Patent Publication Number: US-2023139789-A1

Title: Marine propulsion system and marine vessel

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2021-180106 filed on Nov. 4, 2021. The entire contents of this application are hereby incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a marine propulsion system and a marine vessel, and more particularly, it relates to a marine propulsion system and a marine vessel each including a main propulsion device and an auxiliary propulsion device with different maximum outputs. 
     2. Description of the Related Art 
     A marine vessel including a main propulsion device and an auxiliary propulsion device having different maximum outputs is known in general. Such a marine vessel is disclosed in Japanese Patent Laid-Open No. 2019-199128, for example. 
     Japanese Patent Laid-Open No. 2019-199128 discloses a marine vessel including a hull, a first outboard motor (main propulsion device) attached to the hull, a second outboard motor (auxiliary propulsion device) attached to the hull, and an operator to operate the first outboard motor and the second outboard motor. In the marine vessel described in Japanese Patent Laid-Open No. 2019-199128, the first outboard motor and the second outboard motor have different maximum outputs. Furthermore, in the marine vessel described in Japanese Patent Laid-Open No. 2019-199128, an operation switch is operated to switch between a state in which the first outboard motor is operated by the operator and a state in which the second outboard motor is operated by the operator. In other words, in the marine vessel described in Japanese Patent Laid-Open No. 2019-199128, the first outboard motor and the second outboard motor are not able to be driven simultaneously. In the marine vessel described in Japanese Patent Laid-Open No. 2019-199128, the number of first outboard motors and the number of second outboard motors may be one, or two or more. 
     Although not clearly described in Japanese Patent Laid-Open No. 2019-199128, in a conventional marine vessel as described in Japanese Patent Laid-Open No. 2019-199128, it is necessary to generate a resultant vector of output vectors of a plurality of outboard motors such that a hull moves in a lateral direction in order to move the hull in the lateral direction. In the marine vessel described in Japanese Patent Laid-Open No. 2019-199128, the first outboard motor (main propulsion device) and the second outboard motor (auxiliary propulsion device) are not able to be driven simultaneously, and thus it is necessary to provide at least one of a plurality of first outboard motors or a plurality of second outboard motors in order to move the hull in a lateral direction. Therefore, in a structure including a first outboard motor (main propulsion device) and a second outboard motor (auxiliary propulsion device) having different maximum outputs, it is desired to move a hull in a lateral direction while preventing an increase in the number of outboard motors (propulsion devices). In the field of marine vessels, from the viewpoint of SDGs (Sustainable Development Goals), it is desired to reduce environmental burdens, such as reducing the amount of carbon dioxide emissions associated with driving of propulsion devices. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide marine propulsion systems and marine vessels that each move hulls in a lateral direction while preventing an increase in the number of propulsion devices when including main propulsion devices and auxiliary propulsion devices having different maximum outputs. 
     A marine propulsion system according to a preferred embodiment of the present invention includes a main propulsion device attached to a stern of a hull and operable to rotate in a right-left direction to change a direction of a thrust, an auxiliary propulsion device attached to the stern, including an electric motor to drive an auxiliary thruster to generate a thrust, operable to rotate in the right-left direction to change a direction of the thrust, and having a maximum output smaller than a maximum output of the main propulsion device, and a controller configured or programmed to perform a control to move the hull in a lateral direction by driving both the main propulsion device and the auxiliary propulsion device. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the controller is configured or programmed to perform a control to move the hull in the lateral direction by driving both the main propulsion device and the auxiliary propulsion device having a maximum output smaller than a maximum output of the main propulsion device. Accordingly, both the main propulsion device and the auxiliary propulsion device are driven such that a resultant vector of an output vector of the main propulsion device and an output vector of the auxiliary propulsion device is generated to move the hull in the lateral direction. Thus, the hull is moved in the lateral direction without providing either a plurality of main propulsion devices or a plurality of auxiliary propulsion devices. Consequently, in a structure including the main propulsion device and the auxiliary propulsion device having different maximum outputs, the hull is moved in the lateral direction while an increase in the number of propulsion devices is prevented. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the auxiliary propulsion device used when the hull is moved in the lateral direction includes the electric motor to drive the auxiliary thruster to generate the thrust. Accordingly, unlike the engine, the electric motor does not directly emit carbon dioxide, and thus as compared with a case in which the auxiliary propulsion device including the electric motor is not used when the hull is moved in the lateral direction, from the viewpoint of SDGs, a preferable device structure is achieved. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the main propulsion device is preferably provided on a centerline of the hull in the right-left direction, and the auxiliary propulsion device is preferably provided to one side of the centerline of the hull in the right-left direction. Accordingly, in a structure including the main propulsion device and the auxiliary propulsion device that have different maximum outputs and are asymmetrical to each other in the right-left direction of the hull, the hull is moved in the lateral direction while an increase in the number of propulsion devices is prevented. 
     In such a case, the controller is preferably configured or programmed to perform a control to move the hull in the lateral direction by positioning an intersection of an output vector of the main propulsion device and an output vector of the auxiliary propulsion device on a straight line extending from a center of gravity of the hull toward a side in the lateral direction in which the hull is to move. Accordingly, unlike a case in which the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device is deviated from the straight line extending from the center of gravity of the hull toward a side in the lateral direction in which the hull is to move, a rotational moment is not generated in the hull, and thus the hull is moved in the lateral direction without being rotated. In this description, the term “rotate the hull” indicates changing the orientation of the bow while maintaining the position of the hull, unlike turning of the hull accompanied by forward or backward movement of the hull. 
     In a marine propulsion system including the controller configured or programmed to move the hull in the lateral direction by positioning the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device on the straight line extending from the center of gravity of the hull toward a side in the lateral direction in which the hull is to move, the controller is preferably configured or programmed to perform a control to adjust, according to at least one of a shape of the hull, a size of the hull, and attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, an output of the main propulsion device, a rudder angle of the main propulsion device, an output of the auxiliary propulsion device, and a rudder angle of the auxiliary propulsion device when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction in response to an operation on an operator to move the hull in the lateral direction. Accordingly, the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device is adjusted according to the shape and size of the hull, the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc. to be positioned on the straight line extending from the center of gravity of the hull toward a side in the lateral direction in which the hull is to move. That is, regardless of the shape and size of the hull, the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc., the hull is moved in the lateral direction without being rotated. 
     In a marine propulsion system including the main propulsion device provided on the centerline of the hull in the right-left direction and the auxiliary propulsion device provided to one side of the centerline of the hull in the right-left direction, the controller is preferably configured or programmed to perform a control to move the hull in a diagonal direction in addition to the control to move the hull in the lateral direction by driving both the main propulsion device and the auxiliary propulsion device. Accordingly, in a structure including the main propulsion device and the auxiliary propulsion device having different maximum outputs, the hull is moved in the diagonal direction in addition to the lateral direction while an increase in the number of propulsion devices is prevented. 
     In such a case, the controller is preferably configured or programmed to perform a control to move the hull in the diagonal direction by positioning an intersection of an output vector of the main propulsion device and an output vector of the auxiliary propulsion device on a straight line extending from a center of gravity of the hull toward a side in the diagonal direction in which the hull is to move. Accordingly, unlike a case in which the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device is deviated from the straight line extending from the center of gravity of the hull toward a side in the diagonal direction in which the hull is to move, a rotational moment is not generated in the hull, and thus the hull is moved in the diagonal direction without being rotated. 
     In a marine propulsion system including the controller configured or programmed to move the hull in the diagonal direction by positioning the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device on the straight line extending from the center of gravity of the hull toward a side in the diagonal direction in which the hull is to move, the controller is preferably configured or programmed to perform a control to adjust, according to at least one of a shape of the hull, a size of the hull, and attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, an output of the main propulsion device, a rudder angle of the main propulsion device, an output of the auxiliary propulsion device, and a rudder angle of the auxiliary propulsion device when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the diagonal direction in response to an operation on an operator to move the hull in the diagonal direction. Accordingly, the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device is adjusted according to the shape and size of the hull, the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc. to be positioned on the straight line extending from the center of gravity of the hull toward a side in the diagonal direction in which the hull is to move. That is, regardless of the shape and size of the hull, the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc., the hull is moved in the diagonal direction without being rotated. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the main propulsion device preferably includes an engine having a maximum value and a minimum value of a power range larger than a maximum value and a minimum value of a power range of the electric motor to drive a main thruster to generate the thrust, and the controller is preferably configured or programmed to limit the power range of the engine by matching an upper limit value of the power range of the engine with the maximum value of the power range of the electric motor while both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction, and limit the power range of the electric motor by matching a lower limit value of the power range of the electric motor with the minimum value of the power range of the engine while both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction. Accordingly, the power range of the engine and the power range of the electric motor are limited within the same range while both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction, and thus when the hull is moved in the lateral direction, both the main propulsion device and the auxiliary propulsion device having different maximum outputs are easily driven. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the controller is preferably configured or programmed to cause a direction of an output vector of the main propulsion device and a direction of an output vector of the auxiliary propulsion device to be opposite to each other in a forward-rearward direction when the hull is moved in the lateral direction. Accordingly, the forward-rearward component of the output vector of the main propulsion device and the forward-rearward component of the output vector of the auxiliary propulsion device cancel each other out, and thus the direction of the resultant vector of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device is set to be lateral such that the hull is moved in the lateral direction. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the controller is preferably configured or programmed to perform a control to move the hull in the lateral direction by driving both the main propulsion device and the auxiliary propulsion device when a joystick corresponding to an operator to operate the hull is tilted in the lateral direction. Accordingly, the direction (lateral direction) of an operation on the joystick (operator) and the direction (lateral direction) in which the hull is moved are the same as each other, and thus an operation on the joystick (operator) to move the hull in the lateral direction is performed in an intuitively easy-to-understand state. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the main propulsion device is preferably an engine-type outboard motor including an engine to drive a main propeller corresponding to a main thruster that generates the thrust and provided on a centerline of the hull in the right-left direction, and the auxiliary propulsion device is preferably an electric outboard motor including the electric motor to drive an auxiliary propeller corresponding to the auxiliary thruster and provided to one side of the centerline of the hull in the right-left direction. The maximum value of the power range of the engine is generally larger than the maximum value of the power range of the electric motor. Therefore, as described above, the main propulsion device and the auxiliary propulsion device are an engine outboard motor and an electric outboard motor, respectively, such that a structure in which both the main propulsion device and the auxiliary propulsion device having a maximum output smaller than that of the main propulsion device are driven is easily achieved. 
     A marine propulsion system according to a preferred embodiment of the present invention includes a main propulsion device attached to a stern of a hull and operable to rotate in a right-left direction to change a direction of a thrust, an auxiliary propulsion device attached to the stern, operable to rotate in the right-left direction to change a direction of a thrust, and having a maximum output smaller than a maximum output of the main propulsion device, and a controller configured or programmed to perform a control to move the hull in a lateral direction by driving both the main propulsion device and the auxiliary propulsion device. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the controller is configured or programmed to perform a control to move the hull in the lateral direction by driving both the main propulsion device and the auxiliary propulsion device having a maximum output smaller than a maximum output of the main propulsion device. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, in a structure including the main propulsion device and the auxiliary propulsion device having different maximum outputs, the hull is moved in the lateral direction while an increase in the number of propulsion devices is prevented. 
     A marine vessel according to a preferred embodiment of the present invention includes a hull, and a marine propulsion system provided on or in the hull. The marine propulsion system includes a main propulsion device attached to a stern of the hull and operable to rotate in a right-left direction to change a direction of a thrust, an auxiliary propulsion device attached to the stern, including an electric motor to drive an auxiliary thruster to generate a thrust, operable to rotate in the right-left direction to change a direction of the thrust, and having a maximum output smaller than a maximum output of the main propulsion device, and a controller configured or programmed to perform a control to move the hull in a lateral direction by driving both the main propulsion device and the auxiliary propulsion device. 
     In a marine vessel according to a preferred embodiment of the present invention, the controller is configured or programmed to perform a control to move the hull in the lateral direction by driving both the main propulsion device and the auxiliary propulsion device having a maximum output smaller than a maximum output of the main propulsion device. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, in a structure including the main propulsion device and the auxiliary propulsion device having different maximum outputs, the hull is moved in the lateral direction while an increase in the number of propulsion devices is prevented. 
     In a marine vessel according to a preferred embodiment of the present invention, the auxiliary propulsion device used when the hull is moved in the lateral direction includes the electric motor to drive the auxiliary thruster to generate the thrust. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, as compared with a case in which the auxiliary propulsion device including the electric motor is not used when the hull is moved in the lateral direction, from the viewpoint of SDGs, a preferable device structure is achieved. 
     In a marine vessel according to a preferred embodiment of the present invention, the main propulsion device is preferably provided on a centerline of the hull in the right-left direction, and the auxiliary propulsion device is preferably provided to one side of the centerline of the hull in the right-left direction. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, in a structure including the main propulsion device and the auxiliary propulsion device that have different maximum outputs and are asymmetrical to each other in the right-left direction of the hull, the hull is moved in the lateral direction while an increase in the number of propulsion devices is prevented. 
     In such a case, the controller is preferably configured or programmed to perform a control to move the hull in the lateral direction by positioning an intersection of an output vector of the main propulsion device and an output vector of the auxiliary propulsion device on a straight line extending from a center of gravity of the hull toward a side in the lateral direction in which the hull is to move. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the hull is moved in the lateral direction without being rotated. 
     In a marine vessel including the controller configured or programmed to move the hull in the lateral direction by positioning the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device on the straight line extending from the center of gravity of the hull toward a side in the lateral direction in which the hull is to move, the controller is preferably configured or programmed to perform a control to adjust, according to at least one of a shape of the hull, a size of the hull, and attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, an output of the main propulsion device, a rudder angle of the main propulsion device, an output of the auxiliary propulsion device, and a rudder angle of the auxiliary propulsion device when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction in response to an operation on an operator to move the hull in the lateral direction. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, regardless of the shape and size of the hull, the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc., the hull is moved in the lateral direction without being rotated. 
     In a marine vessel including the main propulsion device provided on the centerline of the hull in the right-left direction and the auxiliary propulsion device provided to one side of the centerline of the hull in the right-left direction, the controller is preferably configured or programmed to perform a control to move the hull in a diagonal direction in addition to the control to move the hull in the lateral direction by driving both the main propulsion device and the auxiliary propulsion device. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, in a structure including the main propulsion device and the auxiliary propulsion device having different maximum outputs, the hull is moved in the diagonal direction in addition to the lateral direction while an increase in the number of propulsion devices is prevented. 
     In such a case, the controller is preferably configured or programmed to perform a control to move the hull in the diagonal direction by positioning an intersection of an output vector of the main propulsion device and an output vector of the auxiliary propulsion device on a straight line extending from a center of gravity of the hull toward a side in the diagonal direction in which the hull is to move. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the hull is moved in the diagonal direction without being rotated. 
     In a marine vessel including the controller configured or programmed to move the hull in the diagonal direction by positioning the intersection of the output vector of the main propulsion device and the output vector of the auxiliary propulsion device on the straight line extending from the center of gravity of the hull toward a side in the diagonal direction in which the hull is to move, the controller is preferably configured or programmed to perform a control to adjust, according to at least one of a shape of the hull, a size of the hull, and attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, an output of the main propulsion device, a rudder angle of the main propulsion device, an output of the auxiliary propulsion device, and a rudder angle of the auxiliary propulsion device when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the diagonal direction in response to an operation on an operator to move the hull in the diagonal direction. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, regardless of the shape and size of the hull, the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc., the hull is moved in the diagonal direction without being rotated. 
     In a marine vessel according to a preferred embodiment of the present invention, the main propulsion device preferably includes an engine having a maximum value and a minimum value of a power range larger than a maximum value and a minimum value of a power range of the electric motor to drive a main thruster to generate the thrust, and the controller is preferably configured or programmed to limit the power range of the engine by matching an upper limit value of the power range of the engine with the maximum value of the power range of the electric motor while both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction, and limit the power range of the electric motor by matching a lower limit value of the power range of the electric motor with the minimum value of the power range of the engine while both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, when the hull is moved in the lateral direction, both the main propulsion device and the auxiliary propulsion device having different maximum outputs are easily driven. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram showing a marine propulsion system according to a preferred embodiment of the present invention. 
         FIG.  2    is a schematic view showing a marine vessel according to a preferred embodiment of the present invention. 
         FIG.  3    is a side view showing a main propulsion device of a marine vessel according to a preferred embodiment of the present invention. 
         FIG.  4    is a side view showing an auxiliary propulsion device of a marine vessel according to a preferred embodiment of the present invention. 
         FIG.  5    is a diagram showing the power range of an engine of a main propulsion device and the power range of an electric motor of an auxiliary propulsion device according to a preferred embodiment of the present invention. 
         FIG.  6    is a diagram showing a joystick of a marine vessel according to a preferred embodiment of the present invention. 
         FIG.  7    is a schematic view showing lateral movement of a hull of a marine vessel according to a preferred embodiment of the present invention. 
         FIG.  8    is a schematic view showing diagonal movement of a hull of a marine vessel according to a preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are hereinafter described with reference to the drawings. 
     The structures of a marine propulsion system  100  and a marine vessel  110  according to preferred embodiments of the present invention are now described with reference to  FIGS.  1  to  8   . In the figures, arrow FWD represents the front of the marine vessel  110 , arrow BWD represents the rear of the marine vessel  110 , arrow L represents the left (port side) of the marine vessel  110 , and arrow R represents the right (starboard side) of the marine vessel  110 . 
     As shown in  FIG.  1   , the marine vessel  110  includes a hull  10  and the marine propulsion system  100 . The marine propulsion system  100  is provided on or in the hull  10 . The marine propulsion system  100  propels the marine vessel  110 . The marine vessel  110  may be a relatively small marine vessel used for sightseeing or fishing, for example. 
     The marine propulsion system  100  includes a main propulsion device  20 , an auxiliary propulsion device  30 , an operator  40 , and a controller  50 . The operator  40  and the controller  50  are provided on and in the hull  10 . 
     As shown in  FIG.  2   , only one main propulsion device  20  is attached to a stern  11  of the hull  10 . The main propulsion device  20  is located on a centerline  91  of the hull  10  in a right-left direction. 
     As shown in  FIG.  3   , the main propulsion device  20  includes a main propulsion device main body  20   a  and a bracket  20   b . The main propulsion device main body  20   a  is attached to the stern  11  of the hull  10  via the bracket  20   b.    
     The main propulsion device  20  is an engine outboard motor including an engine  22  to drive a main propeller  21  that generates a thrust. Specifically, the main propulsion device main body  20   a  includes the engine  22 , a drive shaft  23 , a gearing  24 , a propeller shaft  25 , and the main propeller  21 . The engine  22  is an internal combustion engine that generates a driving force. The driving force of the engine  22  is transmitted to the main propeller  21  via the drive shaft  23 , the gearing  24 , and the propeller shaft  25 . The main propeller  21  generates a thrust by rotating in the water by the driving force transmitted from the engine  22 . The main propeller  21  is an example of a “main thruster”. 
     The main propulsion device main body  20   a  includes a shift actuator  26  that switches the shift state of the main propulsion device  20 . The shift actuator  26  switches the shift state of the main propulsion device  20  between a forward movement state, a backward movement state, and a neutral state by switching the meshing of the gearing  24 . In the forward movement state, a driving force is transmitted from the engine  22  to the main propeller  21  to generate a forward thrust from the main propeller  21 . In the backward movement state, a driving force is transmitted from the engine  22  to the main propeller  21  to generate a backward thrust from the main propeller  21 . In the neutral state, a driving force is not transmitted from the engine  22  to the main propeller  21  in order to not generate a thrust in the main propeller  21 . In the main propulsion device  20 , when the shift state of the main propulsion device  20  is switched, the gearing  24  generates relatively loud noises and vibrations. 
     The main propulsion device  20  rotates in the right-left direction to change the direction of a thrust. 
     Specifically, a steering  27  is provided on the bracket  20   b . The steering  27  includes a steering shaft  27   a  that extends in an upward-downward direction. The main propulsion device main body  20   a  is rotated in the right-left direction by the steering  27  about the steering shaft  27   a  with respect to the bracket  20   b . When the main propulsion device main body  20   a  rotates in the right-left direction about the steering shaft  27   a , the orientation of the main propeller  21  also rotates in the right-left direction. Thus, the direction of the thrust of the main propeller  21  is changed. In the following description, changing the direction of the thrust of the main propeller  21  by rotating the orientation of the main propeller  21  in the right-left direction is referred to as “steering the main propulsion device  20 ”. 
     As shown in  FIG.  2   , the main propulsion device  20  is steerable by about 30 degrees to each of the L side and the R side. That is, a steering angular range A 10 , which is an angular range in which the main propulsion device  20  is steerable, is about 60 degrees. 
     As shown in  FIG.  1   , the main propulsion device  20  includes an engine control unit (ECU)  28  and a steering control unit (SCU)  29 . The ECU  28  controls driving of the engine  22  and driving of the shift actuator  26  based on control by the controller  50 . The SCU  29  controls driving of the steering  27  based on control by the controller  50 . The ECU  28  and the SCU  29  include a control circuit including a central processing unit (CPU), for example. 
     As shown in  FIG.  2   , only one auxiliary propulsion device  30  is attached to the stern  11  of the hull  10 . The auxiliary propulsion device  30  is provided to one side of the centerline of the hull  10  in the right-left direction. In the marine propulsion system  100 , the auxiliary propulsion device  30  is provided to the L side of the hull  10 . 
     As shown in  FIG.  4   , the auxiliary propulsion device  30  includes a cowling  30   a , an upper case  30   b , a lower case  30   c , and a duct  30   d . The cowling  30   a , the upper case  30   b , the lower case  30   c , and the duct  30   d  are aligned in this order from top to bottom. The cowling  30   a  is attached to the stern  11  of the hull  10 . 
     The auxiliary propulsion device  30  is an electric outboard motor including an electric motor  32  to drive an auxiliary propeller  31  that generates a thrust. Specifically, the auxiliary propulsion device  30  includes the electric motor  32  and the auxiliary propeller  31 . The electric motor  32  is provided in the duct  30   d . The auxiliary propeller  31  is provided in the duct  30   d . The electric motor  32  is driven by power from a battery (not shown) provided in the hull  10 . The electric motor  32  includes a stator  32   a  that is integral and unitary with the duct  30   d , and a rotor  32   b  that is integral and unitary with the auxiliary propeller  31 . The auxiliary propeller  31  generates a thrust by rotating in the water by a driving force transmitted from the electric motor  32 . The auxiliary propeller  31  is an example of an “auxiliary thruster”. 
     When the auxiliary propeller  31  is rotated forward, a forward thrust is generated from the auxiliary propeller  31 . When the auxiliary propeller  31  is rotated backward, a backward thrust is generated from the auxiliary propeller  31 . When the auxiliary propeller  31  is stopped, a thrust is not generated from the auxiliary propeller  31 . That is, in the auxiliary propulsion device  30 , it is not necessary to switch the meshing of the gearing  24  (see  FIG.  3   ) unlike the main propeller  21  (see  FIG.  3   ) of the main propulsion device  20  (see  FIG.  3   ). Thus, the auxiliary propulsion device  30  does not generate relatively loud noises or vibrations unlike the main propulsion device  20 . 
     The auxiliary propulsion device  30  rotates in the right-left direction to change the direction of a thrust. Specifically, a steering  33  is provided in the auxiliary propulsion device  30 . The steering  33  includes a steering shaft  33   a  fixed to the lower case  30   c  and extending in the upward-downward direction. An upper end of the steering shaft  33   a  is located in the upper case  30   b . A lower end of the steering shaft  33   a  is fixed to the duct  30   d . The duct  30   d  and the lower case  30   c  are rotatable in the right-left direction by the steering  33  about the steering shaft  33   a  with respect to the cowling  30   a  and the upper case  30   b . When the duct  30   d  rotates in the right-left direction about the steering shaft  33   a , the orientation of the auxiliary propeller  31  also rotates in the right-left direction. 
     Thus, the direction of the thrust of the auxiliary propeller  31  is changed. In the following description, changing the direction of the thrust of the auxiliary propeller  31  by rotating the orientation of the auxiliary propeller  31  in the right-left direction is referred to as “steering the auxiliary propulsion device  30 ”. 
     As shown in  FIG.  2   , the auxiliary propulsion device  30  is steerable by about 70 degrees to each of the L side and the R side. That is, a steering angular range A 20 , which is an angular range in which the auxiliary propulsion device  30  is steerable, is about 140 degrees. 
     As shown in  FIG.  1   , the auxiliary propulsion device  30  includes a motor control unit (MCU)  34  and a steering control unit (SCU)  35 . The MCU  34  and the SCU  35  include a control circuit including a CPU, for example. The MCU  34  controls driving of the electric motor  32  based on control by the controller  50 . The SCU  35  controls driving of the steering  33  based on control by the controller  50 . 
     As shown in  FIG.  5   , the maximum output of the auxiliary propulsion device  30  is smaller than that of the main propulsion device  20 . Specifically, the maximum value T 11  and the minimum value T 12  of the power range T 10  of the engine  22  of the main propulsion device  20  are larger than the maximum value T 21  and the minimum value T 22  of the power range T 20  of the electric motor  32  of the auxiliary propulsion device  30 , respectively. The minimum value T 12  of the power range T 10  of the engine  22  is smaller than the maximum value T 21  of the power range T 20  of the electric motor  32 . That is, the power range T 10  of the engine  22  of the main propulsion device  20  and the power range T 20  of the electric motor  32  of the auxiliary propulsion device  30  overlap each other between the maximum value T 21  of the power range T 20  of the electric motor  32  and the minimum value T 12  of the power range T 10  of the engine  22 . 
     As shown in  FIG.  1   , the operator  40  receives a user&#39;s operation in order to operate (maneuver) the hull  10 . The operator  40  includes a remote control  41 , a steering wheel  42 , and a joystick  43 . The joystick  43  is an example of an “operator”. 
     The remote control  41  includes a lever. The steering wheel  42  is rotatable. The hull  10  is operated by combining an operation on the lever of the remote control  41  and an operation to rotate the steering wheel  42 . 
     As shown in  FIG.  6   , the joystick  43  includes a base  43   a  and a lever  43   b . The lever  43   b  is tiltably and rotatably attached to the base  43   a . The lever  43   b  is urged by an urging member such as a spring to automatically return to a neutral position P 10  when not operated by the user. At the neutral position P 10 , the lever  43   b  is upright and is not rotated. 
     Operations on the joystick  43  are roughly divided into three operations: an operation to tilt the lever  43   b , an operation to tilt and rotate the lever  43   b , and an operation to rotate the lever  43   b . The operation to tilt the lever  43   b  corresponds to an operation to translate the hull  10  (see  FIG.  1   ). The translation includes forward and backward movements, lateral movements, and diagonal movements. The operation to tilt and rotate the lever  43   b  corresponds to an operation to turn the hull  10 . The turning includes clockwise turning and counterclockwise turning. The operation to rotate the lever  43   b  corresponds to an operation to rotate the hull  10 . In the following description, for convenience of explanation, “tilting the lever  43   b ” is referred to as “tilting the joystick  43 ”. 
     A joystick mode switch  43   c  is provided on the base  43   a  of the joystick  43 . In the marine propulsion system  100 , the joystick mode switch  43   c  is pressed to switch between a state in which the controller  50  controls driving of the main propulsion device  20  and driving of the auxiliary propulsion device  30  based on an operation on the joystick  43  (joystick mode) and a state in which the controller  50  controls driving of the main propulsion device  20  and driving of the auxiliary propulsion device  30  based on operations on the remote control  41  and the steering wheel  42  (non-joystick mode). When the marine propulsion system  100  is in the joystick mode, operations on the remote control  41  and the steering wheel  42  are not received. When the marine propulsion system  100  is in the non-joystick mode, an operation on the joystick  43  is not received. 
     As shown in  FIG.  1   , the controller  50  controls the ECU  28  of the main propulsion device  20 , the SCU  29  of the main propulsion device  20 , the MCU  34  of the auxiliary propulsion device  30 , and the SCU  29  of the auxiliary propulsion device  30  based on an operation on the operator  40 . The controller  50  includes a control circuit including a CPU, for example. 
     As shown in  FIGS.  7  and  8   , the controller  50  (see  FIG.  1   ) performs a control to move the hull  10  in a lateral direction and in a diagonal direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30 . When the joystick  43  is tilted in the lateral direction and the diagonal direction, the controller  50  performs a control to move the hull  10  in the lateral direction and the diagonal direction, respectively, by driving both the main propulsion device  20  and the auxiliary propulsion device  30 . 
     As shown in  FIG.  5   , the controller  50  (see  FIG.  1   ) limits the power range T 10  of the engine  22  by matching the upper limit value of the power range T 10  of the engine  22  with the maximum value T 21  of the power range T 20  of the electric motor  32  while both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  (see  FIG.  1   ) in the lateral and diagonal directions, and limits the power range T 20  of the electric motor  32  by matching the lower limit value of the power range T 20  of the electric motor  32  with the minimum value T 12  of the power range T 10  of the engine  22  while both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral and diagonal directions. Specifically, the controller  50  performs a control to limit each of the power range T 10  of the engine  22  and the power range T 20  of the electric motor  32  to a range in which the power range T 10  of the engine  22  and the power range T 20  of the electric motor  32  overlap each other (between the maximum value T 21  of the power range T 20  of the electric motor  32  and the minimum value T 12  of the power range T 10  of the engine  22 ) when both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral direction and the diagonal direction. 
     As shown in  FIG.  7   , the controller  50  (see  FIG.  1   ) performs a control to move the hull  10  in the lateral direction by positioning an intersection  82  of an output vector V 11  of the main propulsion device  20  and an output vector V 21  of the auxiliary propulsion device  30  on a straight line  92  extending from the center of gravity  81  of the hull  10  toward a side in the lateral direction in which the hull  10  is to move. Specifically, the controller  50  (see  FIG.  1   ) controls the output T 1  (see  FIG.  5   ) of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  (see  FIG.  5   ) of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  such that the direction of a resultant vector V 31  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  becomes a direction (lateral direction) in which the joystick  43  is tilted, and the magnitude of the resultant vector V 31  becomes a magnitude corresponding to the amount of tilting of the joystick  43  when the marine propulsion system  100  is in the joystick mode and the joystick  43  (see  FIG.  1   ) is tilted in the lateral direction. Furthermore, the controller  50  controls the output T 1  of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  such that the intersection  82  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  is positioned on the straight line  92  extending from the center of gravity  81  of the hull  10  toward a side in the lateral direction in which the hull  10  is to move.  FIG.  7    shows an example in which the joystick  43  is tilted to the left and the marine vessel  110  is moved to the L side. Furthermore,  FIG.  7    shows an example in which the rudder angle A 1  of the main propulsion device  20  and the rudder angle A 2  of the auxiliary propulsion device  30  are A 11  and A 21 , respectively. 
     The output T 1  (see  FIG.  5   ) of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  (see  FIG.  5   ) of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30 , at which the intersection  82  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  is positioned on the straight line  92  extending from the center of gravity  81  of the hull  10  toward a side in the lateral direction in which the hull  10  is to move, differ depending on the shape and size of the hull  10 , the attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , etc. 
     Therefore, the controller  50  (see  FIG.  1   ) performs a control (calibration control) to adjust, according to at least one of a shape of the hull  10 , a size of the hull  10 , and attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , the output T 1  of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  when both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral direction in response to an operation on the joystick  43  (see  FIG.  1   ) to move the hull  10  in the lateral direction. 
     Specifically, in the marine vessel  110  in which the calibration control is not performed, a vessel operator tilts the joystick  43  (see  FIG.  1   ) such that the hull  10  moves in the lateral direction. At this time, the tilting direction of the joystick  43  is deviated from the lateral direction. That is, in the marine vessel  110  in which the calibration control is not performed, the tilting direction of the joystick  43  and the moving direction of the hull  10  do not match. Then, while tilting the joystick  43  to move the hull  10  in the lateral direction, the vessel operator performs an operation (pressing a calibration button, for example) to memorize the tilting direction of the joystick in which the hull  10  moves in the lateral direction. After that, when the joystick  43  is tilted in the lateral direction, the controller  50  (see  FIG.  1   ) controls the main propulsion device  20  and the auxiliary propulsion device  30  to move the hull  10  in the lateral direction. The calibration control may be performed at the time of the initial operation of the marine propulsion system  100 , or after the attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10  are changed, for example. 
     When both the main propulsion device  20  and the auxiliary propulsion device  30  attached to the stern  11  of the hull  10  are driven to move the hull  10  in the lateral direction, a forward-rearward component of the output vector V 11  of the main propulsion device  20  and a forward-rearward component of the output vector V 21  of the auxiliary propulsion device  30  are opposite to each other in a forward-rearward direction. That is, when the hull  10  is moved in the lateral direction, the controller  50  (see  FIG.  1   ) causes the direction of the output vector V 11  of the main propulsion device  20  and the direction of the output vector V 21  of the auxiliary propulsion device  30  to be opposite to each other in the forward-rearward direction. 
     As shown in  FIG.  8   , the controller  50  (see  FIG.  1   ) performs a control to move the hull  10  in the diagonal direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30 . Specifically, the controller  50  moves the hull  10  in the diagonal direction by positioning an intersection  83  of an output vector V 12  of the main propulsion device  20  and an output vector V 22  of the auxiliary propulsion device  30  on a straight line  93  extending from the center of gravity  81  of the hull  10  toward one side in the diagonal direction that is to be the moving direction of the hull  10 . Furthermore, the controller  50  performs a control to move the hull  10  in the diagonal direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30  when the joystick  43  is tilted in the diagonal direction. 
     Specifically, when the vessel propulsion system  100  is in the joystick mode and the joystick  43  (see  FIG.  1   ) is tilted in the diagonal direction, the controller  50  (see  FIG.  1   ) controls the output T 1  (see  FIG.  5   ) of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  (see  FIG.  5   ) of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  such that the direction of a resultant vector V 32  of the output vector V 12  of the main propulsion device  20  and the output vector V 22  of the auxiliary propulsion device  30  becomes a direction (diagonal direction) in which the joystick  43  is tilted, and the magnitude of the resultant vector V 32  becomes a magnitude corresponding to the amount of tilting of the joystick  43 . Furthermore, the controller  50  controls the output T 1  of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  such that the intersection  83  of the output vector V 12  of the main propulsion device  20  and the output vector V 22  of the auxiliary propulsion device  30  is positioned on the straight line  93  extending from the center of gravity  81  of the hull  10  toward one side in the diagonal direction that is to be the moving direction of the hull  10 .  FIG.  8    shows an example in which the joystick  43  is tilted to the left rear to move the marine vessel  110  to the L side and the BWD side. Furthermore,  FIG.  8    shows an example in which the rudder angle A 1  of the main propulsion device  20  and the rudder angle A 2  of the auxiliary propulsion device  30  are A 12  and A 22 , respectively. A 12  may be equal to or different from A 11 . A 22  may be equal to or different from A 21 . 
     The controller  50  performs a control (calibration control) to adjust, according to the hull  10 , the output T 1  (see  FIG.  5   ) of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  (see  FIG.  5   ) of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  when both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the diagonal direction in response to an operation on the joystick  43  to move the hull  10  in the diagonal direction, similarly to the control to move the hull  10  in the lateral direction. 
     According to the various preferred embodiments of the present invention described above, the following advantageous effects are achieved. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to move the hull  10  in the lateral direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30  having a maximum output smaller than a maximum output of the main propulsion device  20 . Accordingly, both the main propulsion device  20  and the auxiliary propulsion device  30  are driven such that the resultant vector V 31  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  is generated to move the hull  10  in the lateral direction. Thus, the hull  10  is moved in the lateral direction without providing either a plurality of main propulsion devices  20  or a plurality of auxiliary propulsion devices  30 . Consequently, in a structure including the main propulsion device  20  and the auxiliary propulsion device  30  having different maximum outputs, the hull  10  is moved in the lateral direction while an increase in the number of propulsion devices is prevented. 
     According to a preferred embodiment of the present invention, the auxiliary propulsion device  30  used when the hull  10  is moved in the lateral direction includes the electric motor  32  to drive the auxiliary propeller  31  (auxiliary thruster) that generates a thrust. Accordingly, unlike the engine  22 , the electric motor  32  does not directly emit carbon dioxide, and thus as compared with a case in which the auxiliary propulsion device  30  including the electric motor  32  is not used when the hull  10  is moved in the lateral direction, from the viewpoint of SDGs, a preferable device structure is achieved. 
     According to a preferred embodiment of the present invention, the main propulsion device  20  is provided on the centerline  91  of the hull  10  in the right-left direction, and the auxiliary propulsion device  30  is provided to one side of the centerline of the hull  10  in the right-left direction. Accordingly, in a structure including the main propulsion device  20  and the auxiliary propulsion device  30  that have different maximum outputs and are asymmetrical to each other in the right-left direction of the hull  10 , the hull  10  is moved in the lateral direction while an increase in the number of propulsion devices is prevented. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to move the hull  10  in the lateral direction by positioning the intersection  82  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  on the straight line  92  extending from the center of gravity  81  of the hull  10  toward one side in the lateral direction that is to be the moving direction of the hull  10 . Accordingly, unlike a case in which the intersection  82  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  is deviated from the straight line  92  extending from the center of gravity  81  of the hull  10  toward one side in the lateral direction that is to be the moving direction of the hull  10 , a rotational moment is not generated in the hull  10 , and thus the hull  10  is moved in the lateral direction without being rotated. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to adjust, according to at least one of a shape of the hull  10 , a size of the hull  10 , and attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , the output T 1  of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  when both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral direction in response to the operation on the joystick  43  to move the hull  10  in the lateral direction. Accordingly, the intersection  82  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  is adjusted according to the shape and size of the hull  10 , the attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , etc. to be positioned on the straight line  92  extending from the center of gravity  81  of the hull  10  toward one side in the lateral direction that is to be the moving direction of the hull  10 . That is, regardless of the shape and size of the hull  10 , the attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , etc., the hull  10  is moved in the lateral direction without being rotated. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to move the hull  10  in the diagonal direction in addition to the control to move the hull  10  in the lateral direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30 . Accordingly, in a structure including the main propulsion device  20  and the auxiliary propulsion device  30  having different maximum outputs, the hull  10  is moved in the diagonal direction in addition to the lateral direction while an increase in the number of propulsion devices is prevented. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to move the hull  10  in the diagonal direction by positioning the intersection  83  of the output vector V 12  of the main propulsion device  20  and the output vector V 22  of the auxiliary propulsion device  30  on the straight line  93  extending from the center of gravity  81  of the hull  10  toward one side in the diagonal direction that is to be the moving direction of the hull  10 . Accordingly, unlike a case in which the intersection  83  of the output vector V 12  of the main propulsion device  20  and the output vector V 22  of the auxiliary propulsion device  30  is deviated from the straight line  93  extending from the center of gravity  81  of the hull  10  toward one side in the diagonal direction that is to be the moving direction of the hull  10 , a rotational moment is not generated in the hull  10 , and thus the hull  10  is moved in the diagonal direction without being rotated. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to adjust, according to the hull  10 , the output T 1  of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  when both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the diagonal direction in response to the operation on the joystick  43  to move the hull  10  in the diagonal direction. Accordingly, the intersection  83  of the output vector V 12  of the main propulsion device  20  and the output vector V 22  of the auxiliary propulsion device  30  is adjusted according to the shape and size of the hull  10 , the attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , etc. to be positioned on the straight line  93  extending from the center of gravity  81  of the hull  10  toward one side in the diagonal direction that is to be the moving direction of the hull  10 . That is, regardless of the shape and size of the hull  10 , the attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , etc., the hull  10  is moved in the diagonal direction without being rotated. 
     According to a preferred embodiment of the present invention, the main propulsion device  20  includes the engine  22  having a maximum value and a minimum value of the power range larger than a maximum value and a minimum value in the power range of the electric motor  32  to drive the main propeller  21  (main thruster) that generates a thrust, and the controller  50  is configured or programmed to limit the power range T 10  of the engine  22  by matching the upper limit value of the power range T 10  of the engine  22  with the maximum value T 21  of the power range T 20  of the electric motor  32  while both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral direction, and limit the power range T 20  of the electric motor  32  by matching the lower limit value of the power range T 20  of the electric motor  32  with the minimum value T 12  of the power range T 10  of the engine  22  while both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral direction. Accordingly, the power range T 10  of the engine  22  and the power range T 20  of the electric motor  32  are limited within the same range while both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral direction, and thus when the hull  10  is moved in the lateral direction, both the main propulsion device  20  and the auxiliary propulsion device  30  having different maximum outputs are easily driven. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to cause the direction of the output vector V 11  of the main propulsion device  20  and the direction of the output vector V 21  of the auxiliary propulsion device  30  to be opposite to each other in the forward-rearward direction when the hull  10  is moved in the lateral direction. Accordingly, the forward-rearward component of the output vector V 11  of the main propulsion device  20  and the forward-rearward component of the output vector V 21  of the auxiliary propulsion device  30  cancel each other out, and thus the direction of the resultant vector V 31  of the output vector V 11  of the main propulsion device  20  and the output vector V 21  of the auxiliary propulsion device  30  is set to be a lateral direction such that the hull  10  is moved in the lateral direction. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to move the hull  10  in the lateral direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30  when the joystick  43  corresponding to the operator to operate the hull  10  is tilted in the lateral direction. Accordingly, the direction (lateral direction) of an operation on the joystick  43  (operator) and the direction (lateral direction) in which the hull  10  is moved are the same as each other, and thus an operation on the joystick  43  (operator) to move the hull  10  in the lateral direction is performed in an intuitively easy-to-understand state. 
     According to a preferred embodiment of the present invention, the main propulsion device  20  is an engine outboard motor including the engine  22  to drive the main propeller  21  corresponding to the main thruster that generates a thrust and provided on the centerline  91  of the hull  10  in the right-left direction, and the auxiliary propulsion device  30  is an electric outboard motor including the electric motor  32  to drive the auxiliary propeller  31  corresponding to the auxiliary thruster and provided to one side of the centerline of the hull  10  in the right-left direction. The maximum value T 11  of the power range T 10  of the engine  22  is larger than the maximum value T 21  of the power range T 20  of the electric motor  32 . Therefore, as described above, the main propulsion device  20  and the auxiliary propulsion device  30  are an engine outboard motor and an electric outboard motor, respectively, such that the maximum output of the auxiliary propulsion device  30  is smaller than the maximum output of the main propulsion device  20 , and thus a structure in which both the main propulsion device  20  and the auxiliary propulsion device  30  having a maximum output smaller than a maximum output of the main propulsion device  20  are driven is easily achieved. 
     The preferred embodiments of the present invention described above are illustrative in all points and not restrictive. The extent of the present invention is not defined by the above description of the preferred embodiments but by the scope of the claims, and all modifications within the meaning and range equivalent to the scope of the claims are further included. 
     For example, while the main propulsion device  20  is preferably an engine outboard motor including the engine  22  to drive the main propeller  21  corresponding to a main thruster that generates a thrust, and the auxiliary propulsion device  30  is preferably an electric outboard motor including the electric motor  32  to drive the auxiliary propeller  31  corresponding to an auxiliary thruster in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the main propulsion device may alternatively be an electric outboard motor including an electric motor to drive the main propeller corresponding to a main thruster. Furthermore, the main propulsion device and the auxiliary propulsion device may alternatively be inboard motors enclosed within the hull instead of outboard motors, or inboard-outboard motors partially enclosed within the hull. 
     While the controller  50  preferably performs a control to move the hull  10  in the diagonal direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30  when the joystick  43  corresponding to an operator to operate the hull  10  is tilted in the diagonal direction in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the controller may alternatively perform a control to move the hull in the diagonal direction by driving both the main propulsion device and the auxiliary propulsion device when an operation is performed on an operator other than the joystick to move the hull in the diagonal direction. 
     While the controller  50  preferably performs a control to move the hull  10  in the lateral direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30  when the joystick  43  corresponding to an operator to operate the hull  10  is tilted in the lateral direction in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the controller may alternatively perform a control to move the hull in the lateral direction by driving both the main propulsion device and the auxiliary propulsion device when an operation is performed on an operator other than the joystick to move the hull in the lateral direction. 
     While the controller  50  preferably performs a control to adjust, according to the hull  10 , the output T 1  of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  when both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the diagonal direction in response to the operation on the joystick  43  (operator) to move the hull  10  in the diagonal direction in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the controller  50  may not perform a control to adjust, according to the hull, the output of the main propulsion device, the rudder angle of the main propulsion device, the output of the auxiliary propulsion device, and the rudder angle of the auxiliary propulsion device when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the diagonal direction in response to the operation on the operator to move the hull in the diagonal direction. In such a case, the output of the main propulsion device, the rudder angle of the main propulsion device, the output of the auxiliary propulsion device, and the rudder angle of the auxiliary propulsion device may be manually set by the vessel operator when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the diagonal direction, for example. 
     While the controller  50  preferably performs a control to move the hull  10  in the diagonal direction in addition to the control to move the hull  10  in the lateral direction by driving both the main propulsion device  20  and the auxiliary propulsion device  30  in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the controller may not perform a control to move the hull in the diagonal direction by driving both the main propulsion device and the auxiliary propulsion device. 
     While the controller  50  preferably performs a control to adjust, according to at least one of a shape of the hull  10 , a size of the hull  10 , and attachment positions of the main propulsion device  20  and the auxiliary propulsion device  30  to the hull  10 , the output T 1  of the main propulsion device  20 , the rudder angle A 1  of the main propulsion device  20 , the output T 2  of the auxiliary propulsion device  30 , and the rudder angle A 2  of the auxiliary propulsion device  30  when both the main propulsion device  20  and the auxiliary propulsion device  30  are driven to move the hull  10  in the lateral direction in response to the operation on the joystick  43  (operator) to move the hull  10  in the lateral direction in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the controller may not perform a control to adjust, according to at least one of a shape of the hull, a size of the hull, and attachment positions of the main propulsion device and the auxiliary propulsion device to the hull the output of the main propulsion device, the rudder angle of the main propulsion device, the output of the auxiliary propulsion device, and the rudder angle of the auxiliary propulsion device when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction in response to the operation on the operator to move the hull in the lateral direction. In such a case, the output of the main propulsion device, the rudder angle of the main propulsion device, the output of the auxiliary propulsion device, and the rudder angle of the auxiliary propulsion device may be manually set by the vessel operator when both the main propulsion device and the auxiliary propulsion device are driven to move the hull in the lateral direction, for example. 
     While the auxiliary propulsion device  30  is preferably provided to the L side (left side) of the centerline of the hull  10  in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the auxiliary propulsion device may alternatively be provided to the right side of the centerline of the hull. 
     While the main propulsion device  20  is preferably provided on the centerline  91  of the hull  10  in the right-left direction, and the auxiliary propulsion device  30  is preferably provided to one side of the hull  10  in the right-left direction in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the main propulsion device may alternatively be provided to one side of the hull in the right-left direction, or the auxiliary propulsion device may alternatively be provided on the centerline of the hull in the right-left direction. 
     While only one main propulsion device  20  is preferably attached to the stern  11  of the hull  10  in preferred embodiments described above, the present invention is not restricted to this. In the present invention, two or more main propulsion devices may alternatively be attached to the stern of the hull. 
     While only one auxiliary propulsion device  30  is preferably attached to the stern  11  of the hull  10  in preferred embodiments described above, the present invention is not restricted to this. In the present invention, two or more auxiliary propulsion devices may alternatively be attached to the stern of the hull. 
     While the main propulsion device  20  is preferably steerable by about 30 degrees to each of the L side (the left side of the hull) and the R side (the right side of the hull) in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the main propulsion device may alternatively be steerable by an angle other than about 30 degrees to each of the left and right sides of the hull. 
     While the auxiliary propulsion device  30  is preferably steerable by about 70 degrees to each of the L side (the left side of the hull) and the R side (the right side of the hull) in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the auxiliary propulsion device may alternatively be steerable by an angle other than about 70 degrees to each of the left and right sides of the hull. 
     While preferred embodiments of the present invention have been described above, variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.