges 5, 6. A non-drive end, NDE, outer rotor end flange 5 connects the perforated tube 4 to an NDE outer shaft 47. A drive end, DE, outer rotor end flange 6 connects the perforated tube 4 to a DE outer shaft 7. The DE outer shaft 7 transmits the torque of the outer rotor 3 to the outer shaft propeller 9. The outer shaft propeller 9 comprises a plurality of first blades 21, of which two are visible in Fig. 1. The inner rotor 2 is connected to an NDE inner shaft 48 and to a DE inner shaft 8. The DE inner 8 shaft transmits the torque of the inner rotor 2 to the inner shaft propeller 10. The inner shaft propeller 10 comprises a plurality of second blades 22, of which two are visible in Fig. 1. In the embodiment of Fig. 1, the outer shaft propeller 9 and the inner shaft propeller 10 are arranged in apulling configuration. In particular, the first blades 21 and the second blades 22 are configured to operate in a pulling mode.

[0346] The NDE inner shaft 48 is supported in the pod 30 by an NDE inner bearing 42. The NDE outer shaft 47 is supported in the pod 30 by an NDE outer bearing 41. The NDE outer bearing 41 and the NDE inner bearing 42 typically comprise an oil seal, respectively. The DE outer shaft 7 is supported in the pod 30 by a DE outer bearing 11. The DE inner shaft 7 is supported in the DE outer shaft 8 by a DE inner bearing 12. The DE outer bearing 11 and the DE inner bearing 12 typically comprise an oil and water seal, respectively.

[0347] The dual rotor electric motor 1 is provided with electric energy via a slip ring unit 19. The slip ring unit 19 is typically arranged on the non-drive end side of the dual rotor electric motor 1 and particularly to contact the NDE outer shaft 47 as shown in Fig. 1. The NDE outer shaft 47 and the NDE outer rotor end flange 5 are providing an electrical connection between the slip ring unit 19 to the dual rotor electric motor 1. The slip ring unit 19 comprises at least one sliding contact to transmit electricity from power supply cables 20 to the dual rotor electric motor 1 and particularly to the outer rotor 3 of the dual rotor electric motor 1. From the outer rotor 3, electricity is provided to windings of the dual rotor electric motor 1. The power supply cables 20 provide electrical power from a marine vessel, and particular from a power supply of the marine vessel to the dual rotor electric motor 1 via the slip ring unit 19. The slip ring unit 19 comprises a slip ring unit housing 39. The slip ring unit housing 39 separates the slip ring unit 19 from a further interior of the pod 30 and particularly is configured to prevent dust generated inside the slip ring unit 19, particularly generated by the at least one sliding contact of the slip ring unit 19, to escape to the interior of the pod 30.

[0348] Inside the pod 30 of the azimuthing propulsion unit 1000, air is circulated. The azimuthing propulsion unit 1000 comprises a cooling air unit 16. In the embodiment of Fig. 1, the cooling air unit 16 is arranged within a hull of a marine vessel. In the typical embodiment shown in Fig. 1, the cooling air unit 16 comprises an air fan 17 to circulate air. The cooling air unit 16 typically comprises a heat exchanger 18. By the heat exchanger 18, warm air entering the heat exchanger 18 from the pod 30 is cooled with heat being at least partially transferred to a cooling agent of the heat exchanger 18. The cooling air unit 16 provides cool air to the dual rotor electric motor 1 via a DE ingoing air channel 31 and an NDE ingoing air channel 32 in the pod 30. The DE ingoing air channel 31 is physically separated from an outgoing air channel 33 by an DE air channel separating wall 34 in Fig. 1. The NDE ingoing air channel 32 is physically separated from the outgoing airchannel 33 by an NDE air channel separating wall 35 in Fig. 1. Typically, the outgoing air channel 33 substantially extends in the center of the pod 30 and particularly along a vertical central axis of the pod 30. Air passing through the DE ingoing air channel 31 and / or the NDE ingoing air channel 32 passes through openings of the perforated tube 4 and / or the outer rotor end flanges 5, 6 into an interior of the dual rotor electric motor 1. Within the dual rotor electric motor 1, the air may be heated by the dual rotor electric motor 1, in particular when in operation. The air may exit the dual rotor electric motor 1 via radial openings of the perforated tube 4 towards the annular air channel 14. The annular air channel 14 is connected to the outgoing air channel 33.

[0349] In Fig. 2, the azimuthing propulsion unit 1000 is configured to operate in a pushing mode. In particular, the first blades 21 and the second blades 22 are configured to operate in a pushing mode. In Fig. 3, a side view of the azimuthing propulsion unit 1000 of the embodiment of Fig. 2 is schematically shown.

[0350] In Fig. 4, the azimuthing propulsion unit 1000 is arranged in a push-pull-configuration. In particular, in Fig. 4, the outer shaft propeller 9 and the inner shaft propeller 10 are arranged at opposite ends of the pod 30. The outer shaft propeller 9 acts as a pushing propeller and the inner shaft propeller 10 acts as a pulling propeller. In embodiments not shown in the figures, the outer shaft propeller may act as the pulling propeller and the inner shaft propeller may act as the pushing propeller.

[0351] In Fig. 5 and Fig. 6, a marine propulsion unit 2000 is schematically illustrated. The marine propulsion unit 2000 is arranged within the hull 2100 of the marine vessel. Particularly, the marine propulsion unit 2000 is arranged in a shaft-line configuration with the dual rotor electric motor 1 being arranged within the hull 2100 of the marine vessel. Similar to the azimuthing propulsion unit 1000, as shown in Fig. 1 - 3, the marine propulsion unit 2000 comprises the dual rotor electric motor 1, a drive shaft connecting the dual rotor electric motor 1 to the propeller unit with the outer shaft propeller 9 and the inner shaft propeller 10. The outer shaft propeller 9 and the inner shaft propeller 10 are arranged at a skeg of the hull 2100 of the vessel. Generally, the drive shaft, the dual rotor electric motor 1, the outer shaft propeller 9 and the inner shaft propeller 10, the DE and NDE bearings 41, 42 and the slip ring unit 19 of the marine propulsion unit 2000 can be arranged similar or substantially identical to the azimuthing propulsion unit as shown in Fig. 1 - 3.

[0352] In Fig. 5, the marine propulsion unit 2000 comprises a motor block 2050. Within the motor block 2050, the drive shaft, the dual rotor electric motor 1, the DE and NDE bearings 41, 42 andthe slip ring unit 19 of the marine propulsion unit 2000 are arranged. The motor block 2050 comprises an outgoing air channel 33 and, typically, a DE ingoing air channel and an NDE ingoing air channel (not explicitly shown in Fig. 5). In embodiments not shown in the Figures, the marine propulsion unit may comprise an axial air cooling. Particularly, for the axial air cooling, air may enter the dual rotor electric motor 1 from a DE side and exit the dual rotor electric motor 1 from an NDE side or vice versa. The outgoing air channel 33 and the ingoing air channels are connected to the cooling air unit 16. Typically, the cooling air unit 16 is arranged outside the motor block 2050. In some embodiments (not shown in the Figures), particularly for a large motor block 2050, the cooling air unit 16 may be arranged inside the motor block 2050. The motor block 2050 follows a contour of the hull 2100 of the vessel. Particularly, the motor block 2050 forms a skeg of the hull 2100 of the vessel. The motor block 2050 is typically welded to the hull 2100 at a welding area 61.

[0353] In Fig. 6, the marine propulsion unit 2000 comprises a marine propulsion unit housing 2010. Within the marine propulsion unit housing 2010, the drive shaft, the dual rotor electric motor 1, the slip ring unit 19 and the NDE bearings 41, 42 are arranged. The marine propulsion unit housing 2010 is configured to be inserted in the hull 2100 via the skeg of the hull 2100.

[0354] In Fig. 7, the dual motor electric motor 1, the slip ring unit 19 and the NDE bearings 41, 42 are arranged within the hull of the marine vessel. The dual rotor electric motor 1 is connected to the contra rotating propeller 9, 10 via the drive shaft. In Fig. 7, the drive shaft is longer that in the embodiments shown in Fig. 5 and 6. Particularly, the drive shaft may have a length of at least 5 times a length of the dual rotor electric motor 1. In part, the drive shaft extends outside the hull of the marine vessel as an exposed shaft. The drive shaft is supported by support bearings 45, 46. In the hull, the dual motor electric motor 1, the slip ring unit 19 and the DE and NDE bearings 41, 42 are accessible for maintenance.

[0355] Fig. 8 schematically illustrates a marine propulsion unit 1000 according to typical embodiments described herein. The marine propulsion unit 1000 comprises the cooling air unit 16. The cooling air unit 16 is arranged within a hull of a marine vessel. In the typical embodiment shown in Fig. 8, the cooling air unit 16 comprises an air fan 17 to circulate air. The cooling air unit 16 typically comprises a heat exchanger 18. By the heat exchanger 18, warm air entering the heat exchanger 18 from the pod 30 is cooled with heat being at least partially transferred to a cooling agent of the heat exchanger 18. The cooling air unit 16 provides cool air to the dual rotor electric motor 1 via a DE ingoing air channel 31 and an NDE ingoing air channel 32 in the pod 30. TheDE ingoing air channel 31 is physically separated from an outgoing air channel 33 by an DE air channel separating wall 34 in Fig. 8. The NDE ingoing air channel 32 is physically separated from the outgoing air channel 33 by an NDE air channel separating wall 35 (not shown) in Fig. 8.

[0356] Fig. 9 schematically illustrates a marine propulsion unit 1000 according to a further embodiment described herein. The embodiment of the marine unit 1000 shown in Fig. 9 has similar features as the embodiment of the marine propulsion unit shown in Fig. 8, but the marine propulsion unit 1000 can include an intake heat exchanger 270 arranged at the second position 257 of the air channel arrangement 260. An outflow filter 265 can be arranged at the second position 257 of the air channel arrangement. The intake heat exchanger 270 may be connected to an air intake channel arrangement 272 which is connected to the slip-ring housing 19. The air intake channel arrangement 272 can be configured to guide an intake cooling airflow 282 from the intake heat exchanger 270 to the slip-ring housing 19. As already described in Fig. 8 the cooling airflow 250 can exit the slip-ring housing 19 at the first position 255 of the air channel arrangement 260 and can enter the intake heat exchanger 270 at the second position 257 of the air channel arrangement 260 via the outflow filter 265. The intake heat exchanger 270, the air intake channel arrangement 272, the slip-ring housing 19 and the air channel arrangement 260 can be configured as a closed-loop system, which is separated from the motor cooling airflow 232. The intake heat exchanger 270 can be configured to transfer heat from the cooling airflow 250 to the motor cooling airflow 232 without mixing the intake cooling airflow 282 with the motor cooling airflow 232. An inflow filter unit (not shown) can be provided between the slip-ring housing 19 and the air intake channel arrangement 272 to filter the intake cooling airflow 282 before entering the slip-ring housing 19.

[0357] In Fig. 10, the dual rotor electric motor 1 is shown in a cross-sectional view. In Fig. 10, the cross-sectional view along a plane perpendicular to the rotating axis 50 of Fig. 1 at a central position of the dual rotor electric motor 1 is shown. The dual rotor electric motor 1 is arranged within the pod 30 of the marine propulsion unit. Between a wall of the pod 30 and the dual rotor electric motor 1, the annular air channel 14 is present. Through the annular air channel 14, the air exiting the dual rotor electric motor 1, and particularly exiting the outer rotor 3, may pass to the outgoing air channel 33. At the position of the cross-sectional view of Fig. 10, air inside the dual rotor electric motor 1 may exit the dual rotor electric motor 1 towards the outgoing air channel 33. The inner rotor 2 of the dual rotor electric motor 1, having a free space 124 between poles of the inner rotor 2 for air passing along the inner rotor 2, is arranged within the outer rotor 3. Between the inner rotor 2 and the outer rotor 3, an air gap 23 is present. The outer rotor 3 comprises an outerrotor winding installed in an outer rotor core. The outer rotor core comprises cooling air slots 125 arranged in a radial direction to allow air to flow from the inner rotor 2 and the outer rotor winding towards the outgoing air channel 33 via the perforated tube 4. The perforated tube 4 is connected with the outer rotor 3 via a plurality of axial beams 114. The perforated tube 4 comprises a plurality of radial openings 104. Particularly, the perforated tube 4 comprises a plurality of first openings connected to the at least one ingoing air channel (not shown in Fig. 10) and a plurality of second openings 105 connected to the outgoing air channel 33.

[0358] In some embodiments, particularly at axial positions towards the axial ends of the dual rotor electric motor 1, air may enter the dual rotor electric motor 1 through the radial openings. A cross-sectional view at such a position (not shown in the figures) could resemble the cross-sectional view shown in Fig. 10 with the air flow being inverted. Geometrical relations described for the cross-sectional view of Fig. 10 may thus be applicable to axial positions towards the axial ends of the dual rotor electric motor 1 as well.

[0359] In Fig. 11, a detail of a marine propulsion unit according to embodiments described herein in a longitudinal cross-section. In Fig. 11, part of the dual rotor electric motor is shown. The inner rotor 2 and the outer rotor 3 rotate about the rotational axis 50, particularly in opposite directions. The inner rotor 2 is connected to the drive end shaft 8. The outer rotor 3 is connected to the perforated tube 4 via a plurality of axial beams (not shown in Fig. 11). The perforated tube 4 is configured to transmit the torque via the drive end outer rotor end flange 6 to the drive end outer shaft 7. The drive end outer rotor end flange 6 comprises at least one flange opening 106. The at least one flange opening 106 is configured to allow air entering from the at least one ingoing air channel into the dual rotor electric motor. The perforated tube 4 comprises a plurality of first openings 104 connected to the at least one ingoing air channel and a plurality of second openings 105 connected to the outgoing air channel. The outer rotor comprises the outer rotor winding 101 and the outer rotor core 103. The outer rotor core 103 comprises a plurality of cooling air slots 125 arranged in a radial direction to allow air to flow between the outer rotor winding 101 and the perforated tube 4. From the first openings 104, air can flow through the plurality of cooling air slots 125 to the outer rotor winding 101 and the inner rotor 2. An air sealing 131 is arranged between the perforated tube 4 and the outer rotor core 103 to separate the first openings 104 and the second openings 105. Between the static ingoing air channel and outgoing air channel and the rotatable perforated tube 4, an outer rotor air sealing 110 is arranged. The outer rotor air sealing 110 may be connected to the at least one air channel separating wall (not shown in Fig. 11). The outer air sealing 110 comprises a small gap.

[0360] Fig. 12 shows a detail of the marine propulsion unit, in particular the dual rotor electric motor 1, in a side view. The inner rotor is connected to the DE inner shaft 8 and the NDE inner shaft 48. The outer rotor is connected to the perforated tube 4. The perforated tube 4 transmits the torque of the outer rotor to the DE outer shaft 7 via the DE outer rotor end flange 6. The perforated tube 4 transmits the torque of the outer rotor to the NDE outer shaft 47 via the DE outer rotor end flange 5. The DE outer rotor end flange 5 comprises a plurality of flange openings 106. The plurality of flange openings 106 are arranged substantially symmetrical around a rotation axis of the perforated tube 4 and / or the dual rotor electric motor 1. The perforated tube 4 comprises a plurality of radial openings. The plurality of radial openings comprises a plurality of first openings 104 and a plurality of second openings 105. In the embodiments of Fig. 12, the plurality of radial openings are substantially quadratically with rounded comers. In the embodiments of Fig. 12, the plurality of radial openings are arranged in a substantially rectangular, and particularly quadratical, pattern.

[0361] Fig. 13 shows a method 190 of cooling a contra rotating electric motor, or a dual rotor electric motor, with an outer rotor and an inner rotor, of a marine propulsion unit. The method comprises providing 192 cooling air to the contra rotating motor and drawing 194 the cooling air from the contra rotating motor via the perforated tube.

[0362] Fig. 14 schematically illustrates a cross-section of an isometric view of a marine propulsion unit, such as an azimuthing propulsion unit 1000, according to typical embodiments described herein. The marine propulsion unit, such as the azimuthing propulsion unit 1000, comprises a hull of the marine propulsion unit or a pod 30 and a pod hull 300. A rotatable drive end (DE) inner shaft 8, runs at least partially within a DE outer shaft 7. A DE inner bearing 12 is arranged between the DE outer shaft 7 and the DE inner shaft 8. The DE outer shaft 7 comprises a hatch 302.

[0363] The exemplary azimuthing propulsion unit 1000 of Fig. 14 as described herein may permit the marine propulsion unit, particularly the azimuthing propulsion unit 1000, to be maintained without requiring the marine vessel to be necessarily dry-docked. Dry docking a marine vessel is a time and resource consuming process which ultimately adversely affects an efficiency of the marine vessel.

[0364] The hatch 302 is configured to provide access to the DE inner bearing 12. The hatch 302 is, for example, configured to be accessed by a user from within the marine propulsion unit, particularly the azimuthing propulsion unit 1000. In order for the hatch 302 to provide sufficientaccess to the DE inner bearing 12, the hatch 302 typically has substantially the size of a man-hole.

[0365] The embodiment of Fig. 14 comprises the DE inner bearing 12 with inner bearing pads 312. For example, the DE inner bearing 12 may comprise two or more inner bearing pads 312. The inner bearing pads 312 are arranged around the DE inner shaft 8, and in particular around an entire circumference of the DE inner shaft 8.

[0366] The embodiment of Fig, 14 comprises a DE inner distal seal 304, wherein the DE inner distal seal 304 is arranged between the DE inner shaft 8 and the DE outer shaft. The DE inner distal seal 304 is arranged towards a drive end (DE) of the azimuthing propulsion unit 1000.

[0367] The exemplary azimuthing propulsion unit 1000 of Fig. 14 comprises a DE inner proximal seal 306, wherein the DE inner proximal seal 306 is arranged between the DE inner shaft 8 and the DE outer shaft. The DE inner proximal seal 306 is arranged towards a non-drive end (NDE) of the azimuthing propulsion unit 1000.

[0368] The azimuthing propulsion unit 1000 shown in Fig. 14 comprises a DE outer bearing 11. As with typical embodiments, the DE outer bearing 11 comprises outer bearing pads 511.

[0369] The DE inner bearing 12 and the DE outer bearing 11 are arranged coaxially on the rotation axis 50. In the exemplary embodiment of Fig. 14, the DE outer bearing 11 is at least partially overlapping the DE inner bearing 12.

[0370] Fig. 15 illustrates a flow chart of a method 350 of maintaining a marine propulsion unit such as an azimuthing propulsion unit according to the embodiments described herein. The method 350 comprises opening a hatch of a DE outer shaft of the marine propulsion unit 352. The method 350 comprises accessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft 354.

[0371] Fig. 16 illustrates a flow chart of a method 350 of maintaining a marine propulsion unit such as an azimuthing propulsion unit according to the embodiments described herein. The method 350 comprises opening a hatch of a DE outer shaft of the marine propulsion unit 352. The method 350comprises accessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft 354. The method 360 further comprises, after accessing the DE inner bearing the hatch, displacing the DE inner bearing 356.

[0372] Fig. 17 illustrates a flow chart of a method 350 of maintaining a marine propulsion unit such as an azimuthing propulsion unit according to the embodiments described herein. The method 350comprises opening a hatch of a DE outer shaft of the marine propulsion unit 352. The method 350comprises accessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft 354. The method 350further comprises, after accessing the DE inner bearing the hatch, displacing the DE inner bearing 356. The method 350further comprises, after displacing the DE inner bearing, accessing a DE inner distal seal through the hatch, and displacing the DE inner distal seal 358.

[0373] Fig. 18 illustrates a flow chart of a method 350 of maintaining a marine propulsion unit such as an azimuthing propulsion unit according to the embodiments described herein. The method 350comprises opening a hatch of a DE outer shaft of the marine propulsion unit 352. The method 350comprises accessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft 354. The method 350further comprises, after accessing the DE inner bearing the hatch, displacing the DE inner bearing 356. The method 350further comprises, after displacing the DE inner bearing, accessing a DE inner distal seal through the hatch, and displacing the DE inner distal seal 358. The method 350, further comprising, accessing a DE inner proximal seal arranged between the DE outer shaft and a DE inner shaft 359.

[0374] Fig. 19 illustrates a flow chart of a method 350 of maintaining a marine propulsion unit such as an azimuthing propulsion unit according to the embodiments described herein. The method 350 comprises opening a hatch of a DE outer shaft of the marine propulsion unit 352. The method 350 comprises accessing a D...

Claims

1. CLAIMS1. A marine propulsion unit (1000, 2000) with a motor air cooling system and a contra rotating electric motor (1) having an inner rotor (2) and an outer rotor (3), whereinthe contra rotating motor comprises a perforated tube (4) with a plurality of radial openings (104, 105), the perforated tube being configured to transmit a torque of the outer rotor to a propeller unit and to support an outer rotor winding;the motor air cooling system comprises at least one ingoing air channel (31, 32) and at least one outgoing air channel (33); andthe at least one ingoing air channel is connected to the at least one outgoing air channel via at least some of the plurality of radial openings of the perforated tube.

2. The marine propulsion unit of claim 1, wherein the marine propulsion unit is an azimuthing propulsion unit (1000).

3. The marine propulsion unit of any of claims from 1 to 2, whereinthe propeller unit comprises a contra rotating propeller (9, 10);the inner rotor is configured to drive an inner shaft (8, 48) connected to an inner shaft propeller (10) of the contra rotating propeller; andthe outer rotor is configured to drive an outer shaft (7, 47) connected to an outer shaft propeller (9) of the contra rotating propeller.

4. The marine propulsion unit of claim 3, whereinthe outer rotor is connected to the outer shaft via at least one outer rotor end flange (5, 6), andthe at least one outer rotor end flange comprises at least one flange opening (106).

5. The marine propulsion unit of any of claims from 1 to 4, wherein the perforated tube comprises at least 50 radial openings.

6. The marine propulsion unit of any of claims from 1 to 5, whereinthe plurality of radial openings is arranged substantially symmetrically with respect to the perforated tube; and / orthe plurality of radial openings is equally spaced with respect to each other in at least one dimension.

7. The marine propulsion unit of any of claims from 1 to 6, wherein the plurality of radial openings cover at least 20% of a side surface of the perforated tube.

8. The marine propulsion unit of any of claims from 1 to 7, wherein the outer rotor comprises a plurality of radial slots (125) in a core (103) of the outer rotor winding (101).

9. The marine propulsion unit of any of claims from 1 to 8, wherein the outer rotor comprises a plurality of axial beams (114) between a core of the outer rotor winding and the perforated tube.

10. The marine propulsion unit of any of claims from 1 to 9, wherein at least 80% of air passing through the at least one ingoing air channel enters the at least one outgoing air channel via the perforated tube.

11. The marine propulsion unit of any of claims from 1 to 10, whereinthe motor air cooling system is configured to first guide air along an axial direction of the perforated tube and subsequently in a radial direction of the perforated tube, andwherein the motor air cooling system is preferably configured such that a temperature of the air remains substantially identical in axial direction.

12. The marine propulsion unit of any of claims from 1 to 11, wherein the motor air cooling system is arranged such that air from the at least one ingoing air channel enters the contra rotating motor via the at least one flange opening and exits the contra rotating motor via at least part of the plurality of radial openings.

13. The marine propulsion unit of any of claims from 1 to 12, whereinthe plurality of radial openings comprises first openings (104) connected to the at least one ingoing air channel and comprises second openings (105) connected to the at least one outgoing air channel; andthe motor air cooling system is arranged such that at least part of the air from the at least one ingoing air channel enters the contra rotating motor via the first openings and exits the contra rotating motor via the second openings.

14. The marine propulsion unit of any of claims from 1 to 13, whereinthe motor air cooling system further comprises an air fan (17) and a heat exchanger (18);the air fan and the heat exchanger are arranged within a hull-integrated section of the marine propulsion unit; andthe motor air cooling system is a closed loop air cooling system.

15. A marine vessel comprising a marine propulsion unit according to any of claims from 1 to 14.14116. A method (190) of cooling a contra rotating electric motor with an outer rotor and an inner rotor of a marine propulsion unit, the contra rotating motor comprising a perforated tube configured to transmit a torque of the outer rotor to a propeller unit and to support an outer rotor winding, the method comprising:providing (192) cooling air to the contra rotating motor; anddrawing (194) the cooling air from the contra rotating motor via the perforated tube.

17. A marine propulsion unit with a slip-ring cooling system and a contra rotating motor having an inner rotor and an outer rotor, comprising:a slip-ring housing;a slip-ring assembly arranged within the slip-ring housing;wherein the slip-ring assembly comprises at least one slip-ring element being in contact to the outer rotor;an air channel arrangement comprising a first position being connected to the slip-ring housing and a second position;an air fan device configured to generate a cooling airflow that flows from the first position to the second position of the air channel arrangement creating a negative pressure within the slip-ring housing; andan outflow filter unit arranged at the second position of the air channel arrangement for filtering the cooling airflow exiting the air channel arrangement.

18. The marine propulsion unit according to claim 17, wherein the cooling airflow is part of a motor cooling airflow of a motor cooling system before the cooling airflow enters the slip-ring housing.

19. The marine propulsion unit according to any of claims from 17 to 18, whereinthe cooling airflow is part of a motor cooling airflow of a motor cooling system after the cooling airflow exits the second position of the air channel arrangement.

20. The marine propulsion unit according any of claim from 17 to 19, further comprisingan inflow filter unit at the slip-ring housing of the slip-ring assembly.

21. The marine propulsion unit according to any of claims from 17 to 20, further comprisinga set of seals at both ends of the slip-ring assembly at the slip-ring housing and the outer rotor, to seal the slip ring housing against the outside.

22. The marine propulsion unit according to claim 21, whereinthe set of seals comprises at least one lip seal and / or at least one labyrinth seal.

23. The marine propulsion unit according to any of claims from 21 to 22, whereinan air barrier is provided by instrumentation air within at least one seal.

24. The marine propulsion unit according to any of claims from 17 to 23, whereinthe slip-ring housing comprises a top part accommodating the slip-ring arrangement and a bottom part which is connected to first position of the air channel arrangement, in particular whereinthe bottom part of the slip-ring housing comprises dust collecting means.

25. The marine propulsion unit according to any of claim from 20 to 24, further comprising an intake heat exchanger connected to the second position of the air channel arrangement, andoptionally an air intake channel arrangement which is connected to the slip-ring housing and the intake heat exchanger, wherein the intake heat exchanger is configured to provide an intake cooling airflow via the air intake channel arrangement to the slip-ring housing.

26. The marine propulsion unit according to any of claims from 17 to 25, whereinthe air channel arrangement runs, at least in sections, along the longitudinal axis of the outer rotor, and / or wherein the air channel arrangement runs, at least in sections, around the circumference of the outer rotor.

27. The marine propulsion unit according to any of claims from 17 to 26,wherein the air fan device is part of a motor cooling system.

28. The marine propulsion unit according to any of claims from 17 to 27, whereinthe first position of the air channel arrangement is situated at a lower altitude than the second position of the air channel arrangement.

29. The marine propulsion unit of any of claims from 17 to 28, wherein the marine propulsion unit is an azimuthing propulsion unit.

30. A marine vessel comprising a marine propulsion unit according to any of claims from 17 to 29.

31. A method for cooling a slip-ring arrangement in a marine propulsion unit with a contra rotating motor having an inner rotor and an outer rotor, comprising:144Cooling a slip-ring assembly within a slip-ring housing by generating a negative pressure in an air channel arrangement connected by a first position to the slip-ring housing, wherein a cooling airflow flows from the first position to a second position of the air channel arrangement; andfiltering the cooling airflow exiting the second position of the air channel arrangement by an outflow filter.

32. The method for cooling a slip-ring arrangement according to claim 15, further comprising:Filtering the cooling air flow entering the slip-ring housing by an inflow filter.

33. A marine propulsion unit (1000, 2000), the marine propulsion unit (1000, 2000) comprising:- a rotatable drive end (DE) inner shaft (8);- a rotatable DE outer shaft (7), wherein the DE inner shaft (8) runs at least partially within the DE outer shaft (7); and- a DE inner bearing (12) arranged between the DE outer shaft (7) and the DE inner shaft (8);- wherein the DE outer shaft (7) comprises at least one hatch (302).

34. The marine propulsion unit (1000) of claim 33, wherein the marine propulsion unit is an azimuthing propulsion unit.

35. The marine propulsion unit (1000, 2000) of any of claims from 33 to 34, wherein the hatch (302) is configured to provide an access to the DE inner bearing (12).

36. The marine propulsion unit (1000, 2000) of claim 35, wherein the hatch (302) is configured to be accessed by a user from within the marine propulsion unit (1000).14537. The marine propulsion unit (1000, 2000) of any of claims from 33 to 36, wherein the DE inner bearing (12) comprises at least one inner bearing pad (312).

38. The marine propulsion unit (1000, 2000) of any of claims from 33 to 37, further comprising a DE inner distal seal (304), wherein the DE inner distal seal (304) is arranged between the DE inner shaft (8) and the DE outer shaft (7), and wherein the DE inner distal seal (304) is arranged towards a drive end.

39. The marine propulsion unit (1000, 2000) of any of claims from 33 to 38, further comprising a DE inner proximal seal (306), wherein the DE inner proximal seal (306) is arranged between the DE inner shaft (8) and the DE outer shaft (7), and wherein the DE inner proximal seal (306) is arranged towards a non-drive end.

40. The marine propulsion unit (1000, 2000) of any of claims from 33 to 39, further comprising a hull of the marine propulsion unit.

41. The marine propulsion unit (1000, 2000) of any of claims from 33 to 40, further comprising a DE outer bearing (11), wherein the DE outer bearing (11) preferably comprises at least one outer bearing pad.

42. The marine propulsion unit (1000, 2000) of claim 41, wherein the DE inner bearing (12) and the DE outer bearing (11) are arranged coaxially to a rotation axis (50), wherein the DE outer bearing (11) is at least partially overlapping the DE inner bearing (12).

43. A method (350) of maintaining an marine propulsion unit, particularly the marine propulsion unit according to any of claims from 33 to 42; the method comprising:146opening a hatch of a drive end (DE) outer shaft of the marine propulsion unit (352); andaccessing a DE inner bearing arranged between the DE outer shaft and a DE inner shaft (354).

44. The method of claim 43, comprising, after accessing the DE inner bearing through the hatch: displacing the DE inner bearing (356).

45. The method of claim 44, comprising, after displacing the DE inner bearing, accessing a DE inner distal seal through the hatch; anddisplacing the DE inner distal seal (358).

46. The method of any of claims from 43 to 45, comprising, accessing a DE inner proximal seal arranged between the DE outer shaft and a DE inner shaft; anddisplacing the DE inner proximal seal (359).

47. The method of any of claims from 43 to 46, wherein displacing any of: the DE inner bearing, the DE inner distal seal, the DE inner proximal seal, or any combination thereof, comprises axially displacing along the DE inner shaft.

48. The method of any of claims from 43 to 47, further comprising displacing any of: a DE outer proximal seal, a DE outer bearing, a DE outer distal seal, or any combination thereof (360).

49. A marine propulsion unit (1000, 2000) for a vessel, the marine propulsion unit (1000, 2000) comprising:- a rotatable drive end (DE) shaft (7);- a DE outer bearing housing (510);147- a DE outer bearing (11) arranged between the DE shaft (7) and the DE outer bearing housing (510), wherein the DE outer bearing (11) is configured to be displaced, and wherein the DE outer bearing (11) comprises outer bearing pads (511); and- a DE outer distal seal, wherein the DE outer distal seal is configured to be accessed from within the marine propulsion unit.

50. The marine propulsion unit (1000) of claim 49, wherein the marine propulsion unit is an azimuthing propulsion unit.

51. The marine propulsion unit (1000, 2000) of any of claims from 49 to 50, wherein the marine propulsion unit is a contra rotating propeller (CRP) marine propulsion unit and wherein the DE shaft is a DE outer shaft of the marine propulsion unit, the azimuthing propulsion unit (1000) further comprising a rotatable DE inner shaft (8), which runs at least partially within the DE outer shaft (7).

52. The marine propulsion unit (1000, 2000) of claims from 49 to 51, wherein the outer bearing pads are configured to be displaced axially and / or the DE outer distal seal is configured to be displaced axially.

53. The marine propulsion unit (1000, 2000) of any of claims from 49 to 52, wherein the DE outer distal seal (504) is arranged between the DE shaft (7) and the DE outer bearing housing (510).

54. The marine propulsion unit (1000, 2000) of any of the claims from 49 to 53, further comprising a DE outer proximal seal (506), wherein the DE outer proximal seal (506) is arranged between the DE shaft (7) and the DE outer bearing housing (510).14855. The marine propulsion unit (1000, 2000) of any of the claims from 49 to 54, wherein the DE outer bearing (11), the DE outer distal seal (504), and / or the DE outer proximal seal (506) is replacable from within a hull of the marine propulsion unit (1000).

56. The marine propulsion unit (1000, 2000) of any of the claims from 51 to 55, wherein the DE outer shaft (7) comprises a hatch (302), which is configured to provide an access to a space between the DE outer shaft (7) and the DE inner shaft (8).

57. The marine propulsion unit (1000, 2000) of claim 56, wherein the hatch (302) is configured to provide an access to a DE inner bearing (12) being arranged between the DE inner shaft (8) and the DE outer shaft (7); preferably wherein the DE inner bearing (12) comprises inner bearing pads (312) being configured to be accessed through the hatch (302).

58. The marine propulsion unit (1000, 2000) of claim 57, wherein the DE inner bearing (12) and the DE outer bearing (11) are arranged coaxially on a rotation axis (50), wherein the DE outer bearing (11) is at least partially overlapping the DE inner bearing (12).

59. A method (550) of maintaining a marine propulsion unit, particularly the marine propulsion unit according to any of previous claims; the method comprising:accessing a DE shaft from an interior of a hull of the marine propulsion unit (552);accessing a DE outer bearing arranged between the DE shaft and a DE outer bearing housing (554);displacing the DE outer bearing; andaccessing a DE outer distal seal (556) from within the hull of the marine propulsion unit.14960. The method (550) of claim 59, further comprising releasing and displacing a DE outer proximal seal prior to accessing the DE outer bearing (558).

61. The method (550) of any of claims from 59 to 60, further comprising, displacing the DE outer bearing after accessing the DE outer bearing, and / or displacing the DE outer distal seal after accessing the DE outer distal seal (559).

62. The method (550) of any of claims from 59 to 61, wherein displacing any of: the DE outer bearing, the DE outer distal seal, the DE outer proximal seal, or any combination thereof, comprises axially displacing along the DE shaft and / or radially displacing from the DE shaft.

63. The method (550) of claim 62, wherein axially displacing the DE outer bearing, the DE outer distal seal, the DE outer proximal seal, or any combination thereof, comprises, axially displacing the DE outer bearing, the DE outer distal seal, or the DE outer proximal seal to a service position.

64. The method (550) of any of claims from 59 to 63, wherein the DE shaft of the marine propulsion unit is a DE outer shaft of a contra rotating propeller (CRP) marine propulsion unit, the CRP marine propulsion unit further comprising:a hatch in the DE outer shaft; a rotatable DE inner shaft, which runs at least partially within the DE outer shaft; a DE inner bearing arranged between the DE inner shaft and the DE outer shaft; a DE inner proximal seal arranged proximally between the DE inner shaft and the DE outer shaft; and / or a DE inner distal seal arranged distally between the DE inner shaft and the DE outer shaft;the method further comprising:displacing any of: the DE inner proximal seal, the DE inner bearing, the DE inner distal seal, or any combination thereof, through the hatch (560).15065. Bearing unit (40) for a marine propulsion unit (1000), the marine propulsion unit (1000) comprising a rotatable inner shaft (48) and a rotatable outer shaft (47), wherein the inner shaft (48) runs at least partially within the outer shaft (47),the bearing unit (40) comprising:- a bearing arrangement (401) comprising at least one axial bearing (402-404) for the inner shaft (48) and the outer shaft (47), wherein the bearing arrangement is configured for supporting at least a part of the inner shaft (48) and the outer shaft (47); and,- a bearing housing (407) for housing the bearing arrangement (401) and the part (471; 481) of the inner shaft (48) and the outer shaft (47) to be supported by the bearing arrangement (401);- wherein the bearing arrangement (401) is configured for allowing a transfer of axial forces between the outer shaft (47) and the inner shaft (48).

66. The bearing unit according to claim 65, wherein the bearing arrangement (401) comprises a first axial bearing (403) between the inner shaft (48) and the outer shaft (47) for allowing the transfer of axial forces between the inner shaft (48) and the outer shaft (47).

67. The bearing unit according to any of claims from 65 to 66, wherein the bearing arrangement (401) comprises the first axial bearing (403) between the inner shaft (48) and the outer shaft (48), a second axial bearing (402) arranged between a bearing housing wall (408) and the inner shaft (48), and a third axial bearing (404) arranged between a bearing housing wall (409) and the outer shaft (47).

68. The bearing unit according to any of claims from 65 to 67, wherein the bearing housing (407) comprises at least one hatch (411; 412) for reaching into the inside of the bearing housing (407).

69. The bearing unit according to claim 68, wherein the at least one hatch (411; 412) is configured for allowing access to one of the axial bearings (402; 403; 404), maintenance of the axial bearings151(402; 403; 404) and / or replacement of the axial bearings (402; 403; 404) of the bearing arrangement (401) for the inner shaft (48) and the outer shaft (47).

70. The bearing unit according to any of claims from 65 to 69, wherein at least one of the axial bearings (402; 403; 404) of the bearing arrangement is a pad bearing.

71. The bearing unit according to any of claims from 65 to 70 in a marine propulsion unit, especially an azimuthing propulsion unit (1000), the marine propulsion unit (1000) comprising a dual electric motor (1), the inner shaft (48) and the outer shaft (47), at least one of the inner shaft (48) and the outer shaft (47) being driven by the dual electric motor (1), a propeller unit comprising an outer shaft propeller (9) and an inner shaft propeller (10), wherein the inner shaft propeller (10) is driven by the inner shaft (48) and the outer shaft propeller (9) is connected to the outer shaft (47), and wherein the drive chain of the marine propulsion unit (1000) comprises a driven end (DE), which is the end, where the propeller unit is arranged, and a non-driven end (NDE) on the end of the drive chain opposite to the propeller unit.

72. The bearing unit according to claim 71, wherein the bearing unit (401) is arranged at the NDE side of the drive chain of the marine propulsion unit (1000).

73. A marine propulsion unit, especially an azimuthing propulsion unit (1000), comprising a bearing unit (40) according to any of claims from 65 to 70.

74. The marine propulsion unit according to claim 73, wherein the bearing housing (407) has at least one hatch (411; 412) for maintenance, repair and replacement of the bearing arrangement (401) or parts of the bearing arrangement, and wherein the marine propulsion unit (1000) is configured for allowing access of a person to the at least one hatch (411; 412).15275. Method (420) of supporting an inner shaft (48) and an outer shaft (47) in a marine propulsion unit (1000), the marine propulsion unit (1000) comprising the inner shaft (48) and the outer shaft (47), wherein the inner shaft (48) runs at least partially within the outer shaft (47), the method comprising:- Providing (421) a bearing arrangement (401) and a bearing housing (407) for housing the bearing arrangement, the bearing arrangement comprising at least one axial bearing (402; 403; 404) for the inner shaft (48) and the outer shaft (47); and,- Arranging (422) the axial bearing (402; 403; 404) of the bearing arrangement (401) for allowing a transfer of axial forces between the outer shaft (47) and the inner shaft (48).

76. The method according to claim 75, wherein arranging (422) the axial bearing (402; 403; 404) for a transfer of axial forces between the outer shaft (47) and the inner shaft (48) comprises arranging a first axial bearing (403) between the inner shaft (48) and the outer shaft (47).

77. The method according to claim 76, wherein arranging the first axial bearing (403) between the inner shaft (48) and the outer shaft (47) comprises utilizing a bearing pad mounted between the inner shaft (48) and the outer shaft (47).

78. The method according to any of claims from 75 to 77, wherein the bearing housing (407) comprises at least one hatch (411; 412) and wherein the method further comprises: accessing the bearing arrangement (401) within the bearing housing (407) through the at least one hatch (411; 412); and, in particular, performing repair, maintenance, and / or replacement of the bearing arrangement (401) through the at least one hatch (411; 412).

79. The method according to any of claims from 75 to 78, wherein providing the bearing unit (40) comprises mounting the bearing unit (40) in a marine propulsion unit, especially an azimuthing propulsion unit (1000), especially in a marine propulsion unit (1000) according to any of claims 73 and 74.

80. A marine propulsion unit (2000) comprising:- a motor;- an inner shaft (48) coupled to the motor; and- a outer shaft (47) coupled to the motor, whereinthe inner shaft (48) runs at least partially within the outer shaft (47); and whereinthe inner shaft (48) comprises a distal inner segment (620) and a proximal inner segment (610).

81. A marine propulsion unit (2000) according to claim 80, wherein the motor is a dual rotor electric motor (1) comprising an outer rotor (3), and an inner rotor (2) arranged coaxially within the outer rotor (3), wherein- the inner shaft (48) is coupled to the inner rotor (2) of the dual rotor electric motor (1); and wherein- the outer shaft (47) is coupled to the outer rotor (3) of the dual rotor electric motor (1).

82. A marine propulsion unit (2000) according to any claim from 80 to 81, wherein the outer shaft (47) comprises a distal outer segment (640) and a proximal outer segment (630).

83. A marine propulsion unit (2000) according to any claim from 80 to 82, wherein at least one of the inner shaft (48) and the outer shaft (47) comprises a dismountable flange, wherein the dismountable flange forms a segment of the respective shaft.

84. A marine propulsion unit (2000) according to any claim from 80 to 83, wherein the distal inner segment (620) and the proximal inner segment (610) are releasably joint together.

85. A marine propulsion unit (2000) according to any claim from 80 to 84, whereinthe proximal inner segment (610) comprises a proximal inner flange (612); and / or whereinthe distal inner segment (620) comprises a distal inner flange (622).

86. A marine propulsion unit (2000) according to any of claims from 82 to 85, whereinthe proximal outer segment (630) comprises a proximal outer flange (5); andthe distal outer segment (640) comprises a distal outer flange (642); wherein preferablythe proximal outer flange (5) is coupled to the outer rotor (3); andthe proximal inner flange (612) is coupled to the inner rotor (2).

87. A marine propulsion unit (2000) according to any claim from 80 to 86, wherein the inner shaft (48) comprises a section with a hollow cross section (679); and / orwherein at least one integral ring shaped component (699) is mounted onto a surface of the outer shaft and is located in between the proximal outer flange (5) and the distal outer flange (642).

88. A marine propulsion unit (2000) according to any claim from 80 to 87, comprising an enclosed volume (660), which is defined as the volume in between the inner shaft (48) and the outer shaft (47) and a bearing housing (665); and wherein the enclosed volume (660) is sealed.

89. A marine propulsion unit (2000) according to any of claims 80 and from 82 to 88, wherein the motor is coupled to a gearbox, and wherein the gearbox propels the outer shaft (3) and the inner shaft (2).15590. A marine propulsion unit (2000) according to any claim from 80 to 89, wherein the marine propulsion unit (2000) is an azimuthing propulsion unit (1000).

91. A method for mounting a marine propulsion unit (2000), preferably a marine propulsion unit (2000) according to any of the claims from 80 to 90, comprising:providing an outer shaft (47) with a hollow cross section; andproviding an inner shaft (48); wherein the inner shaft (48) comprises a distal inner segment (620) and a proximal inner segment (610), wherein the method further comprises:- inserting at least one of or both of the distal inner segment (620) and the proximal inner segment (610) into the outer shaft (47); and- coupling the distal inner segment (620) to the proximal inner segment (610).

92. A method according to claim 91, wherein providing the outer shaft (47) comprises providing a distal outer segment (640) and a proximal outer segment (630); and wherein the method further comprises:- coupling the distal outer segment (640) to the proximal outer segment (630) to form the outer shaft (47), before coupling the distal inner segment (620) to the proximal inner segment (610).

93. A method according to claim 92, wherein the method further comprises:- mounting an integral ring shaped component (699) onto the outer shaft (47), before coupling the distal outer segment (640) to the proximal outer segment (630).

94. A method according to any of the claims from 92 to 93further comprising:- coupling the proximal inner segment (610) to an inner rotor (2) using an inner rotor connection (681); and156- coupling the proximal outer segment (630) to an outer rotor (3) using an outer rotor connection (683).

95. A sealing unit for a marine propulsion unit, the marine propulsion unit comprising a rotatable inner shaft (8) and a rotatable outer shaft (7), wherein the inner shaft (8) runs at least partially within the outer shaft (7) and wherein the outer shaft (7) runs at least partially within a sealing housing (801) of a marine vessel,the sealing unit comprising:- a plurality of chamber systems, wherein each chamber system comprises an inner shaft seal chamber (817a, 817b, 817c), an outer shaft seal chamber (827a, 827b, 827c) and a passage through the outer shaft fluidly connecting the inner shaft seal chamber (817a, 817b, 817c) and the outer shaft seal chamber (827a, 827b, 827c);- an inner shaft sealing (810) between the inner shaft (8) and the outer shaft (7), wherein the inner shaft sealing (810) seals the inner shaft seal chambers (817a, 817b, 817c) of the plurality of chamber systems; and- an outer shaft sealing (820) between the outer shaft (7) and the sealing housing (801), wherein the outer shaft sealing (820) seals the outer shaft seal chambers (827a, 827b, 827c) of the plurality of chamber systems.

96. A sealing unit according to claim 95, wherein the inner shaft sealing (810) seals an inside of the outer shaft (7) from an outside of the marine vessel; and / or wherein the outer shaft sealing (820) seals an inside of the marine vessel from the outside of the marine vessel.

97. A sealing unit according to any claim from 95 to 96,- wherein the inner shaft sealing (810) comprises an inner composure (811), an outer composure (813) and a plurality of inner sealing elements (815); and / or- wherein the outer shaft sealing (820) comprises an inner composure (821), an outer composure (823) and a plurality of outer sealing elements (825).15798. A sealing unit according to any claim from 95 to 97, wherein at least one passage through the outer shaft (7) comprises an inner groove (835a, 835b, 835c), and wherein the inner groove (835a, 835b, 835c) typically is in at least one of: the inside of the outer shaft (7); and / or the inner shaft sealing (810).

99. A sealing unit according to any claim from 95 to 98, wherein at least one passage through the outer shaft (7) comprises an outer groove (833a, 833b, 833c), and wherein the outer groove (833a, 833b, 833c) typically is in at least one of: the outside of the outer shaft (7); and / or the outer shaft sealing (820).

100. A sealing unit according to any claim from 95 to 99, wherein at least one passage through the outer shaft (7) comprises a plurality of channels (831a, 831b, 831c) through the outer shaft (7) fluidly connecting the inner shaft seal chamber (817a, 817b, 817c) and the outer shaft seal chamber (827a, 827b, 827c).

101. A sealing unit according any claim from 95 to 100, wherein the plurality of chamber systems comprises:- a proximate chamber system, wherein the proximate chamber system is fluidly connected to an oil reservoir;- a distant chamber system; and- an intermediate chamber system, wherein the intermediate chamber system is fluidly connected to an air reservoir.

102. A sealing unit according to any claim from 95 to 101, wherein each chamber system of the plurality of chamber systems contains at least one of:158- oil;- air; and / or- leakage fluid.

103. A sealing unit according to any claim from 95 to 102, wherein each fluid connection of a chamber system of the plurality of chamber systems to a reservoir comprises:- a supply groove (843) in at least one of: the sealing housing (801); and the outer shaft sealing (820).

104. A sealing unit according to any claim from 95 to 103, wherein each fluid connection of a chamber system of the plurality of chamber systems to a reservoir comprises:- at least one supply channels (841) fluidly connecting the chamber system and the reservoir.

105. A sealing unit according to any claim from 95 to 104, the propulsion unit further comprising:- an inner bearing (12) inside an inner bearing chamber (851) between the inner shaft (8) and the outer shaft (7); and- an outer bearing (11) inside an outer bearing (853) chamber between the outer shaft (7) and a bearing housing (803);the sealing unit further comprising:- an inner bearing sealing (855), wherein the inner bearing sealing (855) seals the inside of the marine vessel from the inner bearing chamber (851);- an outer bearing sealing (857), wherein the outer bearing sealing (857) seals the inside of the marine vessel from the outer bearing chamber (853).159106. A sealing unit according to claim 105, wherein the inner bearing chamber (851) and the outer bearing chamber (853) are fluidly connected.

107. A sealing unit according to any of the claims from 105 to 106,- wherein the inner shaft sealing (810) seals the outside of the marine vessel from the inner bearing chamber (851); and / or- wherein the outer shaft sealing (820) seals the outside of the marine vessel from the outer bearing chamber (853).

108. A method for servicing a sealing unit, typically for servicing a sealing unit according to any of claims from 95 to 107, in a marine propulsion unit, the propulsion unit comprising a rotatable inner shaft (8) and a rotatable outer shaft (7), wherein the inner shaft (8) runs at least partially within the outer shaft (7) and wherein the outer shaft (7) runs at least partially within a sealing housing (801) of a marine vessel, the method comprising:- providing (891) a service sealing arrangement, wherein the service sealing arrangement seals the inner shaft sealing (810) from the outside of the marine vessel;- dismounting (892), at least partially, through a hatch (860) provided in the outer shaft (7), an inner bearing (12) between the inner shaft (8) and the outer shaft (7);- dismounting (893), at least partially, the inner shaft sealing (810) through the hatch (860);- servicing (894) the inner shaft sealing (810);- mounting (895) the serviced inner shaft sealing (810) through the hatch (860); and- mounting (896) the inner bearing (12) through the hatch (860).160109. A method according to claim 108, wherein the service sealing arrangement seals the outer shaft sealing (820) from the outside of the marine vessel;the method further comprising:- dismounting, at least partially, an outer bearing (11) between the outer shaft (7) and a bearing housing (803);- dismounting, at least partially, the outer shaft sealing (820);- servicing the outer shaft sealing (820);- mounting the serviced outer shaft sealing (820); and- mounting the outer bearing (11).

110. A marine propulsion unit (2000) comprising:a dual rotor electric motor (1) having an inner rotor and an outer rotor;a contra rotating propeller having an inner shaft propeller (10) and an outer shaft propeller (9);a drive shaft (2500) having an inner shaft connecting the inner rotor to the inner shaft propeller and an outer shaft connecting the outer rotor to the outer shaft propeller; anda slip-ring unit (19) for transmitting an electric current to the dual rotor electric motor.

111. The marine propulsion unit of claim 110, wherein a non-drive end, NDE, thrust bearing (41, 42) supporting the drive shaft comprises a slide bearing.

112. The marine propulsion unit of claim 111, wherein the NDE thrust bearing is arranged separately from the dual rotor electric motor.161113. The marine propulsion unit of any of claims from 110 to 112, wherein the dual rotor electric motor has a rated electric power of at least 200 kW.

114. The marine propulsion unit of any of claims from 110 to 113, wherein a torque of the dual rotor electric motor is transmitted to the contra rotating propeller without a gearbox.

115. The marine propulsion unit of any of claims from 110 to 114, wherein the slip-ring unit is arranged within a slip-ring unit housing separate from the dual rotor electric motor.

116. The marine propulsion unit of any of claims from 110 to 116, wherein the slip-ring unit is cooled using a slip-ring cooling system independent of a cooling air system (16) for cooling the dual rotor electric motor.

117. The marine propulsion unit of claim 116, wherein the slip-ring cooling system is connectable to a low temperature liquid cooling medium vessel cooling system.

118. The marine propulsion unit of claim 117, wherein the low temperature liquid cooling medium vessel cooling system is a low temperature water vessel cooling system.

119. The marine propulsion unit of any of claims from 110 to 118, wherein the marine propulsion unit comprises at least one shaft coupling (2510, 2520).

120. The marine propulsion unit of claim 119, wherein the at least one shaft coupling is arranged for removably separating the drive shaft between the contra rotating propeller and the dual rotor electric motor.162121. The marine propulsion unit of any of claims from 110 to 120, wherein a rotating part of the slip-ring unit is connected to the outer rotor of dual rotor electric motor with a dismountable connection.

122. The marine propulsion unit of any of claims from 110 to 122, wherein an axial distance of a motor-facing end of the contra rotating propeller to a propeller-facing end of the dual rotor electric motor is at least two times an axial length of the dual rotor electric motor.

123. The marine propulsion unit of any of the claims from 110 to 122, further comprising at least one support bearing (45, 46) for supporting the drive shaft between a propeller bearing (2530) and a drive end, DE, bearing.

124. A marine vessel comprising a marine propulsion unit according to any of claims from 110 to 123.

125. A marine propulsion unit (2000) comprisinga dual rotor electric motor (1) having an inner rotor and an outer rotor;a contra rotating propeller having an inner shaft propeller (10) and an outer shaft propeller (9);whereinan axial distance of a motor-facing end of the contra rotating propeller to a propeller-facing end of the dual rotor electric motor is at most three times an axial length of the dual rotor electric motor.

126. The marine propulsion unit of claim 125, wherein the dual rotor electric motor has a rated electric power of at least 200 kW.163127. The marine propulsion unit of any of the claims from 125 to 126, further comprisinga slip-ring unit (19) for transmitting an electric current to the dual rotor electric motor; and / ora cooling air system (16) for providing cooling air to the dual rotor electric motor.

128. The marine propulsion unit of any of the claims from 125 to 127, further comprisinga drive shaft having an inner shaft connecting the inner rotor to the inner shaft propeller and an outer shaft connecting the outer rotor to the outer shaft propeller.

129. The marine propulsion unit of claim 128, further comprising a marine propulsion unit assembly structure (2010, 2050), whereinthe dual rotor electric motor and the drive shaft are arranged inside the marine propulsion unit assembly structure and are mechanically connected to the marine propulsion unit assembly structure; andthe marine propulsion unit assembly structure comprises an installation interface for installing the marine propulsion unit to a marine vessel via the marine propulsion unit assembly structure.

130. The marine propulsion unit of claim 129, wherein at least one of a drive shaft bearing (41, 42) or the slip-ring unit are arranged inside the marine propulsion unit assembly structure and are mechanically connected to the marine propulsion unit assembly structure.

131. The marine propulsion unit of any of claims from 129 to 130, wherein the marine propulsion unit assembly structure comprises at least one air passage (33) for cooling air from the cooling air system to pass to the dual rotor electric motor.164132. The marine propulsion unit of any of claims from 129 to 131, wherein the marine propulsion unit assembly structure substantially extends along a rotation axis of the marine propulsion unit.

133. The marine propulsion unit of any of claims from 129 to 132, wherein a diameter of the marine propulsion unit assembly structure is at most 3 times of a diameter of the dual rotor electric motor.

134. The marine propulsion unit of any of claims from 129 to 133, wherein the marine propulsion unit assembly structure has an n-fold symmetry along an axis of the marine propulsion unit, with n being a natural number of at least 4.

135. The marine propulsion unit of any of claims from 129 to 134, wherein the marine propulsion unit assembly structure is configured to transmit at least 75% of a propulsion force of the marine propulsion unit to the marine vessel.

136. The marine propulsion unit of any of claims from 129 to 135, wherein the marine propulsion unit assembly structure comprises a part of a hull (2100) of a marine vessel, particularly a part of a skeg of the marine vessel.

137. A marine vessel comprising a marine propulsion unit according to any of the claims from 125 to 136.

138. A method (3400) of installing a marine propulsion unit according to any of claims from 125 to 135in a marine vessel, the method comprising:165assembling (3410) the marine propulsion unit in a marine propulsion unit assembly structure outside the marine vessel;inserting (3420) the marine propulsion unit assembly structure into the marine vessel, particularly via an opening in the stem of the marine vessel; andmechanically connecting (3430) the marine propulsion unit assembly structure with the marine vessel.

139. A method (3500) of installing a marine propulsion unit according to any of claims from 125 to 136in a marine vessel, the method comprising:assembling (3510) the marine propulsion unit in the marine propulsion unit assembly structure outside the marine vesselconstructing (3515) a hull of the marine vessel with an omission of a skeg of the hull;attaching (3520) the marine propulsion unit assembly structure to the hull of the marine vessel at the omission, particularly wherein the marine propulsion unit assembly structure acts as the skeg of the hull; andmechanically connecting (3530) the marine propulsion unit assembly structure with the marine vessel.166

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