TECHNICAL FIELD

This disclosure relates to control of propulsion units, such as combustion engines and electric motors, used to maneuver marine vessels such as leisure craft boats.

BACKGROUND

When operating marine vessels, it is sometimes desired to maneuver the vessel at low speed, such as during docking or station keeping. In this context, the wording “low speed” is defined as speeds around 5 knots or lower. Docking control functions for marine vessels based on movement of a joystick lever are known. Based on the movement of the joystick lever, a vessel steering command can be calculated and executed.

An example of a common docking manoeuvre is a sideways displacement to place the vessel alongside a jetty. For performing a sideways displacement, the marine vessel can comprise a first and a second steerable propulsion unit and a bow thruster. Alternatively, a first and a second rudder can be associated with a first and a second fixed propulsion unit, respectively, and a bow thruster. In a conventional vessel such a docking manoeuver will involve extensive use of the bow thruster, as this is the most convenient way of providing transverse thrust. For instance, the sideways displacement can be achieved by operating the stern thrusters at a constant speed and angular position to provide a sideways thrust which is balanced by the sideways thrust from the bow thruster.

A problem with the known systems is that frequent use of a bow thruster will cause an excessive draining of electric power from an on-board power source such as a battery. A bow thruster will also generate significantly more noise than the main thrusters. The invention aims to provide a solution for solving these problems.

SUMMARY

It is an object of the present disclosure to provide a method and a control unit for improved propulsion control of propulsion units for marine vessels.

This object is achieved by a method and a control unit according to the appended claims. The invention relates to a method for automatic control of multiple propulsion units when maneuvering a marine vessel comprising at least two steerable main propulsion units and at least one transverse propulsion unit. The invention is primarily intended for use during docking, station keeping and other or similar low speed maneuvers. In that context, the term“low speed” should be interpreted as a speed around 1-5 knots (approx. 0,5-2, 5 m/s), or lower. Under these conditions the engines driving main propulsion units are operated at or marginally above idling speed between maneuvers, while the engine speeds are increased as required when a maneuver is being performed. However, some maneuvers can be carried out at speeds up to around 10 knots (see e.g. Figs.3A-3B), which speeds can be considered as being“low speed” in relation to the cruising speed of the vessel.

The method is intended for use with main propulsion units in the form of steerable stern drive installations or outboard installations placed at the rear of a marine vessel. In the subsequent text, the terms main propulsion unit, stern drive and outboard drive should be interpreted as being interchangeable. The main propulsion units are preferably, but not necessarily, powered by internal combustion engines. The main propulsion units are controllable to provide forward, reverse and transverse thrust. Additional transverse thrust can be provided by one or more transverse propulsion units, also termed bow thrusters. In the subsequent text, the terms transverse propulsion unit and bow thruster should also be interpreted as being interchangeable. The term“thrust vector” denotes the direction and magnitude of a thrust force exerted on the marine vessel by a propulsion unit. The direction of the thrust vector is controlled by the steering angle and/or by operating the propulsion unit in forward or reverse. The magnitude of the thrust vector is controlled by the propeller, which is in turn driven by a motor or an engine, optionally via a transmission that may or may not comprise multiple selectable gears. By controlling the propulsion thrust vector for each propulsion unit being operated, the speed and direction of the vessel can be controlled.

The inventive method comprises the steps of:

- receiving input indicating a requested displacement of the vessel towards a desired position and heading; - calculating a required thrust vector for each main propulsion unit in order to achieve the requested displacement;

- determining whether the main propulsion units are able to provide the required thrust vectors; and

if all main propulsion units are able to provide the required thrust vectors:

- controlling the main propulsion units to perform the requested displacement; and if at least one main propulsion unit is unable to provide a required thrust vector:

- controlling the main propulsion units and the transverse propulsion unit to perform the requested displacement.

The input indicating a requested displacement can be commanded by an operator using a suitable controller, such as a multi-axis joystick, a keypad or a graphical user interface (GUI). According to a first example, the determination whether the main propulsion units are able to provide the required thrust vectors can be made by determining when a requested steering angle for at least one main propulsion unit exceeds a maximum steering angle for any one unit. In stern drives the maximum steering angle is measured as the angle between a longitudinal axis through the center of rotation or pivot point of the drive and an axis through the propeller shaft when the steerable drive unit is rotated into its end position. The longitudinal axis is parallel to the center line of the vessel. Commonly, stern drives have a maximum steering angle of 25-30° to either side of the longitudinal axis. According to a second example, the determination whether the main propulsion units are able to provide the required thrust vectors can be made by determining when a requested throttle level, or thrust force magnitude, for at least one main propulsion unit exceeds a throttle level causing cavitation in the propeller of either propulsion unit. Cavitation is most likely to occur when a negative thrust vector is required, that is, when a propulsion unit is reversed. When operated in reverse, the propeller must displace water past the lower housing of the stern drive which will reduce the efficiency of the propeller and require a higher throttle level in order to produce the same thrust force as a propulsion unit operated in the forward direction to provide a positive thrust vector. If the determination according to both the first and the second examples are positive, then all main propulsion units are able to provide the required thrust vectors. In that case, the requested displacement is performed by controlling the main propulsion units only. However, if the determination according to any one of the first or the second examples is negative, then at least one main propulsion unit is unable to provide a required thrust vector. In that case, the requested displacement is performed by controlling the main propulsion units and the transverse propulsion unit. According to the invention, it is desired to perform all displacements of the marine vessel using the main propulsion units, without the assistance of a transverse propulsion unit. However, sudden changes in an input signal to an electronic control unit from the operator, such as a request for an increased rate of displacement or a change in direction requiring a combined transverse and rotational displacement may require thrust vectors outside the operational range of one or more of the main propulsion units. Other operating conditions that may cause sudden changes in the input signal to the electronic control unit can be environmental conditions, such as wind, wave or current conditions. An unexpected displacement or drift can be detected by the operator or by a navigation unit monitoring the vessel position and heading. When the operator or the electronic control unit attempts to compensate for unexpected movement of the vessel, then the required thrust vectors may be outside the operational range of one or more of the main propulsion units.

If and when it has been determined that the main propulsion units are unable to provide the required thrust vectors, the method can perform the additional steps of:

- calculating a required thrust vector for each main propulsion unit and the transverse propulsion unit in order to achieve the requested displacement; and

- controlling at least the main propulsion units and the transverse propulsion unit to perform the requested displacement when at least one main propulsion unit is unable to provide a required thrust vector.

The electronic control unit can continuously monitor whether the required thrust vectors are within the operating range of the main propulsion units or not. If it is detected that the required thrust vectors are within the operating range of the main propulsion units, then the transverse propulsion unit can be switched off. Additional transverse thrust for assisting the main propulsion units can be provided using a transverse propulsion unit in the form of a bow thruster. The bow thruster is operable only during demanding manoeuvers, such as a docking manoeuver involving simultaneous transverse and rotational displacement of the marine vessel. The transverse propulsion unit can be an electric bow thruster connected to batteries, fuel cells or other on-board sources of electric power. The transverse propulsion unit can also be a hydraulic bow thruster. As described above, the main propulsion units are provided in the form of steerable stern drives or outboard drives. The transverse propulsion unit can be provided as a deployable bow thruster or as a thruster placed in a transverse duct through the hull located at the forward end of the vessel.

The input indicating a requested displacement of the vessel towards a desired position and heading can be received from a joystick controlled by the operator. The joystick is usually spring loaded towards a neutral or centred position. From this position it can be tilted in any direction and can also be independently or simultaneously rotated about its own axis. Tilting of the joystick indicates a displacement in a straight line in a desired direction from the current position. Rotation of the joystick while in its neutral position indicates that the vessel should be rotated about its centre of mass in the selected direction of rotation. Consequently, simultaneous tilting and rotation of the joystick indicates a displacement of the vessel in a straight line in a desired direction under simultaneous rotation. Transducers in the joystick can detect the direction and magnitude of the tilting and rotational forces applied to the joystick. In this way, the rate of displacement in a desired direction can be controlled by increasing or decreasing the tilting angle and/or angle of rotation, or by increasing or decreasing the force applied to the joystick. According to one example, the method involves determining whether the main propulsion units are able to perform the requested maneuver based on a detected joystick force request. The electronic control unit receives signals from sensors such as transducers in the joystick, indicating a requested displacement. Signals indicating the direction of tilt and the magnitude of force applied in this direction, as well as the direction of rotation and the degree or magnitude of the rotational movement, the electronic control unit can calculate a required thrust vector for each main propulsion unit in order to achieve the requested displacement. The calculated required thrust vector can then be compared to the maximum thrust vectors that can be supplied by the main propulsion unit for achieving the requested displacement. If at least one main propulsion unit is unable to provide a required thrust vector, then the electronic control unit will control the main propulsion units together with the transverse propulsion unit to perform the requested displacement.

According to an alternative example, the input indicating a requested displacement of the vessel towards a desired target position and heading can be received from a graphical user interface (GUI). The actions in a GUI are usually performed through direct manipulation of the graphical elements, for instance using a touch sensitive screen. A GUI can be provided as a fixed device or screen or in the form of a handheld mobile device. Human interface devices, for the efficient interaction with a GUI can include a keyboard, a keypad, a pointing device for a cursor, a touchpad, a trackball, a joystick, a virtual keyboard or similar devices.

When indicating a requested displacement of the vessel using a GUI, the user can indicate a desired direction or a desired target position. In the latter case the electronic control unit will maneuver the vessel from a starting position to the target position using signals from a position detection system (PDS). The PDS can comprise an electronic compass and/or a satellite global positioning system (GPS) device for providing navigational data to the electronic control unit. The electronic control unit will calculate the required thrust vectors for each main propulsion unit in order to achieve the requested displacement and monitor the progress towards the target position. If required, the thrust vectors for the main propulsion units can be re- calculated and if necessary supplemented by a thrust vector from the transverse propulsion unit. The invention further relates to an electronic control unit arranged to control a propulsion operation of a marine vessel comprising at least two steerable main propulsion units and at least one transverse propulsion unit during docking, station keeping and other low speed maneuvers. The electronic control unit comprises processing circuitry, which processing circuitry is configured to receive an input indicating a requested displacement of the vessel from an operator. The processing circuitry is configured to:

- calculate a required thrust vector for each main propulsion unit in order to achieve the requested displacement;

- determine whether the main propulsion units are able to provide the required thrust vectors;

- control only the main propulsion units to perform the requested displacement if all main propulsion units are able to provide the required thrust vectors; and

- control at least the main propulsion units and the transverse propulsion unit to perform the requested displacement when at least one main propulsion unit is unable to provide a required thrust vector.

The processing circuitry is further configured to determine that the main propulsion units are unable to perform the maneuver if a requested steering angle for at least one main propulsion unit exceeds a maximum steering angle. Alternatively, or in addition, the processing circuitry is configured to determine that the main propulsion units are unable to perform the maneuver if a requested throttle level for at least one main propulsion unit exceeds a throttle level that will cause cavitation in either propulsion unit. If it is determined that either or both of the main propulsion units are unable to provide the required thrust vectors, then the processing circuitry is configured to calculate a required thrust vector for each main propulsion unit and the transverse propulsion unit in order to enable the requested displacement; if at least one main propulsion unit is unable to provide a required thrust vector.

Finally, the invention relates to a propulsion arrangement for a marine vessel comprising at least two steerable main propulsion units and at least one transverse propulsion unit and the electronic control unit as described above. An advantage of the invention is that the transverse propulsion unit or bow thruster is only operated when absolutely necessary. In the case of electrically driven bow thrusters, this will allow battery power to be conserved and/or the load on the generator to be reduced. Further, the computational load on the ECU can be reduced. In the simplest case, involving two main propulsion units, the ECU will most frequently only be required to handle two thrust vectors. Whenever additional thrust vectors are added to the calculations the complexity will increase. A further advantage is that the vessel can be operated more quietly, as bow thrusters can generate more noise and vibrations that the main propulsion units. By utilizing the invention, the bow thruster will only be operated under extreme conditions, such as difficult wind conditions, strong current conditions and/or when performing maneuvers involving simultaneous sideways and rotational displacement of the vessel.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The inventive concept is described below by way of examples, with reference to the accompanying drawings, in which:

Fig. 1 shows a schematically illustrated marine vessel suitable for performing the method according to the invention;

Figs. 2A-2B show a schematically illustrated marine vessel performing a transverse displacement;

Figs. 3A-3B show a schematically illustrated marine vessel performing a combined transverse/forward displacement;

Figs. 4A-4B show a schematically illustrated marine vessel performing a rotational displacement;

Figs. 5A-5B show a schematically illustrated marine vessel performing a combined transverse/rotational displacement in a first direction;

Figs. 6A-6B show a schematically illustrated marine vessel performing a simultaneous transverse/rotational displacement in a second direction; and Fig. 7 shows a schematically illustrated control unit for implementing the method according to the invention.

DETAILED DESCRIPTION

The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art.

Figure 1 shows a schematic overview of a marine vessel 100, a main propulsion arrangement 110 and a steering and propulsion control arrangement 120 for operating the marine vessel 100. The steering and propulsion control arrangement 120 comprises a helm station 121. The helm station 121 is provided with a joystick

122, a steering wheel 123, throttle and shift levers 124 and instrument and navigational data interface 125. The steering wheel 123 and the throttle and shift levers 124 function in a conventional manner, such that rotation of the steering wheel 123 for example activates a transducer that provides a signal to a central electronic control unit 130 regarding a desired steering direction of the marine vessel 100. The throttle and shift levers 124 send signals to the electronic control unit 130 regarding the desired gear (forward, reverse, or neutral) of a pair of main propulsion units 1 11 , 112 and the desired rotational speed of the engines of the main propulsion units 11 1 , 112. A bow thruster or transverse propulsion unit 113 is provided near the bow of the vessel. Figure 1 shows a schematic transverse propulsion unit 1 13 connected to the control unit 130 and does not indicate the actual position of said transverse propulsion unit.

The joystick 122 represents a single driver interface. A single driver interface enables a driver of the marine vessel to operate the steering and the propulsion of the marine vessel in a desired direction using only one single driver interface. A joystick is an example of such single driver interface. Another example is a touch pad interface representing a virtual joystick or a similar graphical user interface (GUI). The joystick 122 can be tilted in any direction from a neutral position and can also be independently or simultaneously rotated about its axis. Tilting of the joystick indicates a displacement in a straight line in a desired direction while maintaining the heading of the vessel. Rotation of the joystick indicates that the vessel should be rotated about its centre of mass in the selected direction of rotation. Consequently, simultaneous tilting and rotation of the joystick indicates a displacement in a straight line in a desired direction under simultaneous rotation of the heading of the vessel. Transducers in the joystick can detect the direction and magnitude of the tilting and rotational forces applied to the joystick. In this way, the rate of displacement in a desired direction can be controlled by increasing or decreasing the tilting angle and/or the angle of rotation, or by increasing or decreasing the force applied to the joystick in the above-mentioned directions.

A steering actuator 131 is operatively connected to a first and a second main propulsion unit 11 1 , 1 12 and controlled via the joystick 122 and/or the steering wheel 123. It should be noted that the steering actuator 131 could comprise one or more individual steering actuators (one shown in Fig.1 ). Each main propulsion unit 1 11 , 112 can be provided with an individual steering actuator, or use one common steering actuator. The first and the second main propulsion unit 1 11 , 112 can also be referred to as port and starboard main propulsion units 11 1 , 112, respectively. The steering actuator 131 governs the positioning of the first and the second main propulsion unit 1 11 , 112 in response to an input signal to the electrical steering actuator. The first and the second main propulsion unit 1 11 , 112 is arranged in working cooperation with a first and a second propeller 115, 116. The first and the second main propulsion units 1 11 , 112 can also be referred to as port propulsion unit 11 1 and starboard propulsion unit 112. The first and the second propulsion units in this example are steerable stern propulsion units. The electronic steering and thruster control unit (ECU) 130 operates as an integrating hub between the helm station 121 and the first and the second main propulsion unit 11 1 , 1 12. A navigation unit 132 such as an electronic compass and/or a satellite global positioning system (GPS) device provides navigational data to the ECU 130 and the operator. The electronic compass can be a solid state, rate gyro electronic compass that detects the direction of the earth's magnetic field using solid state magnetometers and indicates the marine vessel heading relative to magnetic north.

The steering and propulsion arrangement 110 further comprises a bow thruster 113 positioned in the bow of the marine vessel 100. A bow thruster is located forward of the midship position of a marine vessel, preferably in the proximity of the bow, and provides a thrust in the transverse direction of the vessel during low speed manoeuvres, such as docking. The first and the second main propulsion units 1 11 , 112 are steered to control the direction of the thrust from the first and the second propellers 1 15, 116. The first and second main propulsion units can as a rule be rotated over an angle a of +/- 25-30° relative to a longitudinal axis X-i, X ₂ of the vessel through a pivot point P-i, P ₂ for each respective main propulsion unit 1 11 , 1 12 and its associated propeller 115, 116. Figure 1 indicates the signs, i.e. positive/negative, of the steering angle a for the first main propulsion unit 11 1 relative to a longitudinal axis Xi of the vessel through the axis of rotation of the propulsion unit. For both units, a positive angle indicates that the direction of the thrust vector for the propulsion unit intersects the longitudinal centreline C _L of the vessel in front of the propulsion unit. This can also be described as rotating the propulsion unit outwards relative to the longitudinal axis Xi through the axis of rotation of the propulsion unit. Consequently, a negative angle indicates that the direction of the thrust vector for the propulsion unit intersects the longitudinal centreline C _L of the vessel to the rear of the propulsion unit, i.e. an inwards rotation. These signs (+/-) will be adhered to when describing the steering angles a-i, a ₂ in the subsequent text. The magnitude of the thrust is controlled by the engine speed and any intermediate transmission gearing, where provided, driving the propellers. Each propulsion unit can provide a controllable thrust vector acting on the vessel to control the displacement thereof.

The steering and propulsion control arrangement 120 can be in signal communication with the electronic control unit (ECU) 130 via, for example, a CAN bus to control the respective main and transverse propulsion units 1 11 , 1 12, 1 13.

At least the electronic control unit (ECU) 130 can include a memory and a programmable processor. The processor can be communicatively connected to a computer readable medium that includes volatile or non-volatile memory upon which computer readable code is stored. The memory can store data relating to steering angle and thrust force commands to be applied in response to input signals received from an operator, or algorithms for calculating such commands. The processor can access the computer readable code, and the computer readable medium, upon executing the code, carries out functions to displace the vessel. In other examples signal transmission can be performed via wireless communication rather than by a serially wired CAN bus. Note that the connecting lines shown in Figure 1 are meant to show only that the various control elements are capable of communicating with one another, and do not represent actual wiring connecting the control elements, nor do they represent the only paths of communication between the elements.

The method offers the possibility to maneuver the marine vessel sideways and in other transverse directions using the main propulsion units, or stern thrusters as far as possible. The bow thruster will only be operated as a last resort, under operating conditions where the magnitude and/or the direction of the thrust vectors required to perform a desired displacement are outside the operating parameters of the main propulsion units. The method can be implemented on marine vessels having steerable propellers, that is, steerable stern drives of the inboard or outboard type. The method will be disclosed in greater detail with reference to the figures below. The examples given below describe a vessel with two main propulsion units and a single bow thruster, but the method is also applicable to vessels comprising three or more main propulsion units and multiple bow thrusters. The main propulsion units can be powered by combustion engines such as diesel engines, electric motors connected to batteries, fuel cells or the like, or hybrid motors. The bow thruster preferably comprises an electric motor. The propulsion units described in this text imparts the thrust via propellers, although the method is also applicable to jet propulsion units.

Figure 2A schematically illustrates a marine vessel 100 that is to be displaced in a transverse direction at right angles to the longitudinal axis of the vessel and without rotation of the vessel. Figure 2A further illustrates a control signal input device in the form of a joystick 122 for controlling the vessel and a schematic diagram of propulsion unit thrust vectors required for achieving a desired displacement. In order to perform this displacement, the operator tilts the joystick 122 in the desired direction Ti as indicated in the figure. This action causes the vessel 100 to be displaced in a transverse direction D-i towards a desired vessel position 100’. Note that the magnitude and direction of the respective thrust vector indicated in Figure 2A and the subsequent figures is only schematic and not to scale. In operation, the magnitude and direction of each thrust vector may be corrected at any time in order to maintain the displacement of the vessel in the requested direction. In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested transverse displacement of the vessel 100 towards a desired position and heading. In this example the heading remains unchanged, as a transverse displacement is requested. The ECU 130 calculates a required thrust vector F-i, F ₂ for each main propulsion unit 1 11 , 1 12 in order to achieve the requested transverse displacement and determines whether the main propulsion units 1 1 1 , 112 are able to provide the required thrust vectors F-i, F ₂ . The example in Figure 2A indicates a relatively small joystick displacement T-i, whereby all main propulsion units 11 1 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The main propulsion units 11 1 , 1 12 are then controlled to perform the requested displacement D-i. This involves rotating the first propulsion unit 1 11 through a positive angle cq until the direction of its thrust vector intersects the center of mass of the vessel. Similarly, the second propulsion unit 1 12 is rotated through a positive angle a ₂ until the direction of its thrust vector intersects the center of mass of the vessel. The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F-i and the second propulsion unit 1 12 is operated in the reverse direction to produce a second thrust vector F ₂ . The main propulsion units are operated to generate thrust vectors having equal and opposite magnitudes in the longitudinal direction of the vessel, and as they pass through the mass center of the vessel zero net moment is generated about the mass center C _M of the vessel. However, the trust vectors F-i, F ₂ will generate a resultant force in the transverse direction of the vessel, causing a sideways displacement D-i. The displacement is maintained until the joystick is returned to its neutral position or until a change in the control signal indicating a new displacement request is detected. Note that the position of the mass center indicated in the drawing figures can change as the vessel is moving, due to movement of liquid in the fuel or ballast tanks or by weight displacement or redistribution caused by passengers moving about the vessel. The electronic control unit will compensate for such changes using input signals from various suitable sensors.

Figure 2B schematically illustrates a marine vessel 100 that is to be displaced in a transverse direction for the case where at least one main propulsion unit is unable to provide a required thrust vector. Such an event can occur when the operator requests a relatively large and/or fast rate of displacement. In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading, in the same way as described for Figure 2A. The ECU 130 calculates a required thrust vector F’i, F’ ₂ for each main propulsion unit 1 11 , 1 12 in order to achieve the requested transverse displacement and determines whether the main propulsion units 11 1 , 1 12 are able to provide the required thrust vectors F’-i, F’ ₂ . The example in Figure 2B indicates a relatively large joystick displacement T2, whereby it is determined that at least one of the main propulsion units 11 1 , 1 12 is unable to provide the required thrust vectors F’-i, F’ ₂ . A reason for this can be that the magnitude of the required second thrust vector would cause cavitation in the reversing second propulsion unit, and/or that the required steering angle exceeds the maximum steering angle for either propulsion unit 11 1 , 112. The main propulsion units 11 1 , 1 12 are then controlled together with the transverse propulsion unit 1 13 to perform the requested displacement D ₂ . This involves a recalculation of the thrust vectors F’-i, F’ ₂ to take the third thrust vector F ₃ into consideration. The first propulsion unit 11 1 is then rotated through a positive angle a'i until the direction of its thrust vector intersects the center of mass of the vessel. Similarly, the second propulsion unit 1 12 is rotated through a positive angle a' ₂ until the direction of its thrust vector intersects the center of mass of the vessel. The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F’ _I and the second propulsion unit 1 12 is operated in the reverse direction to produce a second thrust vector F’ ₂ . The main propulsion units 11 1 , 112 are initially operated to generate thrust vectors having equal and opposite magnitudes in the longitudinal direction of the vessel, and as they pass through the mass center of the vessel zero net moment is generated about the mass center. The transverse propulsion unit 113 is operated to generate a transverse, third thrust vector F ₃ in the desired direction D ₂ . The first and second trust vectors F’-i, F’ ₂ will then be adjusted to generate a moment about the mass center, in order to balance the moment generated by the third thrust vector F ₃ from the transverse thruster 113. This can be achieved by rotating the first propulsion unit 1 11 to increase the positive angle a ^' i so that the direction of its thrust vector F’ _I intersects the center line C _L to the rear of the center of mass C _M of the vessel, as indicated in Figure 2B, and if necessary increasing the magnitude of the first thrust vector F’ _I . Together the main and transverse thrusters 1 11 , 1 12, 1 13 will generate a resultant force in the transverse direction of the vessel, causing a sideways displacement D ₂ while maintaining the heading of the vessel. The displacement is maintained until the joystick is returned to its neutral position or until a change in the control signal indicating a new displacement request is detected. Figure 3A schematically illustrates a marine vessel 100 that is to be displaced in a combined transverse and forward direction while maintaining the heading of the vessel, i.e. without rotation of the vessel. Figure 3A further illustrates a control signal input device in the form of a joystick 122 for controlling the vessel and a schematic diagram of propulsion unit thrust vectors required for achieving a desired displacement. In order to perform this displacement, the operator tilts the joystick 122 sideways and forwards in the desired direction Ti as indicated in the figure. This action causes the vessel 100 to be displaced in a combined transverse and forward direction D-i towards a desired vessel position 100’. In operation, the electronic control unit (ECU) 130 (see Fig.1 ) receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading. In this example the heading remains unchanged, as a combined transverse and forward displacement is requested. The heading is maintained as there is no rotation of the joystick. The ECU 130 calculates a required thrust vector F-i, F ₂ for each main propulsion unit 1 11 , 1 12 in order to achieve the requested displacement and determines whether the main propulsion units 1 11 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The example in Figure 3A indicates a relatively small joystick displacement T-i, whereby all main propulsion units 1 11 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The main propulsion units 11 1 , 1 12 are then controlled to perform the requested displacement D-i. This involves rotating the first propulsion unit 11 1 through a positive angle cq until the direction of its thrust vector F-i is directed through, in front of, or to the rear of the center of mass C _M of the vessel, depending on the angle of the selected displacement D-i. The case illustrated in Figure 3A shows the thrust vector F-i directed in front of the center of mass. Similarly, the second propulsion unit 1 12 is rotated through a negative angle a ₂ so that the direction of its thrust vector is offset from the center of mass of the vessel. The first and the second propulsion units 11 1 , 112 are then operated in the forward direction to produce a first thrust vector F-i a second thrust vector F ₂ . The first propulsion unit 1 11 is operated to generate a first thrust vector F-i that displaces the vessel in the transverse and forward direction, but which will generate a small clockwise rotation about the mass center. The second propulsion unit 1 12 is operated to generate a second thrust vector F ₂ that will counteract the rotation about the mass center generated by the first thrust vector F-i, so that zero net moment is generated about the mass center C _M - However, the combined trust vectors F-i, F ₂ will produce a resultant force in the transverse and forward direction of the vessel, causing the desired displacement D-i. The displacement is maintained until the joystick is returned to it neutral position or until a change in the control signal indicating a new displacement request is detected. Note that the position of the mass center indicated in the drawing figures can change as the vessel is moving, due to movement of liquid in the fuel or ballast tanks or by weight displacement caused by passengers moving about the vessel. The electronic control unit will compensate for such changes using input signals from various sensors. Figure 3B schematically illustrates a marine vessel 100 that is to be displaced in a combined transverse and forward direction, while maintaining the heading of the vessel, for the case where at least one main propulsion unit is unable to provide a required thrust vector. Such an event can occur when the operator requests a relatively large and/or fast rate of displacement.

In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading, in the same way as described for Figure 3A. The ECU 130 calculates a required thrust vector F’i, F’ ₂ for each main propulsion unit 11 1 , 1 12 in order to achieve the requested displacement and determines whether the main propulsion units 1 11 , 112 are able to provide the required thrust vectors F’-i, F’ ₂ . The example in Figure 3B indicates a relatively large joystick displacement T ₂ , whereby it is determined that at least one of the main propulsion units 11 1 , 112 is unable to provide the required thrust vectors F’-i, F’ ₂ . One reason for this can be that the magnitude of the required second thrust vector would cause cavitation in the reversing second propulsion unit, and/or that the required steering angle exceeds the maximum steering angle for either propulsion unit 11 1 , 112. The main propulsion units 11 1 , 112 are then controlled together with the transverse propulsion unit 1 13 to perform the requested displacement D ₂ . This involves a recalculation of the thrust vectors F’-i, F’ ₂ to take the third thrust vector F ₃ into consideration. The first propulsion unit 1 11 is then rotated through a positive angle a’i until the direction of its thrust vector F’i is directed through the center of mass of the vessel. Similarly, the second propulsion unit 1 12 is rotated through a negative angle a’ ₂ so that the direction of its thrust vector is offset from the center of mass of the vessel. The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F’ _I and the second propulsion unit 112 is operated in the forward direction to produce a second thrust vector F’ ₂ . The transverse propulsion unit is operated to produce a third thrust vector F ₃ to generate displacement at an increased rate in the desired transverse direction. The first propulsion unit 1 1 1 is operated to generate an increased first thrust vector F’ _I that displaces the vessel in the transverse and forward direction, which vector will not generate a rotation about the mass center as long as it intersects the mass center. The second propulsion unit 112 is operated to generate a second thrust vector F’ ₂ that will balance the resultant rotation about the mass center generated by at least the third thrust vector F ₃ , so that zero net rotation is generated about the mass center. Depending on the requested displacement D ₂ and the desired rate of displacement, the magnitude, angle and direction of the thrust vectors are continuously controlled by the ECU 130. Together the main and transverse thrusters 1 11 , 112, 1 13 will generate a resultant force in the combined transverse and forward direction of the vessel, causing the desired increased rate of displacement D ₂ . The displacement is maintained until the joystick is returned to it neutral position or until a change in the control signal indicating a new displacement request is detected.

Figure 4A schematically illustrates a marine vessel 100 that is to be rotated about the center of mass of the vessel, in a clockwise direction in this example. Figure 4A further illustrates a control signal input device in the form of a joystick 122 for controlling the vessel and a schematic diagram of propulsion unit thrust vectors required for achieving a desired displacement. In order to perform this displacement, the operator rotates the joystick 122 in the desired direction T-i, without tilting, as indicated in the figure. This action causes the vessel 100 to be rotated about the center of mass in the direction D-i towards a desired vessel position 100’.

In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading. In this example the heading will change, as a rotational displacement is requested. The ECU 130 calculates a required thrust vector F ₂ for each main propulsion unit 1 11 , 1 12 in order to achieve the requested rotational displacement and determines whether the main propulsion units 11 1 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The example in Figure 4A indicates a relatively small joystick rotation T-i, whereby all main propulsion units 11 1 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The main propulsion units 1 11 , 1 12 are then controlled to perform the requested displacement D-i. This involves setting the first propulsion unit 1 11 at a zero angle (cq = 0; not shown) so that the direction of its thrust vector F-i is parallel to the center line C _L . Similarly, the second propulsion unit 1 12 is set at a zero angle (a ₂ = 0; not shown) so that the direction of its thrust vector F ₂ is parallel to the center line C _L . The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F-i and the second propulsion unit 1 12 is operated in the reverse direction to produce a second thrust vector F ₂ . The main propulsion units are operated to generate thrust vectors having equal and opposite components in the longitudinal direction of the vessel. However, a rotation is generated about the center of mass C _M that is sufficient to achieve the desired rate of rotation. The rate of rotation can be controlled by varying the magnitude and/or the angle of the respective thrust vectors. However, the magnitude and angle of the trust vectors F-i, F ₂ can be adjusted by the ECU 130 to avoid any sideways or longitudinal displacements during the rotation caused by wind or water currents. The rotational displacement is maintained until the joystick is released or until a change in the control signal indicating a new displacement request is detected. Note that the position of the mass center indicated in the drawing figures can change as the vessel is moving, due to movement of liquid in the fuel or ballast tanks or by weight displacement caused by passengers moving about the vessel. The electronic control unit will compensate for such changes using input signals from various sensors.

Figure 4B schematically illustrates a marine vessel 100 that is to be displaced in a transverse direction for the case where at least one main propulsion unit is unable to provide a required thrust vector. Such an event can occur when the operator requests a relatively large and/or fast rotational rate of displacement.

In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested clockwise rotational displacement of the vessel 100 towards a desired position and heading, in the same way as described for Figure 4A. The ECU 130 calculates a required thrust vector F’i, F’ ₂ for each main propulsion unit 1 1 1 , 112 in order to achieve the requested transverse displacement and determines whether the main propulsion units 1 1 1 , 1 12 are able to provide the required thrust vectors F’-i, F’ ₂ . The example in Figure 4B indicates a relatively large joystick displacement T ₂ , whereby it is determined that at least one of the main propulsion units 1 11 , 1 12 is unable to provide the required thrust vectors F’-i, F’ ₂ . This can, for instance, be caused by a limitation of the maximum thrust vector supplied by the reversing second propulsion unit, e.g. due to propeller cavitation. The main propulsion units 11 1 , 1 12 are then controlled together with the transverse propulsion unit 1 13 to perform the requested displacement D ₂ . This involves a recalculation of the thrust vectors F’ _I , F’ ₂ to take the third thrust vector F ₃ into consideration. The first and second propulsion units 11 1 , 1 12 are maintained at a zero angle (a'i = a' ₂ = 0; not shown) so that the direction of their thrust vectors F’ _I , F’ ₂ are parallel to the center line C _L . The first propulsion unit 1 1 1 is then operated in the forward direction to produce a first thrust vector F’ _I and the second propulsion unit 1 12 is operated in the reverse direction to produce a second thrust vector F’ ₂ . The main propulsion units are operated to generate thrust vectors having equal and opposite components in the longitudinal direction of the vessel. However, a rotation is generated about the center of mass C _M that is sufficient to achieve a portion of the desired rate of rotation. The transverse propulsion unit 1 13 is operated to generate a transverse thrust F ₃ together with the main propulsion units 1 11 , 1 12 to generate the remaining portion of the desired rate of rotation in the desired direction D ₂ . However, the magnitude and angle of the thrust vectors F’ _I , F’ ₂ can be adjusted by the ECU 130 to avoid any sideways or longitudinal displacement during the rotation caused by wind or water currents. The first and second thrust vectors F’-i, F’ ₂ will then be adjusted to generate a rotation about the mass center and to complement the rotation generated by the third thrust vector F ₃ from the transverse thruster 113. Together the main and transverse thrusters 1 11 , 1 12, 1 13 will generate a resultant force about the mass center of the vessel, causing a rotational displacement D ₂ . The displacement is maintained until the joystick is returned to it neutral position or until a change in the control signal indicating a new displacement request is detected.

Figure 5A schematically illustrates a marine vessel 100 that is to be displaced in a transverse direction while being rotated about the center of mass of the vessel. In this example rotation in a clockwise direction is requested. Figure 5A further illustrates a control signal input device in the form of a joystick 122 for controlling the vessel and a schematic diagram of propulsion unit thrust vectors required for achieving a desired displacement. In order to perform this displacement, the operator tilts the joystick 122 in the desired direction Ti during simultaneous clockwise rotation T’i, as indicated in the figure. This action causes the vessel 100 to be simultaneously displaced sideways and rotated clockwise about the center of mass in the direction D-i towards a desired vessel position 100’. In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading. In this example the heading changes during the transverse displacement. The ECU 130 calculates a required thrust vector F-i, F ₂ for each main propulsion unit 1 1 1 , 1 12 in order to achieve the requested rotation and transverse displacement and determines whether the main propulsion units 1 1 1 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The example in Figure 5A indicates a relatively small transverse and rotational joystick displacement T-i, T’ _I , whereby all main propulsion units 1 1 1 112 are able to provide the required thrust vectors F-i, F ₂ . The main propulsion units 11 1 , 1 12 are then controlled to perform the requested displacement D-i. This initially involves rotating the first propulsion unit 1 11 through a positive angle cq until the direction of its thrust vector intersects the center of mass of the vessel. Similarly, the second propulsion unit 1 12 is initially rotated through a positive angle a ₂ until the direction of its thrust vector intersects the center of mass of the vessel. The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F-i and the second propulsion unit 1 12 is operated in the reverse direction to produce a second thrust vector F ₂ . The main propulsion units are initially operated to generate thrust vectors having equal and opposite magnitudes in the longitudinal direction of the vessel, and as they pass through the mass center of the vessel zero net rotation is generated about the mass center. The thrust vectors F-i, F ₂ will initially produce a resultant force in the transverse direction of the vessel, causing a sideways displacement. The ECU 130 will then adjust the angle cq of the first propulsion unit 1 11 so that the first thrust vector F-i intersects the center line C _L in front of the center of mass in order to generate a clockwise rotation about the center of mass C _M of the vessel. In this way, a simultaneous sideways displacement and rotation in the requested direction D-i can be achieved. The displacement is maintained until the joystick is returned to its neutral position or until a change in the control signal indicating a new displacement request is detected. Note that the position of the mass center indicated in the drawing figures can change as the vessel is moving, due to movement of liquid in the fuel or ballast tanks or by weight displacement caused by passengers moving about the vessel. The electronic control unit will compensate for such changes using input signals from various sensors.

Figure 5B schematically illustrates a marine vessel 100 that is to be simultaneously rotated and displaced in a transverse direction for the case where at least one main propulsion unit is unable to provide a required thrust vector. Such an event can occur when the operator requests a relatively large and/or fast rate of displacement.

In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading, in the same general direction as described for Figure 5A. The ECU 130 calculates a required thrust vector F’-i, F’ ₂ for each main propulsion unit 1 11 , 1 12 in order to achieve the requested rotational and transverse displacement and determines whether the main propulsion units 11 1 , 1 12 are able to provide the required thrust vectors F’-i, F’ ₂ . The example in Figure 5B indicates a relatively large transverse and rotational joystick displacement T ₂ , T’ ₂ , whereby it is determined that at least one of the main propulsion units 11 1 , 1 12 is unable to provide the required thrust vectors F’-i, F’ ₂ . The main propulsion units 1 11 , 1 12 are then controlled together with the transverse propulsion unit 1 13 to perform the requested displacement D ₂ . This involves a recalculation of the thrust vectors F’-i, F’ ₂ to take the third thrust vector F ₃ into consideration. The first propulsion unit 1 11 is then rotated through a positive angle a’i until the direction of its thrust vector F’i intersects the center of mass of the vessel. Similarly, the second propulsion unit 112 is rotated through a positive angle a’ ₂ until the direction of its thrust vector F’ ₂ intersects the center of mass of the vessel. The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F’ _I and the second propulsion unit 112 is operated in the reverse direction to produce a second thrust vector F’ ₂ . The main propulsion units 1 11 , 1 12 are initially operated to generate thrust vectors having equal and opposite magnitudes in the longitudinal direction of the vessel, and as they pass through the mass center of the vessel zero net rotation is generated about the mass center. The thrust vectors F’-i, F’ ₂ will initially produce a resultant force in the transverse direction of the vessel, causing a sideways displacement. The transverse propulsion unit 113 then is operated to generate a transverse thrust F ₃ to generate at least a rotational component for the displacement in the desired direction D ₂ . The magnitude of the first and second thrust vectors F’-i, F’ ₂ can then be adjusted to increase the rate of displacement in the transverse direction. Alternatively, or in addition, the ECU 130 can adjust at least the angle a’i of the first propulsion unit 1 1 1 so that the first thrust vector F’i intersects the center line C _L in front of the center of mass in order to increase the rotation in the requested direction D ₂ . Together the main and transverse thrusters 11 1 , 1 12, 1 13 will generate a desired resultant transverse and rotational force in the requested direction D ₂ . The displacement is maintained until the joystick is returned to its neutral position or until a change in the control signal indicating a new displacement request is detected.

Figure 6A schematically illustrates a marine vessel 100 that is to be displaced in a transverse direction while being rotated about the center of mass of the vessel. In this example rotation in an anti-clockwise direction is requested. Figure 6A further illustrates a control signal input device in the form of a joystick 122 for controlling the vessel and a schematic diagram of propulsion unit thrust vectors required for achieving a desired displacement. In order to perform this displacement, the operator tilts the joystick 122 in the desired direction T-i during simultaneous anti- clockwise rotation T’-i, as indicated in the figure. This action causes the vessel 100 to be simultaneously displaced sideways and rotated about the center of mass in the direction D-i towards a desired vessel position 100’.

In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading. In this example the heading changes during the transverse displacement. The ECU 130 calculates a required thrust vector F-i, F ₂ for each main propulsion unit 11 1 , 1 12 in order to achieve the requested rotation and transverse displacement and determines whether the main propulsion units 11 1 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The example in Figure 6A indicates a relatively small transverse and rotational joystick displacement T-i, T’i, whereby all main propulsion units 1 1 1 , 1 12 are able to provide the required thrust vectors F-i, F ₂ . The main propulsion units 11 1 , 1 12 are then controlled to perform the requested displacement D-i. This initially involves rotating the first propulsion unit 1 11 through a positive angle a-i until the direction of its thrust vector intersects the center of mass of the vessel. Similarly, the second propulsion unit 1 12 is rotated through a positive angle a ₂ until the direction of its thrust vector intersects the center of mass of the vessel. The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F-i and the second propulsion unit 1 12 is operated in the reverse direction to produce a second thrust vector F ₂ . The main propulsion units are operated to generate thrust vectors having equal and opposite magnitudes in the longitudinal direction of the vessel, and as they pass through the mass center of the vessel zero net rotation is generated about the mass center.

The trust vectors F-i, F ₂ will initially produce a resultant force in the transverse direction of the vessel, causing a sideways displacement. The ECU 130 will then adjust at least the angle cq of the first propulsion unit 1 11 so that the first thrust vector F-i intersects the center line C _L to the rear of the center of mass C _M , as shown in Figure 6A, in order to achieve a simultaneous sideways displacement and anti- clockwise rotation in the requested direction D-i. The displacement is maintained until the joystick is returned to its neutral position or until a change in the control signal indicating a new displacement request is detected. Note that the position of the mass center indicated in the drawing figures can change as the vessel is moving, due to movement of liquid in the fuel or ballast tanks or by weight displacement caused by passengers moving about the vessel. The electronic control unit will compensate for such changes using input signals from various sensors.

Figure 6B schematically illustrates a marine vessel 100 that is to be simultaneously rotated and displaced in a transverse direction for the case where at least one main propulsion unit is unable to provide a required thrust vector. Such an event can occur when the operator requests a relatively large and/or fast rate of displacement.

In operation, the electronic control unit (ECU) 130 receives an input from the joystick 122 indicating a requested displacement of the vessel 100 towards a desired position and heading, in the same way as described for Figure 6A. The ECU 130 calculates a required thrust vector F’-i, F’ ₂ for each main propulsion unit 11 1 , 1 12 in order to achieve the requested rotational and transverse displacement and determines whether the main propulsion units 1 11 , 1 12 are able to provide the required thrust vectors F’-i, F’ ₂ . The example in Figure 6B indicates a relatively large transverse and rotational joystick displacement T ₂ , T’ ₂ , whereby it is determined that at least one of the main propulsion units 11 1 , 1 12 is unable to provide the required thrust vectors F’-i, F’ ₂ .

The main propulsion units 11 1 , 1 12 are then controlled together with the transverse propulsion unit 1 13 to perform the requested displacement D-i’. This involves a recalculation of the thrust vectors F’i, F’ ₂ to take the third thrust vector F ₃ into consideration. The first propulsion unit 11 1 is then rotated through a positive angle a’i until the direction of its thrust vector intersects the center of mass of the vessel. Similarly, the second propulsion unit 112 is rotated through a positive angle a’ ₂ until the direction of its thrust vector intersects the center of mass of the vessel. The first propulsion unit 1 11 is then operated in the forward direction to produce a first thrust vector F’ _I and the second propulsion unit 112 is operated in the reverse direction to produce a second thrust vector F’ ₂ . The main propulsion units 1 11 , 1 12 are initially operated to generate thrust vectors having equal and opposite magnitudes in the longitudinal direction of the vessel, and as they pass through the mass center of the vessel zero net rotation is generated about the mass center. The thrust vectors F’ _I , F’ ₂ will initially produce a resultant force in the transverse direction of the vessel, causing a sideways displacement. The transverse propulsion unit 113 is operated to generate a transverse thrust F ₃ to generate a rotation about the mass center of the vessel. Together the main and transverse thrusters 1 11 , 112, 1 13 will generate a simultaneous transverse displacement and rotation of the vessel, causing the vessel to be displaced in the desired direction D ₂ . The first thrust vector F’ _I can if necessary be adjusted subsequently to generate an additional rotation about the mass center, in order to supplement the rotation generated by the third thrust vector F ₃ from the transverse thruster 113. Alternatively, the third thrust vector F ₃ can be reversed intermittently to increase the rate of the transverse displacement generated by the first and second trust vectors F’-i, F’ ₂ . The displacement is maintained until the joystick is returned to its neutral position or until a change in the control signal indicating a new displacement request is detected.

Figure 7 shows a schematic block diagram illustrating a non-limiting embodiment of the method for controlling a marine vessel as described above. In this example, the block diagram illustrates how to perform a method for a sideways displacement of a vessel. Initially a driver operates the single driver interface 700, in this case a joystick (see Fig.1 ;“122”), to move the marine vessel sideways straight to starboard with a maintained heading. Subsequently a steering and thruster control module 710 receives the input signal carrying the displacement command via the single driver interface, in this case the joystick. When the steering and thruster control module has received the command signal, the steering and thruster control module calculates required magnitudes and angles for the thrust vectors of the first and the second propulsion units. If the thrust vectors are attainable by the main propulsion units, the control module actuates only the first and the second propulsion units, i.e. the port and the starboard propulsion units, in accordance with the received command.

If the thrust vectors are not attainable by the main propulsion units, the control module calculates new required magnitudes and angles for the thrust vectors of the first and the second propulsion units, as well as the magnitude and direction for the thrust vector of the bow thruster. The main propulsion units and the bow thruster are then actuated in response to the received command. Controllers 720 and 730 for the port and starboard main propulsion units are actuated to put the respective propulsion units in gear in accordance with a given command from the control module 710. In this case, the port propulsion unit is put in forward gear Fwd and the starboard propulsion unit is put in reverse gear Rew. The throttle is set to a corresponding value to the inclination of the joystick, i.e. with respect to the indicated value by the driver using the single driver interface. If required by the control module 710, the bow thruster can be controlled to port or starboard by a controller 740, as indicated by the references Port and Stbd in Figure 7, thus pushing the bow in a desired direction. The amount of thrust is set to a corresponding value to the inclination of the joystick, i.e. with respect to the indicated value by the driver using the single driver interface. A steering controller 750 causes the steering angle of the port and starboard propulsion units to be set by a steering actuator (see Figure 1 ;“131”) in accordance with a preset value as a function of the total thrust. In this case, the steering angle values are retrieved from a memory module 751 connected to the steering and thrust control module in response to a joystick displacement. As an option, the steering angle can be set to a corresponding value to the direction of inclination of the joystick, i.e. with respect to the indicated value by the driver using the single driver interface. For instance, if the direction of inclination of the joystick is set at 0° when travelling straight ahead, then a transverse displacement to starboard would be indicated by tilting the joystick in a direction of 90° to the right of the straight- ahead position. The port and starboard steering actuators 752 are operated in parallel to the set main propulsion unit angles. The reference number 760 indicates that a number of sensors are continuously detecting and forwarding measured values to the steering and thrust control module. The sensors may be one or more sensors such as steering angle sensors, throttle level sensors, GPS sensors, gear selection sensors, pressure sensors, temperature sensors and the like.

The steering and thruster control module can comprise a storage medium for storing data relating to the operational capabilities of the different propulsion units. The storage medium can comprise any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory. The control unit comprises an interface module for communications with at least one external port and/or sensor device. As such the interface module can comprise one or more transmitters and receivers, comprising analogue and digital components and a suitable number of ports for wireline or wireless communication. Processing circuitry in the steering and thruster control module controls the general operation of the control unit e.g. by sending data and control signals to the interface module and the storage medium, by receiving data and reports from the interface module, and by retrieving data and instructions from the storage medium. Other components, as well as the related functionality, of the control unit are omitted in order not to obscure the concepts presented herein.

The storage medium can further comprise vessel profiles and/or user profiles which can be configured in order to allow for different control characteristics based on different hull types and the like. Also, a user may configure the control mechanism for personalization. Consequently, according to some aspects, the control unit is arranged to control the propulsion operation of the propulsion unit to perform docking maneuvers based on a marine vessel type. This way the control system can be optimized based on, e.g., hull type and on how the dynamical properties of the vessel changes when ballast tanks are full or empty, or on vessel behavior when subjected to wind and/or currents. Thus, advantageously, a more refined control method is obtained leading to a more consistent docking performance under different operating conditions.