ELECTRIC PROPULSION AND STEERING SYSTEM FOR A WATERCRAFT

Abstract

 A propulsion and steering system for a watercraft comprises at least three propulsion units and an electronic controller device. Each of the at least three propulsion units comprises an electric motor and a propeller with a respective axis orientation, a respective forward direction of rotation, and a respective reverse direction of rotation. The propeller is rotationally coupled to the electric motor. The electronic controller device is adapted to be electronically coupled to the at least three propulsion units to individually adjust the rotation speeds of their respective electric motors to adjust the rotational speeds of their respective propellers. The at least three propulsion units are adapted to be arranged such that the axis orientations of the propellers are fixed and essentially parallel to each other according to a top view. The electronic controller device is adapted to adjust the rotation speed of a first propeller of the propellers according to its forward direction of rotation to generate a forward thrust, to adjust the rotation speeds of a second propeller and a third propeller of the propellers according to their respective reverse directions of rotation to generate an aft thrust; such that the propellers generate a transverse thrust exceeding a total longitudinal thrust comprising the forward thrust and the aft thrust.

Description

TECHNICAL FIELD

[0001] The disclosure relates to a marine propulsion and steering system, and more specifically to a fixed-axis propulsion and steering system, in particular for achieving a transverse movement of a watercraft.

BACKGROUND

[0002] A conventional propulsion system for motorized watercraft uses a propulsion unit based on an engine, such as a diesel or gasoline combustion engine, which drives a propeller sitting on a rotary shaft. In the most power-efficient propulsion systems available, the rotary shaft has a fixed axis orientation essentially along the longitudinal direction of the watercraft. This type of propulsion unit may optimize the power efficiency for forward propulsion, but the aforementioned components do not provide significant maneuverability. A transverse movement, especially at low speed, or a movement along a selected target direction with both a forward and transverse component are not easily achieved. The capability to perform such a low speed transverse movement is particularly desirable when the watercraft is to navigate in a narrow environment such as a marina or a harbor.

[0003] Consequently, for the purpose of maneuverability, additional mechanical components are typically added, which generally reduce the power efficiency of the forward propulsion and increase the overall cost of the system. Moreover, the additional mechanical components may require expensive maintenance. For example, a mechanism may be provided for rotating the entire propulsion unit or the rotary shaft with the propeller, for example by rotating an outboard motor, a pod of a pod drive, or a rotary shaft of a z-drive. Alternatively, a moveable flap, bucket, and/or nozzle may be provided aft the propeller, implementing a jet drive. The component(s) aft the propeller increase drag and affect the efficiency of forward propulsion. Rotatable components, like a pod of a pod drive, cause similar problems.

[0004] The aforementioned approaches allow for directing (vectoring) the thrust generated by the propulsion unit over a large angular range. However, a slow transverse movement is not easily achieved using a single propulsion unit, as the idle speed of the combustion engine driving the propeller tends to be high, for example 10% of the maximum power of the engine. Consequently, when the thrust generated by the propulsion units is directed sideways, the engine will produce an overly large speed of the propeller (and thrust) to allow for the slow transverse movement, even at its lowest speed setting. To avoid this, at least two propulsion units have been applied in steering systems, with their thrust directed at essentially opposite directions, such that they widely compensate each other. The (vector) difference between the thrusts of the individual units, which can be adjusted to a much smaller and finer level than the thrust generated by the individual propulsion units itself, is used to generate the slow transverse movement. This approach, as well, relies on the additional mechanics to allow for directing (vectoring) the thrust generated by the individual propulsion unit over a large angular range.

[0005] Alternatively, or in addition, watercraft may be equipped with tunnel, side, bow, and/or stern thrusters to improve maneuverability and allow for a slow transverse movement. These systems comprise a propeller with an axis orientation perpendicular to the longitudinal direction of the watercraft. Consequently, they do not contribute to the forward propulsion of the watercraft. The tunnel, side, bow, and/or stern thruster systems are dedicated to generating the slow transverse movement and comprise an engine or a transmission to drive the propeller at a sufficiently low rotation speed. They increase the overall cost of the system and require space on the watercraft. They contribute to the weight of the watercraft and increase its power consumption. Moreover, the tunnel, side, bow, and/or stern thrusters are typically arranged in transverse channels perpendicular to the longitudinal direction of the watercraft. These transverse channels may increase the drag of the watercraft and further increase its power consumption for forward propulsion, for example by generating turbulences at cruising speed. Like the mechanical components mentioned above, they may require expensive maintenance.

OVERVIEW

[0006] In view of the technical problems laid out above, there is a need for an improved propulsion and steering system for a watercraft which facilitates a transverse movement, especially at low speed, or a movement along a selected target direction combining a forward and transverse component.

[0007] In a first aspect, a propulsion and steering system for a watercraft comprises at least three propulsion units and an electronic controller device. Each of the at least three propulsion units comprises an electric motor and a propeller with a respective axis orientation, a respective forward direction of rotation, and a respective reverse direction of rotation. The propeller is rotationally coupled to the electric motor. The electronic controller device is adapted to be electronically coupled to the at least three propulsion units to individually adjust the rotation speeds of their respective electric motors to adjust the rotational speeds of their respective propellers. The at least three propulsion units are adapted to be arranged such that the axis orientations of the propellers are fixed and essentially parallel to each other according to a top view. The electronic controller device is adapted to adjust the rotation speed of a first propeller of the propellers according to its forward direction of rotation to generate a forward thrust, to adjust the rotation speeds of a second propeller and a third propeller of the propellers according to their respective reverse directions of rotation to generate an aft thrust; such that the propellers generate a transverse thrust exceeding a total longitudinal thrust comprising the forward thrust and the aft thrust.

[0008] The use of electric motors may provide a propulsion and steering system without local CO2 emissions. This poses an important step towards establishing a fully sustainable watercraft. Moreover, the electric motors may improve the comfort on board. Indeed, not only the emission of combustions product, but also the noise and vibrations emitted by the system may be reduced.

[0009] The disclosed propulsion and steering system may beneficial be used to implement both functions, propulsion and steering, using the same/a minimum of components. A need for additional mechanical components (on top of the propulsion system) to improve maneuverability may thus be avoided. This may reduce the overall weight of the system and avoid the additional drag related to the additional mechanical components of the state of the art. Consequently, an overall energy efficiency of the propulsion and steering system (and a watercraft equipped therewith) may be improved. This may be particularly important for electrically driven watercraft, as the overall energy efficiency is directly linked to a possible travel range which may be achieved with a given battery capacitance.

[0010] The propulsion system may provide for propulsion of the watercraft with high power efficiency making use of propellers with fixed axis orientations. In addition to providing the forward propulsion, each of the propellers may provide a transverse thrust onto the watercraft, for example due to propeller walk and/or flowing water against a side (starboard or portside) of the watercraft. According to some embodiments, rudders may be provided starboard or portside of the propellers to enhance the transverse thrust without significantly increasing drag. The arrangement of the rudders starboard or portside of the propellers may advantageously enhance the transverse thrust both when the propellers are driven according to their forward and to their reverse direction of rotation.

[0011] The use of at least three propulsion units may allow for arranging the propellers on the watercraft such that an overall transverse thrust results, and at the same time, adjusting the rotation speeds of the propellers such that the longitudinal movement is reduced, minimized or even avoided. Therefore, one propeller maybe driven according to its forward direction, i.e. to provide a forward thrust to the watercraft, whereas two propellers may be driven according to the reverse directions, i.e. to provide a reverse thrust to the watercraft. Since providing the forward thrust is typically more efficient than providing the reverse thrust, the system may effectively reduce or minimize the longitudinal movement.

[0012] The use of electric motors may significantly improve the control over the system especially at low speed. The rotational speed and/or the provided power of the electric motors may be controlled with minimum delay and/or at a high frequency, facilitating complex maneuvers and prompt reactions to changes in external conditions such as wind or waves. Importantly, the rotational speed of the electric motor, and hence of the propeller, may be regulated over a wide range starting from zero, without a minimum (non-zero) rotational speed dictated by an idle speed which may be required to keep the engine running, like, for example, in case of a combustion engine.

[0013] The total longitudinal thrust may refer to a sum of the forward thrust and the aft thrust. Alternatively, or in addition, the total longitudinal thrust may comprise any longitudinal thrusts onto the watercraft generated by any propulsion system(s) of the watercraft and/or by external forces such as wind or waves.

[0014] The propulsion and steering system may comprise at least one external condition sensor, such as a wind sensor and/or a wave sensor, adapted to generate an external condition information and to send the external condition information to the electronic controller device.

[0015] The electronic controller device may comprise at least one electronic controller, each comprising a processor and/or a memory.

[0016] For example, the electronic controller device may comprise or consist of a (single) central electronic controller associated with the plurality of propulsion units.

[0017] Alternatively, or in a addition, the electronic controller device may be a distributed system.

[0018] The electronic controller device may comprise at least one electronic controller associated with a propulsion unit. According to an embodiment, the electronic controller device may comprise a plurality of electronic controllers, wherein a different electronic controller may be associated with each of the propulsion units.

[0019] Optionally, the electronic controller device may further comprise at least one electronic controller on the watercraft or remote from the watercraft.

[0020] The electronic controller device may be adapted to receive the external condition information. The electronic controller device may be adapted to adjust the rotation speeds of the first propeller, the second propeller and the third propeller according to the received external condition information, such that the propellers generate the transverse thrust exceeding the total longitudinal thrust.

[0021] For example, the electronic controller device may be adapted to receive the external condition information from the at least one external condition sensor.

[0022] Alternatively, or in addition, the electronic controller may be adapted to receive the external condition information from an external sender, for example external of the watercraft.

[0023] The external condition information may comprise information about wind or waves or a current of a body of water at a position of the propulsion system and/or of the watercraft.

[0024] The electronic controller device may be adapted to determine the external forces based on the external condition information.

[0025] The electronic controller may be adapted to adjust the rotation speeds of the first propeller, the second propeller and the third propeller according to the received external condition information and/or to determine the external forces based on the external condition information using a reference dataset. The reference dataset may comprise or be based on previously acquired external condition information and corresponding previously acquired movement information. The previously acquired external condition information and the corresponding previously acquired movement information may be based on a reference operation of the propulsion and steering system. The reference operation may comprise acquiring external condition information and adjusting the rotation speeds of the first propeller, the second propeller and the third propeller such that the generated thrust compensates the external forces (for example, such that the propulsion and steering system and/or the watercraft does not move, e. g. according to movement information received by the electronic controller).

[0026] The total longitudinal thrust may be smaller than both the forward thrust and the aft thrust at least by a factor of 2, in particular at least by at least a factor of 5, in particular at least by at least a factor of 10 or at least by a factor of 20.

[0027] The transverse thrust may exceed the total longitudinal thrust at least by a factor of 2, in particular at least by at least a factor of 5, in particular at least by at least a factor of 10 or at least by a factor of 20.

[0028] The at least three propulsion units may be adapted to provide a forward propulsion for the watercraft, in particular a main or entire forward propulsion for the watercraft.

[0029] The electronic controller device may be adapted to adjust the rotation speed of at least one of the propellers according to its forward direction of rotation to provide the forward propulsion for the watercraft, in particular to adjust the rotation speeds of (all) the propellers of the least three propulsion units according to their respective forward directions of rotation to provide the forward propulsion for the watercraft.

[0030] The electronic controller device may be adapted to not adjust the rotation speed of any propeller of the least three propulsion units according to its reverse direction of rotation when providing the forward propulsion for the watercraft.

[0031] The propellers may have rigid shapes. For example, the propellers may not be variable-pitch propellers.

[0032] The transverse thrust may refer to a thrust perpendicular to the axis orientation of the first propeller and/or the second propeller and/or the third propeller, for example according to the top view.

[0033] The first (second, third) propeller may (each) refer to a single propeller or a respective plurality of propellers.

[0034] The second propeller may be different from the first propeller. The third propeller may be different from the first propeller and the second propeller. The first, second, and third propeller may be arranged at different positions along a transverse direction of the watercraft.

[0035] The third propeller may be arranged on a same side of both the first propeller and the second propeller.

[0036] The second propeller may be arranged on a same side of both the first propeller and the third propeller.

[0037] The same side may refer to a portside or to a starboard side.

[0038] The first propeller may comprise a first forward direction of rotation. The second propeller may comprise a second forward direction of rotation. The first forward direction of rotation may be opposite to the second forward direction of rotation. For example, the first forward direction of rotation may be clockwise and the second forward direction of rotation may be counterclockwise, or vice versa. The third propeller may comprise the second forward direction of rotation.

[0039] In such embodiments, the transverse thrusts generated by the first propeller, the second propeller, and the third propeller (e. g. as a consequence of propeller walk) may add up when the rotation speeds of the propellers are adjusted as described above in the context of the steering and propulsion system of the first aspect. On the other hand, when the three propellers are driven according to their forward directions to provide forward propulsion, the transverse thrusts generated by the propellers may cancel to allow for a straight and power-efficient forward propulsion.

[0040] The electronic controller device may be adapted to store and/or to receive the forward directions or rotation and/or the reverse directions of rotation of the propellers. For example, the at least three propulsion units may be adapted to send information regarding the forward directions or rotation and/or the reverse directions of rotation of the propellers to the electronic controller device, and the electronic controller device may be adapted to receive the information regarding the forward directions or rotation and/or the reverse directions of rotation of the propellers, for example in an installation or setup process.

[0041] Alternatively, or in addition, the electronic controller device may be adapted to store and/or to receive the forward directions or rotation and/or the reverse directions of rotation of the propellers according to a user input.

[0042] In some examples, the stored data may be used for future calculations for steering inputs to refine the maneuverability.

[0043] The first (second, third) propeller may be the propeller of a first (second, third) propulsion unit of the at least three propulsion units. The first propulsion unit may be different from the second propulsion unit and the third propulsion unit. The second propulsion unit may be different from the third propulsion unit. The first, second, and third propulsion unit may be arranged at different positions along a transverse direction of the watercraft.

[0044] The at least three propulsion units may be arranged (in particular, mounted to the watercraft) such that the axis orientations of the propellers are fixed and essentially parallel according to a top view or according to a projection onto a horizontal plane or within a horizontal plane.

[0045] The essentially parallel axis orientations of the propellers according to the top view may refer to a maximum angle between a horizontal component of an axis orientation of a propeller of any of the at least three propulsion units and a horizontal component of an axis orientation of a propeller of any other one of the at least three propulsion units of at most 10°, in particular at most 5°, in particular at most 2°, in particular at most 1°, in particular at most 0.5° or at most 0.2°.

[0046] For each propeller, a horizontal component of the axis orientation of the propeller may refer to a projection of the axis orientation of the propeller onto a horizontal plane.

[0047] The horizontal plane may refer to a plane that intersects the propellers of the at least three propulsion units, in particular all axis orientations or all axes of the at least three propulsion units. Alternatively, or in addition, the propulsion and steering system may be adapted to propel and/or steer the watercraft on a body of water, and the horizontal plane may refer to a plane parallel to a surface of the body of water.

[0048] The axis orientation of any of the propellers may be tilted within a vertical plane comprising the axis orientation of the respective propeller, for example by up to 15° or by up to 10°. The axis orientations of the propellers may be tilted within respective vertical planes by the same angle or by different angles.

[0049] The electronic controller device may be adapted to calculate, according to a target velocity or a target position of the propulsion system and/or of the watercraft, rotation speeds of the first propeller, the second propeller, and the third propeller. The electronic controller device may be adapted to adjust the rotation speeds of the first propeller, the second propeller, and the third propeller according to the calculated rotation speeds of the first propeller, the second propeller, and the third propeller. The target velocity may comprise a direction and a magnitude.

[0050] The propulsion and steering system may comprise a user input device electronically coupled to the electronic controller device, such as a joystick or a touchscreen. The user input device may be adapted to receive from a user the target velocity and/or a target position of the propulsion system and/or of the watercraft. The user input device may be adapted to electronically transmit the target velocity and/or the target position to the electronic controller device. The electronic controller device may be adapted to receive the target velocity and/or the target position from the user input device. The electronic controller device may be adapted to, upon receiving the target position, calculate the target velocity based on the target position.

[0051] The forward thrust generated by the first propeller and the aft thrust generated by the second propeller may be adapted to generate a first torque around a vertical axis. The aft thrust generated by the third propeller may be adapted to generate a second torque around the vertical axis. The electronic controller device may be adapted to adjust the rotation speeds of the first propeller, the second propeller and the third propeller such that the second torque essentially compensates the first torque.

[0052] The propulsion and steering system according to corresponding embodiments may allow for a purely translational movement of the watercraft, without a rotation of the watercraft around its center of mass or its center of rotation. Such a purely translational movement may make navigating the watercraft in a narrow environment such as a marina or a harbor even easier. It may provide a safe and intuitive steering option, without a necessity of a tugboat or a professional helmsman.

[0053] The first torque and/or the second torque may refer to respective torques onto the watercraft. Alternatively, or in addition, the vertical axis may comprise a center of mass and/or a center of rotation of the watercraft.

[0054] The electronic controller device may be adapted to store a position of the vertical axis, the center of mass and/or the center of rotation; for example, relative to at least one of the propellers and/or relative to at least one of the at least three propulsion units.

[0055] The forward thrust generated by the first propeller and the aft thrust generated by the second propeller may be adapted to together (in sum) generate the first torque.

[0056] The second torque may essentially compensate the first torque when an overall torque comprising the first torque and the second torque is smaller than the first torque and the second torque, in particular at least by a factor of 2, in particular at least by a factor of 5 or at least by a factor of ten.

[0057] The overall torque may further comprise a third torque generate by external forces such as wind or waves.

[0058] The electronic controller device may be adapted to calculate the third torque based on the external condition information, and optionally based on the position of the vertical axis, the center of mass and/or the center of rotation stored on the electronic controller device.

[0059] The first torque may refer to a sum of the torques (total torque, net torque) resulting from the forward thrust generated by the first propeller and the aft thrust generated by the second propeller.

[0060] The electronic controller device may be adapted to receive a movement information.

[0061] The electronic controller device may be adapted to adjust the rotation speeds of the first propeller, the second propeller and the third propeller according to the received movement information and/or the received external condition information, such that the propellers generate the transverse thrust exceeding the total longitudinal thrust.

[0062] The electronic controller device may be adapted to adjust the rotation speeds of the first propeller, the second propeller and the third propeller according to the received movement information, such that the propellers generate the transverse thrust exceeding the total longitudinal thrust.

[0063] The electronic controller device may use movement information, provided for example by sensors connected to the electronic controller device or a receivers such as a weather information or GPS receiver, to ensure that the transverse thrust, or a transverse movement, is achieved with the rotation speeds of the propellers. The electronic controller device may readjust the rotation speeds of the propellers to ensure the desired movement of the propulsion system and/or of the watercraft based on the movement information.

[0064] The propulsion and steering system may further comprise a movement sensor electronically coupled to the electronic controller device and adapted to send the movement information to the electronic controller device. The movement sensor may be adapted to generate the movement information.

[0065] The movement information may comprise information about a location of the propulsion system (in particular of the electronic controller device or of at least one of the least three propulsion units), of the movement sensor, and/or of the watercraft.

[0066] Alternatively, or in addition, the movement information may comprise information about at least one inclination of the propulsion system (in particular of the electronic controller device or of at least one of the least three propulsion units), of the movement sensor, and/or of the watercraft. The at least one inclination may refer to a roll, a pitch, and/or a yaw.

[0067] Alternatively, or in addition, the movement information may comprise information about a transverse and/or longitudinal velocity of the propulsion system (in particular of the electronic controller device or of at least one of the least three propulsion units), of the movement sensor, and/or of the watercraft.

[0068] Alternatively, or in addition, the movement information may comprise information about a transverse and/or longitudinal acceleration of the propulsion system (in particular of the electronic controller device or of at least one of the least three propulsion units), of the movement sensor, and/or of the watercraft.

[0069] Alternatively, or in addition, the movement information may comprise information about a rotation of the propulsion system (in particular of the electronic controller device or of at least one of the least three propulsion units), of the movement sensor, and/or of the watercraft, in particular around the vertical axis.

[0070] The electronic controller device may be adapted to adjust the rotation speeds of the first propeller, the second propeller and the third propeller such that the second torque essential compensates the first torque according to the received movement information, in particular, wherein the movement information comprises information about a rotation of the sensor, of the propulsion system (in particular of the electronic controller device or of at least one of the least three propulsion units) and/or of the watercraft, in particular around the vertical axis.

[0071] The electronic controller device may be adapted to determine the position of the vertical axis, the center of mass and/or the center of rotation of the watercraft according to the received movement information; for example relative to at least one of the propellers and/or relative to at least one of the at least three propulsion units.

[0072] For example, the electronic controller device may be adapted to vary the rotation speeds of the first propeller, the second propeller and the third propeller and to identify at least three independent sets of rotation speeds of the first propeller, the second propeller and the third propeller wherein the second torque essential compensates the first torque according to the received movement information. The electronic controller device maybe adapted to determine the position of the vertical axis, of the center of mass and/or of the center of rotation of the watercraft based on the at least three independent sets of rotation speeds wherein the second torque essential compensates the first torque according to the received movement information.

[0073] The electronic controller device may be adapted to re-determine the position of the vertical axis, the center of mass and/or the center of rotation of the watercraft, for example when the movement information indicates a change of the corresponding position, and/or in response to a change in the external condition information and/or in response to a change in the received movement information not accompanied by a change in the rotation speed of the first propeller, the second propeller or the third propeller.

[0074] The at least three propulsion units may each comprise a respective propeller shaft. The propeller of each of the at least three propulsion units may be rotationally coupled to the propeller shaft of the respective propulsion unit. A single plane may exist, which is essentially perpendicular to the axis orientation of the first propeller and/or the second propeller and/or the third propeller according to a top view, and which intersects the propeller shafts and/or the propellers of the at least three propulsion units.

[0075] Corresponding systems may provide propulsion for the watercraft with high energy efficiency or high speed, implementing, for example, a fixed-shaft drive, a stern drive, or a surface drive.

[0076] The propeller shaft of each of the at least three propulsion units may be rotationally coupled to the electric motor of the respective propulsion unit to rotationally couple the propeller of the respective propulsion unit to the electric motor of the respective propulsion unit.

[0077] Axis orientations of the propellers and/or the propeller shafts may be fixed relative to other components of the at least three propulsion units (such as a housing) and/or relative to the watercraft.

[0078] In the context of this disclosure, the term essentially perpendicular may refer to an angle of at least 80°, in particular at least 85°, in particular at least 88°, in particular at least 89°, in particular at least 89.5° or at least 89.9°.

[0079] In the context of this disclosure, the term essentially perpendicular may refer to an angle of at most 100°, in particular at most 95°, in particular at most 92°, in particular at most 91°, in particular at most 90.5° or at most 90.2°.

[0080] Vertical positions of the propellers and/or of the at least three propulsion units may differ, in particular in embodiments wherein the at least three propulsion units are mounted to the watercraft. In particular, vertical positions of propellers and/or of propulsion units arranged closer to a centerline of the watercraft may be lower than vertical positions of propellers and/or of propulsion units arranged further away from the centerline of the watercraft.

[0081] In embodiments wherein the at least three propulsion units are mounted to a watercraft, a horizontal plane may exist which intersects the first propeller, the second propeller, and the third propeller.

[0082] The electric motors of the at least three propulsion units may each be adapted to provide a rotational movement along a first direction of rotation to drive the respective propeller along its forward direction of rotation, and to provide a rotational movement along a second direction of rotation opposite to the first direction of rotation to drive the respective propeller along its reverse direction of rotation.

[0083] Rotation along either direction may easily be achieved using the electric motors, which may be an advantage over conventional systems with combustion engines, whose direction of rotation is typically fixed. In such conventional systems, an additional clutch and/or gearset may be applied to control the direction of rotation of the propellers, increasing the weight, initial cost, and maintenance cost of the conventional propulsion system.

[0084] The electronic controller device may further be adapted to adjust the rotation speed of the first propeller of the propellers according to its reverse direction of rotation to generate a reverse thrust, to adjust the rotation speeds of the second propeller and the third propeller of the propellers according to their respective forwards directions of rotation to generate an aft thrust to generate an opposite transverse thrust (i. e., with a direction opposite to the one of the transverse thrust described above in the context of the first aspect) exceeding the total longitudinal thrust comprising the reverse thrust and the aft thrust.

[0085] The at least three propulsion units are adapted to provide a main forward propulsion system for the watercraft.

[0086] In such embodiments, the propulsion and steering system may not only allow for maneuvering at low speed, but also provide the main or entire propulsion system for the watercraft, for example for cruising and/or traveling long distance. Consequently, a need to equip the watercraft with separate engines and/or propellers for forward propulsion on the one hand and maneuvering on the other may be avoided, thus reducing the cost and the weight of the watercraft. The propellers and engines of the propulsion and steering system according to the description may provide both functions.

[0087] The at least three propulsion units maybe adapted to provide the majority of mechanical power for forward propulsion of the watercraft.

[0088] According to embodiments, at least one, at least two, or each of the at least three propulsion units may comprise a hybrid drive comprising the electric motor and a combustion engine. The propeller(s) of the respective propulsion unit(s) may be rotationally coupled to the respective combustion engine(s) and or to the respective hybrid drive(s). The electronic controller device may be adapted to be electronically coupled to the at least three propulsion units to individually adjust the rotation speeds of their respective electric motors and their respective combustion engines to adjust the rotational speeds of their respective propellers.

[0089] The hybrid drive and/or the combustion engine may extend a range of a watercraft equipped with the propulsion and steering system. In addition, the hybrid drive and/or the combustion engine may provide additional mechanical power for forward propulsion of the watercraft, for example for a larger acceleration and/or a larger maximum speed.

[0090] The electric motor(s) and/or the hybrid drive(s) and/or the combustion engine(s) may be adapted to provide a (majority of a) mechanical power of the respective propulsion unit, in particular for the propeller of the respective propulsion unit and/or for forward propulsion of the watercraft.

[0091] The hybrid drive (in particular, the electric motor and the combustion engine together) may be adapted to provide a majority of a mechanical power of the respective propulsion unit, in particular for the propeller of the respective propulsion unit and/or for forward propulsion of the watercraft.

[0092] Alternatively, the electric motor of each of the at least three propulsion units may be adapted to provide a majority of a mechanical power of the respective propulsion unit, in particular for the propeller of the respective propulsion unit and/or for forward propulsion of the watercraft. In such embodiments, at least one, at least two, or each of the at least three propulsion units may not comprise the combustion engine.

[0093] The majority may refer to at least 50%, in particular to at least 60%, in particular to at least 70%, in particular to at least 80%, in particular to at least 90%, or to at least 95%.

[0094] The at least three propulsion units may be mounted to the watercraft, and the at least three propulsion units may comprise the highest-power propulsion unit for the watercraft.

[0095] A hybrid drive (in particular, the respective electric motor and the respective combustion engine together) or an electric motor of the at least three propulsion units may be the highest-power engine for the watercraft or mounted to the watercraft, and/or the highest-power engine adapted to propel the watercraft along its forward direction.

[0096] The hybrid drives (in particular, the electric motors and the combustion engines together) or the electric motors of the at least three propulsion units may be adapted to provide an average mechanical power per propulsion unit. The average mechanical power per propulsion unit may be higher than a mechanical power provided by any other propulsion unit for/of the watercraft (not comprised in the propulsion system, in particular with a propeller with an axis orientation deviating from the one of the propellers of the propulsion system) or of any other engine for/of the watercraft (not comprised in the propulsion system, in particular coupled to a propeller with an axis orientation deviating from the one of the propellers of the propulsion system) adapted to propel the watercraft along its forward direction.

[0097] Three of the hybrid drives (in particular, the respective electric motor and combustion engine together) or the electric motors of the at least three propulsion units may be adapted to provide the three highest-power engines mounted to the watercraft, or the three highest-power engines adapted to propel the watercraft along its forward direction.

[0098] The hybrid drives (in particular, the respective electric motor and the respective combustion engine together) or the electric motors of the at least three propulsion units may each be adapted to provide a mechanical power of at least 50 kW, in particular of at least 100 kW, in particular of at least 200 kW or of at least 500 kW.

[0099] In particular, the hybrid drives (in particular, the respective electric motor and the respective combustion engine together) or the electric motors of the at least three propulsion units may each be adapted to propel the watercraft along its forward direction with a mechanical power of at least 50 kW, in particular of at least 100 kW, in particular of at least 200 kW, or of at least 500 kW.

[0100] The at least three propulsion units may each comprise a transmission rotationally coupled to the hybrid drive or to the electric motor of the respective propulsion unit and to the propeller of the respective propulsion unit to rotationally couple the propeller to the electric motor and/or to the hybrid drive.

[0101] The transmission of each of the at least three propulsion units may comprise a gear ratio between a revolution speed of the electric motor or the respective hybrid drive and a revolution speed of the propeller of at most 2, in particular at most 1.5 in particular at most 1.3 or at most 1.25.

[0102] The electric motors of the at least three propulsion units may be axial flux motors.

[0103] Axial flux motors may provide an optimized power density (minimum weight per mechanical power they are adapted to provide). They may enable a modular design, wherein a second or third axial flux motor of a same propulsion unit may be easily added, removed, or replaced to adjust the mechanical power provided by the respective propulsion unit.

[0104] The propulsion and steering system may comprise a first rudder associated with the first propeller. The electronic controller device may be adapted to adjust an angle of attack of the first rudder to a first direction while adjusting the rotation speed of the first propeller according to its forward direction of rotation.

[0105] The first rudder may be arranged in a vicinity of the first propeller.

[0106] The first rudder may be adapted to modify and/or deflect a flow of water that the first propeller is adapted to induce.

[0107] The first rudder may be arranged starboard or portside of the first propeller.

[0108] The propulsion and steering system may further comprise a first rudder associated with the first propeller and a second rudder associated with the second propeller. The electronic controller device may be adapted to adjust an angle of attack of the first rudder to a first direction while adjusting the rotation speed of the first propeller according to its forward direction of rotation. The electronic controller device may be adapted to adjust an angle of attack of the second rudder to a second direction while adjusting the rotation speed of the second propeller according to its reverse direction of rotation. The second direction may be opposite to the first direction.

[0109] The second rudder may be arranged in a vicinity of the second propeller.

[0110] The second rudder may be adapted to modify and/or deflect a flow of water that the second propeller is adapted to induce.

[0111] The electronic controller device may be adapted to individually adjust the respective angles of attack of the first rudder and the second rudder.

[0112] The rudders may be adapted to enhance the transverse thrust generated by the propellers.

[0113] The first direction may refer to a starboard direction and the second direction may refer to a portside direction or vice versa.

[0114] The first rudder may be arranged starboard or portside of the first propeller. The second rudder may be arranged starboard or portside of the second propeller.

[0115] In such embodiments, moving parts aft the propellers, which would increase drag and therefore power consumption of the forward propulsion, may be avoided. In addition, the rudder may enhance the transverse thrust generated by the propeller both when the propeller is driven according to its forward direction and when it is driven according to its reverse direction of rotation.

[0116] The propulsion and steering system may comprise a third rudder associated with the third propeller. The electronic controller device may be adapted to adjust an angle of attack of the third rudder to the second direction while adjusting the rotation speed of the third propeller according to its reverse direction of rotation.

[0117] The third rudder may be arranged in a vicinity of the third propeller.

[0118] The third rudder may be adapted to modify and/or deflect a flow of water that the third propeller is adapted to induce.

[0119] The third rudder may be arranged starboard or portside of the third propeller.

[0120] Each of the at least three propulsion units may comprise a rudder associated with its respective propeller, for example arranged in a vicinity of the respective propeller and/or adapted to modify and/or deflect a flow of water that the respective propeller is adapted to induce.

[0121] The rudders of the propulsion units maybe arranged starboard or portside of the propeller of the respective propulsion unit.

[0122] The electronic controller device may be adapted to adjust the rudders of the at least three propulsion units individually.

[0123] Each of the at least three propulsion units may comprise at least two rudders associated with its respective propeller, for example arranged in a vicinity of the respective propeller and/or adapted to modify and/or deflect a flow of water that the respective propeller is adapted to induce.

[0124] The at least two rudders of the propulsion units may be arranged starboard and portside of the propeller of the respective propulsion unit.

[0125] The at least two rudders may be adapted to provide individually adjustable angles of attack.

[0126] The electronic controller device may be adapted to individually adjust the respective angles of attack of the at least two rudders.

[0127] Each of the at least three propulsion units may comprise a waterproof housing. The waterproof housing of each of the at least three propulsion units may enclose the electric motor and/or the hybrid drive and/or a section of the transmission and/or a section of the propeller shaft of the respective propulsion unit.

[0128] The waterproof housing enclosing the electric motor may improve the electrical safety (inside) of the watercraft.

[0129] The angles of attack of the rudders may be within a range defined by respective stall angles of the rudders, for example each within a range of -35° to 35°.

[0130] Aft cross sections of the propellers and/or sections aft of the propellers may be unobstructed and/or unobscured. In particular, the aft cross sections of the propellers or the sections aft of the propellers may not be covered or obscured by a component of a propulsion and steering system, such as a moveable component, like, for example, a rudder, a bucket, a nozzle, or a channel.

[0131] In other words, the propellers may be adapted to expel water freely towards the aft direction, without encountering an object (in particular a component of the/a propulsion and steering system), such as a moveable component, which may increase drag, such as a rudder, a channel, a nozzle, or a bucket.

[0132] Lower halves of fore cross sections of the propellers and/or sections forward of the lower halves of the propellers may be unobstructed and/or unobscured. In particular, the lower halves of the fore cross sections of the propellers or the sections forward of the lower halves of the propellers may not be covered or obscured by a component of a propulsion and steering system, in particular by a moveable component such as a rudder, a bucket, a nozzle, or a channel.

[0133] In other words, the lower halves of the propellers may be adapted to expel water freely towards the fore direction, without encountering an object (in particular a component of a propulsion and steering system) which might otherwise increase drag, such as a rudder, a channel, a nozzle, or a bucket.

[0134] The unobstructed and/or unobscured aft cross section of the propellers and/or sections aft of the propellers may refer to at least 70% of the respective (cross) sections, in particular to at least 80% of the respective (cross) sections, in particular to at least 90% of the respective (cross) sections, in particular to at least 95% of the respective (cross) sections or to the entire respective (cross) sections.

[0135] Each of the at least three propulsion units may comprise a connection element adapted to connect the respective propulsion unit to the watercraft. Each of the at least three propulsion units may be adapted to be connected as a whole to the watercraft.

[0136] Corresponding embodiments may allow for a modular design of the propulsion and steering system. For example, the at least three propulsion units may be produced with similar or identical shapes, electrical, or mechanical characteristics for a maximized production efficiency and to facilitate fast and efficient repair and/or replacement of any of the units. The fast and efficient repair or replacement may further be improved by the option to connect (or disconnect) the unit as a whole to the watercraft, for example in case of a failure, thereby avoiding time-consuming and expensive on-site diagnostics, which typically require qualified personal in case of conventional propulsion systems.

[0137] The connection element for connecting the propulsion unit to the watercraft may not only facilitate the fast and simple connection (or disconnection). It may, in addition, define the axis orientation of the propeller relative to the watercraft, and thus ensure a geometry for highly efficient forward propulsion. Each propulsion unit may comprise a similar connection element, ensuring that the propellers of the propulsion units are arranged in parallel to each other and that the propulsion units are interchangeable.

[0138] Each of the at least three propulsion units may comprise a fixed relative orientation of the axis orientation of its respective propeller with respect to its respective connection element. For example, the connection element may comprise or be a surface, and the fixed relative orientation may refer to the axis orientation of the propeller with respect to the surface of the connection element.

[0139] The at least three propulsion units may comprise the same fixed relative orientation of their respective axis orientations of their respective propellers with respect to their respective connection elements.

[0140] Each of the at least three propulsion units may be adapted to define the axis orientation of its respective propeller relative to the watercraft, in particular via its respective waterproof housing and/or via its respective connection element.

[0141] Each of the at least three propulsion units may be adapted to be connected as a whole to the watercraft from outside the watercraft, in particular by moving at least a section of the respective propulsion unit through an opening in a hull of the watercraft and by fixing it to the hull with the opening. The connection element may be adapted to define an orientation and/or a position of the respective propulsion unit related to the fixing the respective propulsion unit to the hull with the opening.

[0142] Each of the at least three propulsion units may be adapted to be connected to the transom of a watercraft, in particular as a whole.

[0143] Installation at the transom may be beneficial for implementing a high-speed watercraft, since it facilitates implementation of a stern drive and/or a surface drive, which maybe particularly energy efficient at high speed of the watercraft.

[0144] Each of the at least three propulsion units may be adapted to be mounted to and/or dismounted from the watercraft while the electric motor and/or the hybrid drive and/or the section of the propeller shaft and/or the section of the transmission of the respective propulsion unit is (are) arranged in its respective waterproof housing.

[0145] The at least three propulsion units may comprise a same connection element and/or a same shape and/or same physical dimensions and/or may be adapted to provide a same mechanical power for propulsion of the watercraft.

[0146] The propulsion and steering system may comprise at least four propulsion units, each comprising an electric motor and a propeller with a respective axis orientation, a respective forward direction of rotation, and a respective reverse direction of rotation, wherein the propeller is rotationally coupled to the electric motor. The electronic controller device may be adapted to be coupled to the at least four propulsion units to individually adjust the rotation speeds of their respective electric motors to adjust the rotational speeds of their respective propellers. The at least four propulsion units may be adapted to be arranged such that the axis orientations of the propellers are fixed and essentially parallel according to a top view. The electronic controller device may be adapted to adjust the rotation speeds of at least two of the propellers according to their forward directions of rotation to generate the forward thrust, and to adjust the rotation speeds of at least two of the propellers according to their reverse directions of rotation to generate the aft thrust; such that the propellers generate the transverse thrust exceeding the total longitudinal thrust.

[0147] The electronic controller device maybe adapted to reverse the rotation speeds of the propellers of the at least four propulsion units; such that the propellers generate an opposite transverse thrust (e. g., along a direction opposite to a direction of the transverse thrust).

[0148] Corresponding embodiments may provide an additional parameter to distribute the transverse thrust to be generated between the propulsion units, or their propellers, respectively. This additional parameter may be used to maximize the power efficiency of the system.

[0149] In addition, corresponding embodiments may be optimized for the use in multihull watercraft such as catamarans. For example, to propulsion units may be provided on a starboard hull of the multihull watercraft, and two of the propulsion units may be provided on a portside hull of the watercraft.

[0150] The at least four propulsion units may be characterized by one or all the features disclosed in the context of the at least three propulsion units.

[0151] The at least four propulsion units may comprise the at least three propulsion units.

[0152] The at least two of the propellers with their rotation speeds adjusted according to their forward directions of rotation may be the propellers of a at least a first propulsion unit and at least a second propulsion unit. The first propulsion unit may be different from the second propulsion unit.

[0153] The at least two of the propellers with their rotation speeds adjusted according to their reverse directions of rotation may be the propellers of a at least a third propulsion unit and at least a fourth propulsion unit. The third propulsion unit maybe different from the fourth propulsion unit. The third (fourth) propulsion unit may be different from both the first and the second propulsion unit.

[0154] At least two of the at least four propulsion units may be arranged in a starboard half of the watercraft. At least two of the at least four propulsion units may be arranged in a portside half of the watercraft.

[0155] A propeller of the at least two of the propellers with their rotation speeds adjusted according to their forward directions of rotation may be arranged in a starboard half of the watercraft. Another propeller of the at least two of the propellers with their rotation speeds adjusted according to their forward directions of rotation may be arranged in a portside half of the watercraft.

[0156] A propeller of the at least two of the propellers with their rotation speeds adjusted according to their reverse directions of rotation may be arranged in a starboard half of the watercraft. Another propeller of the at least two of the propellers with their rotation speeds adjusted according to their reverse directions of rotation may be arranged in a portside half of the watercraft.

[0157] The at least two of the propellers with their rotation speeds adjusted according to their forward directions of rotation may comprise a first forward direction of rotation. The at least two of the propellers with their rotation speeds adjusted according to their reverse directions of rotation may comprise a second forward direction of rotation. The first forward direction of rotation may be opposite to the second forward direction of rotation. For example, the first forward direction of rotation may be clockwise, and the second forward direction of rotation may be counterclockwise, or vice versa.

[0158] A watercraft may comprise a propulsion and steering system as described above. The at least three propulsion units may be arranged on the watercraft such that horizontal components of the axis orientations of the propellers are essentially parallel to a centerline of the watercraft.

[0159] This arrangement may maximize, and thus optimize, the forward propulsion provided by the propulsion units.

[0160] The axes of the propellers of the at least three propulsion units may be offset from a centerline of the watercraft, in particular along a starboard/portside direction. Alternatively, a propeller of the at least three propulsion units, in particular the first propeller, may be arranged on a vertical plane comprising the centerline of the watercraft.

[0161] At least two of the at least three propulsion units may be arranged at different vertical positions. In particular, a vertical position of a propulsion unit closer to the centerline may be lower than a vertical position of a propulsion unit arranged further away from the centerline. Vertical positions of propulsion units with a same distance from the centerline may be arranged at a same vertical position.

[0162] A single horizontal plane may exist, which intersects the at least three propulsion units, in particular the propellers of the at least three propulsion units.

[0163] A watercraft may comprise a propulsion and steering system as described above. The propellers or the at least three propulsion units may be arranged in a stern section of the watercraft.

[0164] Corresponding embodiments may implement a watercraft with a stern drive or a surface drive, which may be particularly beneficial (energy-efficient) as a high-speed watercraft.

[0165] According to an embodiment, the propellers are arranged in the stern section of the watercraft. Alternatively, or in addition, the entire at least three propulsion units may be arranged in the stern section of the watercraft.

[0166] The stern section may refer to a half of the watercraft closest to the stern, in particular to a third of the watercraft closest to the stern, in particular to a quarter of the watercraft closest to the stern, or to a fifth of the watercraft closest to the stern.

[0167] The stern section may refer to section aft of the hull of the watercraft.

[0168] The hull of the watercraft may comprise a transom. The propellers may be arranged aft the transom.

[0169] The propulsion and steering system may be comprised in or adapted to provide a stern drive and/or a surface drive of the watercraft.

[0170] The propulsion system may be arranged on the watercraft such that the propellers are under a static water line of the watercraft.

[0171] The propulsion system may be arranged on the watercraft such that first sections of the propellers are under a planing-speed water line of the watercraft, and second sections of the propellers are above a planing-speed water line of the watercraft.

[0172] A watercraft may comprise a propulsion and steering system as described above. The watercraft may be a multihull watercraft. At least one of the propellers may be arranged on a starboard hull of the multihull watercraft, and at least one of the propellers may be arranged on a portside hull of the multihull watercraft.

[0173] The distribution of the steering and propulsion system over at least three (four) propulsion units may be particularly beneficial for a multihull watercraft, which typically provides a limited space (height) for the propulsion system in each of its hulls, in particular in the stern sections of the respective hulls. The distributed steering and propulsion system may operate with one or two compact electric motors in each of the hulls. It this minimizes the space requirement to each of the hulls, respectively, and in particular to the stern sections of the hulls, where the motors are to be placed. Batteries for supplying the electric motors with energy may be flexibly be arranged on (distributed across) the ship, with, for example, at least some of them distant from the electric motors.

[0174] The multihull watercraft may be a catamaran or a trimaran.

[0175] At least two of the propellers may be arranged on the starboard hull of the multihull watercraft.

[0176] At least two of the propellers may be arranged on a portside hull of the multihull watercraft.

[0177] The first rudder may be arranged on a first hull of the multihull watercraft, such as a center hull, the starboard hull or the portside hull.

[0178] The second rudder may be arranged on a second hull of the multihull watercraft, in particular on a second hull opposite to the first hull, such as the starboard hull if the first hull is the portside hull or the portside hull if the first hull is the starboard hull.

[0179] A fourth rudder may be arranged on the first hull of the multihull watercraft. A fifth rudder may be arranged on the second hull.

[0180] The watercraft may not comprise any propulsion unit arranged closer to its bow than to its stern, in particular with a propeller arranged closer to the bow than to the stern.

[0181] By avoiding additional (transverse) thrusters, such as a bow thruster, the watercraft may be formed with hydrodynamics optimized for energy efficiency. For example, a channel transversing the hull, in particular the bow, may be avoided, which may otherwise negatively affect the hydrodynamics of the hull. Moreover, the overall weight of the watercraft may be reduced.

[0182] The watercraft may not comprise any propulsion unit or propeller with an axis oriented along the transverse direction of the watercraft.

[0183] The watercraft may not comprise any bow thruster or stern thruster. The watercraft may not comprise any channel transversing the hull of the watercraft below the waterline.

[0184] In a second aspect, a method is provided for operating a propulsion and steering system of a watercraft, comprising a transverse propulsion mode and a longitudinal propulsion mode. The propulsion and steering system comprises at least three propulsion units, each comprising a propeller with a respective axis orientation, a respective forward direction of rotation, and a respective reverse direction of rotation. The propulsion and steering system further comprises an electronic controller device electronically coupled to the at least three propulsion units. The at least three propulsion units are adapted to be arranged such that the axis orientations of the propellers are fixed and essentially parallel to each other according to a top view. The method comprises, in the transverse propulsion mode, selecting, using the electronic controller device, a rotation speed of a first propeller according to its forward direction of rotation, and rotation speeds of the second propeller and the third propeller according to their respective reverse directions of rotation. In the transverse propulsion mode, the method further comprises adjusting, using the electronic controller device, the rotation speed of the first propeller according to its selected rotation speed to generate a forward thrust; and adjusting, using the electronic controller device, the rotation speeds of the second propeller and the third propeller according to their respective selected rotation speeds to generate an aft thrust; wherein the selecting the rotation speeds of the first propeller, the second propeller, and the third propeller is performed by the electronic controller device (104) such that a transverse thrust generated by the propellers exceeds a total longitudinal thrust comprising the forward thrust and the aft thrust. In the longitudinal propulsion mode, the method comprises driving at least one of the propellers according to its forward direction of rotation to generate a forward thrust; and not driving any of the propellers according to its reverse direction of rotation to generate an aft force onto the watercraft.

[0185] The propulsion and steering system of the method may be characterized by one or all the features described above in the context of the first aspect of the disclosure. Within the method, the electronic controller device may perform any process step that it has been described to be adapted to perform in the context of the disclosure above relating to the propulsion and steering system.

[0186] In the transverse propulsion mode, the driving the at least one of the propellers according to its forward direction of rotation may comprise selecting, by the electronic controller device, the rotation speeds of the first propeller, the second propeller, and the third propeller such that the transverse thrust matches a transverse thrust according to the target velocity and/or the target position received from the user input device.

[0187] In the transverse propulsion mode, the adjusting the rotation speed the first propeller and the second propeller may comprise generating a first torque onto the watercraft around the vertical axis, the adjusting the rotation speed of the third propeller may comprise generating a second torque onto the watercraft around the vertical axis, and the method may further comprise selecting, by the electronic controller device, the rotation speeds of the first propeller, the second propeller, and the third propeller such that the second torque essentially compensates the first torque.

[0188] The propulsion system may comprise at least four propulsion units. In the transverse propulsion mode, the method may comprise adjusting, by the electronic controller device, the rotation speeds of at least two of the propellers according to their forward directions of rotation to generate the forward thrust and adjusting, by the electronic controller device, the rotation speeds of at least two of the propellers according to their reverse directions of rotation to generate the aft thrust. The selecting the rotation speeds of the at least two of the propellers with their rotation speeds adjusted according to their forward direction and the rotation speeds of the at least two of the propellers with the rotation speeds adjusted according to their reverse direction may be performed by the electronic controller device such that the propellers generate the transverse thrust exceeding the total longitudinal thrust.

[0189] In the longitudinal propulsion mode, the driving the at least one of the propellers according to its forward direction of rotation may comprise driving at least two of the propellers according to their forward directions or driving at least three of the propellers according to their forward directions of rotation or driving at least four of the propellers according to their forward directions of rotation. In the longitudinal propulsion mode, the method may comprise driving the first propeller, the second propeller and/or the second propeller according to their forward directions of rotation.

[0190] In the transverse propulsion mode, the method may further comprise receiving, by the electronic controller device, the movement information from the movement sensor.

[0191] The rotation speeds of the first propeller, the second propeller, and the third propeller may be selected by the electronic controller device such that the transverse thrust exceeds the total longitudinal thrust according to the received movement information.

[0192] The rotation speeds of the first propeller, the second propeller, and the third propeller may be selected by the electronic controller device such that the second torque essentially compensates the first torque according to the received movement information.

[0193] The at least three propulsion units may each comprise an electric motor, wherein the propeller of each of the at least three propulsion units is rotationally coupled to the electric motor of the respective propulsion unit. The electronic controller device may be electrically coupled to the at least three propulsion units to individually adjust the rotation speeds of their respective electric motors. The adjusting the rotation speeds of the first propeller, the second propeller, and the third propeller may comprise adjusting, using the electronic controller device, the rotation speeds of the respective electric motors.

[0194] The propulsion and steering system may further comprise a first rudder associated with the first propeller and a second rudder associated with the second propeller. The method may further comprise adjusting, using the electronic controller device, an angle of attack of the first rudder to a first direction while adjusting the rotation speed of the first propeller according to its forward direction of rotation; and adjusting, using the electronic controller device, an angle of attack of the second rudder to a second direction while adjusting the rotation speed of the second propeller according to its reverse direction of rotation. The second direction may be opposite to the first direction.

[0195] The propulsion and steering system may further comprise a fourth rudder associated with the first propeller, and the method may comprise deflecting an angle of attack of the fourth rudder to the same direction as the angle of attack of the first rudder, in particular wherein a value of the angle of attack of the fourth rudder is different from a value of the angle of attack of the first rudder.

[0196] The propulsion and steering system may further comprise a fifth rudder associated with the second propeller, and the method may comprise deflecting an angle of attack of the fifth rudder to the same direction as the angle of attack of the second rudder, in particular wherein a value of the angle of attack of the fifth rudder is different from a value of the angle of attack of the second rudder.

[0197] In a third aspect, a computer program is adapted to instruct a controller device to execute the method described above.

[0198] The electronic controller device may comprise a processor and a memory coupled to the processor and adapted to store the computer program. The computer program maybe adapted to instruct the processor of the electronic controller device to execute the method.

BRIEF DESCRIPTION OF THE FIGURES

[0199] The techniques of the present disclosure and the advantages associated therewith will be best apparent from a description of exemplary embodiments in accordance with the accompanying drawings, in which:

Fig. 1a

shows a top view of a propulsion and steering system according to a first embodiment;

Fig. 1b

shows a stern view of the propulsion and steering system according to the first embodiment;

Fig. 1c

shows a side view of the propulsion and steering system according to the first embodiment;

Fig. 2a

shows a side view of a propulsion and steering system according to another embodiment;

Fig. 2b

shows a side view of a propulsion and steering system according to another embodiment;

Fig. 3

shows a top view of a propulsion and steering system according to another embodiment;

Fig. 4

shows a top view of a propulsion and steering system according to another embodiment;

Fig. 5

shows a stern view of a propulsion and steering system according to another embodiment;

Fig. 6a

shows a cross section of a propulsion unit;

Fig. 6b

shows a perspective view of the propulsion unit;

Fig. 6c

shows a stern view of the propulsion unit;

Fig. 6d

shows a hull prepared for connecting the propulsion system as a surface drive;

Fig. 7

shows a top view of a propulsion and steering system according to another embodiment;

Fig. 8

shows a top view of a propulsion and steering system according to another embodiment;

Fig. 9a

shows a top view of a propulsion and steering system according to another embodiment;

Fig. 9b

shows a top view of a propulsion and steering system according to another embodiment; and

Fig. 10

shows a method for operating a propulsion and steering system.

DETAILED DESCRIPTION OF EMBODIMENTS

[0200] Fig. 1a, Fig. 1b, and Fig. 1c show a propulsion and steering system 100 for a watercraft 102, hereafter also referred to as system 100, according to a first embodiment. Fig. 1a gives a top view of the system 100, Fig. 1b a stern view, and Fig. 1c a view from portside.

[0201] The system 100 of Fig. 1a, Fig. 1b, and Fig. 1c comprises an electronic controller 104 and three propulsion units 110, 120, 130 each electronically coupled to the electronic controller 104. Accordingly, according to the depicted embodiment, the electronic controller device consists of the central electronic controller 104. In other embodiments, the electronic controller device may comprise a plurality of electronic controllers, such as one electronic controller per propulsion unit.

[0202] The propulsion units 110, 120, 130 each comprise an electric motor 310, 320, 330 driving a propeller 112, 122, 132.

[0203] The propellers 112, 122, 132 are seated rotatably around axes with parallel orientations 112a, 122a, 132a according to a top view such as the one of Fig. 1a. In a side view, or in a vertical plane, respectively, the axis orientations 112a, 122a, 132a of the propellers are tilted by approximately 5°, see also Fig. 1c.

[0204] The propellers 112, 122, 132 have respective forward directions of rotation 112f, 122f, 132f and reverse directions of rotation 112r, 122r, 132r determined by the (blade) structure of the propellers, as best visible in Fig. 1b.

[0205] Rotation speeds of the electric motors 310, 320, 330 can individually be tuned over a wide range starting from zero, both along the clockwise and the anticlockwise direction. This allows for individually adjusting the rotation speeds of the propellers 112, 122, 132 of the individual propulsion units 110, 120, 130 over continuous ranges starting from zero, both along their respective forward directions of rotation 112f, 122f, 132f and their reverse directions of rotation 112r, 122r, 132r.

[0206] According to the embodiment of Fig. 1a, Fig. 1b, and Fig. 1c, the electric motors 310, 320, 330 are axial flux motors, each providing a mechanical power of 50 kW to 300 kW at full load, for instance 200 kW at full load. Actual flux motors provide an optimized power density (provided mechanical power at full load per weight of the electric motor 310, 320, 330). However, alternative motor designs such as radial flux motors may in principle be used.

[0207] The electronic controller 104 is electronically coupled to the electric motors 310, 320, 330 to individually adjust their rotation speeds. The electronic coupling is achieved using a wired or a wireless connection. The electronic controller 104 comprises at least one processor and memory with software instructions for the processor stored thereon. The memory may also comprise stored data of previous movements and behaviours of the boat (from sea trials, but also general use) in certain conditions e.g. wind, weight and power settings.

[0208] The electronic controller receives a user input directed at moving the watercraft 100 to a desired speed or position, from a user input device at the helm of the watercraft 100 or at a control center remote from the ship. The user input device is implemented as a joystick or a touchscreen, but may also be adapted to receive instructions from a different program responsible for automated or autonomous docking.

[0209] In the depicted embodiment, the electronic controller device consists of a single electronic controller 104 in the bow section 102b of the watercraft 102, for example at a helm, whereas the propulsion units 110, 120, 130 are arranged in a stern section 102s. In alternative embodiments, the electronic controller 104 is arranged in the stern section 102s near the propulsion units 110, 120, 130. According to embodiments, the electronic controller device is a distributed system, with one electronic controller 104 comprised in or arranged in a vicinity of each of the propulsion units 110, 120, 130 and optionally with one or several central electronic controllers 104 located on the watercraft 100 (for example at the helm(s)) or at the remote control center.

[0210] Via the electronic coupling, the electronic controller sends control signals to the propulsion units 110, 120, 130 to adjust the rotation speeds of their electric motors 310, 320, 330 and consequently of their propellers 112, 122, 132. The control signal for each propulsion unit 110, 120, 130 contains information about, and thereby adjusts, the rotation speed 114, 124, 134 of the electric motor 310, 320, 330 and consequently of the propeller 112, 122, 132 of the respective propulsion unit 110, 120, 130. The rotation speed is adjusted in terms of its direction (along/according to the forward 112f, 122f, 132f or the reverse direction of rotation 112r, 122r, 132r of the respective propeller 112, 122, 132). In addition, the control signals contain information about, and thereby control, the (absolute) values of the rotation speeds of the electric motors 310, 320, 330 and consequently of the propellers 112, 122, 132.

[0211] The propulsion units 110, 120, 130 receive the control signals via the electronic coupling, and the rotation speeds of the electric motors 310, 320, 330 and consequently the propellers 112, 122, 132 are adjusted accordingly. Therefore, the electric motors 310, 320, 330 are connected to ship batteries via pulse inverters. The pulse inverters generate an AC voltage and current to drive the electric motors 310, 320, 330 from the typically DC output of the ship batteries. In some embodiments, the pulse inverters are comprised in the propulsion units and optimized for the electric motors 310, 320, 330, but they may, in principle, be provided separately. The rotation speeds of the electric motors 310, 320, 330 and consequently the propellers 112, 122, 132 are adjusted by controlling the (output of the) pulse inverters according to the control signals from the electronic controller 104.

[0212] The propulsion units 110, 120, 130 provide a sufficient mechanical power to propel the watercraft 102 forward over long distances at cruising speed. For this purpose, at least one, and typically all, the electric motors 310, 320, 330 are operated to drive the propellers 112, 122, 132 according to their respective forward directions of rotation 112f, 122f, 132f.

[0213] Referring to Fig. 1a and Fig. 1b, the directions of the rotation speeds 114, 124, 134 (as set by the control signals from electronic controller 104) are along the forward direction of rotation 112f for the first propeller 112 and along the reverse directions of rotation 122f, 132f for the second and third propeller 122, 132. Consequently, the first propeller 112 generates a forward thrust 116f. The second propeller 122 generates a reverse thrust 106r. The third propeller 132 enhances the reverse thrust 106r.

[0214] In this description, the arrows 106f, 106r refer to the thrust onto the watercraft 102. In other words, they refer to the direction of movement that the respective propulsion unit 110, 120, 130 would drive the (center of mass of the) watercraft to if it were operated in the absence of the other propulsion units 110, 120, 130. The flow of water induced by the rotation of the propellers 112, 122, 132 is not depicted in Fig. 1a, Fig. 1b, Fig. 1c. If depicted, it would on average be directed mainly along a direction opposite to the one of the thrust 106f, 106r, 108.

[0215] According to the embodiment depicted in Fig. 1a, Fig. 1b, the forward (or reverse) directions of rotation 112f, 122f, 132f of the propellers 112, 122, 132 are electronically stored in the respective propulsion units 110, 120, 130. When the propulsion unit 110 receives the signal from the electronic controller 104 to adjust the rotation speed 114 according to the forward direction 112f of the propeller 112, it sets the direction of rotation of the motor 310, and consequently of the propeller 112, accordingly. Similarly, when the propulsion units 120, 130 receive the signals from the electronic controller 104 to adjust the rotation speeds 124, 134 according to the reverse direction 122r, 132r of the propellers 122, 132, they set the directions of rotation of the motors 320, 330, and consequently of the propellers 122, 132, accordingly. If a forward direction of rotation of one of the propellers 112, 122, 132 changes, for example upon replacing the propeller with a different one with an opposite forward direction of rotation, the new forward direction of rotation is electronically stored in the respective propulsion unit.

[0216] In alternative embodiments, the forward (or reverse) directions of rotation 112f, 122f, 132f of the propellers 112, 122, 132 and/or associated directions of the motors 310, 320, 330 are electronically stored in the electronic controller 104. For this purpose, they are manually input into the electronic controller 104 by a user, or the propulsion units 110, 120, 130 electronically register the forward (or reverse) directions of rotation 112f, 122f, 132f of their propellers 112, 122, 132 and/or the associated directions of the motors 310, 320, 330 with the electronic controller 104. In corresponding embodiments, the control signal from the electronic controller 104 to the propulsion units 110, 120, 130 contains concrete information about the (absolute) direction of rotation of the motors 310, 320, 330 and/or the propellers 112, 122, 132. The electronic registration may take place automatically upon establishing the electronic coupling between electronic controller 104 and propulsion units 110, 120, 130.

[0217] In addition to producing the forward or reverse thrust 106f, 106r, the rotation of the propellers 112, 122, 132 produces a transverse thrust 108. The transverse thrust 108 results from the direction of rotation 114, 124, 134 of the propeller 112, 122, 132 (clockwise or counterclockwise) and/or from its arrangement relative to the hull of the watercraft 102.

[0218] The transverse thrust 108 resulting from the direction of rotation 114, 124, 134 of the propeller 112, 122, 132 is also referred to as propeller walk. It occurs both for a rotation along the forward 112f, 122f, 132f and the reverse direction 112r, 122r, 132r. Its direction depends on the (absolute) rotation direction of the propeller 112, 122, 132, which may be clockwise or counterclockwise. For example, in case of a surface drive, wherein above planing speed only the lower halves of the propellers 112, 122, 132 are submerged in the surrounding body of water, the rotation 124 of the propeller 122 along its counterclockwise reverse direction 122r (as seen from stern, see Fig. 1b) induces a starboard flow of water and a portside force onto the propulsion unit 120 (and onto the watercraft 102). The directions of the flow and of the transverse force 108 are reversed when the direction of rotation of the propeller 122 is reversed (e. g. by replacing the propeller 122 of Fig. 1b with its clockwise forward direction of rotation 122f with a propeller having a clockwise reverse direction of rotation and driving this new propeller according to its clockwise reverse direction of rotation).

[0219] In addition, when the propellers 112, 122, 132 are operated according to their reverse directions of rotation 112r, 122r, 132r, they flow water against the hull of the watercraft 102. This flow of water transfers part of its momentum (and its angular momentum) onto the hull, thus generating a transverse force onto the watercraft 102 and the propulsion units 110, 120, 130. This transverse force also depends on the direction of rotation (clockwise or counterclockwise) of each of the propellers 112, 122, 132. According to the example depicted in Fig. 1a, Fig. 1b, and Fig. 1c, the propellers 112, 122, 132 (in particular, the propellers 124, 134 located off the centerline of the watercraft 102, thereby typically producing major contributions to the transverse thrust 108) all rotate in the same (counterclockwise) direction 114, 124, 134, resulting in the transverse thrust 108.

[0220] The magnitude of the transverse thrust 108 produced by any of the propellers 110, 120, 130, for example propeller 120, is typically significantly smaller than the magnitude of the forward thrust 106f (or the reverse thrust 106r) produced by the same propeller. Therefore, the overall thrust produced the exemplary propeller 122, which may be expressed as the vector sum of its reverse thrust 106r and its transverse thrust 108, is directed mainly along the longitudinal direction. This situation is drastically different from the one of a propeller with a rotatable axis orientation, e. g. due to rotating (around a vertical axis) an outboard motor, a pod of a pod drive, or a rotary shaft of a z-drive, or to the situation of a jet drive with a moveable flap, bucket, and/or nozzle aft the propeller to deflect the thrust by a large angle. Conventional methods exist for providing an essentially transverse thrust for a transverse movement of the watercraft using propellers with rotatable axes orientation or a jet drive. In contrast, providing the essentially transverse thrust for the transverse movement using propellers with fixed axis orientations has so far been a challenge.

[0221] According to the depicted embodiment, the transverse thrust 108 is directed to the portside direction, resulting in a movement of the watercraft 102 into this direction. To drive the watercraft 102 to the opposite (starboard) direction, the directions of rotation 114, 124, 134 of all the propellers 112, 122, 132 are reversed. This is easily achieved due to the use of the electric motors 310, 320, 330, without a need for a clutch or an additional gearset.

[0222] Similarly, the direction of the transverse thrust 108 maybe reversed in any of the embodiments described below by reversing the directions of rotation 114, 124, 134 of all the propellers 112, 122, 132. In embodiments with rudders, the angles of attack of the rudders are reversed accordingly.

[0223] The propulsion and steering system 100 combines the electric motors 310, 320, 330 and the electronic controller 104 to improve control over the rotation speeds of the propellers 112, 122, 132 (both in terms of direction and in terms of their absolute values) and thus over the thrusts io6f, io6r, 108.

[0224] The rotational speeds of the electric motors 310, 320, 330 can be controlled over continuous ranges starting from zero. This is an advantage over conventional combustion engines, which require a non-zero minimum idle (rotation) speed to maintain operation. The electric motors 310, 320, 330 can inherently be controlled (e. g., driven by the pulse inverter) from their forward directions of rotation 112f, 122f, 132f to their reverse directions of rotation 112r, 122r, 132f, without adjusting or requiring additional, external mechanical components such as a clutch or a gear set. Consequently, the rotation speed of any of the propellers 112, 122, 132 may smoothly and continuously be varied, e. g. from 1000 rounds per minute (rpm) to 50 rpm along the forward direction of rotation 112f, 122f, 132f and to 0 rpm, and from there to 50 rpm and to 1000 rpm along the reverse directions of rotation 112r, 122r, 132f, and may be kept at any of those rotation speeds or any rotational speed in between for an extended amount of time. In an embodiment with a conventional combustion engine, this would typically not be possible without stalling the engine and/or moving a clutch.

[0225] In addition, the rotational speeds of the propellers 112, 122, 132 driven by the electric motors 310, 320, 330 can be adjusted or controlled to a desired speed much more quickly than rotational speeds of propellers driven by conventional combustion engines providing the same mechanical power as the electric motors 310, 320, 330. This is, in part, due to the smaller mass and inertia of the moving parts of the electric motors 310, 320, 330, which permits to change their rotational speeds faster. In addition, the electronic controller 104 addresses the electric motors 310, 320, 330 in a fully electronic way (e. g. via a pulse inverter), without a need for an intermediate electromechanical actuator to convert the electronic signal from the electronic controller 104 into a mechanical movement. In contrast, in a conventional combustion engine, an electromechanical actuator is typically used to convert an electronic signal into a mechanical movement controlling the rotation speed (or mechanical power) of the engine and the propellers, such as a flow valve controlling a flow of fuel.

[0226] The electronic controller 104 performs a fast (e. g., at a rate of 100 Hz, 200 Hz, or 500 Hz) analysis of the actual thrusts 106f, 106r, 108 or of the actual rotation speeds of the electric motors 310, 320, 330. At this fast rate, the electronic controller 104 determines whether the total longitudinal thrust is actually balanced (i. e., smaller or much smaller than the transverse thrust 108) and accordingly re-adjusts the rotation speeds of the electric motors 310, 320, 330 and thus of the propellers 112, 122, 132 to achieve the balancing.

[0227] According to the embodiment depicted in Fig. 1a, Fig. 1b, Fig. 1c, the total longitudinal thrust may be expressed as the sum over the forward thrust 106f and the reverse thrust 106r. In alternative embodiments, however, the total longitudinal thrust also includes the effect of external forces such as wind or waves. In addition, the transverse thrust 108, in some embodiments, includes the effect of external forces such as a print or waves.

[0228] The fast analysis of the actual thrusts 106f, 106r, 108 and readjustment of the rotational speeds of the propellers 112, 122, 132 by the electronic controller 104, in combination with the fast control capability of the electric motors 310, 320, 330 thus allows the system 100 to precisely balance the longitudinal thrust (e. g., to compensate the forward thrust 106f and the reverse thrust 106r), such that the transverse thrust 108 exceeds the remaining total thrust along the longitudinal direction. An essentially transverse movement is thus achieved. Indeed, the system 100 is capable of balancing the longitudinal thrust to a value 20 times smaller than the transverse thrust 108, ensuring that the watercraft 102 performs a practically purely transverse movement.

[0229] According to various embodiments, the controller 104 further determines whether the electric steering and propulsion system 100 (e. g. a sensor at or connected to the controller 104 or one of the propulsion units 110, 120, 130) and thus the watercraft 102 is overall rotating (around a vertical axis). When a transverse movement without an overall rotation is desired by a user, the electronic controller 104 adjusts the rotation speeds 114, 124, 134 of the electric motors 310, 320, 330 to minimize or fully avoid the overall rotation. In particular, the electronic controller 104 introduces an asymmetry between the rotational speeds 124, 134 of the electric motors 320, 330 rotating according to their reverse directions 122r, 132r. In other words, the electronic controller 104 adjusts the rotation speeds 124, 134 of the electric motors 320, 330 such that one of them 320 produces a larger thrust 106r than the other. This generates a torque onto the ship, which is used to compensate other torques on to the ship and control an overall torque to essentially zero, while the two electric motors 320, 330 provide the forward thrust to balance the longitudinal thrust.

[0230] Fig. 2a depicts a propulsion and steering system 100 according to a second embodiment. This second embodiment is similar to the one of Fig. 1a, Fig. 1b, and Fig. 1c, but, in addition, the propulsion units 110, 120, 130 comprise a housing 202 with a connection surface 200 to define the axis orientation of the propeller 112, 122, 132 relative to the watercraft.

[0231] A (any) propulsion unit 110, 120, 130 of the propulsion and steering system 100 of Fig. 2a is optimized for providing a stern drive or a surface drive. Therefore its connection surface 200 is arranged on the housing 200 opposite to the propeller 112, 122, 132. The connection surface 200 is optimized for being mounted to a transom at the stern 102s of the watercraft. Therefore, the connection surface 200 is arranged essentially along a vertical direction.

[0232] The housing 200 of the propulsion unit 110, 120, 130 has a top surface defining a horizontal plane. The connection surface 200 for arrangement along the vertical direction v is essentially perpendicular to the horizontal plane related to the upper surface of the housing 200.

[0233] The propulsion units 110, 120, 130 of the embodiment of Fig. 2a facilitate a modular propulsion and steering system 100. For this purpose, the connection surface 200 provides means for quick and simple mounting to/dismounting from the hull, for example via a screw or bolt connection.

[0234] Each of the propulsion units 110, 120, 130 may have a similar housing 202 and a similar connection plane 200, such that the housings 202 and connection surfaces 200 define a similar (i. e. parallel) axis orientation of the propellers 112, 122, 132.

[0235] As a consequence, the propulsion units 110, 120, 130 are interchangeable. A single type of propulsion units 110, 120, 130 may be produced for the propulsion system and steering 100, reducing the cost of fabrication.

[0236] Using a single type of propulsion units 110, 120, 130 also facilitates quick and efficient installation and replacement. For example, when a propulsion unit 110, 120, 130 fails, a replacement part may be ordered and quickly delivered from a central facility storing replacement propulsion units 110, 120, 130 of this (single) type.

[0237] In preferred embodiments, the propulsion units 110, 120, 130 are monolithic units in a sense that they can be mounted to or dismounted from the hull of the watercraft 102 as a hole, using the connection plane 200. In such embodiments, the propulsion unit with the failure may be replaced by the quickly delivered replacement part particularly quickly and easily, making use of the screw or bolt connection of the connection plane 200. Expert knowledge of (marine) propulsion units is not required for performing the replacement.

[0238] Fig. 2b depicts a propulsion and steering system 100 according to an embodiment similar to the one of Fig. 2a.

[0239] According to the embodiment of Fig. 2b, the connection surface 200 defines the axis orientation of the propeller 112, 122, 132 essentially parallel (at an angle of <10°) to the connection surface 200. A corresponding embodiment may be particularly attractive for establishing a sail drive.

[0240] The connection surface 200 is adapted to be mounted to the bottom of the hull, and thus essentially coincides with a horizontal plane h. In other words, it is essentially perpendicular to the vertical direction v.

[0241] According to the embodiment depicted in Fig. 2b, the housing 202 and the propeller 112, 122, 132 form a modular unit. Corresponding modular units of the propulsion and steering system 100 are interchangeable, with the advantages laid out above in the context of the embodiment of Fig. 2a.

[0242] Propulsion and steering systems 100 of any of the other embodiments may be provided with a housing 202 and/or a connection surface 200 as described in the context of Fig. 2a and Fig. 2b.

[0243] Fig. 3 depicts a propulsion and steering system 100 according to an embodiment similar to the one of Fig. 1a, Fig. 1b, and Fig. 1c. However, several modifications will be described for the propulsion and steering system 100 of Fig. 3. According to alternative embodiments, propulsion and steering systems 100 comprises any single one or any combination of these modifications.

[0244] Fig. 3 depicts a propulsion and steering system 100 for a trimaran 102. For this purpose, the propulsion units 110, 120, 130 are mounted to a center hull 302, a portside hull 304, and to a starboard hull 306 of the trimaran. Such a distribution of the propulsion units 110, 120, 130 makes best possible use of the limited space available in and on the individual hulls 302, 304, 306 of the trimaran 102.

[0245] The propellers 112, 122, 132 are rotationally coupled to the electric motors 310, 320, 330 via (rotational and/or torque) transmissions 312, 322, 332. Therefore, the propellers 112, 122, 132 are rotationally coupled to propeller (rotary) shafts 312a, 322a, 332a. The propeller shafts 312a, 322a, 332a are rotationally coupled to gearboxes 312b, 322b, 332b, which in turn are rotationally coupled to the electric motors 310, 320, 330 via motor (rotary) shafts 312c, 322c, 332c. According to an alternative embodiment (not depicted), the propeller shafts 312a, 322a, 332a with the propellers 112, 122, 132 mounted thereto are directly rotationally coupled to the electric motors 310, 320, 330, without gearboxes 312b, 322b, 332b and motor shafts 312c, 322c, 332c distinct from the propeller shafts 312a, 322a, 332a.

[0246] The transmissions 312, 322, 332 with the gearboxes 312b, 322b, 332b permit to operate both the electric motors 310, 320, 330 and the propellers 112, 122, 132 at rotational speeds associated with their highest power efficiency, in particular at a power setting for providing the forward propulsion to operate the watercraft 102 at cruising speed.

[0247] For example, axial flux motors 310, 320, 330 have their highest power efficiency at revolution speeds of 1500 to 3500 rounds per minute. In embodiments, wherein the propulsion units 110, 120, 130 implement a surface drive, the surface drive typically has its highest power efficiency at rotational speeds of the propellers just slightly below the optimum ones of the axial flux motors 310, 320, 330. In such embodiments, the gearbox 312b, 322b, 332b may have a gear ratio between the rotational speed of the motor shaft 312c, 322c per rotational speed of the propeller shaft 312a, 322a, 332a of around 1.2. However, the gear ratio may be optimized with respect to the electric motors 310, 320, 330 applied in the propulsion units 110, 120, 130 and the type of propulsion system to be implemented.

[0248] In various embodiments, the transmissions 312, 322, 332 are also used to implement a vertical offset between the axis of the electric motor 310, 320, 330 and the axis 112a, 122a, 132a of the propeller 112, 122, 132.

[0249] The propulsion units 110, 120, 130 are arranged such that their propeller shafts 312a, 322a, 332a (and their propellers 112, 122, 132) are intersected by a single vertical reference plane 308. The corresponding side-by-side arrangement of the propulsion units 110, 120, 130 provides a high-efficiency propulsion system, implementing, for example, a stern drive or a surface drive. In addition, it ensures that the forward 106f and reverse 106r thrusts generated by the propellers 122, 132 generate opposite torques that compensate each other to keep the watercraft 102 from rotating during the transverse movement.

[0250] The side-by-side arrangement on the vertical reference plane 308 is determined by the similar connection surfaces 200 of the propulsion units 110, 120, 130. More specifically, the connection surface 200 of each of the propulsion units 110, 120, 130 has the same relative orientation (e. g, essentially perpendicular) to the axis orientation 112a, 122a, 132a of the propeller 112, 122, 132 of the respective propulsion unit 110, 120, 130.

[0251] According to the embodiment of Fig. 3, the connection surfaces 200 are part of housings 202.

[0252] The housing 202 of each of the propulsion units 110, 120, 130 encloses the electric motor 310, 320, 330 and part of the transmission 312, 322, 332 in a waterproof way.

[0253] The housings 202 are configured for being mounted to or dismounted from the transom of the watercraft 102 as a whole. Therefore, a section of the housing 202 containing the electric motor 310, 320, 330 is inserted into the transom from the aft direction. An aft section of the housing 202 is wider than the section with the electric motor 310, 320, 330 and encompasses part of the propeller shaft 312a, 322a, 332a. The connection surface 200 is formed at the boundary between the section with the electric motor 310, 320, 330 and the wider section, determining how far the housing 202 is inserted into the transom. After inserting the housing 202 to this point, the connection surface 200 is fixed to the transom using a screw or bolt connection. Consequently, the propulsion units 110, 120, 130 represent monolithic, integrated, modular units in a sense that they can be easily connected, replaced, and be exchanged for one another. The steering and propulsion system 100 of Fig. 3 comprises a rudder 314, 324, 334 sidewards of each of the propellers 112, 122, 132. More specifically, a portside rudder 314p, 324p, 334p is provided portside of each of the propellers 112, 122, 132 and a starboard rudder 314s, 324s, 334s is provided starboard of each of the propellers 112, 122, 132. However, in alternative embodiments (not depicted), only one rudder is provided for each propeller 112, 122, 132, arranged starboard or portside of the propeller.

[0254] The arrangement of the rudders 314, 324, 334 sidewards of the propellers 112, 122, 132 minimizes the drag produced by the rudders 314, 324, 334 when the propellers 112, 122, 132 are driven according to the forward directions 112f, 122f, 132f to promote forward propulsion of the watercraft 102, for example at cruising speed. In particular, parts aft of the propellers 112, 122, 132 are avoided which may otherwise increase the drag and reduce the power efficiency of the system 100.

[0255] The electronic controller 104 is electronically coupled to the propulsion units 110, 120, 130 to adjust the angles of attack of the rudders 314, 324, 334. Therefore, the electronic controller 104 sends a signal with information regarding a set angle of attack to the propulsion units 110, 120, 130. The propulsion units 110, 120, 130 receive the signal, and the angle of attack of its rudder is adjusted accordingly.

[0256] More specifically, the propulsion units 110, 120, 130 comprise electromechanical rudder actuators (not depicted) which exert a mechanical force onto the rudders 314, 324, 334 to adjust them to the set angles of attack, in response to the signal received from the electronic controller 104.

[0257] According to the embodiment depicted in Fig. 3, the rotation speed 114 of the propeller 112 is adjusted according to its forward direction 112f, and the rotation speed 124, 134 of the propellers 122, 132 are adjusted according to their reverse directions 122r, 132r to generate the transverse thrust 108 exceeding the total longitudinal thrust. Directions (of the angles of attack) of the rudders 314, 324, 334 are set to generate (or enhance) the transverse thrust 108. Therefore, the direction of the rudder 314 associated with the propeller 112 rotating according to its forward direction 112f is opposite to the direction of the rudders 324, 334 associated with the propellers 122, 132 rotating according to their reverse directions 122r, 132r.

[0258] For example, and according to embodiment depicted in Fig.3, the rudder 314 associated with the propeller 112 rotating 114 forward 112f is adjusted to direct the aft flow of water generated by the propeller 112 starboard, thus generating a portside thrust 108 onto the propulsion unit 110 and the watercraft 102. The rudders 324, 334 associated with the propellers 122, 132 rotating 124, 134 according to their reverse directions 124r, 134r are adjusted to direct the forward flow of water generated by the propellers 122, 132 starboard, also generating a portside thrust 108 onto the propulsion units 120, 130 and the watercraft 102. The portside thrust 108 generated by the propulsion units 110, 120, 130 adds up and is used to induce the transverse movement of the watercraft 102.

[0259] An asymmetry (or difference, respectively) is introduced between the rotation speeds 124, 134 of the propellers 122, 132 rotating along the reverse-direction 122r, 132r to minimize or avoid an overall rotation of the watercraft if requested by the user, as describe in the context of the embodiment of Fig. 1a, Fig. 1b, and Fig. 1c.

[0260] The angle of attack of each rudder 314s, 314p, 324s, 324p, 334s, 334p is adjusted individually, to a value which may differ from the angles of attack of the other rudders 314s, 314p, 324s, 324p, 334s, 334p. In alternative embodiments, a (or any) pair of rudders 314s, 314p; 324s, 324p; 334s, 334p associated with the same propeller 112, 122, 132 is adjusted to the same angle tech, for example the rudders 314s, 314p associated with the propeller 112.

[0261] Similar to adjusting the rotation speeds 114, 124, 134 of the electric motors 310, 320, 330, the electronic controller 104 adjusts the angles of attack of the rudders 314, 324, 334 to facilitate a transverse movement of the system 100 and the watercraft 102. In particular, the electronic controller 104 determines whether the electric steering and propulsion system 100 and thus the watercraft 102 is overall rotating. Similar to controlling the rotation speeds 124, 134 of the propellers 122, 132 as described above in the context of Fig. 1a, Fig. 1b, Fig. 1c, the electronic controller 104 adjusts the angles of attack of the rudders 324, 334 for the propellers 122, 132 individually and asymmetrically to keep the overall torque onto the propulsion system 100 and thus the watercraft 102 balanced. In other words, the angle(s) of attack of the rudder(s) 324 may be adjusted to a different value(s) (while maintaining the same direction) as the angle(s) of attack of the rudder(s) 334 to minimize the overall rotation of the system 100 and the watercraft 102 when a purely transverse movement is requested by the user.

[0262] Fig. 4 depicts a propulsion and steering system 100 according to an embodiment similar to the one of Fig. 3. However, several modifications will be described for the propulsion and steering system 100 of Fig. 4. Propulsion and steering systems 100 according to alternative embodiments comprise any single one or any combination of these modifications.

[0263] Fig. 4 depicts a propulsion and steering system 100 for a catamaran 102. For this purpose, two of the propulsion units 110, 120, 130 are mounted to a portside hull 304, and two are mounted to a starboard hull 306 of the catamaran. Such a distribution of the propulsion units 110, 120, 130 makes best possible use of the limited space available in and on the individual hulls 302, 304, 306 of the catamaran 102.

[0264] According to the embodiment of Fig. 4, one rudder 314, 324, 334 is provided for each propeller 112, 122, 132, arranged starboard or portside of the propeller 112, 122, 132. In alternative embodiments (not depicted), a pair of rudders is provided for each propeller 112, 122, 132, arranged starboard and portside of the propeller 112, 122, 132.

[0265] According to the embodiment depicted in Fig. 4, propellers 112 of the two propulsion units 110 are adjusted to rotate 114 according to their respective forwards directions of rotation 112f. In other words, the plurality of propellers 112 acts as the forward-rotating 114, 112f propeller 112 to provide the forward thrust 106f.

[0266] According to alternative embodiments (not depicted), additional propellers or propulsion units are provided and comprised in the propulsion and steering system 100. In particular, an additional propeller or propulsion unit may act together with the propeller 122 or the propeller 132 to provide the reverse thrust 106r, forming with the respective propeller 122, 132 a plurality of (second or third) propellers to provide the reverse thrust 106r.

[0267] Fig. 5 depicts a propulsion and steering system 100 according to an embodiment similar to the one of Fig. 1a, Fig. 1b, Fig. 1c, Fig. 3 and Fig. 4. However, several modifications will be described for the propulsion and steering system 100 of Fig. 5. Propulsion and steering systems 100 according to alternative embodiments comprise any single one or any combination of these modifications.

[0268] Fig. 5 depicts a propulsion and steering system 100 for a monohull watercraft 102. In other words, the propulsion units 110, 120, 130 are mounted to the single hull in a side-by-side arrangement. A single vertical reference line (not shown, parallel to the plane of the figure) intersects the propellers 112, 122, 132 and the propeller shafts (not shown) of the propulsion units 110, 120, 130 perpendicular to the axis orientations 112a, 122a, 132a or centerline of the monohull watercraft 102.

[0269] The propulsion units 110, 120, 130, for example their respective propellers 112, 122, 132, are arranged at different positions along the vertical direction. Propulsion units 110 (e. g., their propellers 112) closer to the centerline of the watercraft 102 are arranged at a lower vertical position than propulsion units 120, 130 (e. g., their propellers 122, 132) arranged further away from the centerline. The propulsion units 120, 130 (e. g., their propellers 122, 132) arranged starboard and portside at essentially the same distance from the centerline of the watercraft 102 are arranged at essentially the same vertical position.

[0270] This way, the vertical arrangement of the propulsion units 110, 120, 130 follows the shape of the (lower edge of the) hull of the watercraft 102. The arrangement is particularly beneficial for establishing a surface drive. When a watercraft 102 with a surface drive planes, the resulting dynamical waterline essentially forms along the lower edge of the hull of the watercraft. Consequently, the arrangement of the propulsion units 110, 120, 130 of the depicted embodiment is along the dynamical waterline, such that all the propulsion units 110, 120, 130 contribute to the surface drive.

[0271] The difference in the vertical positions of the propellers 112, 122, 132 is smaller than the diameter of the propellers 112, 122, 132. In other words, a single horizontal reference line intersects the propellers 112, 122, 132.

[0272] The propulsion units 110, 120, 130, of the propulsion and steering systems 100 according to Fig. 3 and Fig. 4 may similarly be arranged at different positions along the vertical direction. However, when the propulsion and steering system 100 is installed on the multihull watercraft, the difference between the vertical positions of any two of the propellers is smaller than the radius of the respective propellers.

[0273] Fig. 6a, Fig. 6b, and Fig. 6c show a propulsion unit 110 according to an embodiment. The description and the reference numerals refer to the propulsion unit 110 of Fig. 6a, Fig. 6b, and Fig. 6c as the first propulsion unit 110 (i. e., with the forward rotating propeller 112). However, the second and/or third propulsion units 120, 130 (i. e., with the reverse rotating propellers 122, 132) are formed similarly.

[0274] The propulsion system 110 forms a monolithic unit comprising the electric motors 310 and the transmission 312 coupled to the electric motor 310, as well as a pulse inverter 610 providing an electrical supply power to the electric motor 310. The monolithic design of the propulsion unit 110 allows for equipping a watercraft 102 with the propulsion unit 110 in a few simple steps.

[0275] The propeller shaft 312a comprises a propeller coupling 312p for mounting the propeller 112. The propulsion unit 110 (more specifically, the transmission 312) includes any mechanical component required to couple the propeller shaft 312a, or the propeller coupling 312p, and the propeller 112 rotationally to the electric motor 310.

[0276] The transmission 312 with the gearbox 312b serves to match the highest-efficiency rotation speed of the motor shaft 312c to the highest-efficiency rotation speed of the propeller 112. The highest efficiency rotation speed of the motor shaft 312c refers to the rotation speed of the motor shaft 312c, at which the overall electrical power to mechanical power conversion efficiency of the electric motor 310 is maximum. Mechanical power refers to the mechanical power generated at the motor shaft 312c due to its rotational movement. The electrical power refers to an input power provided to the pulse inverter 118 via a power inlet 612 of the pulse inverter from an external current source, such as a battery.

[0277] The propulsion system 110 further comprises a thrust bearing 616. The thrust bearing 616 transfers the force (propulsion, thrust) generated by the rotation of the propeller 112 onto the housing 202, thereby generating a propulsion 202 of the housing and ultimately of the watercraft 102. Therefore, the thrust bearing 616 is connected to the transmission 312 and to the housing 202 to couple the two rotationally, i. e. its inner ring is rigidly connected to the propeller shaft 312a and its outer ring is rigidly connected to the housing 202.

[0278] The components of the propulsion unit 110 i. e. the electric motor 310, the inverter 610, the transmission 312, and the thrust bearing 616 are fully optimized with respect to each other. Therefore, by equipping his or her watercraft with the propulsion unit 110, a user installs a high-power, high-efficiency system for an optimized range of the watercraft. No further selection of additional components and no corresponding expert knowledge is required, and the risk of losing efficiency or range is eliminated.

[0279] Moreover, the integrated (monolithic) design allows for replacing the propulsion unit 110 as a whole quickly and easily in case of a failure of one of the components, i. e. with all essential components mounted in their respective locations for operation. The defective component may be diagnosed and replaced later, for example in a dedicated facility, as the watercraft with the replaced propulsion system is already back in operation. The housing 202 may be mechanically sealed or locked to prevent a user from opening it and to permit access only in a controlled environment, such as a maintenance and repair facility.

[0280] The electric motor 310 is an axial flux motor. Axial flux motors are particularly light-weight and compact, for example compared to radial flux motors. Therefore, the use of an axial flux motor renders the installation and exchange of the integrated propulsion system 100 as a hole more manageable and secure. Depending on the embodiment, the electric motor 310 provides a mechanical power of 100 kW or 200 kW. The axial flux motor 102 adapted to provide the mechanical power of 100 kW has a weight of 25 kg, and the axial flux motor 102 adapted to provide the mechanical power of 200 kW has a weight of 50 kg.

[0281] The housing 202 protects the components it surrounds from external influences, such as seawater or weather conditions, in particular on the watercraft. On the other hand, the housing 202 protects a user from electrical hazards related to the electric motor 310, in particular on the inside of the hull of the watercraft 102. For this purpose, the housing 202 comprises a layer of insulating material or a layer of grounded, conductive material.

[0282] Moreover, the housing 202 provides an acoustic shielding for the motor 310 and an enclosed section of the transmission 312, and reduces noise on board emerging from those components.

[0283] The propulsion unit 110 is compatible with various boat drive layouts such as a fixed-shaft drive, a sail drive for a sailing boat, a stern drive, or a surface drive. In preferred embodiments, the propulsion unit 110 pierces through the transom of the watercraft 102 and is arranged part inside, part outside of the watercraft 102.

[0284] The propulsion unit 110 further comprises a heat exchanger 620.

[0285] The heat exchanger 620 is thermally coupled via its secondary side to any component of the propulsion unit 110 requiring cooling, in particular the electric motor 310, but also to the pulse inverter 610, the transmission 312 and the thrust bearing 616. The secondary side of the heat exchanger comprises cooling channels filled with a coolant and connecting the heat exchanger 620 to the respective components. The coolant has an optimized composition and comprises a sufficient amount of glycol to prevent freezing in any relevant situation. The heat exchanger 620 further comprises a coolant pump (not shown) to generate a flow of the coolant in the channels of its secondary side.

[0286] The secondary side of the heat exchanger 620 further provides two openings 624, namely an outlet and an inlet for coolant to an external device, such as a battery or a cabin. If not required, the openings 624 are bridged.

[0287] A primary side of the heat exchanger 620 connects to openings 622 outside the housing 202. In operation, the openings 622 are either directly exposed to a body of water surrounding the watercraft and take up water as a coolant therefrom. Alternatively, the openings 622 are connected to the surrounding body of water using additional external tubing, for example through a feedthrough in the hull of the watercraft 102. A coolant pump (not shown) may be provided to ensure a sufficient flow of water at the primary side of the heat exchanger 622.

[0288] The propulsion unit 110 is preferably mounted to a transom of a watercraft 102.

[0289] The housing 202 of the propulsion unit 110 comprises a fore (motor) section 202a wherein the motor is arranged and an aft (transmission) section 202b wherein a section of the transmission 312 is arranged. The transmission section 202b has a larger width than the motor section 202a. The widths refer to widths of the respective cross sections of the housing 202, for example in planes perpendicular to the longitudinal direction of the propulsion unit 110 intersecting the housing 202 at different positions along the longitudinal direction.

[0290] The fore (motor) section 202a is located directly fore of the aft (transmission) section 202b and its cross section is completely comprised in a fore projection of the aft (transmission) section 108b.

[0291] For mounting the propulsion unit 110 to the transom of the watercraft 102, it is inserted through an opening in the transom, such that the motor section 202a is taken up completely by the watercraft 102, whereas the transmission section 202b serves as a stopper to define the depth to which the propulsion unit 110 is introduced. A portion of the transmission section 202b remains outside of the watercraft 102. A seal (not shown) between the housing 202 and the hull ensures a waterproof connection.

[0292] Thus, an ideal geometry is realized for a surface drive, with the propeller 112 aft of the transom and the entire hull. The surface drive is particularly energy efficient for high speeds exceeding 20 kn, making the system 100 particularly attractive for high-speed, electrically driven watercraft. The high efficiency of the surface drive helps to make best possible use of the charge capacity of the battery and to improve the range of the high-speed, electrically driven watercraft.

[0293] To further optimize the propulsion unit 110 for this purpose, it is designed with a linear arrangement along its longitudinal direction (i. e., the direction along which it pierces through the transom). In other words, the electric motor 310, the transmission 312 (e. g, the gearbox 312b, and the motor shaft 312c and/or the propeller shaft 312a) and the propeller 112 are all intersected by a single line extending along the longitudinal direction.

[0294] A connecting frame 600 is optionally provided for placement and connection between the propulsion unit 110 and the hull. The connecting frame 600 is first mounted to the watercraft 102, and thereafter the propulsion unit 110 is mounted to the connecting frame 600.

[0295] The connecting frame 600 comprises a first ring-shaped element 604 for the inside of the hull and second ring-shaped element 602 for the outside of the hull.

[0296] Threaded holes 606 of the first ring-shaped element 604 and slightly larger through holes of the second ring-shaped element 602 facilitate a connection between the two. Through holes similar to the ones of the first ring-shaped element are formed in the hull. Connecting the ring-shaped elements 602, 604 with bolts clamps them together and to the hull, and sealing rings (not shown) between the ring-shaped elements 602, 604 and the hull establish a waterproof connection between the connecting frame 600, 602, 604 and the hull.

[0297] The propulsion unit 110 comprises through holes formed on the connection surface 200.

[0298] The ring-shaped elements 602, 604 further comprise through holes and threaded holes 608, which serve to establish a detachable connection of the propulsion unit 110. The arrangements of both the through holes and the threaded holes correspond to the arrangement of the through holes of the connection surface 200. Therefore, inserting bolts from the aft direction through the through holes of the connection surface 200 through the second ring-shaped element 602 and tightening them to the threaded holes 608 of the first ring-shaped element 604 connects the propulsion unit 110 to the hull. A sealing ring (not shown) between the connection surface 200 and the second ring-shaped element 602 ensures a waterproof connection between the two.

[0299] A corresponding connection using a connecting frame 600 is optionally also applied in any of the other embodiments. It ensures a reliably detachable connection between the propulsion units 110 and the watercraft 102, without any risk of touching or damaging the watercraft 102, in particular its hull, in the process of attaching or detaching the propulsion unit 110 from or to the watercraft 102.

[0300] The connecting frame 600 further permits to install and remove the propulsion unit 110 from outside of the watercraft using a detachable connection, thus avoiding any need to work inside the typically narrow inside space of the watercraft, or its hull, respectively.

[0301] The thrust bearing 616 provides a waterproof connection between the housing 200 and the propeller shaft 312a, and therefore forms a section of the waterproof housing 200.

[0302] The gearing mechanism 312b provides an offset, or a displacement, respectively, between the motor shaft 312c and the propeller shaft 312a along a direction perpendicular to their respective axes. The offset is implemented by using a spur gear in the gearing mechanism 302b, alone or in combination with a planetary gear. The offset improves the design flexibility of the propulsion unit 110. In particular, it helps to lower the propeller 112 to the water line of the watercraft.

[0303] The propulsion unit uses two axial flux motors 310. An electric supply power is provided to the axial flux motors 310 by the pulse inverter 610. The pulse inverter 610 receives its input power from a power inlet 612 fed through the housing 202 in a waterproof manner to connect to a battery located outside of the housing 202. When the propulsion unit 110 is mounted to the watercraft, the power inlet 612 is located inside the watercraft 102 and accessible there.

[0304] A watercraft battery providing a DC voltage may be connected to the power inlet 612. The pulse inverter 610 generates the AC electrical supply current for the electric motors 310 from the DC voltage. The pulse inverter 610 is also coupled to a data line 614 to receive control commands and software updates, such as updates of parameters related to the operation of the pulse inverter 610.

[0305] The propulsion unit 110 according to the embodiment of Fig. 6a, Fig. 6b, and Fig. 6c further comprises a propeller 112 optimized for a surface drive.

[0306] Referring to Fig. 6c, which shows a stern projection of the propulsion unit 110, the propeller 112 comprises radial sections 632 extending away from the center (or shaft 312a, or axis 112a) of the propeller 112.

[0307] An essentially flat section 634 extends away from the radial section 632 along the azimuthal direction of the propeller 112 with an angle β of essentially 90° between the radial section 632 and an outer edge 636 of the essentially flat section 634.

[0308] According to alternative embodiments (not shown) the propulsion unit 110 comprises a single electric motor of 310 instead of two electric motors. Instead of the second electric motor, a corresponding propulsion unit 110 comprises a motor upgrade space to receive an additional engine, such as the second electric motor 310.

[0309] According to alternative embodiments (not depicted), the motor upgrade space houses a heat/combustion engine, thus implementing a hybrid drive (first electric motor 310 and heat/combustion engine). The hybrid drive, or the heat/combustion engine, respectively, may be used to extend the range of the propulsion system 100 or the watercraft 102 equipped therewith, for example by driving the propulsion system 100 or the watercraft 102 using the heat/combustion engine when the ship battery is exhausted (or getting exhausted), or by recharging the ship battery using mechanical power from the heat/combustion engine. In addition, the hybrid drive, or the heat/combustion engine, respectively, may be operated at cruising speed of the propulsion system 100, or of the watercraft 102, respectively, to increase the cruising speed or save the energy stored in the ship batteries.

[0310] Such an embodiment improves the design flexibility of the propulsion unit 110, making use of the applied axial flux motor 310. The geometry of the axial flux motor 310 beneficially permits to add or remove an electric motor and thus improves the design flexibility and the modularity of the propulsion unit 110. In such embodiments, all other components, in particular the pulse inverter 610 and the transmission 312, are provided for with specification in terms of electrical and mechanical power corresponding to the propulsion unit 110 with the maximum number of electric motors 310.

[0311] The propulsion unit 110 further comprises an electromechanical rudder actuator (not shown), and optionally a second electromechanical rudder actuator, which receive(s) signals from the electronic controller 104 via the data input connector 614. The rudder actuator(s) actuate(s) a starboard tiller arm and a portside tiller arm (not shown), thereby actuating a starboard rudder 314 and a portside rudder (not shown). In embodiments with a single rudder actuator, the single direct rudder actuator actuates a central tiller arm which, actuates the starboard tiller arm and the portside tiller arm together.

[0312] The propulsion unit 110 integrates the propulsion as such, and optionally also the steering for the watercraft 102. The entire unit 110 is provided as a monolithic and fully optimized system. Thus, it renders installation or replacement as easy as possible. Components are optimized for each other, improving the power efficiency of the system.

[0313] Figure 6d illustrates a transom 640 of a watercraft 102, prepared for connecting the propulsion unit 110 as a surface drive.

[0314] For connecting the propulsion unit 110 as a surface drive, an opening 642 is generated in the hull of the watercraft 102, typically in the lower region of the transom 640. An upper edge of the opening 642 is formed in a proximity of a static water line 644 of the hull, or of the watercraft 102 comprising the hull, respectively. The static water line 644 refers to the water line when the hull or watercraft is not moving.

[0315] Watercraft with a surface drive typically has a high cruising speed and a hull adapted for planing. When the watercraft moves at/above its planning speed, the transom 640 lifts up, resulting in a lower water line 646. The opening is formed with its lower edge 650 at the level of this lower, planing-speed water line 646.

[0316] Through holes 648 are formed around the opening 642 in an arrangement matching the arrangement of the through holes on the connection surface 200 of the propulsion unit 110, and/or of the through holes or the threaded holes of the connecting frame 600, respectively. The propulsion unit 110 may be connected to the watercraft 102 with the transom 640 by pushing bolts through the through holes 648 of the connection surface 200 and the transom 640 and screwing them into the threaded holes of the ring-shaped element 604 of the connecting frame 600.

[0317] When the propulsion unit 110 is connected to the transom 640 according to the embodiment of Fig. 6d, the propeller 112 (or its axis, respectively) is arranged in the proximity of the planing-speed water line 646. Above planning speed, part of the propeller 112 is below the planing-speed water line 646, whereas the remaining part of the propeller 112 is above the planing-speed water line 646, as is characteristic of a surface drive. However, with respect to the resting watercraft, propeller 112 is in a vicinity of the static water line 644 below the static water line 644, typically up to 10 or 20 cm below the static water line 644.

[0318] The surface drive may provide a high power efficiency, i. e. a strong forward propulsion per electric power supplied to the propulsion system, for example through the power inlet. This may improve the efficiency of an electric watercraft comprising the electrically driven propulsion system. In particular, a propeller 112 of a surface drive has an optimum revolution speed similar to a revolution speed of an electric motor 310 such as an axial flux motor 310. Installing the propulsion unit 110 as a surface drive therefore supports the use of a transmission 312 with a small gear ratio, which improves the energy efficiency and thus the range further.

[0319] Fig. 7 depicts a propulsion and steering system 100 according to an embodiment similar to the one of Fig. 3. However, several modifications will be described for the propulsion and steering system 100 of Fig. 7. Propulsion and steering systems 100 according to alternative embodiments comprise any single one or any combination of these modifications.

[0320] The system 100 of Fig. 7 comprises three propulsion units 110, 120, 130, which maybe similar to any of the previously described propulsion units (electric motors of the propulsion units 110, 120, 130 are not shown in Fig. 7).

[0321] The system 100 of Fig. 7 comprises a user input device 708 electrically coupled to the electronic controller 104.

[0322] The user input device 708 comprises, for example, a joystick or a touchscreen.

[0323] In case of a joystick, the user input device 708 receives a user input relating to a desired movement direction and speed of the watercraft 102 in the form of a direction and magnitude of a deflection of the joystick 708. The user deflects the joystick 708 along a first direction to induce a longitudinal movement of the watercraft 102. To induce a transverse movement of the watercraft 102, the user deflects the joystick 708 along a second direction perpendicular to the first direction. The deflections along the two directions may be combined to induce a diagonal movement. The magnitude of the deflection reflects the desired speed of the movement. The user device 708 sends an electronic signal to the electronic controller 104, reflecting the desired movement direction and speed of the watercraft 102.

[0324] In case of a touchscreen 708, the user may also input direction and speed of the desired movement. Alternatively, the user may input a target location, and optionally a target heading. The user device 708 sends an electronic signal to the electronic controller 104, reflecting the desired movement direction and speed of the watercraft 102, or alternatively the target location and optionally the target heading. Alternatively, the user device calculates a movement direction and speed of the watercraft 102 based on the target location (and the target heading), or a course with a series of calculated movement directions and speeds of the watercraft 102. The calculated movement or course is then sent to the electronic controller 104 as an electronic signal.

[0325] The electronic controller 104 receives the electronic signal from the user input device 708 and, based on direction and speed of the desired movement, calculates rotation speeds of the propellers 112, 122, 132 and optionally angles of attack of the rudders 314, 324, 334. If the electronic controller 104 receives a target location (and the target heading), it calculates the direction and speed of the desired movement based on the target location (and the target heading).

[0326] The electronic controller 104 adjusts the propellers 112, 122, 132 (via the rotation speeds of the associated electric motors 310, 320, 330, not shown in Fig. 7) according to the calculated rotation speeds and optionally the rudders 314, 324, 334 according to the calculated angles of attack, for example as described in the context of the embodiment of Fig. 3.

[0327] The system 100 according to the embodiment of Fig. 7 further comprises a movement sensor 700 electronically coupled to the electronic controller 104. The movement sensor 700 generates electronic movement information and sends it to the electronic controller 104.

[0328] The movement sensor 700 typically comprises a plurality of individual sensors to generate electronic movement information about position, velocity, or acceleration of the sensor, and thus of the system 100 and ultimately of the watercraft 102.

[0329] The individual sensors may be integrated into a single device, for example with a common housing, or be provided in the form of multiple, e. g. separate, devices.

[0330] The movement information refers to any combination of a position in a horizontal plane, an inclination (yaw, pitch, and/or attitude), and/or a rotation (in particular around a vertical axis). A typical combination consists of information about a longitudinal movement 700b (in terms of position and acceleration), a transverse movement 700a (in terms of position and acceleration) and a rotation 700c around the vertical axis (in terms of angular velocity). The information about the rotation 700c around the vertical axis may be determined based on of information about the longitudinal movement 700b and the transverse movement 700a of several corresponding sensors, or be determined based on an independent sensor.

[0331] The information about the longitudinal movement 700b, the transverse movement 700a, and the rotation 700c typically comprises both absolute movement information (relative to an externally defined reference frame, such as longitude and altitude; obtained, for example, using a GPS receiver or a compass) and relative movement information (relative to a previous position or movement of the system 100, obtained, for example, using an inertial measurement unit or a gyroscope), and optionally referenced movement information (relative to a reference object, such as a buoy or a pier, obtained, for example, using a camera or a sonar/ultrasound distance meter) when a reference object is available.

[0332] The electronic controller 104 receives the electronic movement information. It uses the received electronic movement information to determine whether the actual movement of the system 100 (and thus of the watercraft 102) matches the desired movement, both in terms of direction and of speed.

[0333] If the actual movement of the system 100 (and thus of the watercraft 102) deviates from the desired movement, for example by more than a predetermined amount, the electronic controller 104 readjusts the rotation speeds of the propellers 112, 122, 132, and optionally the angles of attack of the rudders 314, 324, 334, to new values. The movement sensor 700 generates new electronic movement information and sends it to the electronic controller 104. The electronic controller 104 receives the new electronic movement information, determines whether the actual movement of the system 100 (and thus of the watercraft 102) according to the new electronic movement information matches the desired movement, and, if they deviate, readjusts the rotation speeds of the propellers 112, 122, 132, and optionally the angles of attack of the rudders 314, 324, 334, to new values. They procedure is repeated until the actual movement of the system 100 (and thus of the watercraft 102) according to the electronic movement information matches the desired movement. A corresponding procedure is also referred to as a closed loop control. The closed loop control makes use of techniques known from the state of the art, such as a PID control loop.

[0334] In particular, the actual movement of the system 100 as measured by the movement sensor 700 may comprise a rotation 700c. The rotation 700c is undesired if a purely transverse, translational movement has been requested by the input device 708. Consequently, the electronic controller 104 sets the rotation speeds of the propellers 112, 122, 132 to minimize the rotation 700c. Therefore, the electronic controller 104 introduces an asymmetry between the rotation speeds 124, 134 of the propellers 122, 132 rotating 124, 134 according to their reverse directions to generate the reverse thrust 106r.

[0335] To illustrate the minimization procedure for the rotation 700c in detail, reference is made in Fig. 7 to the average flows 710, 712, 720, 722, 730, 732 generated by the propellers 112, 122, 132, more specifically, to the average longitudinal flow 710, 720, 730 and the average transverse flow 712, 722, 732.

[0336] The average longitudinal flow 710, 720, 730 gives rise to the longitudinal thrust 106f, 106r.The longitudinal flow 710, 720, 730 and the longitudinal thrust 106f, 106r generated by the same propeller 112, 122, 132 have opposite directions.

[0337] The average transverse flow 712, 722, 732 gives rise to the transverse thrust 108 opposite to the average transverse flow 712, 722, 732.

[0338] According to the embodiment depicted in Fig. 7, the longitudinal flows 710 and 720, 730 generated by the propellers 112 and 122, 132 have opposite directions, resulting in the forward 106f and reverse 106r longitudinal thrusts. The electronic controller 104 adjusts the rotation speeds of the propeller 112, 122, 132 such that the forward 106f and reverse 106r longitudinal thrusts cancel each other, minimizing the longitudinal movement.

[0339] In contrast, the transvers flows 712, 722, 732 and hence the transverse thrusts 108 have same the same direction and add up to induce a transverse movement.

[0340] In the following, the torque generate by each of the flows 710, 712, 720, 722, 730, 732 shall be discussed. The electronic controller 104 balances these torques to minimize the rotation 700c.

[0341] According to the depicted embodiment, the longitudinal flow 710 (the forward thrust 106f) points away from (towards) the center of rotation (center of mass) 702 of the watercraft, and therefore does not induce a rotation or a torque.

[0342] The longitudinal flows 720, 730 (the forward thrusts 106r) are not directed towards or away from the center of rotation 702. Consequently, each of them generates a torque. These torques ideally compensate each other when the longitudinal flows 720, 730 are identical, generating a zero net torque. However, when the longitudinal flows 720, 730 are unequal, a non-zero net torque is generated.

[0343] The transverse flows 712, 722, 732 are not directed at (or away from) the center of rotation 702, and therefore induce corresponding torques. The longitudinal flows 710, 720, 730, or the transverse thrusts 108, respectively, have the same directions and add up, and so do the resulting torques. According to the depicted embodiment, this generates a clockwise torque.

[0344] To compensate the clockwise torque induced by the transverse flows 712, 722, 732, an asymmetry 724 is introduced between the longitudinal flows 720, 730 generating the forward thrust 106r.For this purpose, the electronic controller 104 reduces the rotation speed 134 of the propeller 132 and increases the rotation speed 124 of the propeller 122 until the asymmetry 724 between the longitudinal flows 720, 730 generates the compensating torque. During this process, the electronic controller 104 continuously balances the forward thrust 106f and the reverse thrust 106r according to the corresponding movement in formation 700b, for example by slightly readjusting the rotation speed of the propeller 112.

[0345] In the closed loop control described above, in each iteration, the electronic controller 104 sets new values for the rotation speeds of the propellers 112, 122, 132, and optionally of the angles of attack of the rudders 314, 324, 334. For determining the new values, the electronic controller 104 uses control parameters. More specifically, the control parameters determine the new values for the rotation speeds of the propellers 112, 122, 132 (and of the angles of attack of the rudders 314, 324, 334) based on the current speeds of the propellers 112, 122, 132 (and of the angles of attack of the rudders 314, 324, 334) and the deviation between the desired movement and the actual movement of the system 100 (and thus of the watercraft 102) according to the electronic movement information from the movement sensor 700.

[0346] For example, control parameters may be P, I, and D parameters of a PID control loop provided by the electronic controller 104.

[0347] Alternatively, or in addition, control parameters are comprised in a neural network provided by the electronic controller 104. In such embodiments, the control parameters are derived from test operation of the system 100 to train the neural network, observing the electronic movement information from the movement sensor 700 in response to variations of the rotation speeds of the propellers 112, 122, 132, and optionally of the angles of attack of the rudders 314, 324, 334. In operation, which is also used for further training, the trained neural network is used directly to determine the new values for the rotation speeds of the propellers 112, 122, 132 (and optionally of the angles of attack of the rudders 314, 324, 334), or to provide parameters for a closed loop control, such as a PID control loop, that determines the new values for the rotation speeds of the propellers 112, 122, 132 (and optionally of the angles of attack of the rudders 314, 324, 334).

[0348] As an additional control parameter, the electronic controller 104 optionally determines the inertia (or mass) of the watercraft 102 and the position of the center of rotation 702 relative to the propellers 122, 132. Therefore, the rotation speeds of the propellers 112, 122, 132 are varied, and the movement information from the movement sensor 700 is observed. Based on the velocity of the longitudinal movement 700b as a function of the rotation speed of the propeller 112, the inertia is determined. Based on the measured inertia and on the velocity of the rotation 700c as a function of the rotation speed of each of the propellers 122, 132, an effective distance (actual distance times sine of the angle between axis orientation and direction towards the centerline) between respective propeller 122, 132 and the center of rotation 702 is then determined.

[0349] The electronic controller 104 stores a database of control parameters for various types and models of watercraft 102. In the course of initial installation of the system 100, a user may select stored control parameters of a watercraft similar to the watercraft 102 that the system 100 is being installed on. Thereafter, the controller 100 performs a continuous training to adapt the selected control parameters to the watercraft 102, such that the adapted control parameters minimize the deviations between the desired movement (as input by the user input device 708) and the actual movement of the system 100. The electronic controller 104 stores the adapted control parameters to the database together with parameters describing the watercraft 102. The database enlarged this way is transferred to a central server, which provides the enlarged database to other electronic controllers 104. This way, an ever growing database with optimized parameters for a large variety of watercraft is provided.

[0350] Fig. 8 depicts a propulsion and steering system 100 according to an embodiment similar to the one of Fig. 7. In addition, the system 100 of Fig. 8 comprises an external condition sensor 706.

[0351] The external condition sensor 706 provides an external condition information about an external condition at the position of the propulsion system 100. According to the example of Fig. 8, the external condition comprises wind or waves, and the external condition sensor 706 comprises wind and wave sensors 706.

[0352] According to embodiments, the wind and wave sensors 706 generate the information about the wind or the waves locally at the sensor. According to alternative embodiments, the wind and waves sensors 706 receive the corresponding information from an external device, for example from a server via a wireless wide area network or from an electronic buoy via a wireless local area network.

[0353] The wind and wave sensors 706 send the external condition information to the electronic controller 104. The electronic controller 104 receives the external condition information.

[0354] The electronic controller 104 determines and stores the reaction of the propulsion and steering system 100 to the external condition. More specifically, the electronic controller 104 observes a movement according to the movement sensor 700 while receiving the information from the wind and wave sensors 706. The electronic controller 104 thus determines and stores a longitudinal movement 700b, a transverse movement 700a, and a rotation 700c associated with the currently received external condition information. Optionally, the electronic controller 104 calculates forces onto the watercraft associated with the currently received external condition information from the longitudinal movement 700b, a transverse movement 700a, and a rotation 700c.

[0355] For various sets of external conditions, the electronic controller 104 stores the external condition information, corresponding movement information and optionally the corresponding calculated forces. For example, the electronic controller 104 stores datasets containing external conditions and corresponding movement information (and optionally the calculated forces) in a lookup table. Alternatively, the electronic controller 104 uses the dataset to train a neural network to predict a movement (and optionally the forces) associated with various external conditions.

[0356] The electronic controller 104 uses the stored information about movements associated with external forces to balance the overall longitudinal movement and/or the torque/rotation of the system 100 when adjusting the rotation speeds 114, 124, 134 of the propellers 112, 122, 132. In other words, the calculated or adjusted rotation speeds 114, 124, 134 take into account the movement or the forces caused by the current external conditions as received from the sensor 706.

[0357] As depicted in Fig. 8, the calibration of the electronic controller 104 with respect to the movement information (received from the sensor 700) or the external forces (calculated by the controller based on the movement information) caused by the external condition sensed by the sensor 706 is performed while the propellers stand still and the angles of attack of the rudders 314, 324, 334 are essentially zero. However, additional calibration is optionally performed while the propellers 112, 122, 132 rotate and/or the rudders 314, 324, 334 are set to non-zero angles of attack, in particular in embodiments wherein the calibration is used to train a neural network. The additional calibration, or training of the neural network, respectively, takes place continuously during operation of the watercraft 102.

[0358] This way, optimized rotation speeds of the propellers (and angles of attack of the rudders 314, 324, 334) are determined and provided by the electronic controller 104 to achieve a purely transverse movement for various wind and wave conditions.

[0359] Fig. 9a and Fig. 9b depict propulsion and steering systems 100 according to a embodiments similar to the ones of Fig. 1a, Fig. 1b, Fig. 1c, Fig. 4, Fig. 5, Fig 7 and Fig. 8. Several modifications will be described for the propulsion and steering systems 100 of Fig. 9 and Fig. 9b. Different embodiments may be formed with any or all of those modifications.

[0360] The systems 100 of Fig. 9a and Fig. 9b comprise four propulsion units 110, 110', 120, 130, which may be similar to any of the previously described propulsion units (electric motors of the propulsion units 110, 120, 130 are not shown in Fig. 9a and Fig. 9b).

[0361] The embodiment of Fig. 9a and Fig. 9b is similar to the one of Fig. 7. However, the propellers 112, 112' together provide the forwards thrust 106f, similar to the single propeller 112 of Fig. 7.

[0362] This provides an additional degree of freedom in adjusting the rotation speeds of the propellers 112, 112', 122, 132 to generate the longitudinal thrusts 106f, 106r and the transverse thrust 108, and preventing an undesired rotation at the same time.

[0363] On the one hand, and as illustrated in Fig. 9a, the forward-rotating 114, 114' propellers 112, 112' may be driven symmetrically, for example by adjusting them to the same rotation speed or to produce the same magnitudes of their longitudinal flows 710, 710' or to produce the same amounts of forward thrust 106f, 106f'. In this case, an asymmetry 724 is introduced between the flows 720, 730 generated by the reverse-rotating 124, 134 propellers 122, 132, or between the reverse thrusts 106r produced by these propellers, as similarly described in the context of the corresponding propellers of Fig. 7.

[0364] On the other hand, and as illustrated in Fig. 9b, the reverse-rotating 124, 134 propellers 122, 132 maybe driven symmetrically, for example by adjusting them to the same rotation speed or to produce the same magnitudes of their longitudinal flows 720, 730 or to produce the same amounts of reverse thrust 106r.In this case, an asymmetry 724 is introduced between the flows 710, 710' generated by the forward-rotating 114, 114' propellers 112, 112', or between the forward thrusts 106f produced by these propellers.

[0365] In practice, the movement described in the context of Fig. 9a is overlaid with the movement described in the context of Fig. 9b, resulting in both the forward-rotating 114, 114' propellers 112, 112' and the reverse-rotating 124, 134 propellers 122 rotating in an asymmetric manner (at different rotation speeds).

[0366] The ratio between the asymmetry 724 of the forward-rotating 114, 114' propellers 112, 112' (see Fig. 9b) and the asymmetry 724 of the reverse-rotating 124, 134 propellers 122 (see Fig. 9a) is varied to optimize the electrical power intake of the propulsion units 110, 120, 130.

[0367] For this purpose, a power meter 718 is provided in a power line 716 connecting the propulsion units 110, 120, 130 to ship batteries (not shown) which provide the electrical energy to operate the propulsion units 110, 120, 130. The electronic controller 104 receives the electrical power intake of the propulsion units 110, 120, 130 measured by the power meter 718, while the asymmetries 724 of Fig. 9a and Fig. 9b are varied and the movement of the system 100 is determined using the sensor 700. This way, the electronic controller 104 determines the most efficient rotation speeds of the propellers 112, 112', 122, 132 to achieve a desired movement according to the user input 708, as characterized (among others) by the asymmetries 724. The procedure is repeated for various rotation speeds of the propellers 112, 112', 122, 132 and desired movements according to the user input 708.

[0368] Fig. 10 summarizes a method 1000 for operating a propulsion and steering system 100 of a watercraft 102. The method 1000 comprises a transverse propulsion mode 1010 and a longitudinal propulsion mode 1020.

[0369] In the transverse propulsion mode 1010, the method comprises selecting 1012, using the electronic controller 104, a rotation speed 114 of a first propeller 112 according to its forward direction of rotation 112f, and rotation speeds 124, 134 of the second propeller 122 and the third propeller 132 according to their respective reverse directions of rotation 122r, 132r. In the transverse propulsion mode 1010, the method further comprises adjusting 1014, using the electronic controller 104, the rotation speed 114 of the first propeller 112 according to its selected rotation speed to generate a forward thrust 106f; and adjusting 1016, using the electronic controller 104, the rotation speeds 124, 134 of the second propeller 122 and the third propeller 132 according to their respective selected rotation speeds to generate an aft thrust 106r.The electronic controller selects the rotation speeds of the first propeller 112, the second propeller 122, and the third propeller 132 such that a transverse thrust 108 generated by the propellers 112, 122, 132 exceeds a total longitudinal thrust comprising the forward thrust 106f and the aft thrust 106r.

[0370] In the longitudinal propulsion mode 1020, the method 1000 comprises driving 1022 at least one of the propellers 112, 122, 132 according to its forward direction of rotation 112f, 122f, 132f to generate a forward thrust 106f; and not driving 1024 any of the propellers 112, 122, 132 according to its reverse direction of rotation 112r, 122r, 132r to generate an aft force 106r onto the watercraft 102.

[0371] The description of the embodiments and the Figures merely serve to illustrate the teachings of the present disclosure, but should not be understood to imply any limitation. The scope of the present disclosure is to be determined from the appended claims.

LIST OF REFERENCE SIGNS

[0372] 

100

propulsion and steering system

102

watercraft

102b

bow section of watercraft

102s

stern section of watercraft

104

electronic controller

106f, 106f'

forward thrust

io6r

aft thrust

108

transverse thrust

110, 120, 130, 110'

propulsion unit

112, 122, 132, 112'

propeller

112a, 122a, 132a

axis (orientation) of propeller

112f, 122f, 132f

forward direction of rotation of the propeller

112r, 122r, 132r

reverse direction of rotation of the propeller

114, 124, 134

(direction of) rotation speed of the propeller

h

horizontal plane

v

vertical direction

200

connection element, connecting surface

202

waterproof housing

302

center hull

304

portside hull

306

starboard hull

308

plane

310, 320, 330

engine, electric motor

312, 322, 332

transmission

312a, 322a, 332a

propeller (rotary) shaft

312b, 322b, 332b

gearbox

312c, 322c, 332c

motor (rotary) shaft

314, 324, 334

rudder(s)

314p, 324p, 334p

portside rudder

314s, 324s, 334s

starboard rudder

312p

propeller coupling

314a

rudder actuator

600

connecting frame

602

outboard part of connecting frame

604

inboard part of connecting frame

606

threaded holes for mounting outboard part of connecting frame

608

threaded holes for mounting connection surface/propulsion unit

610

pulse inverter

612

power inlet

614

signal line

616

thrust bearing

620

heat exchanger

622

(inlet and outlet of) primary side of heat exchanger

624

(inlet and outlet of) secondary side of heat exchanger

632

radial section of propeller

634

flat section of propeller

636

outer edge of (flat section of) propeller

640

transom

642

opening in transom

644

static water line

646

cruising speed water line

648

through holes corresponding to connection surface

650

lower edge of opening in transom

700

movement sensor

700a

transverse movement sensor

700b

longitudinal movement sensor

700c

rotation sensor

702

center of mass, center of rotation

704

centerline

706

wind and wave sensor

708

user input device

710, 720, 730, 710'

longitudinal water flow

712, 722, 732, 712'

transverse water flow

716

electric line to ship battery

718

power meter

724

asymmetry

1000

method

1010

transverse propulsion mode

1012

selecting

1014

adjusting first propeller forward

1016

adjusting second and third propeller reverse

1020

longitudinal propulsion mode

1022

driving at least one propeller forward

1024

not driving a propeller of any of the propulsion systems reverse

Claims

1. A propulsion and steering system (100) for a watercraft (102), comprising

at least three propulsion units (110, 120, 130), each comprising an electric motor (310, 320, 330) and a propeller (112, 122, 132) with a respective axis orientation (112a, 122a, 132a), a respective forward direction of rotation (112f, 122f, 132f), and a respective reverse direction of rotation (112r, 122r, 132r), wherein the propeller (112, 122, 132) is rotationally coupled to the electric motor (310, 320, 330); and

an electronic controller device (104) adapted to be electronically coupled to the at least three propulsion units (110, 120, 130) to individually adjust the rotation speeds of their respective electric motors (310, 320, 330) to adjust the rotational speeds (114, 124, 134) of their respective propellers (112, 122, 132);

wherein the at least three propulsion units (110, 120, 130) are adapted to be arranged such that the axis orientations (112a, 122a, 132a) of the propellers (112, 122, 132) are fixed and essentially parallel to each other according to a top view;

wherein the electronic controller device (104) is adapted to adjust the rotation speed (114) of a first propeller (112) of the propellers (112, 122, 132) according to its forward direction of rotation (112f) to generate a forward thrust (106f), and to adjust the rotation speeds (124, 134) of a second propeller (122) and a third propeller (132) of the propellers (112, 122, 132) according to their respective reverse directions of rotation (122r, 132r) to generate an aft thrust (106r); such that the propellers (112, 122, 132) generate a transverse thrust (108) exceeding a total longitudinal thrust comprising the forward thrust (106f) and the aft thrust (106r).

2. The propulsion and steering system (100) according to claim 1,

wherein the forward thrust (106f) generated by the first propeller (112) and the aft thrust (106r) generated by the second propeller (122) are adapted to generate a first torque around a vertical axis (v);

wherein the aft thrust (106r) generated by the third propeller (132) is adapted to generate a second torque around the vertical axis (v); and

wherein the electronic controller device (104) is adapted to adjust the rotation speeds (114, 124, 134) of the first propeller (112), the second propeller (122) and the third propeller (132) such that the second torque essentially compensates the first torque.

3. The propulsion and steering system (100) according to any of the preceding claims,

wherein the electronic controller device (104) is adapted to receive a movement information and/or an external condition information; and

wherein the electronic controller device (104) is adapted to adjust the rotation speeds (114, 124, 134) of the first propeller (112), the second propeller (122) and the third propeller (132) according to the received movement information and/or the received external condition information, such that the propellers (112, 122, 132) generate the transverse thrust (108) exceeding the total longitudinal thrust.

4. The propulsion and steering system (100) according to any of the preceding claims,

wherein the at least three propulsion units (110, 120, 130) each comprise a respective propeller shaft (312a, 322a, 332a);

wherein the propeller (112, 122, 132) of each of the at least three propulsion units (110, 120, 130) is rotationally coupled to the propeller shaft (312a, 322a, 332a) of the respective propulsion unit (110, 120, 130); and

wherein a single plane (308), which is essentially perpendicular to the axis orientation (112a, 122a, 132a) of the first propeller (112) and/or the second propeller (122) and/or the third propeller (132) according to a top view, intersects the propeller shafts (312a, 322a, 332a) and/or the propellers (112, 122, 132) of the at least three propulsion units (110, 120, 130).

5. The propulsion and steering system (100) according to any of the preceding claims, wherein the at least three propulsion units (110, 120, 130) are adapted to provide a main forward propulsion system for the watercraft (102).

6. The propulsion and steering system (100) according to any of the preceding claims, further comprising:

a first rudder (314) associated with the first propeller (112); and

a second rudder (324) associated with the second propeller (122);

wherein the electronic controller device (104) is adapted to adjust an angle of attack of the first rudder (314) to a first direction while adjusting the rotation speed (114) of the first propeller (112) according to its forward direction of rotation (112f, 122f, 132f);

wherein the electronic controller device (104) is adapted to adjust an angle of attack of the second rudder (324) to a second direction while adjusting the rotation speed (124) of the second propeller (122) according to its reverse direction of rotation (122r); and

wherein the second direction is opposite to the first direction.

7. The propulsion and steering system (100) according to claim 6, wherein the first rudder (314) is arranged starboard or portside of the first propeller (112), and the second rudder (324) is arranged starboard or portside of the second propeller (122).

8. The propulsion and steering system (100) according to any of the preceding claims,

wherein each of the at least three propulsion units (110, 120, 130) comprises a connection element (200) adapted to connect the respective propulsion unit (110, 120, 130) to the watercraft (102); and

wherein each of the at least three propulsion units (110, 120, 130) is adapted to be connected as a whole to the watercraft (102).

9. The propulsion and steering system (100) according to any of the preceding claims, comprising at least four propulsion units (110, 110', 120, 130), each comprising an electric motor (310, 320, 330) and a propeller (112, 112', 122, 132) with a respective axis orientation (112a, 112a', 122a, 132a), a respective forward direction of rotation (112f, 112f, 122f, 132f), and a respective reverse direction of rotation (112r, 112r', 122r, 132r), wherein the propeller (112, 112', 122, 132) is rotationally coupled to the electric motor (310, 320, 330);

wherein the electronic controller device (104) is adapted to be coupled to the at least four propulsion units (110, 110', 120, 130) to individually adjust the rotation speeds (114, 114', 124, 134) of their respective electric motors (310, 320, 330) to adjust the rotational speeds of their respective propellers (112, 122, 132);

wherein the at least four propulsion units (110, 110', 120, 130) are adapted to be arranged such that the axis orientations (112a, 112a', 122a, 132a) of the propellers (112, 112', 122, 132) are fixed and essentially parallel according to a top view; and

wherein the electronic controller device (104) is adapted to adjust the rotation speeds (114, 114') of at least two of the propellers (112, 112') according to their forward directions of rotation (1122, 112f) to generate the forward thrust (106f), and to adjust the rotation speeds (124, 134) of at least two of the propellers (122, 132) according to their reverse directions of rotation (112r, 112r') to generate the aft thrust (106r); such that the propellers (112, 112', 122, 132) generate the transverse thrust (108) exceeding the total longitudinal thrust.

10. A watercraft (102) comprising a propulsion and steering system (100) according to any of the preceding claims, wherein the at least three propulsion units (110, 120, 130) are arranged on the watercraft (102) such that horizontal components of the axis orientations (112a, 122a, 132a) of the propellers (112, 122, 132) are essentially parallel to a centerline (704) of the watercraft (102).

11. A watercraft (102) according to claim 10 or comprising a propulsion and steering system (100) according to any of claims 1 to 9, wherein the propellers (112, 122, 132) or the at least three propulsion units (110, 120, 130) are arranged in a stern section of the watercraft (102).

12. A watercraft (102) according to claim 10 or 11 or comprising a propulsion and steering system (100) according to any of claims 1 to 9, wherein the watercraft (102) is a multihull watercraft (102), wherein at least one of the propellers (112, 122, 132) is arranged on a starboard hull (306) of the multihull watercraft (102), and wherein at least one of the propellers (112, 122, 132) is arranged on a portside hull (304) of the multihull watercraft (102).

13. A method (1000) for operating a propulsion and steering system (100) of a watercraft (102), wherein the propulsion and steering system (100) comprises:

at least three propulsion units (110, 120, 130), each comprising a propeller (112, 122, 132) with a respective axis orientation (112a, 122a, 132a), a respective forward direction of rotation (112f, 122f, 132f), and a respective reverse direction of rotation (112r, 122r, 132r); and

an electronic controller device (104) electronically coupled to the at least three propulsion units (110, 120,130);

wherein the at least three propulsion units (110, 120, 130) are adapted to be arranged such that the axis orientations (112a, 122a, 132a) of the propellers (112, 122, 132) are fixed and essentially parallel to each other according to a top view;

the method (1000) comprising a transverse propulsion mode (1010) and a longitudinal propulsion mode (1020);

wherein the method (1000) comprises, in the transverse propulsion mode (1010):

selecting (1012), using the electronic controller device (104), a rotation speed (114) of a first propeller (112) according to its forward direction of rotation (112f), and rotation speeds (124, 134) of the second propeller (122) and the third propeller (132) according to their respective reverse directions of rotation (122r, 132r);

adjusting (1014), using the electronic controller device (104), the rotation speed (114) of the first propeller (112) according to its selected rotation speed to generate a forward thrust (106f);

adjusting (1016), using the electronic controller device (104), the rotation speeds (124, 134) of the second propeller (122) and the third propeller (132) according to their respective selected rotation speeds to generate an aft thrust (106r);

wherein the selecting (1012) the rotation speeds (114, 124, 134) of the first propeller (112), the second propeller (122), and the third propeller (132) is performed by the electronic controller device (104) such that a transverse thrust (108) generated by the propellers (112, 122, 132) exceeds a total longitudinal thrust comprising the forward thrust (106f) and the aft thrust (106r); and

wherein the method (1000) comprises, in the longitudinal propulsion mode (1020):

driving (1022) at least one of the propellers (112, 122, 132) according to its forward direction of rotation (112f, 122f, 132f) to generate a forward thrust (106f);

not driving (1024) any of the propellers (112, 122, 132) according to its reverse direction of rotation (112r, 122r, 132r) to generate an aft force onto the watercraft (102).

14. The method according to claim 13, wherein the propulsion and steering system (100) further comprises a first rudder (314) associated with the first propeller (112) and a second rudder (324) associated with the second propeller (122); and wherein the method further comprises:

adjusting, using the electronic controller device (104), an angle of attack of the first rudder (314) to a first direction while adjusting the rotation speed (114) of the first propeller (112) according to its forward direction of rotation (112f); and

adjusting, using the electronic controller device (104), an angle of attack of the second rudder (324) to a second direction while adjusting the rotation speed (124) of the second propeller (122) according to its reverse direction of rotation (122r);

wherein the second direction is opposite to the first direction.

15. A computer program comprising computer-readable instructions adapted to instruct a controller device to execute the method according to any of claims 13 or 14.

Drawing