Powertrain arrangement for a watercraft

Abstract

A watercraft 200 comprising a powertrain arrangement for powering the watercraft, the watercraft having fore and aft ends and a longitudinal axis 210 extending therebetween. The powertrain arrangement comprises a prime mover 201 configured to output drive via an output shaft configured to rotate about an axis approximately transverse to the longitudinal axis of the watercraft and a propulsion unit configured to propel the watercraft using drive supplied by the prime mover. The powertrain arrangement is configured to reorient the direction of the drive output by the prime mover for supply of the propulsion unit.

Description

FIELD OF THE INVENTION This invention relates to a transverse powertrain arrangement for a watercraft. BACKGROUND Figure 1 shows a top-down schematic of a conventional powertrain arrangement in a watercraft 100. The components of the powertrain are depicted for illustration. Some or all of the components may be covered by a floor, or deck, of the watercraft. An engine 101 is coupled to an output shaft 102. The output shaft 102 is coupled to a propulsion unit 103. In this example, the propulsion unit 103 drives a propellor 104. The propulsion unit may provide rotational drive to the propellor. The propulsion unit 103 may be a sterndrive, also known as inboard / outboard drive. The sterndrive is positioned on an internal side of the transom 105 and the propellor 104 is positioned on an external side of the transom 105. In other words, the engine is positioned within the hull of the watercraft 100 and the propellor is situated outside the hull. This type of powertrain arrangement can be termed a “longitudinal” powertrain, as the components of the powertrain are generally aligned from a fore end to an aft end of the watercraft, along the longitudinal axis 106 of the watercraft. From the perspective of a passenger at the fore end of the watercraft, facing the aft end, the components of the powertrain are arranged in series in the order engine, driveshaft, propulsion unit and propellor. Conventional powertrain arrangements, such as that shown in figure 1, may suffer from several issues. The heaviest components, usually the engine or other prime mover and gear assembly, are typically positioned around the centre of the boat. This may reduce the efficiency and may result in non-ideal hydrodynamics. It is desirable to develop a powertrain arrangement that overcomes such issues. SUMMARY OF THE INVENTION According to a first aspect there is provided a watercraft comprising a powertrain arrangement for powering the watercraft, the watercraft having fore and aft ends and a longitudinal axis extending therebetween, the powertrain arrangement comprising: a prime mover configured to output drive via an output shaft configured to rotate about an axis approximately transverse to the longitudinal axis of the watercraft; and a propulsion unit configured to propel the watercraft using drive supplied by the prime mover; wherein the powertrain arrangement is configured to reorient the direction of the drive output by the prime mover for supply to the propulsion unit. One or more of the following may be true for each of the embodiments of the present invention described herein. The powertrain arrangement may comprise a transmission for transmitting drive output by the prime mover to the propulsion unit. The transmission may be configured to output drive to the propulsion unit via a drive shaft. The drive shaft may couple the transmission and the propulsion unit to transfer drive output by the transmission to the propulsion unit. The powertrain arrangement may be configured to reorient the drive output by the prime mover by about 90 degrees. The transmission may be configured to transmit the reoriented drive to the propulsion unit. The prime mover and the transmission may be coupled by the output shaft. The transmission may comprise a differential gearbox. The propulsion unit may be positioned at the aft end of the watercraft. The propulsion unit may be positioned at the stern of the watercraft. The prime mover may be an engine and / or an electric motor. The powertrain arrangement may further comprise: a further prime mover configured to output drive via a further output shaft configured to rotate about an axis transverse to the longitudinal axis of the watercraft, wherein the propulsion unit is further configured to propel the watercraft using drive supplied by the further prime mover. The further prime mover may be configured to output drive to the transmission. The further prime mover and the transmission may be on opposite sides of an X-Z plane of the watercraft. The prime mover and the further prime mover may be on opposite sides of that X-Z plane. The prime mover and the further prime mover may be on the same side of that X-Z plane. The further prime mover may be configured to output drive to the transmission. The further prime mover may be configured to output drive to the transmission via the further output shaft. The prime mover and the transmission may be on opposite sides of an X-Z plane of the watercraft. The prime mover and transmission may be in a common Y-Z plane. The prime mover and the propulsion unit may not be in a common X-Z plane. The prime mover and the transmission may not be in a common X-Z plane. Central points of the prime mover and the transmission may be on opposite sides of an X-Z plane. In some cases, there may be some overlap between outer parts of the prime mover and the transmission in the y-direction. The prime mover may be an engine and the further prime mover may be an electric motor. The propulsion unit may be a sterndrive. The propulsion unit may comprise a jet drive. The watercraft may further comprise a propellor. The propulsion unit may provide rotational drive to the propellor. The watercraft may further comprise a hull, wherein the powertrain arrangement may be contained within the hull. The powertrain arrangement may be movable along the longitudinal axis of the watercraft. The prime mover and / or the further prime mover may indirectly supply drive to the propulsion unit. For example, the prime mover and / or the further prime mover may supply drive to the propulsion unit via the transmission and / or one or more other components of the powertrain arrangement. The output shaft and / or the further output shaft may extend along the y-axis of the watercraft. DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings: Figure 1 shows a conventional powertrain arrangement. Figure 2 schematically illustrates an example of a transverse powertrain arrangement. Figure 3 schematically illustrates an example of a transverse hybrid powertrain arrangement. Figure 4 schematically illustrates an example of a movable transverse powertrain arrangement. Figure 5 shows an example of a stacked powertrain arrangement. Figure 6 shows an example of a dual transverse arrangement. Figure 7a shows an example of a stacked jet drive powertrain arrangement. Figure 7b shows a side-view of the exemplary powertrain arrangement of figure 7a. DETAILED DESCRIPTION The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art. The general principles defined herein may be applied to other embodiments and applications without departing from the present invention. Thus, the present invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the principles and features disclosed herein. In the present specification the term “engine” is used to mean an internal combustion engine, which burns fuel, such as petrol or diesel, to generate power. The term “motor” is used to mean a device that can use electrical energy to generate power. This power can be used to provide drive for a watercraft. A watercraft, such as a boat or ship, may be propelled by an engine and / or a motor. Such entitles for powering the watercraft may be referred to as a “prime mover”. A prime mover may comprise one or more of such entities. For example, a prime mover may comprise one or more engines, one or more motors or both engine(s) and motor(s). The watercraft may be a marine or freshwater vessel. The watercraft may be, for example but not limited to, a boat, ship, hovercraft, jet ski or submarine. A "powertrain” for a watercraft may comprise one or more of an engine, a motor and a gearbox. As mentioned above, Figure 1 shows a conventional powertrain arrangement. The x-, y- and z- axes of the watercraft are indicated. In the conventional arrangement of Figure 1, the prime mover 101 and propulsion unit 103 are in a common X-Z plane. This may be described as being positioned on either side of a Y-Z plane. The prime mover is configured to output drive via an output shaft 102 configured to rotate about the longitudinal axis of the watercraft. In the watercraft described herein, the x-axis extends between the aft end and the fore end of the watercraft (i.e. between the bow and the stern). The y-axis extends between the port side and the starboard side of the watercraft. The z-axis extends vertically through the hull of the watercraft. The longitudinal axis of the watercraft may be referred to as the central X-Z plane of the watercraft. There are other X-Z planes of the watercraft parallel to but offset from (along the y-direction) the central X-Z plane of the watercraft. Figure 2 shows a watercraft 200 having a transverse powertrain arrangement. The prime mover 201 and transmission 206 are in a common Y-Z plane. The prime mover 201 and transmission 206 are on opposite sides of an X-Z plane. In this example, the prime mover 201 and the transmission 206 are on opposite sides of an X-Z plane parallel to but offset from the longitudinal axis 210 of the watercraft. The prime mover 201 and propulsion unit 203 are not in a common X-Z plane. The prime mover 201 and transmission 206 are not in a common X-Z plane. In this example, the prime mover is an engine 201. The prime mover 201 is disposed away from a centreline 210 of the watercraft. That is, the prime mover is not arranged along the longitudinal axis 210 of the watercraft. One or more components of the powertrain arrangement are configured to reorient (i.e. change the direction of) the drive output by the prime mover for supply to the propulsion unit. In this example, the arrangement comprises a transmission 206 for transmitting drive output by the engine 201 to a propulsion unit 203. The transmission and / or the propulsion unit may be arranged along the longitudinal axis 210 of the watercraft. The transmission 206 is arranged to reorient the drive output by the engine 201 by 90 degrees and to transmit the reoriented drive to the propulsion unit 203. In this example, the engine 201 is coupled to the transmission 206 via an output shaft 207. The output shaft extends generally transverse to the longitudinal axis 210 of the watercraft. The output shaft 207 rotates about an axis approximately transverse to the longitudinal axis of the watercraft. In this example, the axis about which the output shaft 207 rotates is shown as being transverse to the longitudinal axis of the watercraft, The output shaft 207 rotates about an axis with a Y component. In other implementations, the engine may be connected to the transmission directly. Similarly, in this example, the transmission 206 is coupled to a propulsion unit 203 via a drive shaft 202. In other implementations, the transmission may be connected to the propulsion unit directly. The propulsion unit may be contained within a sealable powertrain container, or may be located on the exterior of the watercraft. In this example, the propulsion unit is connected to the drive shaft 202 that is coupled to and transmits drive to a propel lor 204. The drive shaft 202 rotates about an axis with X component. However, the propulsion unit may alternatively be coupled to an impellor or a jet drive. The propellor 204 is positioned outside of the transom 205. The propellor is positioned outside of the hull. The other components of the powertrain arrangement (that is, one or more of the prime mover, the transmission and the propulsion unit) may be contained within the hull and / or below the deck of the watercraft. The engine 201 and propulsion unit 203 are offset from each other relative to the longitudinal direction between the fore and aft ends of the watercraft. Put another way, the watercraft 200 has fore and aft ends and a longitudinal axis 210 extending therebetween. The longitudinal axis 210 bisects the watercraft. The longitudinal axis 210 is the central axis of the watercraft. The longitudinal axis 210 may be in an X-Z plane. The powertrain is arranged such that the engine 201 and transmission 206 are arranged along an axis 220 generally transverse to the longitudinal axis 210 of the watercraft. The axis 220 passes through the prime mover 201. In other words, the axis 220 intersects the prime mover. The axis 220 may approximately bisect the prime mover. The prime mover may be symmetrically arranged about axis 220. The axis 210 and / or axis 220 passes through the transmission 206. In other words, the axis 210 and / or axis 220 intersects the transmission. The axis 210 and / or axis 220 may approximately bisect the transmission. The transmission may be symmetrically arranged about axis 210 and / or axis 220. The axis 220 may be located at the aft end of the watercraft. The axis 220 may pass through the stem of the watercraft. The prime mover and the transmission may be arranged about the axis 220 generally transverse to the longitudinal axis 210 of the watercraft. The transverse axis 220 may be in a Y-Z plane. The prime mover and the propulsion unit may be offset from each other along a direction generally transverse and / or parallel to the longitudinal axis of the watercraft. The prime mover may be an electric motor. The prime mover is configured to output drive to the transmission. In the example shown in Figure 2, the prime mover is configured to output drive to the transmission via output shaft 207. The output shaft extends along the axis 220 generally transverse to the longitudinal axis 210 of the watercraft. The output drive may be rotational drive. For example, the output shaft 207 can be driven to rotate by an electric motor. The transmission may convert rotational drive to linear drive, and may further convert linear drive to rotational drive to be output. The transmission may comprise a gear assembly. The transmission is configured to output drive to the propulsion unit. The transmission 206 may be configured to transform input drive from the prime mover to vary the speed and / or direction of output drive supplied to the propulsion unit (for example by drive shaft 202). The transmission may comprise gears for reorienting the drive and / or varying the speed and direction of output drive supplied to the propulsion unit. In a further embodiment, there is provided a watercraft having a stacked transverse powertrain arrangement with a common longitudinal output. A first prime mover and transmission are provided along an axis 220 generally transverse to the longitudinal axis 210 of the watercraft, as described above. There is a second prime mover positioned above or below the first prime mover. The first and second prime movers may be within the hull. In a cross-sectional view of the watercraft, the prime movers are in a vertically stacked arrangement. The first and second prime movers transmit drive to the transmission, for example via respective output shafts. One or more prime mover may be out of plane with the transmission. One or more prime mover may lie in the same plane as the transmission. The output shaft may be connected to the prime mover via an elbow fitting or similar in order to align the output shaft with the transmission for operation. The stacked arrangement of prime movers is advantageous as additional power is supplied while no additional footprint is occupied within the watercraft. Figure 3 shows a watercraft 300 having a transverse hybrid powertrain arrangement. The word hybrid, in the context of a powertrain, is used to mean of mixed electric and non-electric character. Therefore, a hybrid watercraft is a watercraft having more than one mechanism via which drive can be provided, at least one of which is electric. In the examples described herein, the watercraft may be a hybrid watercraft. In this example, the powertrain comprises an internal combustion engine 301 and an electric drive 308. The electric drive 308 comprises an electric power source, such as a battery. Typically, a battery used in such applications produces a voltage which can range from the order of 250V to what could be considered a high voltage of around 400V or 800V. A voltage of this magnitude is beneficial for producing a suitably high power for driving one or more electric motors, which may also be part of the electric drive 308. The battery may be a DC traction battery. For example, such a battery may be used as the traction source to drive the electric motors to propel an electric or hybrid watercraft such as a boat. However, it is common for the energy from such a battery to be additionally used to drive other components of the watercraft, such as lights, air conditioning units etc. These other components might need to operate at a lower voltage. One or more converters may be used in the system to convert the voltage from the battery to a voltage suitable for use in the one or more other components. Where the electric drive comprises a motor, the motor may comprise multiple windings which are supplied with current from the electric power source (e.g. battery). The current supplied to the electric motor by the battery can be supplied via an inverter circuit, which supplies current to windings of the motor. In one example, the motor may be a three-phase induction motor having three windings. The windings are each wound around a core. When electrical power is supplied to the windings, each respective core is magnetised and drives rotors of the motor. The current in each winding is 120 degrees out of phase with the current in the other windings. A DC voltage may be output by the battery. The DC voltage may be converted to AC by an inverter circuit and the supplied to the electric motor. In Figure 3, the engine 301 and electric drive 308 may each or together supply drive to the propulsion unit. In this example, the engine 301 is coupled to a transmission 306 via an output shaft 307a. The electric motor 308 is coupled to the transmission 306 via an output shaft 307b. The output shafts 307a, 307b that supply output drive to the propulsion unit (in this example via the transmission 306) are configured to rotate about respective axes (in this example, the same axis) that are each approximately transverse to the longitudinal axis of the watercraft. The transmission 306 is coupled to the propulsion unit 303 via a drive shaft 302. The propulsion unit 303 drives a propeller 304. As for the example of Figure 2, the prime movers 301, 308 and / or the propulsion unit 303 can in some implementations be connected to the transmission 306 directly. The prime movers 301,308 are arranged along an axis 320 traverse to the longitudinal axis 310 of the watercraft. The axis 320 may pass through the stem (at the aft end) of the watercraft. Figure 3 shows the prime movers positioned on opposing sides of the transmission 306, however it may be that the prime movers are arranged on a common side of the transmission, for example in a series arrangement, or in a vertically stacked arrangement. The prime movers may be arranged on opposing sides of longitudinal axis 310. The prime movers may be within the hull. The prime movers may be below the deck of the watercraft. The axis 320 may pass through one or more of the prime movers 301, 308. In this example, the axis 320 passes through both of the prime movers 301, 308. In other words, the axis 320 intersects the prime mover(s). The axis 320 may approximately bisect the prime mover(s). The prime mover(s) may be symmetrically arranged about axis 320. The axis 310 and / or 320 passes through the transmission 306. In other words, the axis 310 and / or 320 intersects the transmission. The axis 310 and / or 320 may approximately bisect the transmission. The transmission may be symmetrically arranged about axis 310 and / or 320. The axis 320 may be located at the aft end of the watercraft. In the example shown in Figure 3, the prime movers 301, 308 are arranged along the same axis 320 that is generally transverse to the longitudinal axis 310. In other implementations, the prime movers 301 and 308 may be arranged along respective axes that are offset from each other (e.g. in a direction along a longitudinal axis of the watercraft) but are both generally transverse to the longitudinal axis of the watercraft. The prime movers 301 and 308 are not arranged along the longitudinal axis 310. The axis that prime mover 301 is arranged along may be parallel to but offset from (for example, in a direction parallel to the longitudinal axis 310) the axis that prime mover 308 is arranged along. The respective axes may both intersect the transmission 306. This may allow each of the prime movers to output drive to the transmission, either directly or via a respective output shaft. Each of the prime movers 301, 308 and the propulsion unit 303 may be offset from each other along a direction generally transverse to and / or parallel to the longitudinal axis of the watercraft. The prime movers 301, 308 and transmission 306 are in a common Y-Z plane. The prime mover 301 and transmission 306 are on opposite sides of an X-Z plane. The prime mover 308 and transmission 306 are on opposite sides of another X-Z plane. The prime movers 301 and 308 are on opposite sides of the central X-Z plane 310 (i.e. the longitudinal axis of the watercraft). The engine 301 is configured to output drive to the transmission 306 via output shaft 307a. The electric motor 308 is configured to output drive to the transmission 306 via output shaft 307b. The transmission is configured to reorient the drive output by one or more prime mover by 90 degrees. The transmission is configured to transmit the reoriented drive to the propulsion unit 303. In the example shown in figure 3, the transmission is configured to reorient the drive supplied by the engine 301 via shaft 307a by 90 degrees; the transmission is configured to reorient the drive supplied by the electric motor 308 via shaft 307b by 270 degrees. After reorientation, the drive supplied by both prime movers has the same direction and is suitable to be output by the transmission to the propulsion unit. The transmission may comprise a differential gearbox. The output shafts 307a, 307b may rotate at different speeds to each other, thereby supplying different power levels to the transmission. The electric motor may be part of a generator assembly. The hybrid power supply may increase operational safety, as even if one of the engine or electric motor fails, there is a secondary power source. In the example shown in Figure 3, the two prime movers are on opposing sides of the longitudinal axis of the watercraft. In other implementations, the prime movers may be on the same side of the longitudinal axis of the watercraft. It may also be generally more efficient to position mass behind or towards the aft end of a watercraft than inside or towards the fore end of a watercraft. The hydrodynamic loading is improved by positioning heavy powertrain components towards the transom. However, in some implementations it may be desirable to position the components of the powertrain towards the stern of the watercraft, for example if there is heavy cargo stored on the deck or within the hull towards the stern of the watercraft. It may be desirable to vary the position of the powertrain along the longitudinal axis of the watercraft. Figure 4 shows a watercraft 400 having a movable transverse powertrain arrangement. In this example, the powertrain has two prime movers arranged in series, an engine 401 and an electric motor 408. In other examples of the moveable transverse powertrain arrangement, the powertrain may have a single prime mover, or prime movers on opposing sides of the longitudinal axis, as shown in Figure 3. The engine 401 is coupled to a transmission 406 via an output shaft 407b. The electric motor 408 supplies power to the transmission 406 via an output shaft 407a. The transmission 406 is coupled to the propulsion unit 403 via a drive shaft 402. The drive shaft 402 may be telescopic or otherwise capable of varying in length. The propulsion unit 403 drives a propeller 404. In other implementations, the prime mover(s) and the propulsion unit may be directly coupled to the transmission without intermediate drive shafts. The prime movers 401, 408 are arranged along an axis 420, traverse to the longitudinal axis 410 of the watercraft. The prime movers may be positioned on opposing sides of the transmission 406, may be positioned in a stacked arrangement, or in a series arrangement on a common side of the transmission, as shown in figure 4. The one or more prime movers and transmission are able to be repositioned along the longitudinal axis 410. In other words, the transmission and / or the one or more prime movers can be brought closer to or further away from the propulsion unit and / or the propellor. Positioning the powertrain towards the stern of the watercraft may advantageously improve the weight distribution, thereby enhancing stability and manoeuvrability. Additionally, positioning the powertrain in such a way may provide more interior space in the watercraft. The prime mover 401 and transmission 406 are on opposite sides of an X-Z plane of the watercraft. The prime mover 408 and transmission 406 are on opposite sides of a (different) X-Z plane. The prime movers 401 and 408 are on opposite sides of a (different) X-Z plane. The prime mover and transmission may be repositionable, optionally at predetermined intervals, along the axis 410. That is, they may be moveable along the longitudinal axis of the watercraft. For example, there may be provided a track which runs generally along the longitudinal axis 410 of the watercraft. The track may be provided with detents along its length. The transmission may be retained in a position by the detent. In an alternative arrangement, the prime mover and transmission may be repositioned and affixed to the hull, for example by bolts. The axis 420 may pass through one or more of the prime movers 401, 408. In this example, the axis 420 passes through both of the prime movers 401, 408. In other words, the axis 420 intersects the prime mover(s). The axis 420 may approximately bisect the prime mover(s). The prime mover(s) may be symmetrically arranged about axis 420. The axis 410 and / or 420 passes through the transmission 406. In other words, the axis 410 and / or 420 intersects the transmission. The axis 410 and / or 420 may approximately bisect the transmission. The transmission may be symmetrically arranged about axis 410 and / or 420. The axis 420 may pass through the stern of the watercraft and / or the bow of the watercraft. The axis 420 may be moveable between the bow and the stern, and / or longitudinal positions therebetween. Figure 5 shows a watercraft 500 having two sets of prime movers arranged in a transverse orientation relative to a longitudinal axis 510 of the watercraft. A first set of prime movers 501a, 501 b is arranged with the prime movers on opposing sides of the longitudinal axis 510 of the watercraft. A second set of prime movers 501c, 501 d is arranged with the prime movers on opposing sides of the longitudinal axis 510. Each prime mover 501 a-d is configured to output drive to a transmission via an output shaft. The first set of prime movers 501a, 501b is configured to output drive to a first transmission 506a. The first set of prime movers 501a, 501b is arranged along an axis 530 generally transverse to the longitudinal axis 510 of the watercraft. The second set of prime movers 501c, 501 d is configured to output drive to a second transmission 506b. The second set of prime movers 501c, 501 d is arranged along an axis 520 generally transverse to the longitudinal axis 510 of the watercraft. In this example, the axes 520 and 530 are parallel to each other. The axes 520 and 530 are spaced apart along the longitudinal axis 510 of the watercraft. The second transmission 506b is configured to output drive to the first transmission 506a via drive shaft 502. In this way, the transmission 506a which is closer to the propulsion unit 503 is driven by all of the prime movers 501 a-d. Each transmission is configured to reorient the drive output by each prime mover by 90 degrees and to transmit the reoriented drive to the propulsion unit 503. The power the propulsion unit 503 is able to output to the propellor 504 may be proportional to the power supplied by the prime movers. In the example of figure 5, four prime movers drive the powertrain, thereby supplying four times the power of a single prime mover to the transmission 503. Figure 6 shows an example of a dual transverse powertrain arrangement. A first powertrain arrangement has a prime mover 601 a, an output shaft 607a, a transmission 606a, a drive shaft 602a, a propulsion unit 603a and a propellor 604a. A second powertrain arrangement has a prime mover 601 b, an output shaft 607b, a transmission 606b, a propulsion unit 603b and a propellor 604b. In the example shown, the two powertrain arrangements are mirrored arrangements about a centreline 610 of the vessel 600. Each prime mover may comprise an electric motor, an engine, or a combination of one or more motor and / or engine. The prime movers and the transmission are arranged along an axis 620 generally transverse to the longitudinal axis 610 of the watercraft 600. Figure 7a shows an example of a stacked jet drive powertrain arrangement. In this example, two powertrains are arranged along a longitudinal axis 710 of a watercraft 700. A first powertrain has a first prime mover 701 a and a second prime mover 701 b on opposing sides of the longitudinal axis 710 of the watercraft. The prime movers 701 a and 701 b are arranged along an axis generally transverse to the longitudinal axis of the watercraft. Each prime mover is configured to output drive to the transmission 706a via an output shaft. The transmission is configured to reorient the drive output by each prime mover by 90 degrees. The transmission is configured to transmit the reoriented drive to the jet drive 709a. A second powertrain has a first prime mover 701c and a second prime mover 701 d, each configured to output drive to a transmission 706b. The prime movers 701c and 701 d are arranged along an axis generally transverse to the longitudinal axis of the watercraft. The transmission 706b is similarly configured to reorient the drive supplied by the prime movers and to transmit the reoriented drive to jet drive 709b. Figure 7b shows a side-view of the exemplary powertrain arrangement of figure 7a. A prime mover is shown generally at 701. The first powertrain is positioned towards the stem of the watercraft 700, such that the jet drive 709a may extend past the hull and beyond the stern. The second powertrain is positioned further towards the aft end of the watercraft. The stacked jet drive arrangement may be advantageous for supplying drive to move the craft, without increasing the wake of the craft in water. In the implementations described above, the watercraft may comprise a control architecture for the powertrain. A powertrain control unit (PCU) is a central control unit for controlling the components of the powertrain. The PCU comprises a processor and a memory. The memory stores in a non-transient way software that is executable by the processor. The memory may also store data previously received by the PCU. The PCU may also comprise one or more transceivers for receiving or transmitting data. The PCU may be connected to other components wirelessly or via a wired connection. The components of the control architecture may be connected via a communication bus to the PCU. The control architecture may also comprise a Human Machine Interface (HMI) and one or more of a battery management system (BMS) and an engine controller. The HMI may, for example, comprise a display panel displaying parameters relating to the powertrain. The BMS may perform functions such as protecting the battery from operating outside of its safe operating area and monitoring its state. The BMS may provide signals to the PCU. The engine controller may be a conventional controller for an internal combustion engine and may control for example, the amount of fuel to inject to the engine based on readings from sensors in the engine. The engine controller receives signals from the PCU. The PCU may also be connected to user controls of the watercraft. The user controls allow the user to control, for example, the total drive (from the one or more prime movers) and / or direction of motion of the watercraft and may allow the user to select between different modes of operation. The user controls may comprise a throttle. The PCU may also provide signals to the user controls. The powertrains described herein may be retrofitted to existing watercrafts. The output components, e.g. the propulsion unit and propellor, may be retained for an existing watercraft and the remaining powertrain components replaced to retrofit a transverse powertrain. Retrofitting is conveniently simplified in this way. The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description, it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A watercraft comprising a powertrain arrangement for powering the watercraft, the watercraft having fore and aft ends and a longitudinal axis extending therebetween, the powertrain arrangement comprising:a prime mover configured to output drive via an output shaft configured to rotate about an axis approximately transverse to the longitudinal axis of the watercraft, wherein the prime mover is an engine;a further prime mover configured to output drive via a further output shaft configured to rotate about an axis transverse to the longitudinal axis of the watercraft, wherein the further prime mover is an electric motor; anda propulsion unit configured to propel the watercraft using drive supplied by the prime mover and / or the further prime mover;wherein the powertrain arrangement is configured to reorient the direction of the drive output by the prime mover for supply to the propulsion unit.

2. The watercraft as claimed in claim 1, wherein the powertrain arrangement comprises a transmission for transmitting drive output by the prime mover to the propulsion unit.

3. The watercraft as claimed in claim 2, wherein the prime mover and the transmission are on opposite sides of an X-Z plane of the watercraft.

4. The watercraft as claimed in claim 2 or claim 3, wherein the transmission is configured to output drive to the propulsion unit via a drive shaft.

5. The watercraft as claimed in claim 4, wherein the drive shaft couples the transmission and propulsion unit to transfer drive output by the transmission to the propulsion unit.

6. The watercraft as claimed in any of claims 2 to 5, wherein the transmission is arranged to reorient the drive output by the prime mover by about 90 degrees and to transmit the reoriented drive to the propulsion unit.12 06 257. The watercraft as claimed in any of claims 2 to 6, wherein the prime mover and the transmission are coupled by the output shaft.

8. The watercraft as claimed in any of claims 2 to 7, wherein the transmission comprises a differential gearbox.

9. The watercraft as claimed in any preceding claim, wherein the propulsion unit is positioned at the stern of the watercraft.

10. The watercraft as claimed in any of claims 2 to 8, wherein the further prime mover is configured to output drive to the transmission.

11. The watercraft as claimed in claim 10, wherein the further prime mover and the transmission are on opposite sides of an X-Z plane of the watercraft.

12. The watercraft as claimed in claim 10 or claim 11, wherein the further prime mover is configured to output drive to the transmission via the further output shaft.

13. The watercraft as claimed in any preceding claim, wherein the propulsion unit comprises a jet drive.

14. The watercraft as claimed in any preceding claim, the watercraft further comprising a propellor, wherein the propulsion unit provides rotational drive to the propellor.

15. The watercraft as claimed in any preceding claim, the watercraft further comprising a hull, wherein the powertrain arrangement is contained within the hull.

16. The watercraft as claimed in any preceding claim, wherein the powertrain arrangement is movable along the longitudinal axis of the watercraft.

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