An air supply system for a hull of a vessel and a vessel comprising the air supply system

Abstract

Disclosed is an air supply system for supplying air to an outside of a hull of a vessel. The air supply system comprises a plurality of air discharge units (ADUs) for releasing a compressed air flow to an outside of the hull below a waterline of the vessel. The plurality of ADUs are configured to be arranged around a longitudinal centreline of the hull of the vessel. The air supply system comprises a first flow path for providing a first compressed air flow to a first subset of the plurality of ADUs. The air supply system comprises a second flow path for providing a second compressed air flow to a second subset of the plurality of ADUs. The air supply system comprises a first pressure device configured to feed the first flow path with a first compressed air flow. The air supply system comprises a second pressure device configured to feed the second flow path with a second compressed air flow. The second pressure device is a different type than the first pressure device. 1 to be published

Description

[0001] AN AIR SUPPLY SYSTEM FOR A HULL OF A VESSEL AND A VESSEL COMPRISING

[0002] THE AIR SUPPLY SYSTEM

[0003] The present disclosure pertains to the field of propulsion of vessels. The present disclosure relates to an air supply system for supplying air to an outside of a hull of a vessel and a vessel comprising the air supply system.

[0004] BACKGROUND

[0005] A vessel’s resistance when moving through water is made up of multiple components, of which frictional resistance is the most dominant. Injection of an air flow into a turbulent boundary layer around the hull of the vessel may be used to reduce the frictional resistance of the hull of the vessel in the water. The turbulent boundary layer is located between stationary water and the moving water close to the hull of the vessel.

[0006] Air lubrication of the hull can reduce the frictional loss significantly. Depending on the type of propulsion used for the vessel, an efficiency of the vessel may be drastically improved. The efficiency gain is dependent on speed, hull form, draft of the vessel and / or a distribution and amount of air to a wetted surface of the vessel. The draft of the vessel is the vertical distance from the bottom of a keel of the vessel to the waterline and the wetted surface is the total area of the vessels outer surface in contact with the surrounding water.

[0007] The total net efficiency improvement depends on the power used to pressurize the air flow required to reduce the friction. Hence, a net propulsion efficiency is dependent on the power required to facilitate the air flow and a given discharge pressure at an air outlet in the hull. The discharge pressure corresponds to the water pressure from the water surrounding the vessel acting on the air outlet ports.

[0008] SUMMARY

[0009] Air lubrication systems may use scavenging air from an engine of the vessel to supply a flow of air to a pressure device for increasing the pressure of the scavenging air flow before feeding the air flow to the outside of the hull. However, the scavenging air flow available from the engine of the vessel may under certain conditions, such as at low speeds or when used on large vessel, be too low to sufficiently reduce the friction along the hull of the vessel. Accordingly, there is a need for an air supply system for supplying air to the outside of a hull of a vessel, which mitigates, alleviates, or addresses the shortcomings existing and provides a more efficient air supply system.

[0010] Disclosed is an air supply system for supplying air to an outside of a hull of a vessel. The air supply system comprises a plurality of air discharge units (ADUs) for releasing a compressed air flow to an outside of the hull below a waterline of the vessel. The plurality of ADUs are configured to be arranged around a longitudinal centreline of the hull of the vessel. The air supply system comprises a first flow path for providing a first compressed air flow to a first subset of the plurality of ADUs. The air supply system comprises a second flow path for providing a second compressed air flow to a second subset of the plurality of ADUs. The air supply system comprises a first pressure device configured to feed the first flow path with a first compressed air flow. The air supply system comprises a second pressure device configured to feed the second flow path with a second compressed air flow. The second pressure device is a different type than the first pressure device.

[0011] Disclosed is a vessel comprising a hull, an engine, and the air supply system according to the present disclosure.

[0012] It is an advantage of the air supply system of the present disclosure that the air supply system will provide a flexible amount and distribution of the compressed air across a wetted hull surface of the vessel. The wetted hull surface can herein be seen as the surface of the hull facing the water. By providing the air supply system with a first pressure device and a second pressure device being different to each other and feeding an air flow to a respective flow path of the air supply system, a more stable and / or higher flow of air can be provided to the outside of the hull of the vessel. By making the first pressure device and the second pressure device different to each other, the first pressure device and the second pressure device may cooperatively provide an air flow required for sufficiently reducing the friction between the hull of the vessel and the surrounding water. The second pressure device may for example be controlled to provide the difference between the required air flow and an available scavenging air flow from the engine of the vessel provide to the first pressure device. The air supply system can thus improve the efficiency of large vessels or vessels operating at low speeds. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The above and other features and advantages of the present disclosure will become readily apparent to those skilled in the art by the following detailed description of exemplary embodiments thereof with reference to the attached drawings, in which:

[0014] Fig. 1 illustrates a first example air supply system according to this disclosure, Fig. 2 illustrates a second example air supply system according to this disclosure, Fig. 3 illustrates a third example air supply system according to this disclosure, Fig. 4 illustrates a fourth example air supply system according to this disclosure, and Fig. 5 illustrates a fifth example air supply system according to this disclosure.

[0015] DETAILED DESCRIPTION

[0016] Various exemplary embodiments and details are described hereinafter, with reference to the figures when relevant. It should be noted that the figures may or may not be drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the disclosure or as a limitation on the scope of the disclosure. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated, or if not so explicitly described.

[0017] The figures are schematic and simplified for clarity, and they merely show details which aid understanding the disclosure, while other details have been left out. Throughout, the same reference numerals are used for identical or corresponding parts.

[0018] An air supply system for supplying air to an outside of a hull of a vessel is disclosed herein. The air supply system comprises a plurality of ADUs for releasing a compressed air flow to an outside of the hull below a waterline of the vessel. The plurality of ADUs are configured to be arranged around a longitudinal centreline of the hull of the vessel. The plurality of ADUs may be equally distributed around a longitudinal centreline of the hull of the vessel, such that an ADU on a starboard side of the longitudinal centreline has a corresponding ADU arranged on a port side of the longitudinal centreline at an equal distance from the centreline. The air supply system comprises a first flow path for providing a first air flow, such as a first compressed air flow, to a first subset of the plurality of ADUs. The air supply system comprises a second flow path for providing a second air flow, such as a second compressed air flow, to a second subset of the plurality of ADUs. The air supply system comprises a first pressure device configured to feed the first flow path with the first air flow, such as the first compressed air flow. The air supply system comprises a second pressure device configured to feed the second flow path with the second air flow, such as the second compressed air flow. The second pressure device is a different type than the first pressure device. The second pressure device being a different type than the other can herein be seen as the second pressure device being a different type of mechanical device and / or using a different type of media for the air flow, such as using ambient air vs. scavenging air. The first compressed air flow and the second compressed air flow may each be a portion of a total air flow provided to the outside of the hull of the vessel, such that the first compressed air flow and the second compressed air flow forms the total air flow provided to an outside of the hull. In one or more example air supply devices, the second compressed air flow may be a smaller portion than the first compressed air flow. In one or more example air supply systems, the second compressed air flow is 10-40% of the total air flow, such as 20-30%, such as 25%.

[0019] A compressed air flow can herein be seen as an air flow having an increased pressure when exiting the pressure device compared to the pressure of the air flow when entering the pressure device. An air flow having a boosted pressure, such as a pressure increased using a blower, may herein also be seen as a compressed air flow.

[0020] A flow path can be seen as a route that air will follow between two points of interest, such as from an air supply unit, such as the scavenging air receiver or an ambient air supply, to the respective subset of ADUs. The flow path may comprise piping, such as a piping system, connecting the air supply unit to the respective subset of ADUs. The first pressure device and the second pressure device may be comprised in the first flow path and the second flow path respectively, such that the piping of the respective first flow path or second flow path connects the air supply unit to an inlet of the respective pressure device and connects an outlet of the respective pressure device with the respective subset of ADUs.

[0021] In one or more example air supply systems, the first subset of the plurality of ADUs and the second subset of the plurality of ADUs are separate subsets of the plurality of ADUs. In other words, the first flow path may be connected to a dedicated first subset of ADUs and the second flow path may be connected to a dedicated second set of ADUs, such that the first pressure device and the second pressure device do not provide air flows to the same subset of ADUs. The first subset of ADUs and the second subset of ADUs may be arranged adjacent to each other. In some example air supply systems herein, the first subset of ADUs may be arranged at a different distance from a longitudinal centreline of the vessel than the second subset of ADUs.

[0022] In one or more example air supply systems, the first subset of the plurality of ADUs and the second subset of the plurality of ADUs are overlapping subsets of the plurality of ADUs. Overlapping subsets can herein be seen as one or more of the ADUs of each subset being the same ADU(s), such as the first flow path and the second flow path being connected to, at least partly, the same ADUs. In other words, at least a first ADU of the first subset of ADUs may also be a first ADU of the second subset of ADUs, while a second ADU of the first subset may be dedicated to the first flow path and a second ADU of the second subset is dedicated to the second flow path.

[0023] In one or more example air supply systems, one of the first flow path and the second flow path, such as the first flow path, is configured to receive a scavenging air flow from an engine of a vessel, and the other of the first flow path and the second flow path, such as the second flow path, is configured to receive ambient air, such as air at atmospheric pressure.

[0024] In one or more examples herein, the first flow path is configured to receive the scavenging air flow from the engine and the second flow path is configured to receive ambient air. The first flow path being configured to receive a scavenging air flow can herein be seen as the first flow path being connected to a scavenging air receiver of an engine of the vessel. The first pressure device may thus receive a scavenging air flow from the scavenging air receiver and may increase the pressure of the scavenging air flow before feeding the scavenging air flow to the first subset of ADUs. Using scavenging air as the inlet air flow to the flow path has the benefit that the inlet air flow has already been compressed, thereby reducing the required compression ratio of the first pressure device for providing a flow of compressed air having a pressure exceeding the discharge pressure at the ADUs. Thereby, simpler, and more costefficient pressure devices, such as blowers or compressors, may be used as the first pressure device. The second flow path being configured to receive ambient air can herein be seen as the second flow path having an ambient air inlet where ambient air can enter the second flow path. The second pressure device may thus receive an ambient air flow via the second flow path and may increase the pressure of the ambient air flow, such as may compress the ambient air flow to a pressure larger than the discharge pressure at the ADUs. before feeding the ambient air flow to the second subset of ADUs. Using ambient air as inlet air flow has the benefit that the air supply system is easy to implement in a vessel and may be used as a stand-alone system for controlling the flow of compressed air to the outside of the hull of the vessel, such as to the second subset 20 of ADUs. Furthermore, using ambient air reduces the requirement of cooling the air before providing the air to the first flow path. Thus, the risk of corrosion in the air supply system due to condensation of the air provided to the air supply system is reduce.

[0025] In one or more example air supply systems, the second pressure device is a blower or a compressor, such as a fixed volume displacement blower or compressor or a variable volume displacement blower or compressor. In one or more example air supply systems, such as when the second flow path is connected to ambient air and the second pressure device is receiving ambient air, the second pressure device may be a compressor being capable of compressing the ambient air to a pressure exceeding the discharge pressure at the ADUs. In one or more example air supply systems, such as when the second flow path is connected to scavenging air and the second pressure device is receiving a scavenging air flow, the second pressure device may be a blower having a lower compression ratio than the compressor, since the required pressure increase for exceeding the discharge pressure with the scavenging air is lower than for the ambient air.

[0026] In one or more example air supply systems, the air supply system comprises a first set of valves arranged in the first flow path for controlling the first flow of compressed air to the first subset of the plurality of ADUs, and / or to prevent entry of sea water through the plurality of ADUs. In one or more example air supply systems, the air supply system comprises a second set of valves arranged in the second flow path for controlling the second flow of compressed air to the second subset of the plurality of ADUs, and / or to prevent entry of sea water through the plurality of ADUs.

[0027] In one or more example air supply systems, the air supply system comprises a controller, such as at least one controller, for controlling one or more of the first pressure device, the second pressure device, the first set of valves, and the second set of valves. In one or more example air supply systems, the first pressure device is independently controlled from the second pressure device. In one or more example air supply systems, the first pressure device and the second pressure device are jointly controlled. Jointly controlled can herein be seen as the second pressure device being controlled based on the first pressure device, such as based on a flow of air through the first flow path or a pressure generated be the first pressure device, or vice versa. The second pressure device may for example be controlled to provide a difference between a desired air flow at the ADUs and the air flow being delivered by the first pressure device. The desired air flow in the first flow path and / or the second flow path may be determined based on a speed of the vessel, such as a function of a speed of the vessel. In one or more example air supply systems, the first pressure device and the second pressure device are controlled by respective controllers. In one or more example air supply systems, the one or more controllers are configured to control a flow distribution and / or a pressure distribution between the first flow path and the second flow path, for example by controlling the first pressure device, the second pressure device, the first set of valves, and / or the second set of valves. The flow distribution and / or the pressure distribution may be controlled based on one or more of a speed of the vessel and a load of the engine of the vessel, such as based on an available flow of scavenging air from the engine.

[0028] In one or more example air supply systems, the first pressure device may be a fixed volume displacement pressure device. The fixed volume displacement pressure device may be configured to provide a fixed volume flow of air to the first flow path. The fixed volume displacement pressure device may be arranged in the first flow path for feeding the compressed air flow to the first subset of ADUs with a fixed volume displacement and at pressure larger than a discharge pressure at the ADUs. Having a fixed volume displacement pressure device has the benefit that the pressure device will always provide a fixed flow of compressed air to the flow path irrespective of the pressure of the flow.

[0029] In one or more example air supply systems, the first pressure device may comprise a first outlet for feeding a first branch of the first flow path and a second outlet for feeding a second branch of the second flow path. The first branch of the first flow path may be connected to the ADUs of the first subset of ADUs that are arranged on a port side of the hull of the vessel while the second branch of the first flow path may be connected to the ADUs of the first subset of ADUs that are arranged on a starboard side of the hull of the vessel. Thereby, the fixed volume displacement pressure device will provide a fixed flow of compressed air to the first outlet and second outlet irrespective of the pressure of the flow to each of the first outlet and / or second outlet. If the discharge pressure acting against the flow of compressed air from the pressure device increases, for example due to rolling of the vessel, the fixed volume displacement pressure device will ensure the fixed flow by creating an increased pressure of the flow of compressed air. In one or more example air supply systems, the first pressure device is one or more of a fixed volume displacement blower and a fixed volume displacement compressor.

[0030] In one or more example air supply systems herein, the first pressure device, such as the fixed volume displacement pressure device may comprise a drive unit, and one or more pressure boosting unit(s) for feeding the compressed air to the first and / or the second outlet of the first pressure device. In some example air supply systems herein, the first pressure device may comprise a plurality of pressure boosting units, such as a first pressure boosting unit for feeding compressed air to the first outlet and a second pressure boosting unit for feeding compressed air to the second outlet. The first pressure boosting unit and the second pressure boosting unit may be driven by the same drive unit, so that they are synchronously driven and provide the same air flow. When the vessel rolls around its longitudinal centreline such that the dynamic pressure at the ADUs varies, the pressure that is to be provided by each of the plurality of pressure boosting units depends on a dynamic part of the discharge pressure at the ADUs connected to the corresponding outlets of the pressure boosting units. During rolling of the vessel, such as when the vessel rotates around its longitudinal centreline so that an inclination angle of the vessel changes, the discharge pressure at the ADUs may vary over the ADUs depending on how deep the ADUs are submerged in the water surrounding the vessel. During rolling of the vessel, the depth of the ADUs in the water may depend on the distance of the ADUs from the longitudinal centre line of the vessel. An ADU arranged further away from the longitudinal centreline of the vessel will be submerged deeper in the water or lifted higher out of the water when the vessel is rolling around the longitudinal centreline. If the vessel is rolling along the longitudinal centerline of the vessel, an ADU arranged on the port side diffusor may experience increased discharge pressure when the vessel is leaning towards the port side, such as when the port side is closer to the water. The discharge pressure may comprise a static part P and a dynamic part dP. The discharge pressure for the ADU arranged on the port side (PS) may thus be P+dP(PS). However, for an opposite ADU located at the same distance to the rotation axis on the starboard (SB) side of the vessel, such as to the longitudinal centreline of the vessel, the pressure for this ADU may be P + dP(SB). In this case, since the ADUs are located at the same distance from the longitudinal centreline of the vessel, dP(SB)= - dP(PS). The dynamic pressure will thus decrease on the starboard side with the same amount as the dynamic pressure increases on the port side of the vessel. The same phenomenon will occur as the vessel rolls to the other side in a roll period. The static part P of the discharge pressure comprises the hydrostatic pressure P(draft) at the ADU with no inclination, such as when the vessel is level, and the pressure loss P(loss) in the air supply system upstream of the ADUs. The dynamic part of the pressure is due to the movement, such as the rolling, of the vessel. When the vessel operates at high seas with high inclination angles, the dynamic part of the pressure will be higher than when the vessel is operating at low seas with low inclination angles. When the discharge pressure in one or more of the ADUs arranged on the port side increases, the pressure required at the first pressure boosting unit to provide the fixed volume flow increases. This will increase the power requirement on the drive unit from the first pressure boosting unit. However, since the discharge pressure at the starboard side ADUs simultaneously, such as at the same time, will decrease with the same amount, so will the power requirement on the drive unit from the second boosting unit. The drive unit may thus not experience any net changes, or at least not any substantial net changes, in power demand from the first pressure boosting unit and the second pressure boosting unit. Hence, the example first pressure device, such as the fixed volume displacement pressure device passively adapts the pressure at the first outlet and the second outlet, such as at the first pressure boosting unit and the second pressure boosting unit.

[0031] Experiencing opposite dynamic discharge pressures means that the first pressure boosting unit experiences an increase in discharge pressure with the same amount as the second pressure boosting unit experiences a decrease in discharge pressure, and vice versa. To ensure the fixed volume flow to the ADUs, the first pressure boosting unit thus has to increase the pressure of the flow of compressed air to overcome the increased discharge pressure. At the same time, the second pressure boosting unit may decrease the pressure of the flow of compressed air to overcome the decreased discharge pressure. The increased power requirement experienced by the drive unit for increasing the pressure at the first pressure boosting unit thus corresponds to the reduced power requirement from the second pressure boosting unit, and the changes in power requirements from the first and the second pressure boosting units thus cancel each other out. Correspondingly, the difference in discharge pressures between the ADUs arranged on opposite sides of the longitudinal centreline of the vessel can be compensated without a change in power requirement experienced by the drive unit of the pressure device. In one or more example air supply systems disclosed herein, one pressure boosting unit may feed compressed air to all outlets of the pressure device, such as to the first and the second outlet. The compressed air flow provided to the plurality of outlets, such as to the first and second outlet may thus be the same. The plurality of pressure boosting units, such as the first pressure boosting unit and / or the second pressure boosting unit may be a blower or a compressor, such as a fixed volume displacement blower or compressor. In some example air supply systems, the first pressure boosting unit and / or the second pressure boosting unit may be one or more Roots blower(s) or piston type compressors. The blower may be a simpler pressure boosting means than the compressor but may operate at a lower pressure ratio than the compressor, such as for example a ratio of 1 .1 to 1 .2 for the blower compared to a ratio greater than 1 .2 for the compressor, or higher depending on the configuration of the compressor. The Roots blower comprises two rotary vanes configured to mesh with each other upon rotation. Each rotary vane is arranged on an individual axle, wherein the individual axles are connected to each other via gears so that the axles may be driven synchronously by a single drive unit. Each of the rotary vanes may according to this disclosure be considered as being a pressure boosting unit. The Roots compressor may thus be considered comprising a drive unit, and a first and a second pressure boosting unit. It is an advantage of the example fixed volume displacement pressure device of the air supply system provided herein that a fixed flow control of air to the ADUs, without the need of throttles or valves for controlling the flow of compressed air to the ADUs, can be ensured. The example fixed volume displacement pressure device of the air supply system thus provides a passive solution for controlling the distribution of air to the ADUs during rolling of the vessel.

[0032] In some example air supply systems disclosed herein, the fixed volume displacement pressure device may comprise more than two outlets, such as three, four, five or even more outlets, for feeding the compressed air flow to a subset of the plurality of ADUs, such as to a respective subset of ADUs. In some example air supply systems disclosed herein, the first pressure device, such as the fixed volume displacement pressure device, may comprise as many outlets as the number of ADUs comprised in the first flow path of the air supply system divided by the number of pressure boosting units in the first pressure device. Thereby, an individual control of the flow to each ADU of the first subset of ADUs may be provided. For example, if the first flow path of the air supply system comprises one pressure boosting unit and a number X of ADUs, the pressure device may comprise a maximum of X outlet ports for supplying each ADU individually. If the air supply system comprises more than one pressure device, such as N pressure devices, each pressure device may comprise for example X / N outlets for supplying a subset of the X ADUs individually when the ADUs are evenly distributed between the pressure devices. However, the ADUs may in one or more example air supply systems also be unevenly distributed, so that a first pressure device supplies compressed air to for example X-Y out of X ADUs and a second pressure device supplies compressed air to the remaining Y out of the X ADUs. In this example scenario, the first pressure device may comprise a maximum of X-Y outlets connected to an individual ADU while the second pressure device may comprise a maximum of Y outlets connected to an individual ADU. The number of outlet ports on the pressure device may however also be less than the number of ADUs supplied by the pressure device, since one outlet may supply a plurality of ADUs with compressed air. By supplying more than one ADUs with compressed air from the same outlet, the cost and complexity of the air supply system may be reduced.

[0033] In one or more example fixed volume displacement pressure devices, the first pressure boosting unit and the second pressure boosting unit, may be driven by the drive unit via a common shaft or via a gear system. In one or more example air supply systems, the first pressure boosting unit and the second pressure boosting unit may be individually driven pressure boosting units being synchronously controlled to provide the same flow. Individually driven can herein be seen as the first pressure boosting unit and the second pressure boosting unit being driven by a respective drive unit, such as a respective electric motor. By running the one or more pressure boosting units synchronously, such as by connecting them to the same drive unit or synchronously controlling two individual drive units, the one or more pressure boosting units provide the same volume flow in the two outlets of the fixed volume displacement pressure device, presuming that the first and second pressure boosting units are identical in shape and size. The flow through the plurality of outlets may thereby be equal but the pressure of the compressed flow of air may be different and may depend on the discharge pressure at the ADUs.

[0034] In one or more example air supply systems disclosed herein, the air supply system may comprise one or more turbochargers. The one or more turbochargers may in one or more example air supply systems be configured to supply the scavenging air flow to the scavenging air receiver of the engine.

[0035] Each turbocharger comprises a turbine driven by an exhaust gas flow from the engine of the vessel and a compressor for supplying the scavenging air flow to one of the first flow path and the second flow path. The one or more turbochargers may in one or more example air supply systems be configured to supply the scavenging air flow to the scavenging air receiver of the engine from where the scavenging air flow can be supplied to the first or the second flow path. The compressor of the turbocharger may receive ambient air which is then compressed by the compressor. The compressed air from the compressor of the turbocharger, which compressed air may also be referred to as scavenging air, may then be fed to the engine, such as to the scavenging air receiver of the engine from where it can be supplied to the first or the second flow path. The scavenging air flow may be supplied to the scavenging air receiver via a scavenging air flow path.

[0036] The pressure of the compressed scavenging air flow may be dependent on the load of the engine. At low loads the exhaust gas flow may be low which will cause the turbine of the turbocharger, which is driven by the exhaust gas flow, to rotate at low revolutions per minute (rpm). Consequently, the compressor of the turbocharger will rotate at the same rpm and will not provide its maximum compression performance. At low engine loads, the scavenging pressure may thus be below the discharge pressure at the ADUs. The scavenging air may thus be fed to the first pressure device, where the pressure of the scavenging air flow is boosted, such as increased, to a pressure larger than the discharge pressure at the ADUs. The scavenging air flow having a pressure larger than the discharge pressure at the ADUs is then fed to the ADUs where it is discharged to the outside of the hull of the vessel. Using scavenging air flow as the inlet air flow has the benefit that the inlet air flow has already been compressed, such as pre-compressed, by the one or more turbochargers. The pressure device thus has to perform less compression work compared to the one or more example air supply systems where the inlet air flow is ambient air. When the inlet air flow has been precompressed a blower or a compressor having a lower compression ratio may be used as pressure boosting unit, since the compression work that has to be performed by the pressure device to achieve a desired discharge pressure is lower than if ambient air is to be compressed. Upon the pressure of the compressed air flow upstream of the first pressure device exceeding the discharge pressure at the ADUs, such as at higher engine loads where the pressure of the scavenging air is larger than the discharge pressure, the flow of scavenging air through the first flow path may be restricted to ensure sufficient flow of compressed air, such as scavenging air, to the engine. A lack of scavenging air flow through the engine combustion chamber may otherwise cause the engine of the vessel to overheat. By restricting the flow through the first flow path it can be ensured that the engine receives the air required for cooling and combusting the fuel in the combustion chamber. The flow of scavenging air through the first pressure device may be controlled based on an engine load, and / or a maximum allowed bypass flow of scavenging air at that given engine load, and / or based on a speed of the vessel.

[0037] In one or more example air supply systems, the air supply system may comprise one or more flow control devices arranged in the first flow path and / or in the second flow path for controlling the flow through the flow paths. The flow control device may be a fixed orifice allowing a fixed flow through the first flow path, or a variable orifice, such as a control valve, for allowing a variable flow of air through the first flow path. The flow control device may be controlled based on the engine load, and / or the maximum allowed bypass flow of scavenging air at that given engine load, and / or based on a speed of the vessel.

[0038] In one or more example air supply systems, the air supply system may comprise one or more valves, such as non-return valves, arranged in the first flow path between the first pressure device and the first subset of ADUs for controlling preventing sea water from entering the first flow path through the ADUs. In one or more example air supply systems, the air supply system may comprise one or more non-return valves arranged in the second flow path between the second pressure device and the second subset of ADUs for preventing sea water from entering the second flow path through the ADUs.

[0039] In one or more example air supply systems, the air supply system comprises a controller, such as one or more controllers, for controlling one or more of the first pressure device (30), the second pressure device (40), a first set of valves (14A), and a second set of valves (14B). A vessel comprising a hull and the air supply system according to any one of the examples provided herein is further disclosed. The vessel may further comprise an engine, such as a main engine, for propelling the vessel.

[0040] Fig. 1 illustrates an example air supply system 100 for supplying air to an outside of a hull of a vessel according to the current disclosure. The air supply system 100 comprises a plurality of ADUs 20 for releasing a compressed air flow to an outside of the hull below a waterline of the vessel. The ADUs 20 may be openings in the hull of the vessel through which air can escape to the outside of the hull. The plurality of ADUs 20 may be equally distributed, such as symmetrically arranged, around a longitudinal centreline 202 of the hull of the vessel, such that an ADU 20; 20A, 20B arranged on a starboard side of the longitudinal centreline 202 has a corresponding ADU 20; 20A, 20B arranged on a port side of the longitudinal centreline 202 at an equal distance from the centreline 202. The air supply system 100 comprises a first flow path 11 A for providing a first air flow, such as a first compressed air flow, to a first subset 20A of the plurality of ADUs 20. The air supply system 100 comprises a second flow path 11 B for providing a second air flow, such as a second compressed air flow, to a second subset 20B of the plurality of ADUs 20. The air supply system 100 comprises a first pressure device 30 configured to feed the first flow path 11 A with the first air flow, such as the first compressed air flow. The air supply system 100 comprises a second pressure device 40 configured to feed the second flow path 11 B with the second air flow, such as the second compressed air flow. The second pressure device 40 is of a different type than the first pressure device 30. The first pressure device may for example be a fixed volume displacement pressure device, such as a fixed volume compressor or blower. The second pressure device may for example be a variable volume displacement pressure device, such as a variable volume compressor or blower. The compressor may for example be a screw compressor. The plurality of ADUs 20; 20A, 20B may be arranged to provide an equal flow over the hull of the vessel, such as over a beam of the vessel. In the example air supply system of Fig.1 , the first subset 20A of the plurality of ADUs 20 and the second subset 20B are separate subsets of the plurality of ADUs 20. In other words, the first flow path 11 A are connected to a dedicated first subset 20A of ADUs and the second flow path 11 B are connected to a dedicated second set 20B of ADUs, such that the first pressure device 30 and the second pressure device 40 do not provide air flows to the same subset of ADUs. In the example air supply system 100 of Fig. 1 , the first flow path 11 A is configured to receive a scavenging air flow from an engine 50 of the vessel, such as from a scavenging air receiver of the engine or from a scavenging flow path of the engine 50. The scavenging air may be received at an inlet 34 of the first pressure device 30 in which the pressure of the scavenging air flow is increased, such as compressed, before the scavenging air flow is fed from the first pressure device 30, such as via an outlet of the first pressure device 30, into the first flow path 11 A towards the first set of ADUs 20A. The second flow path 11 B is configured to receive ambient air. The ambient air may enter the second flow path 11 B through an inlet 41 of the second pressure device 40. The second pressure device 40 may increase the pressure of the ambient air flow and feed the ambient air flow to the second subset 20B of the plurality of ADUs.

[0041] The pressure of the compressed air flow, such as of the scavenging air flow, may be dependent on the load of the engine. At low loads the exhaust gas flow EG may be low which will cause the turbine 10A of the turbocharger 10, which is driven by the exhaust gas flow, to rotate at low revolutions per minute (rpm). Consequently, the compressor 10B will rotate at the same rpm and will not provide its maximum compression performance. At low engine loads, the scavenging pressure may thus be below a required or desired air flow at the ADUs 20 for achieving a desired reduction in friction between the hull and the vessel. Using scavenging air flow as the inlet air flow has the benefit that the inlet air flow has already been compressed, such as pre-compressed, by the one or more turbochargers 10, thereby the compression ratio for increasing the pressure of the scavenging air flow to meet or exceed the discharge pressure at the first subset 20A of the plurality of ADUs is lower than would be required if ambient air would be used as input to the first pressure device 30. To provide a sufficient air flow to the outside of the hull of the vessel, the second pressure device 40 may be controlled to provide the required air flow.

[0042] The example air supply system of Fig. 1 may further comprise a controller (not shown in Fig. 1), such as one or more controllers, for controlling one or more of the first pressure device 30, the second pressure device 40, the first set of valves 14A, and the second set of valves 14B. The one or more controllers may be configured to control a flow distribution and / or a pressure distribution between the first flow path 11 A and the second flow path 11 B, for example by controlling the first pressure device 30, the second pressure device 40, the first set of valves 14A, and / or the second set of valves 14B. The flow distribution and / or the pressure distribution may be controlled based on one or more of a speed of the vessel and a load of the engine of the vessel, such as based on an available flow of scavenging air from the engine.

[0043] Fig. 2 shows an example air supply system 100 according to one or more examples herein. The example air supply system of Fig, 2 differs from the example air supply system of Fig. 1 in that the first pressure device 30 is a fixed volume displacement pressure device comprising a plurality of pressure boosting units 32, such as a such as a first pressure boosting unit 32A for feeding compressed air to a first outlet 35A and a second pressure boosting unit 32B for feeding compressed air to a second outlet 35B of the first pressure device 30. In the example shown in Fig. 2, the first pressure boosting unit 35A and the second pressure boosting unit 35B may be driven by a same drive unit 31 , so that they are synchronously driven and provide the same air flow. The drive unit 31 may be an electric motor. In the example air supply system of Fig. 2, the first pressure boosting unit 32A and the second pressure boosting unit 32B are driven by the drive unit 31 via a common shaft 33. The first outlet 35A may be configured to feed the air flow to a primary first flow path 11 A’ for providing the air flow to a primary first subset 20A’ of the plurality of ADUs 20. The second outlet 35B may be configured to feed the air flow to a secondary first flow path 11 A” for providing the air flow to a secondary first subset 20A” of the plurality of ADUs 20. The primary first subset 20A’ of the plurality of ADUs 20 and the secondary first subset 20A” of the plurality of ADUs 20 may be configured to be arranged on opposite sides of the centreline 202 of the hull of the vessel. The primary first subset 20A’ of the ADUs 20 may be configured to be arranged at a same distance from the longitudinal centreline 202 of the vessel as the secondary first subset 20A” of the ADUs 20, so that the first outlet 35A and the second outlet 35B are connected to respective subsets 20A’, 20A” of ADUs 20 arranged at equal distance from but on opposite sides of the longitudinal centreline 202. In other words, the primary first subset 20A’ of ADUs 20 and the secondary first subset 20A” of ADUs 20 may be mirrored around the longitudinal centreline 202. The first pressure boosting unit 32A and / or the second pressure boosting unit 32B may be a blower or a compressor, such as a fixed volume displacement blower or compressor. The fixed volume displacement blower is configured to provide a predetermined flow of air at a predetermined speed, such as revolutions per minute (rpm) of the pressure boosting means. In some example air supply systems 100, the first pressure boosting unit 32A and / or the second pressure boosting unit 32B may be one or more Roots blower(s). The Roots blower comprises two rotary vanes configured to mesh with each other upon rotation. Each rotary vane is arranged on an individual axle, wherein the individual axles are connected to each other via gears so that the axles may be driven synchronously by a single drive unit. Each of the rotary vanes may according to this disclosure be considered as being a pressure boosting unit 32. The Roots compressor may thus be considered comprising a drive unit 31 , and a first and a second pressure boosting unit 32A, 32B.

[0044] Fig. 3 shows an example air supply system 100 according to one or more examples herein. The example air supply system of Fig. 3 differs from the example air supply system in that the first pressure boosting unit 32A and the second pressure boosting unit 32B of the first pressure device 30 are driven by a respective drive unit 31 , such as a respective electric motor. In the example shown in Fig. 3 the first pressure boosting unit 32A is driven by a first drive unit 31 A and the second pressure boosting unit 32B is driven by a second drive unit 31 B. The first drive unit 31 A and the second drive unit 31 B may be synchronously controlled by one or more controllers (not shown in Fig. 3) to provide the same air flow through the first outlet 35A and the second outlet 35B into the primary first flow path 11 A’ and the secondary first flow path 11A”.

[0045] Fig. 4 illustrates an example air supply system 100 according to one or more examples herein. In the air supply system 100 shown in Fig. 4, the inlet air flow fed to the first pressure device 30 is compressed scavenging air flow from the engine 50 of the vessel. The example air supply system 100 shown in Fig. 4, such as the engine 50 of the vessel, comprises one or more turbochargers 10. Each turbocharger 10 comprises a turbine 10A driven by an exhaust gas flow EG from the engine 50 of the vessel. The turbine 10A may comprise a turbine housing and a turbine wheel rotatably arranged in the turbine housing. The turbine wheel may be forced to rotate by an exhaust gas flow EG through the turbine housing. The exhaust gas flow EG may be received from an exhaust gas receiver of the engine. Each turbocharger 10 further comprises a compressor 10B for supplying a compressed air flow to the engine, such as to a scavenging air receiver of the engine 50, via the first flow path 11 A. The compressor may comprise a compressor housing and a compressor wheel, which may also be referred to as an impeller, rotatably arranged within the compressor housing and driven by the turbine 10A. The compressor 10B receives air, such as ambient air. which is then compressed by the rotation of the compressor wheel. The compressed air from the compressor 10B of the turbocharger 10, which compressed air may also be referred to as scavenging air, may then be fed to the engine, such as to the scavenging air receiver of the engine 50 via a scavenging air flow path 12. The scavenging flow path 12 may comprise an air cooler 16 for cooling the compressed air from the compressor 10B of the turbocharger 10, a water mist catcher 18 for removing moisture from the compressed air flow, and / or a nonreturn valve 19 for preventing air to flow from the scavenging air receiver into the scavenging air flow path 11 . The water mist catcher 18 may be arranged downstream of the air cooler 16. The non-return valve 19 may be arranged downstream of the water mist catcher 18. In the example air supply system shown in Fig. 4, the first flow path 11 A is connected to the scavenging air flow 12 for extracting the scavenging air flow. The first flow path 11 A may be connected to the scavenging air flow path 11 between the air cooler 16 and the water mist catcher 18. Extracting the scavenging air downstream the air cooler 16 has the benefit that the extracted scavenging air is cooled. Cooling the air reduces risk of corrosion in the air supply system, which reduces the required maintenance of the system. Cooling the air further allows a higher density flow, which increases the energy efficiency of the system. Extracting the scavenging air upstream the water mist catcher 18 prevents contaminated gases from the combustion process to leak into the first flow path 11 A. Thus, only noncontaminated, such as clean, air is provided to the outside of the hull of the vessel, which may reduce the environmental impact of the air supply system. The air supply system 100 may comprise a changeover valve 13 arranged in the first flow path 11A for opening and / or closing the first flow path 11 A, to allow or prevent a flow of air, such as scavenging air through the first flow path 11 A. Optionally, the scavenging air flow may be provided to the first pressure device 30 from the scavenging air receiver.

[0046] Fig. 5 illustrates an example air supply system 100 according to one or more examples herein. The example air supply system 100 of Fig. 5 differs from the example air supply systems of any of the previous Figs, in that the air supply system comprises a plurality of first pressure devices 30, such as a primary first pressure device 30’, a secondary first pressure device 30”, and a tertiary first pressure device 30”’, and a plurality of second pressure devices 40, such a primary second pressure device 40’, and a secondary second pressure device 40”. The primary first pressure device 30’, the secondary first pressure device 30”, and the tertiary first pressure device 30’” may be any type of first pressure device 30 described in the current disclosure. The primary first pressure device 30’, the secondary first pressure device 30”, and the tertiary first pressure device 30’” may be configured to receive a scavenging air flow from the engine 50. The primary first pressure device 30’ may be a port side pressure device, the secondary first pressure device 30” may be a centre pressure device, and the tertiary first pressure device 30”’ may be a starboard pressure device. The primary second pressure device 40’, and the secondary second pressure device 40” may correspond to the second pressure device 40 described in the current disclosure. The primary second pressure device 40’, and the secondary second pressure device 40” may be configured to receive ambient air. The primary second pressure device 40’ may be a port side second pressure device and the secondary second pressure device 40” may be a starboard side second pressure device. The primary first pressure device 30’ may be connected to and configured to provide an air flow to a primary first subset 20A’ of the plurality of ADUs 20. The secondary first pressure device 30” may be connected to and configured to provide an air flow to a secondary first subset 20A” of the plurality of ADUs 20. The tertiary first pressure device 30’” may be connected to and configured to provide an air flow to a tertiary first subset 20A’” of the plurality of ADUs 20. The primary second pressure device 40’ may be connected to and configured to provide an air flow to a primary second subset 20B’ of the plurality of ADUs 20. The secondary second pressure device 40” may be connected to and configured to provide an air flow to a secondary second subset 20B” of the plurality of ADUs 20. The plurality of first pressure devices 30 and / or the plurality of second pressure devices 40 may be controlled using one or more controllers (not shown in Fig. 5).

[0047] It shall be noted that the features mentioned in the embodiments described in Figs. 1 -5 are not restricted to these specific embodiments. Any features relating to the air supply system and the components comprised therein and mentioned in relation to the air supply system using ambient air of Fig. 1 , are thus also applicable to the air supply system described in relation to Figs. 2-5, and vice versa. For example, any of the example first pressure devices shown in Figs. 1-5, or the engine 50 described in Fig. 4, can also be applied to the example air supply systems shown in any of the other Figs. 1-5.

[0048] It shall further be noted that a vertical axis or centreline, when referred to herein, relates to an imaginary line running vertically through the vessel, such as through the hull of the vessel, and through its centre of gravity, a transverse axis or lateral axis is an imaginary line running horizontally across the ship and through the centre of gravity and a longitudinal axis is an imaginary line running horizontally through the length of the ship through its centre of gravity and parallel to a waterline. Similarly, when referred to herein, a vertical plane relates to an imaginary plane running vertically through the width of the ship, a transverse plane or lateral plane is an imaginary plane running horizontally across the ship and a longitudinal plane is an imaginary plane running vertically through the length of the ship.

[0049] Embodiments of products (air supply system and vessel) according to the disclosure are set out in the following items:

[0050] Item 1 . An air supply system (100) for supplying air to an outside of a hull of a vessel, the air supply system (100) comprising:

[0051] - a plurality of air discharge units, ADUs, (20) for releasing compressed air to the outside of the hull below a waterline of the vessel, wherein the plurality of ADUs (20) are configured to be arranged around a longitudinal centreline (202) of the hull of the vessel,

[0052] - a first flow path (11 A) for providing a first compressed air flow to a first subset (20A) of the plurality of ADUs (20),

[0053] - a second flow path (11 B) for providing a second compressed air flow to a second subset (20B) of the plurality of ADUs (20),

[0054] - a first pressure device (30) configured to feed the first flow path (11 A) with a first compressed air flow, and

[0055] - a second pressure device (40) configured to feed the second flow path (11 B) with a second compressed air flow, wherein the second pressure device (40) is a different type than the first pressure device (30).

[0056] Item 2. The air supply system (100) according to Item 1 , wherein the first subset (20A) of the plurality of ADUs (20) and the second subset (20B) of the plurality of ADUs (20) are separate subsets of the plurality of ADUs (20).

[0057] Item 3. The air supply system (100) according to Item 1 , wherein the first subset (20A) of the plurality of ADUs (20) and the second subset (20B) of the plurality of ADUs (20) are overlapping subsets of the plurality of ADUs (20).

[0058] Item 4. The air supply system (100) according to any one of the previous Items, wherein one of the first flow path (11 A) and the second flow path (11 B) is configured to receive a scavenging air flow from an engine of a vessel, and the other of the first flow path (11 A) and the second flow path (1 1 B) is configured to receive ambient air.

[0059] Item 5. The air supply system (100) according to Item 4, wherein the air supply system (100) comprises one or more turbochargers (10), each turbocharger (10) comprising a turbine (10A) driven by an exhaust gas flow from the engine and a compressor (10B) for supplying the scavenging air flow to one of the first flow path (1 1 A) and the second flow path (11 B).

[0060] Item 6. The air supply system (100) according to any one of the previous Items, wherein the first pressure device (30) is independently controlled from the second pressure device (40).

[0061] Item 7. The air supply system (100) according to any one of the previous Items, wherein the first pressure device (30) and the second pressure device (40) are jointly controlled.

[0062] Item 8. The air supply system (100) according to any one of the previous Items, wherein the first pressure device (30) is a fixed volume displacement pressure device configured to provide a fixed volume flow of air to the first flow path (1 1 A).

[0063] Item 9. The air supply system (100) according to Item 8, wherein the first pressure device (30) is one or more of a fixed volume displacement blower and a fixed volume displacement compressor.

[0064] Item 10. The air supply system (100) according to any one of the previous Items, wherein the second pressure device (40) is a blower or a compressor.

[0065] Item 1 1 . The air supply system (100) according to any one of the previous Items, wherein the air supply system (100) comprises a first set of valves (14A) arranged in the first flow path for controlling the first flow of compressed air to the first subset (20A) of the plurality of ADUs (20), and / or a second set of valves (14B) arranged in the second flow path for controlling the second flow of compressed air to the second subset (20B) of the plurality of ADUs (20).

[0066] Item 12. The air supply system (100) according to any one of the previous Items, wherein the air supply system (100) comprises a controller for controlling one or more of the first pressure device (30), the second pressure device (40), a first set of valves (14A), and a second set of valves (14B).

[0067] Item 13. A vessel (200) comprising a hull (201 ), an engine and the air supply system (100) according to any one of the previous Items.

[0068] The use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not imply any particular order, but are included to identify individual elements. Moreover, the use of the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. does not denote any order or importance, but rather the terms “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used to distinguish one element from another. Note that the words “first”, “second”, “third” and “fourth”, “primary”, “secondary”, “tertiary” etc. are used here and elsewhere for labelling purposes only and are not intended to denote any specific spatial or temporal ordering. Furthermore, the labelling of a first element does not imply the presence of a second element and vice versa.

[0069] It is to be noted that the word "comprising" does not necessarily exclude the presence of other elements or steps than those listed.

[0070] It is to be noted that the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements.

[0071] Although features have been shown and described, it will be understood that they are not intended to limit the claimed disclosure, and it will be made obvious to those skilled in the art that various changes and modifications may be made without departing from the scope of the claimed disclosure. The specification and drawings are, accordingly to be regarded in an illustrative rather than restrictive sense. The claimed disclosure is intended to cover all alternatives, modifications, and equivalents.

Claims

CLAIMS1 . An air supply system (100) for supplying air to an outside of a hull of a vessel, the air supply system (100) comprising:- a plurality of air discharge units, ADUs, (20) for releasing compressed air to the outside of the hull below a waterline of the vessel, wherein the plurality of ADUs (20) are configured to be arranged around a longitudinal centreline (202) of the hull of the vessel,- a first flow path (11 A) for providing a first compressed air flow to a first subset (20A) of the plurality of ADUs (20),- a second flow path (11 B) for providing a second compressed air flow to a- second subset (20B) of the plurality of ADUs (20),- a first pressure device (30) configured to feed the first flow path (11 A) with a first compressed air flow, and- a second pressure device (40) configured to feed the second flow path (11 B) with a second compressed air flow, wherein the second pressure device (40) is a different type than the first pressure device (30).

2. The air supply system (100) according to claim 1 , wherein the first subset (20A) of the plurality of ADUs (20) and the second subset (20B) of the plurality of ADUs (20) are separate subsets or overlapping subsets of the plurality of ADUs (20).

3. The air supply system (100) according to claim 1 , wherein the first subset (20A) of the plurality of ADUs (20) and the second subset (20B) of the plurality of ADUs (20) are overlapping subsets of the plurality of ADUs (20).

4. The air supply system (100) according to any one of the previous claims, wherein one of the first flow path (11 A) and the second flow path (11 B) is configured to receive a scavenging air flow from an engine of a vessel, and the other of the first flow path (11 A) and the second flow path (11 B) is configured to receive ambient air.

5. The air supply system (100) according to claim 4, wherein the air supply system (100) comprises one or more turbochargers (10), each turbocharger (10) comprising a turbine (10A) driven by an exhaust gas flow from the engine and a compressor (10B) for supplying the scavenging air flow to one of the first flow path (11 A) and the second flow path (11 B).

6. The air supply system (100) according to any one of the previous Items, wherein the first pressure device (30) is independently controlled from the second pressure device (40).

7. The air supply system (100) according to any one of the claims 1 to 5, wherein the first pressure device (30) and the second pressure device (40) are jointly controlled.

8. The air supply system (100) according to any one of the previous claims, wherein the first pressure device (30) is a fixed volume displacement pressure device configured to provide a fixed volume flow of air to the first flow path (11 A).

9. The air supply system (100) according to claim 8, wherein the first pressure device (30) is one or more of a fixed volume displacement blower and a fixed volume displacement compressor.

10. The air supply system (100) according to any one of the previous claims, wherein the second pressure device (40) is a blower or a compressor.11 . The air supply system (100) according to any one of the previous claims, wherein the air supply system (100) comprises a first set of valves (14A) arranged in the first flow path for controlling the first flow of compressed air to the first subset (20A) of the plurality of ADUs (20), and / or a second set of valves (14B) arranged in the second flow path for controlling the second flow of compressed air to the second subset (20B) of the plurality of ADUs (20).

12. The air supply system (100) according to any one of the previous claims, wherein the air supply system (100) comprises a controller for controlling one or more of the first pressure device (30), the second pressure device (40), a first set of valves (14A), and a second set of valves (14B).

13. A vessel (200) comprising a hull, an engine (50) and the air supply system (100) according to any one of the previous claims.

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