Patent Description:
Many different types of marine propulsion devices are well known to those skilled in the art. For example, outboard motors that are attached to the transom of a marine vessel, stern drive systems that extend in a rearward direction from the transom of a marine vessel, bow thrusters and other docking thrusters are well known to those skilled in the art. In addition to bow thrusters, certain types of docking thruster systems used in conjunction with marine vessels incorporate a plurality of propulsors that are responsive to the joystick manipulations or other control input by a marine vessel operator.

<CIT> discloses a docking system that utilizes the marine propulsion unit of a marine vessel, under the control of an engine control unit that receives command signals from a joystick or push button device, to respond to a maneuver command from the marine operator. The docking system does not require additional propulsion devices other than those normally used to operate the marine vessel under normal conditions. The docking or maneuvering system of the present invention uses two marine propulsion units to respond to an operator's command signal and allows the operator to select forward or reverse commands in combination with clockwise or counterclockwise rotational commands either in combination with each other or alone.

<CIT> discloses a hydraulic steering system in which a steering actuator is an integral portion of the support structure of a marine propulsion system. A steering arm is contained completely within the support structure of the marine propulsion system and disposed about its steering axis. An extension of the steering arm extends into a sliding joint which has a linear component and a rotational component which allows the extension of the steering arm to move relative to a moveable second portion of the steering actuator. The moveable second portion of the steering actuator moves linearly within a cylinder cavity formed in a first portion of the steering actuator.

<CIT> discloses a hydraulic steering assembly that applies a force to a tiller arms of twin marine, outboard propulsion units and rotates the propulsion units about a steering axis between a center position and hard over positions to each side of the center position. Each propulsion unit is supported for arcuate movement about a tilt axis which is generally perpendicular to the steering axis. There is a hydraulic steering apparatus mounted on a first of the propulsion units which includes a hydraulic cylinder pivotally connected to a member which is pivotally mounted on the tiller arm of the first propulsion unit. A tie-bar is pivotally connected to the steering apparatus and pivotally connected to the tiller arm of a second propulsion unit. For example, the tie-bar may be pivotally connected to the steering apparatus by a ball joint connected to the steering apparatus by a bracket which moves with the member.

<CIT> discloses a steering assist system providing differential thrusts by two or more marine propulsion devices in order to create a more effective turning moment on a marine vessel. The differential thrusts can be selected as a function of the magnitude of turn commanded by an operator of the marine vessel and, in addition, as a function of the speed of the marine vessel at the time when the turning command is received.

<CIT> discloses a method for controlling the movement of a marine vessel that rotates one of a pair of marine propulsion devices and controls the thrust magnitudes of two marine propulsion devices. A joystick is provided to allow the operator of the marine vessel to select port-starboard, forward-reverse, and rotational direction commands that are interpreted by a controller which then changes the angular position of at least one of a pair of marine propulsion devices relative to its steering axis.

<CIT> discloses a system that controls speed of a marine vessel that includes first and second propulsion devices that produce first and second thrusts to propel the marine vessel. A control circuit controls orientation of the propulsion devices between an aligned position in which the thrusts are parallel and an unaligned position in which the thrusts are non-parallel. A first user input device is moveable between a neutral position and a non-neutral detent position. When the first user input device is in the detent position and the propulsion devices are in the aligned position, the thrusts propel the marine vessel in a desired direction at a first speed. When a second user input device is actuated while the first user input device is in the detent position, the propulsion devices move into the unaligned position and propel the marine vessel in the desired direction at a second, decreased speed without altering the thrusts.

<CIT> discloses a method for controlling movement of a marine vessel near an object that includes accepting a signal representing a desired movement of the marine vessel from a joystick. A sensor senses a shortest distance between the object and the marine vessel and a direction of the object with respect to the marine vessel. A controller compares the desired movement of the marine vessel with the shortest distance and the direction. Based on the comparison, the controller selects whether to command the marine propulsion system to generate thrust to achieve the desired movement, or alternatively whether to command the marine propulsion system to generate thrust to achieve a modified movement that ensures the marine vessel maintains at least a predetermined range from the object. The marine propulsion system then generates thrust to achieve the desired movement or the modified movement, as commanded.

<CIT> discloses a tie bar apparatus is for a marine vessel having at least first and second marine drives. The tie bar apparatus comprises a linkage that is geometrically configured to connect the first and second marine drives together so that during turning movements of the marine vessel, the first and second marine drives steer about respective first and second vertical steering axes at different angles, respectively.

<CIT> and <CIT> each describe a marine vessel having a lateral thruster. <CIT> and <CIT> each describe a marine vessel having a pair of propulsion devices with a coupling therebetween.

According to a first aspect of the present invention, there is provided a marine propulsion system as claimed in claim <NUM> and a marine propulsion system as claimed in claim <NUM>.

According to another aspect of the present invention there is provided a method of controlling propulsion of a marine vessel as claimed in claim <NUM>.

The inventors have recognized a need for vessel control systems that provide lateral and rotational user control, such as user control provided by standard joystick systems, for non-steered-by-wire vessels where a steering wheel is mechanically connected via a conventional steering system to propulsion devices mounted to the stern of the marine vessel. For example, on vessels configured for high speed applications, such as racing vessels, the mechanically-steered propulsion devices are typically tied together, such as with a tie bar. This provides robust steering actuation and control at high load conditions and high vessels speeds. As another example, lower cost vessels typically implement conventional mechanical steering systems where the propulsion devices are mechanically connected to the steering wheel and are jointly steered, and the propulsion devices are often connected with a tie bar. In both of these applications, as well as other non-steer-by-wire steering and propulsion systems, the propulsion devices are maintained in parallel such that the thrusts effectuated are parallel to one another. These existing systems do not provide lateral thrust control or automatic rotational thrust control where a user can instruct rotational movement without any forward or backward movement. No joysticking or other lateral thrust control elements are currently available for non-steer-by-wire systems. Currently available joysticking systems require steer-by-wire control where each propulsion device can be steered separately and the propulsion devices can be placed at angles that are not parallel to one another.

Based on the foregoing problems and challenges in the relevant art, the inventors developed the disclosed propulsion system and method allowing lateral and rotational steering control, such as via a joystick, on mechanically steered and other non-steer-by-wire vessels. The disclosed system and method enable lateral and rotational steering control by a user without controlling or adjusting the angle of the propulsion devices with respect to the marine vessel, and thus can be implemented on marine vessels with conventional mechanical steering of the propulsion devices. The system includes a set of two or more parallel propulsion devices that each generate forward and reverse thrusts and a sensor system configured to determine a drive angle of the parallel propulsion devices. The system further include a lateral thruster configured to generate lateral thrusts in each of the starboard and port directions. A user input device, such as a joystick or a keypad, is manually operable by a user to provide at least lateral and rotational steering inputs to command corresponding movements of the marine vessel, and a controller is configured to control magnitude and direction of thrust by the parallel propulsion devices and/or the lateral thruster to effectuate the commanded movement without requiring any steering control over the propulsion devices.

<FIG> is a schematic representation of a marine vessel <NUM> equipped with propulsion system <NUM> including two propulsion devices <NUM> and <NUM> attached to the transom <NUM> and arranged in parallel. The number of propulsion devices is exemplary and a person having ordinary skill in the art will understand in light of the present disclosure that any number of two or more propulsion devices may be utilized in the disclosed system and method. In the depicted example, the propulsion devices <NUM> and <NUM> are connected and maintained in parallel via a tie bar <NUM>. Tie bars are conventional in many marine applications, including high-speed racing vessels, which often employ tie bars between engines to assist in distributing steering loads during high-speed operations. The tie bars may attach to the propulsion devices at the location of the steering axes <NUM> and <NUM> of the parallel propulsion devices <NUM> and <NUM>, respectively. The steering axes <NUM> and <NUM> are separated by a dimension Y and at a distance X from the center of turn <NUM> (COT), which could also be the effective center of gravity (COG). The marine vessel <NUM> is maneuvered by causing the first and second propulsion devices to rotate about their respective steering axis <NUM> and <NUM>. The parallel propulsion devices <NUM> and <NUM> are rotated in response to an operator's manipulation of the steering wheel <NUM>, which is mechanically connected to the steering actuator <NUM> which rotates the propulsion devices <NUM> and <NUM>, as is conventional. Mechanical connection systems <NUM> for transmitting rotational movement of the steering wheel <NUM> to the steering actuator <NUM> are well-known, such as steering linkage systems and or push/pull cable systems, which may include hydraulic actuated steering systems including a hydraulic steering actuator <NUM>. Rotating the parallel propulsion devices <NUM> and <NUM> and effectuating thrusts thereby cause rotation of the marine vessel <NUM> about the effective COT <NUM>.

The propulsion system <NUM> further includes a user input device <NUM>, such as a joystick or a keypad, operable by a user to provide at least a lateral steering input to command lateral movement of the marine vessel and a rotational steering input to command rotational movement of the marine vessel <NUM>. <FIG> illustrate exemplary vessel movements that may be commanded via the user input device <NUM>. In <FIG>, the vessel <NUM> is shown moving laterally in the port direction <NUM> and the starboard direction <NUM> without any forward or reverse motion and without any rotation about its COT <NUM>. <FIG> shows the vessel <NUM> moving in the forward <NUM> direction and backward <NUM> direction. <FIG> shows a combination of forward and starboard motions of the vessel <NUM>, where the forward movement is represented by the dashed arrow <NUM> and the starboard movement is represented by the dashed arrow <NUM>. The resultant motion vector <NUM> moves the vessel in the forward and starboard directions without any rotation. <FIG> illustrates a clockwise rotation <NUM> of the marine vessel <NUM> about the COT <NUM> without any translation movement, including any forward/reverse movement or lateral movement. <FIG> illustrates a combination of rotation <NUM> and translation <NUM>, which is in both the forward and starboard directions.

The disclosed system and method enable lateral and rotational movement of the marine vessel, such as that illustrated in <FIG>, without requiring steering control of the propulsion devices <NUM> and <NUM>, which are mechanically steered by the steering wheel <NUM>. Thus, the disclosed system and method control magnitude and forward or reverse direction of thrust for each parallel propulsion device without adjusting or otherwise controlling the drive angle of the set of parallel propulsion devices.

The user steering inputs provided at the user input device <NUM> are received at the controller <NUM> which is communicatively connected to the engine control module (ECM) <NUM> and <NUM> of each propulsion device <NUM> and <NUM>, respectively. Thereby, the controller <NUM> can communicate instructions to each ECM <NUM> and <NUM> to effectuate a commanded magnitude of thrust and a commanded direction of thrust (forward or reverse), as is necessary to effectuate the lateral and/or rotational steering inputs commanded at the user input device <NUM>. The system <NUM> includes a lateral thruster <NUM> configured to effectuate lateral thrust on the vessel <NUM> in the starboard and port directions. In the depicted example, the lateral thruster <NUM> is a bow thruster positioned at a bow region <NUM> of the vessel <NUM> and configured to effectuate lateral thrust at the bow. Bow thrusters are well known to those skilled in the art, as are other types and locations of docking thruster systems configured to effectuate lateral thrusts on the marine vessel, which may be placed at other locations on the vessel <NUM> besides the bow <NUM>. A person having ordinary skill in the art will understand in view of the present disclosure that the disclosed propulsion system <NUM> may include other types and locations of lateral thrusters <NUM>, which may be an alternative to or in addition to a bow thruster.

The lateral thruster <NUM> includes a fan <NUM> or propeller that is rotated by a bidirectional motor <NUM> in forward or reverse direction in order to effectuate lateral thrust in the starboard and port directions. The controller <NUM> may be communicatively connected to a controller <NUM> for the lateral thruster <NUM> in order to control activation and direction of thrust by the lateral thruster <NUM>. In one embodiment, the rotation, and thus is either on or off and rotates in the clockwise and counterclockwise directions at a single speed. In other embodiments, the lateral thruster <NUM> is a variable speed thruster wherein the motor <NUM> is controllable to rotate the fan <NUM> at two or more speeds. For example, the motor <NUM> may be a brushless DC motor configured for variable multi-speed control of the fan <NUM> in both the clockwise and counterclockwise rotation directions.

The disclosed system and method take advantage of the parallelism of the propulsion devices <NUM> and <NUM>. By effectuating a forward thrust by one of the propulsion devices and a reverse thrust by the other, where the thrust vectors are parallel and equal in magnitude, the translation forces will couple and counteract one another. The coupled forces will impart a torque about the COT <NUM>. If the drive angle of the propulsion devices is known, then vector analysis can be performed in order to effectuate any rotational movement and, an embodiment incorporating a lateral thruster <NUM>, lateral movement in the port direction <NUM> and the starboard direction <NUM>, as well as forward direction <NUM> and reverse direction <NUM> movement. In certain embodiments, the system <NUM> may be configured to provide translational movement in other translational directions combining forward/reverse and port/starboard thrust.

<FIG> exemplify two possible types of user input devices <NUM>. <FIG> depicts a well-known joystick device 40a that comprises a base <NUM> and a moveable handle <NUM> suitable for movement by an operator. Typically, the handle can be moved left and right, forward and back, as well as rotated relative to the base <NUM> in order to provide corresponding movement commands for the propulsion system. The operation of joystick thrust control is well known to those skilled in the art. <FIG> depicts an alternative user input device 40b being a keypad with buttons <NUM> associated with each of the right, left, forward, backward, and rotational movement directions. Thus, a forward button 64a can be pressed by a user in order to provide a forward thrust command to move the marine vessel forward and key 64b can be pressed by a user to input a lateral thrust command to command lateral movement of the marine vessel <NUM>. Similarly, the clockwise rotation key 64c can be pressed by a user to input a clockwise rotational thrust command to command clockwise rotational movement of the marine vessel <NUM>. The other keys on the keypad 40b operate similarly.

The disclosed propulsion system <NUM> enables joystick control, or control by another user input device operable to provide lateral and rotational thrust control, to mechanically linked and steered drives. Thus, steer-by-wire is not required and the controller <NUM> is configured to calculate thrust magnitude and direction utilizing the current position of the marine drives, whatever it may be. The system <NUM> is configured to take advantage of parallelism of the propulsion devices <NUM> and <NUM> such that thrust by the two or more propulsion devices can counteract each other in order to effectuate the desired resultant rotational and translational thrust. One embodiment having a lateral thruster <NUM>, the propulsion system <NUM> can effectuate lateral movement in the lateral movement directions <NUM> and <NUM> and the forward and reverse movement directions <NUM> and <NUM>, as shown in <FIG>.

<FIG> exemplify this force coupling control between the propulsion devices <NUM> and <NUM> and the lateral thruster <NUM> in order to effectuate rotational and translational movement of the vessel without changing or controlling the drive angle of the propulsion devices <NUM> and <NUM>. The controller <NUM> is configured to measure the drive angle θ of the parallel propulsion devices <NUM> and <NUM>, or to otherwise determine the rotational effect of thrusts from the propulsion devices <NUM> and <NUM>. In one claimed embodiment, a drive position sensor <NUM> (<FIG>) is configured to sense a drive angle of at least one of the parallel propulsion devices <NUM> and <NUM>. Given that the propulsion devices <NUM> and <NUM> are maintained in parallel, such as by a tie bar <NUM>, the drive angle of only one propulsion device <NUM>, <NUM> needs to be sensed. However, in other embodiments, each propulsion device <NUM> and <NUM> may be equipped with a position sensor, such as to provide redundancy in case of failure. The drive angle sensed by the position sensor provides information about the drive angle, or steering position, of the propulsion devices, which is manually controlled by the operator via the steering wheel <NUM> and is not controlled by the controller <NUM>. Based on the drive angle, the controller <NUM> can adjust to the scale and the direction of thrust by the parallel propulsion devices <NUM> and <NUM> and/or the lateral thruster <NUM>. If the drive angle θ changes, then the controller <NUM> will adjust the thrust magnitudes and directions to accommodate the new steering position sensed by the drive position sensor <NUM>.

In another claimed embodiment, the controller <NUM> may be configured to utilize yaw rate, such as from an inertial measurement unit <NUM> or other rotational sensor capable of measuring yaw of the marine vessel <NUM>, as the basis for controlling thrust magnitude and direction. A yaw rate sensor, such as an inertial measurement unit (IMU), may be included instead of the drive position sensor <NUM>. In such an embodiment, the controller <NUM> receives yaw position and/or yaw rate from the IMU <NUM> and determines the magnitude of thrust and selects a forward or reverse direction of thrust for each propulsion device <NUM> and <NUM> based on the yaw rate command. In one embodiment, the controller <NUM> estimates a drive angle θ of the parallel propulsion devices based on the sensed yaw rate and calculates the thrust magnitudes and directions accordingly. For example, the controller <NUM> may receive engine speed and/or throttle position from the ECMs <NUM> and <NUM> and may estimate the drive angle based on the yaw rate and the thrust-magnitude-related values, such as RPM or throttle position.

The sensed yaw rate can further be used as feedback control for adjusting the thrust commands. Namely, the controller <NUM> may determine an expected yaw rate associated with the lateral and/or rotational thrust command from the user input device <NUM> and may compare the measured yaw rate from the IMU <NUM> to the expected yaw rate and adjust the thrust commands in order to reduce the difference between the measured yaw rate and the expected yaw rate. Such feedback control can be utilized in embodiments with or without the drive position sensor <NUM>. In such embodiments, the propulsion system <NUM> includes both a drive position sensor <NUM> and an IMU <NUM> or other yaw rate sensor.

<FIG> depict exemplary thrust scenarios to effectuate rotational and translational motion when the drives are at drive angle θ. In <FIG> the propulsion devices <NUM> and <NUM> effectuate opposite thrusts with equal magnitude so as to effectuate a clockwise rotational movement of the vessel <NUM>. The force vectors from the propulsion devices on the port and starboard sides of the center line <NUM> on the stern of the marine vessel, and, where utilized, the thrust vector by the bow thruster <NUM>, are added through normal vector analysis in order to result in the desired rotational and/or translational movement commanded at the user input device <NUM>. Namely, the thrust vector F1 for the first propulsion device <NUM>, or the total thrust of the propulsion devices on the port side of the center line <NUM>, are in the forward thrust direction to effectuate forward movement of the marine vessel. The thrust vector F2 of the starboard-side propulsion device <NUM>, or the sum of the propulsion devices on the starboard side of the center line <NUM> of the marine vessel <NUM> are in the reverse thrust direction so as to effectuate reverse movement of the marine vessel <NUM>. The forward thrust vector F1 and the reverse thrust vector F2 are equal in magnitude such that the translational forces cancel and only a resultant moment is effectuated in order to turn the marine vessel in the clockwise rotational direction. Here, the bow thruster <NUM> is not operated and remains in the off state.

<FIG> depicts force vectors F1 through F3 effectuated to produce lateral movement of the vessel <NUM> in the starboard direction. Here, the lateral thruster <NUM> is activated in order to effectuate a starboard thrust vector F3 at the bow of the marine vessel. The thrust by the bow thruster <NUM> generates a clockwise moment about the center of turn <NUM> in addition to a lateral force in the starboard direction. The moment caused by the bow thruster <NUM> is counteracted by effectuating an equal and opposite moment with the propulsion devices <NUM> and <NUM> such that the resulting moment equals zero and only the lateral force F3 remains such that the marine vessel <NUM> is moved in the starboard direction.

<FIG> depicts force vectors for effectuating forward movement of the marine vessel <NUM> when the propulsion devices <NUM> and <NUM> are at angle θ. Here the bow thruster <NUM> effectuates a thrust F3 in the port direction, which generates a counterclockwise moment about the COT <NUM>. The counterclockwise moment is counteracted by the thrust F1 and F2 of the propulsion devices at the stern of the marine vessel <NUM> where the port side propulsion devices effectuate a forward thrust F1 and the starboard side propulsion devices effectuate a thrust F2 in the reverse direction to generate a clockwise moment. However, the forward thrust vector F1 is greater in magnitude than the reverse thrust vector, and a resultant total thrust is exerted on the marine vessel <NUM> in order to move it forward.

<FIG> depicts an opposite scenario which effectuates a total thrust on the marine vessel <NUM> in order to move it in the reverse direction. The bow thruster <NUM> is commanded to exert a thrust F3 in the port direction, which generates a moment about the center of turn <NUM> that is counteracted by the thrust F1 and F2 of the propulsion devices at the stern of the vessel <NUM>. Here, the thrust vector F2 in the reverse direction is greater in magnitude than the thrust vector F1 in the forward direction, and thus a total thrust is effectuated to move the marine vessel in the reverse direction.

As will be recognized by a person having ordinary skill in the art in view of this disclosure, other combinations of thrusts may be effectuated in order to accomplish the total thrust commanded by the user. <FIG> demonstrate additional exemplary thrust combinations for effectuating forward and reverse thrusts, respectively. In <FIG>, both propulsion devices are controlled to effectuate equal forward thrusts F1 and F2 and the bow thruster <NUM> is commanded to exert a thrust F3 in the starboard direction, which generates a moment about the center of turn <NUM> that counteracts the moment generated by the thrusts F1 and F2. In <FIG>, both propulsion devices are controlled to effectuate equal reverse thrusts F1 and F2 and the bow thruster <NUM> is commanded to exert a thrust F3 in the port direction, which generates a moment about the center of turn <NUM> that counteracts thrusts F1 and F2.

<FIG> depict methods <NUM>, or portions of, for controlling propulsion of a marine vessel in accordance with embodiments of the present disclosure. In <FIG>, a lateral or rotational thrust command is received at a user input device at step <NUM>, such as at a joystick. The drive angle of the parallel propulsion devices and/or the yaw rate of the marine vessel are sensed at step <NUM> and that information is used at steps <NUM> and <NUM> to determine thrust commands. In embodiments where no drive position sensor <NUM> is provided and only IMU data or yaw rate information from another type of motion sensor is available, the system may be configured to estimated drive angle based on yaw rate, as is described above. For example, the drive angle θ may be estimated based on engine speed and/or throttle position by each ECM <NUM> and <NUM> and a yaw rate. An activation command and a starboard or a port direction command are determined for the lateral thruster at step <NUM>, and a thrust magnitude and forward or reverse direction command are determined for each of the parallel propulsion devices at step <NUM>. The lateral thruster and the propulsion devices are then operated at step <NUM> to effectuate the commanded movement.

<FIG> depicts steps for using sensed yaw rate as feedback for controlling the thrusts. An expected yaw rate is determined at step <NUM> based on the lateral and/or rotational command. For example, a lookup table or formula may be used to associate the joystick or keypad input with a yaw rate. The measured yaw rate, such as by the IMU, is then compared to the expected yaw rate at step <NUM>. If the difference between the measured yaw rate and the expected yaw rate exceeds a threshold at step <NUM>, then the thrust magnitudes and or thrust directions by the propulsion devices and/or the lateral thruster are re-determined so as to minimize the difference between the measured and expected yaw rates.

<FIG> depicts method <NUM> steps for controlling the parallel propulsion devices in the lateral thruster using drive position information. The lateral or rotational command via the user input device at <NUM>. The drive angle θ is sensed at <NUM> by a drive position sensor <NUM> configured to sense an angular position of at least one of the parallel propulsion devices on the transom of the marine vessel. The thrust magnitude and directions for each of the parallel propulsion devices and the thruster are then determined at step <NUM>, as is described above, based on the measured drive angle. The thrusts are then effectuated at step <NUM>. If a change in drive angle is detected, as represented at step <NUM>, then the thrust magnitudes and directions for the propulsion devices and the lateral thruster are re-determined at step <NUM> based on the changed drive angle. The new thrusts are then effectuated at step <NUM>. Thereby, if the drive angle θ, or steering position, of the parallel propulsion devices <NUM> and <NUM> changes due to the user providing a steering input at the steering wheel <NUM>, then the thrust vector calculation will be re-performed so as to effectuate thrusts that are appropriate to maintain the commanded motion of the marine vessel.

Claim 1:
A marine propulsion system (<NUM>) comprising:
at least two parallel propulsion devices (<NUM>, <NUM>), each being configured to rotate about a respective steering axis (<NUM>, <NUM>) and each generating forward and reverse thrusts, wherein the parallel propulsion devices (<NUM>, <NUM>) are maintained in parallel such that their thrusts are parallel to one another;
a steering wheel (<NUM>) configured to rotate the parallel propulsion devices (<NUM>, <NUM>) to control the drive angle (θ);
characterized in that the system further comprises
at least one drive position sensor (<NUM>) configured to sense a drive angle (θ) of at least one of the parallel propulsion devices (<NUM>, <NUM>);
a lateral thruster (<NUM>) configured to generate starboard and port thrusts to propel the marine vessel (<NUM>);
a user input device (<NUM>) operable by a user to provide at least one of a lateral thrust command to command lateral movement of the marine vessel (<NUM>) and a rotational thrust command to command rotational movement of the marine vessel (<NUM>); and
a controller (<NUM>) configured to control magnitude and a forward and/or reverse direction of thrust by the parallel propulsion devices (<NUM>, <NUM>) and the lateral thruster (<NUM>) based on the lateral thrust command and/or the rotational thrust command provided by the user input device (<NUM>) and the drive angle (θ) controlled by an operator via the steering wheel (<NUM>) so as to provide the lateral movement and/or the rotational movement commanded by the user without controlling the drive angle (θ).