Method and system of governing a boat or the like

Abstract

A method for governing a vessel having a bow-thruster, a stern-thruster respectively, and two engines includes activating the bow-thruster and/or of the stern-thruster with a predetermined number of revolutions and a predetermined rotation direction of the propeller, and simultaneously activating the engines in combination, with a predetermined number of revolutions and a predetermined setting of forward or reverse gear for each of the two engines, with one or more or settings, which are the steering angles of the engines, the gear direction and/or the neutral condition, and the number of revolutions, and which are applied in combination of only two or of all synchronized as a function of the movement of the vessel generated by the propulsion vector resulting from the sum of the individual propulsion forces acting on a center of application of the forces defined for the vessel.

1 . A method of governing a vessel comprising a bow-thruster and/or a stern-thruster, which is/are provided respectively at a bow area and at a stern area of the vessel, and two engines steerable independently from each other,
 said method comprising, for executing displacements of the vessel:   actuating the bow-thruster and/or the stern-thruster with a predetermined number of revolutions and a predetermined direction of rotation of a propeller, so as to cause a predetermined direction of a flow generated by said bow-thruster and/or by said stern-thruster;   alternatively or in combination, actuating said two engines with a predetermined number of revolutions and a predetermined forward or reverse gear setting for each of said two engines, wherein said two engines are steered independently from each other in a steering direction with respect to a longitudinal axis of the vessel and with a predetermined steering angle; and   generating signals providing commands for an alternative or combined activation of said bow-thruster and/or said stern-thruster and/or of one or both of said two engines with predetermined specific operating conditions thereof or a variation of the operating conditions set by a previous command, alternatively or in combination, of said bow-thruster and/or said stern-thruster and/or of one or both of said two engines,   said commands comprising:   a command of said bow-thruster and/or said stern-thruster relating to an activation of a deviation flow in a predetermined direction or to a modification of a direction of said deviation flow, thereby activating a rotation of a propeller of said bow-thruster and/or said stern-thruster with a predetermined direction of rotation or to a modification of said direction of rotation of the propeller between a first and a second direction, and alternatively, or in combination with, a command for setting a thrust intensity exerted by said deviation flow of said bow-thruster and/or said stern-thruster, thereby setting a predetermined number of revolutions of said propeller of said bow-thruster and/or said stern-thruster, or a command for varying said thrust intensity exerted by said deviation flow, thereby varying said number of revolutions of the propeller of said bow-thruster and/or said stern-thruster between a predetermined minimum value and a predetermined maximum value of said thrust intensity, corresponding to said number of revolutions of the engine;   alternatively or in combination, a command for activating at least one or both of said two engines with a predetermined steering angle of one or of both of said two engines and/or with a predetermined direction of a propulsion flow generated by said one or both of said engines, a predetermined direction of rotation of the propeller of said one or both of said two engines, and alternatively or, in combination with, a command for setting a predetermined thrust intensity of a propulsion flow of said one or both of said engines, with a predetermined number of revolutions of the engine and of the propeller of said one or both of said engines, or a command for modifying a steering angle of one or both of said engines, corresponding to a direction of the propulsion flow generated by a corresponding engine, alternatively, or in combination with, a command for varying the direction of the propulsion flow generated by said one or both of said engines, varying the direction of rotation of the propeller of said one or both of said engines, and alternatively, or in combination with, a command for varying the thrust intensity of the propulsion flow generated by said one or both of said engines, corresponding to the variation of the number of revolutions of said one or both of the engines and correspondingly of the propeller of said one or both of said engines between a minimum value and a maximum value of said number of revolutions,   wherein the steering angles of said two engines is variable and is settable at identical or different values from each other according to concordant or opposite directions, and said angles are settable at values corresponding to an orientation of the two engines symmetrical or asymmetrical with respect to the longitudinal axis of the vessel, and wherein the direction of the propulsion flow or an absence of said flow corresponding to a forward or reverse gear direction and to a neutral condition of a corresponding engine of said two engines is settable to be identical or different from each of said two engines;   the method further comprising providing a temporary initial step, which temporally limited, of automatically increasing, automatically decreasing, or automatically inverting one or more operating conditions of the bow-thruster and/or of the stern-thruster and/or of one or both of said engines defined using one or more of said activation, modification, or variation commands of said operating conditions, wherein, when said temporary initial step is terminated, the operating conditions defined by said one or more commands are restored.   
     
     
         2 . The method according to  claim 1 , wherein a duration of said temporary initial step and/or the increase or the decrease of the operating conditions of the bow-thruster and/or of the stern-thruster and/or of one or both of the engines with respect to the conditions defined by a command or by a combination of commands is defined as a function of contingent navigation conditions of the vessel and/or as a function of a mass thereof, according to a motion inertia resulting from said mass. 
     
     
         3 . The method according to  claim 1 , wherein a duration of the temporary initial step of application of said command or of a combination of said commands and/or the increase or the decrease of the operating conditions set and defined by said command or by the combination of said commands is determined empirically by applying one or a combination of said commands using manual setting members of a target displacement of the vessel, said manual setting members being univocally correlated with one or a combination of said commands, and by verifying delays or differences in execution of an actual displacement of the vessel with respect to a displacement defined by said command or combination of commands, thereby performing manual variations or corrections for compensation of the operating conditions defined by said command or combination of commands and applying said manual variations or corrections for a predetermined period of time using said setting members,
 said manual variations or corrections or said predetermined period of time being stored and used as a determination of the duration of the temporary initial step a the time of application of said command or combination of commands, and for determining an increase of one or more operating conditions defined in the command or combination of commands and being applied automatically in said temporary initial step.   
     
     
         4 . The method according to  claim 1 , wherein further comprising a step of generating setting commands of a target displacement of the vessel using setting members which generate one or more setting signals,
 said one or more setting signals being processed by a control unit to generate a control signal or a combination of control signals of actuators associated with one or more of the bow-thruster and/or the stern-thruster and each of said two engines,   said actuators being configured to respectively modify one of the operating conditions of the bow-thruster or the stern-thruster or of one or both of the two engines respectively with respect to a direction of a deviation flow or to thrust intensity of said deviation flow, corresponding to a direction of rotation of the propellers or to a number of revolutions of the engine or the propeller for the bow-thruster or the stern-thruster, and with respect to the direction of the deviation flow or to the thrust intensity of said deviation flow, corresponding to a direction of rotation of the propellers or to a number of revolutions of a respective engine or of a respective propeller and to a steering angle for one or both of said two engines;   said control signals comprising setting values respectively of:   the direction of the deviation flow, corresponding to the rotation of the propellers or the thrust intensity exerted by said deviation flow, corresponding to a number of revolutions of the respective engine or of the respective propeller of the bow-thruster and/or of the stern-thruster; or   a steering angle of one or both of the two engines;   wherein, in said temporary initial step, one or more of said control signals are applied to one or more corresponding actuators with modified temporarily setting values with respect to values defined in said control signals as a function of said setting signals, and   wherein said variations are defined experimentally during a calibration cycle and consist of incremental variations or decremental variations with respect to the values defined as a function of the setting signals.   
     
     
         5 . The method according to  claim 1 , further comprising increasing, during said temporary initial step, an intensity of the deviation flow due to a rotation of the propeller of the bow-thruster or the stern-thruster when actuating a command for a rotation of the vessel around a vertical rotation axis, so as to overcome an inertia of the vessel, wherein said temporary initial step provides a duration below about twenty seconds. 
     
     
         6 . The method according to  claim 1 ,
 wherein, in combination with executing a displacement of the vessel from a stationary condition, causing, during said temporary initial step, an increase both of the thrust intensity of deviation or propulsion flows generated by one or both of the bow-thruster or by the stern-thruster and by one or both engines, thereby causing an increase of a number of revolutions of a corresponding engine or of a corresponding propeller, and   wherein, steering angles of the two engines are set so as to increase a component of the thrust generated by said two engines according to a displacement direction set by setting members as a function of which control signals are generated, a ratio between the increase of the thrust exerted by the bow-thruster or of the stern-thruster and of one or both engines and a corresponding initial increase or decrease being defined by a translation direction set by the setting members of a target displacement of the vessel.   
     
     
         7 . The method according to  claim 1 , further comprising, in combination with a rapid reduction of a translation speed of a vessel, in which a difference between an initial speed and a final target speed is relatively large, applying, in the temporary initial step when actuating one or more commands for reducing said translation speed, before reducing a propulsion thrust intensity of one or both engines, a command for inverting the direction of the propulsion flow of one or both engines,
 said variation of the steering angle or of said steering angles being carried out in such a way as to invert at least some components of the propulsion flow of one or both engines.   
     
     
         8 . The method according to  claim 1 , further comprising a step of setting a minimum value of a thrust intensity of a deviation flow of the bow-thruster or the stern-thruster, or of a propulsion flow of one or both engines, a thrust in a predetermined translation direction of the vessel, or a speed in said translation direction, being further reduced by modifying a steering angle of one of said two engines with respect to a steering angle of the other one of said two engines, so that the two engines have steering angles that are asymmetric with respect to a central longitudinal axis of the vessel,
 wherein the steering angles of said two engines are modified so as to generate a resultant of the displacement of the vessel in a set target displacement direction which corresponds to a lower intensity of said thrust in said target displacement direction or to a lower displacement speed of the vessel in said target displacement direction, in combination with a number of revolutions of an engine or of a propeller corresponding to a minimum number of revolutions set or settable for the two engines or no lower than said minimum number of revolutions set or settable for the two engines.   
     
     
         9 . The method according to  claim 1 ,
 wherein a set target movement of the vessel is a lateral translation movement, or so-called “sideways” movement, having a transversal displacement direction, corresponding to a displacement direction of the vessel having a predetermined angle with respect to an orientation of the longitudinal axis of the vessel, among which, in particular, a displacement direction perpendicular to said longitudinal axis of the vessel,   wherein a governing command provides an angular positioning of the two engines according to two non-parallel steering directions, the two non-parallel steering directions being oriented according to opposite steering angles with respect to a central longitudinal axis of the vessel, said steering directions being settable with steering angles having an amplitude that is identical or different with respect to said central longitudinal axis of the vessel, said steering angles of said two engines being symmetrical or asymmetrical with respect to said central longitudinal axis of the vessel,   wherein, in combination with said positioning of the engines according to said two non-parallel steering directions, each engine is set independently of the other in a forward, reverse, neutral gear condition, or each engine is regulated independently from the other at a predetermined number of revolutions,   wherein, for said bow-thruster and/or for said stern-thruster, the respective engines of the propellers thereof are set independently in a forward, reverse, or neutral gear condition or are set independently at a predetermined number of revolutions, so as to generate thrust forces of the vessel having components transverse to the longitudinal axis of the vessel and parallel to a desired transversal translation direction, and   wherein the steering angles of the two engines are primarily or initially symmetrical, said steering angles being then varied so as to have asymmetrical magnitudes with respect to said central longitudinal axis of the vessel, so as to generate at least one component of the propulsion flow of at least one of said two engines that causes a reduction of an advancing thrust of said vessel in a translation direction when a displacement speed of the vessel is higher than a desired speed and the two engines are regulated to a minimum value of the number of revolutions, corresponding to the thrust exerted by the propulsion flow thereof, and cannot be further reduced.   
     
     
         10 . The method according to  claim 1 , wherein one or more manual setting signals of a target displacement of the vessel are generated with one or more separate setting members or with a single integrated setting member configured as a joystick. 
     
     
         11 . The method according to  claim 1 , further comprising a step of automatically detecting, with sensors, one or more different parameters selected from the group consisting of:
 position coordinates of the vessel relative to a GPS system or relative to surveys of morphology of a coast or of stationary installations or other references considered stationary, which can be captured in frames of a video camera;   distance of the vessel from one or more stationary references or presence of said stationary references or floating obstacles;   variations in acceleration of the vessel, both in intensity and direction;   orientation of the bow of the vessel, corresponding to an orientation of a longitudinal axis of the vessel with respect to a terrestrial magnetic field, as detected by a compass angle;   wind direction and speed;   current direction and speed;   variations of the vessel's trim;   further comprising a step of processing one or more measurement signals to generate automatic command signals, alternative or applied in combination with command signals generated as a function of manual setting signals.   
     
     
         12 . A method for governing a vessel comprising a bow-thruster and a stern-thruster provided respectively at a bow area and at a stern area of the vessel, and two engines steerable independently from each other,
 said method comprising, for executing displacements of the vessel, activating the bow-thruster or the stern-thruster with a predetermined number of revolutions and a predetermined rotation direction of a propeller by having a predetermined direction of a flow generated by said bow-thruster and/or said stern-thruster, and alternatively or in combination, activating said two engines with a predetermined number of revolutions and a predetermined setting of forward or reverse gear for each of said two engines, said engines being steered each independently from the other in a steering direction with respect to a central longitudinal axis of the vessel and with a predetermined steering angle,   said method comprising a step of generating commands configures as signals for an alternative or combined activation of said bow-thruster and said stern-thruster and/or of one or both of said engines with predetermined specific operating conditions thereof or a variation of operating conditions of the vessel set with a previous command, alternatively or in combination, of said bow-thruster and/or said stern-thruster and/or of one or both of said engines,   said commands comprising:   a command of said bow-thruster or of said stern-thruster related to an activation of a deviation flow in a predetermined direction or to a modification of a direction of said deviation flow, related to the activation of the rotation of the propeller of said bow-thruster or of said stern-thruster with a predetermined rotation direction or to a modification of said rotation direction of the propeller between a first and a second direction, said command being provided alternatively or in combination with a command for setting thrust intensity exerted by said deviation flow of said bow-thruster or said stern-thruster, so as to set a predetermined number of revolutions of a propeller of said bow-thruster or of said stern-thruster, or a command for varying said thrust intensity exerted by said deviation flow, so as to vary said number of revolutions of the propeller of said bow-thruster and/or of said stern-thruster between a predetermined minimum value and a predetermined maximum value of said thrust intensity, corresponding to said number of revolutions of the engine;   alternatively or in combination, a command for activating one or both of said two engines with a predetermined steering angle of one or both engines or with a predetermined direction of a propulsion flow generated by the one or both engines, corresponding to a predetermined rotation direction of the propeller of the one or both engines, and alternatively or in combination with a command for setting a predetermined thrust intensity of the propulsion flow of the one or both engines corresponding to a predetermined number of revolutions of the one or both engines, corresponding to a predetermined number of revolutions of the propellers of the one or both engines, or a command for modifying the steering angle of the one or both engines, provided by a direction of the propulsion flow generated by a corresponding engine, alternatively or in combination with a command for varying a direction of the propulsion flow generated by the one or both engines, so as to vary rotation directions of the propellers of the one or both engines, and alternatively or in combination with a command for varying the thrust intensity of the propulsion flow generated by the one or both engines, so as to vary a number of revolutions of the one or both of said engines and of the propellers of the one or both engines between a minimum value and a maximum value of said number of revolutions;   the steering angles of said two engines being variable and being settable to identical or different values from each other according to concordant or opposite directions, said steering angles being settable to values corresponding to a symmetric or asymmetric orientation of the two engines with respect to the central longitudinal axis of the vessel, and the direction of the propulsion flow or an absence of said propulsion flow corresponding to a forward or reverse gear direction, a neutral condition of a corresponding engine of said two engines being settable identical or different from each for said two engines;   further comprising a step of setting a minimum admissible number of revolutions for the two engines, for the bow-thruster, or for the stern-thruster corresponding to a predetermined displacement speed of the vessel and of additionally reducing said displacement speed of the vessel by modifying the steering angle of one of said two engines with respect to the steering angle of the other engine, so that the two engines have steering angles asymmetric with respect to the central longitudinal axis of the vessel, a modification of the steering angle of said two engines being carried out so as to generate a resultant of the displacement of the vessel in a set target displacement direction which corresponds to a lower intensity of said thrust in said direction or a lower displacement speed of the vessel in said direction, in combination with a number of revolutions of the engine or of the propeller corresponding to the minimum number of revolutions set or settable for the two engines or not lower than said minimum number of revolutions set or settable for the two engines.   
     
     
         13 . (canceled) 
     
     
         14 . A system for governing a vessel for implementing a method according to  claim 1 ,
 wherein said system is provided in combination with a vessel comprising a bow-thruster and a stern-thruster positioned respectively in correspondence with a bow area and a stern area of the vessel, and two engines steerable independently from each other,   said system comprising one or more of:   an independent steering actuator for each of the two engines, the independent steering actuator commanding a steering mechanism of a respective engine;   an independent gear direction switching actuator for each of said two engines, the independent gear direction switching actuator commanding a gear switching mechanism of a respective one of said two engines, thereby switching a propulsion flow direction, including one or both of a direction of rotation of the propeller or a direction of a jet flow of a of the respective engine;   an independent power command actuator for each of said two engines, the independent power command actuator actuating an intensity of a propulsion flow thrust or a number of revolutions of a respective engine or of a propeller, thereby commanding a regulation mechanism of a delivered power of a respective engine;   a rotation direction switching actuator of one or more of the propeller of said bow-thruster or of said stern-thruster, or a power command actuator of said bow-thruster or said stern-thruster, for actuating an intensity of a deviation flow thrust corresponding to a number of revolutions of a respective engine or propeller;   independent regulating members of the steering direction of each of said two engines independently from each other;   a member or a combination of separate members for generating one or more setting signals of a target displacement of the vessel, said target displacement comprising maintaining a vessel position or maintaining an orientation of a central longitudinal axis of the vessel, said one or more setting signals comprising setting information on parameters of the operating conditions of respectively the bow-thruster, the stern-thruster, or of one or both engines, said operating conditions comprising setting or variation information to be applied independently or in combination with each other and consisting of:   information on a steering angle to be applied to one or both engines;   information on a gear direction or on a setting of a neutral condition of each of said two engines, jointly or independently from each other;   information on setting or varying a power delivered by said two engines, including information on the thrust intensity of the propulsion flow or the number of revolutions of each engine or of the propeller of each engine independently from each other;   information on setting a direction of a deviation flow, which includes a direction of rotation of the engine or of the propeller of the bow-thruster or of the stern-thruster;   information on setting or varying the delivered power or on the number of revolutions of the engine or of the propeller of the bow-thruster or of the stern-thruster; and   a control unit, in which a control program is loaded that comprises instructions for processing said one or more setting signals generated by one or more setting members of a target displacement of the vessel, to generate, as a function of said one or more setting signals, one or more command signals of one or more of said actuators, so that the thrust exerted on the vessel determines a displacement thereof corresponding to the target displacement set by said one or more setting members,   wherein said control unit is associated with or comprises a clock, and an interface for setting a settable duration of an initial temporary period of application of said one or more command signals to one or more of said actuators, said clock measuring said duration starting from an instant of application of said command signals to said one or more actuators,   wherein said control program comprises instructions for increasing, decreasing, or inverting, by a preset and settable amount, the operating conditions defined by said one or more setting information of said one or more actuators defined by said one or more command signals generated by said processing of said one or more setting signals,   wherein an activation of said clock is caused by said application of said one or more command signals to said one or more actuators, and the control unit is configured to cancel said increase, decrease or invert said one or more command signals during said period when the clock has measured said duration, and   wherein said control unit is provided with or is connected or connectable to an interface for setting an amount of said increase, decrease, or inversion.   
     
     
         15 . The system according to  claim 14 , wherein said one or more setting members of a target displacement of the vessel comprise a combination of members, each intended for generating the one or more setting signals of at least one condition of the bow-thruster, the stern-thruster, or one or both of the two engines, or
 wherein, alternatively, said one or more setting members are configured as a single unified control device comprising a control member movable according to different degrees of freedom with respect to a neutral position, which is an inactive control position, each degree of freedom corresponding to a displacement direction of the vessel with an execution power of said displacement,   wherein said unified control device generates command signals, in which command information of said one or more actuators are encoded, said unified control device being configured as a joystick, and   wherein said control program further comprises instructions for decoding the setting commands generated by said unified control device for said one or more actuators, and a plurality of pre-programmed routines containing instructions for setting a combination of two or more of said actuators, so as to actuate the actuators of said combination in a synchronized manner with each other to obtain a displacement of the vessel according to the direction and/or with a propulsion power corresponding to a movement of said unified setting member with respect to said neutral position thereof.   
     
     
         16 . The system according to  claim 14 , further comprising one or more detection sensors that are activatable manually or automatically for measuring or detecting one or more measurement signals said one or more detection sensors being selected from the group consisting of:
 sensors for detecting position coordinates of the vessel relative to a GPS system or relative to topographic surveys, which can be captured in frames of a video camera;   sensors for measuring a distance of the vessel from one or more stationary references;   sensors of vessel acceleration in one or more spatial directions, both in terms of intensity and direction;   one or more magnetic and/or gyroscopic compasses;   sensors of wind direction and speed;   sensors of current direction and speed;   sensors of variations of the vessel trim;   said control unit being provided with at least one or more inputs for said one or more detection sensors, said control unit being loaded with programs containing instructions for managing functionalities of said one or more detection sensors and/or for receiving signals generated by said one or more detection sensors;   said control unit being loaded or loadable with, and executing, a control program comprising instructions for processing one or more of said measurement signals from said one or more sensors and for generating or automatic varying setting signals or command signals of one or more of said actuators as a function of the measurement signals generated by said one or more sensors or of temporal variations of the measurement signals from said one or more sensors, said setting or command signals that are automatically generated as a function of the measurement signals from said one or more sensors being applied to said one or more actuators alternatively to the command signals generated from the manual setting signals generated by said one or more setting members of a target displacement of the vessel, or being applied in combination with said command signals generated from said manual setting signals generated by said one or more setting members of a target displacement of the vessel as correction signals, which modify the settings as a function of navigation and environmental conditions detected by said one or more sensors,   optionally, further comprising a manual or automatic selector for an alternative or combined application of the command signals generated as a function of the measurement signals from one or more of the sensors, the selector being activated as a function of a variation over time of the measurement signals of at least one or of a number of said one or more sensors.   
     
     
         17 . The system according to  claim 14 ,
 wherein the control unit is connected or connectable to an interface for inputting a preset minimum or maximum limit of the power delivered by one or both engines, the bow-thruster, or the stern-thruster, the power corresponding to a minimum or maximum settable number of revolutions of said engines or of said propellers, and   wherein the control unit executes a control program configured to modify the steering angle of at least one of said two engines with respect to the steering angle of the other one of said two engines so as to have different steering angles for said two engines, which are asymmetric with respect to a central longitudinal axis of the vessel, so as to further reduce the displacement speed of the vessel while maintaining said minimum number of revolutions and generating, with one of said two engines, a component of the propulsion flow that counteracts the set displacement of the vessel.   
     
     
         18 . A system for governing a vessel, wherein the system is provided in combination with a vessel comprising one or both of a bow-thruster and a stern-thruster, and two propulsion engines steerable independently from each other, the system comprising:
 one or more of:   an independent steering actuator for each propulsion engine, the independent steering actuator being configured to control a steering mechanism of the propulsion engine;   an independent gear direction switching actuator for each propulsion engine, the independent gear direction switching actuator being configured to control a gear switching mechanism of the propulsion engine to switch a propulsion flow direction, including a direction of rotation of a propeller or a direction of a jet flow of the propulsion engine;   an independent power control actuator for each propulsion engine, the independent power control actuator actuating an intensity of a propulsion flow thrust or a number of revolutions of the propulsion engine or of the propeller and being configured to control a regulation mechanism of delivered power of the propulsion engine;   further comprising one or more of:   a rotation direction switching actuator of the propeller of the bow-thruster and/or of the stern-thruster, and/or a power control actuator of the bow-thruster and/or the stern-thruster, or a power control actuator for an intensity of a deviation flow thrust;   independent regulating members of the steering direction of each of the two propulsion engines independently from each other; or   a member or a combination of several separate members for generating one or more setting signals of a target displacement of the vessel, the target displacement also comprising maintaining a vessel position and/or maintaining of an orientation of a central longitudinal axis of the vessel, the one or more setting signals comprising setting information on parameters of operating conditions of one or more of the bow-thruster, the stern-thruster, or one or both propulsion engines, the operating conditions comprising setting or varying information to be applied independently or in combination with each other consisting of:
 the steering angle to be applied to one or both propulsion engines; 
 the gear direction and/or on the setting of a neutral condition of each of the two propulsion engines, independently from each other; 
 setting or varying a delivered power of the two engines, or a thrust intensity of the propulsion flow or the number of revolutions of each propulsion engine or of a propeller of each engine independently from each other; 
 a direction of a deviation flow, or on a direction of rotation of the engine and/or of the propeller of the bow-thruster and/or of the stern-thruster; or 
 setting or varying a delivered power or a number of revolutions of the engine or of the propeller of the bow-thruster and/or of the stern-thruster; 
   a control unit in which a control program is loaded, comprising instructions for processing the one or more setting signals generated by one or more setting members of a target displacement of the vessel to generate, as a function of setting information, one or more command signals of one or more actuators, so that a thrust exerted on the vessel determines a displacement thereof corresponding to a target displacement set by the one or more setting members,   wherein the control unit is connected or connectable to an interface for inputting a preset minimum and maximum limit of the power delivered by one or both of the propulsion engines or the engines of the bow-thruster and/or of the stern-thruster, corresponding to a minimum and/or maximum settable number of revolutions of the propulsion engines, the engines of the bow-thruster and/or of the stern-thruster, or of the propellers, and   wherein the control unit executes a control program for modifying a steering angle of at least one of the two propulsion engines with respect to that of the other one of the two propulsion engines so as to have different steering angles for the two propulsion engines, the different steering angles being asymmetric with respect to the central longitudinal axis of the vessel, so as to further reduce a displacement speed of the vessel while maintaining a minimum number of revolutions and generating, with one of the two propulsion engines, a component of the propulsion flow that counteracts a set displacement of the vessel.