Patent Publication Number: US-2023140061-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. 2021-180109 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 plurality of propulsion devices and a controller to perform a control to rotate a hull. 
     2. Description of the Related Art 
     A marine vessel including a plurality of propulsion devices and a controller to perform a control to rotate a hull is known in general. Such a marine vessel is disclosed in Japanese Patent Laid-Open No. 2011-140272, for example. 
     Japanese Patent Laid-Open No. 2011-140272 discloses a marine vessel including a hull, a plurality of outboard motors (propulsion devices) to provide a propulsive force for the hull, and a hull ECU (controller) to control driving of the plurality of outboard motors. In the marine vessel described in Japanese Patent Laid-Open No. 2011-140272, the plurality of outboard motors include a right outboard motor attached on the starboard side of the hull and a left outboard motor attached on the port side of the hull. When a vessel operator operates an operator to rotate the hull, the hull ECU performs a control to rotate the hull by driving both the right outboard motor and the left outboard motor. In this description, the terms “rotate the hull”, “the hull is rotated”, “rotating the hull”, etc. indicate changing the orientation of the bow while maintaining the position of the hull, unlike turning of the hull accompanied by forward or rearward movement of the hull. 
     Although not clearly described in Japanese Patent Laid-Open No. 2011-140272, in the marine vessel described in Japanese Patent Laid-Open No. 2011-140272, the plurality of outboard motors conceivably have the same structure as each other. That is, in the marine vessel described in Japanese Patent Laid-Open No. 2011-140272, the plurality of outboard motors conceivably have the same maximum output as each other. On the other hand, a conventional marine vessel as described in Japanese Patent Laid-Open No. 2011-140272 may include a plurality of outboard motors (propulsion devices) having different maximum outputs. In such a case, a hull ECU (controller) needs to perform a control to rotate a hull by driving both the outboard motors having different maximum outputs, and thus the control to rotate the hull is conceivably relatively complex. Therefore, in a structure including a plurality of outboard motors having different maximum outputs, it is desired to rotate a hull while preventing a control by a hull ECU (controller) from being complex. In the field of marine vessels, from the viewpoint of SDGs (Sustainable Development Goals), it is desired to reduce the environmental burdens, such as reducing the amount of carbon dioxide emissions associated with driving propulsion devices. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide marine propulsion systems and marine vessels that each rotate hulls while preventing controls by controllers from being complex when including a plurality of propulsion devices having different maximum outputs. 
     A marine propulsion system according to a preferred embodiment of the present invention includes a main propulsion device to be 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 to be 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, having a maximum output smaller than a maximum output of the main propulsion device, and having a steering angle range wider than a steering angle range of the main propulsion device, and a controller configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device without generating the thrust from the main 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 rotate the hull by driving the auxiliary propulsion device having a maximum output smaller than a maximum output of the main propulsion device and a steering angle range wider than a steering angle range of the main propulsion device without generating a thrust from the main propulsion device. Accordingly, although the main propulsion device and the auxiliary propulsion device have different maximum outputs, the auxiliary propulsion device is driven without generating a thrust from the main propulsion device in the control to rotate the hull, and thus as compared with a case in which a thrust is generated from the main propulsion device and the auxiliary propulsion device is driven, the control by the controller to rotate the hull is prevented from being complex. Furthermore, the auxiliary propulsion device has a steering angle range wider than a steering angle range of the main propulsion device, and thus even when a thrust is not generated from the main propulsion device, the hull is easily rotated by driving the auxiliary propulsion device. Consequently, in a structure including a plurality of propulsion devices having different maximum outputs, the hull is rotated while the control by the controller is prevented from being complex. 
     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 rotate the hull by driving the auxiliary propulsion device including the electric motor to drive the auxiliary thruster to generate a thrust without generating a thrust from the main propulsion device. 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 rotated, 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, it is not necessary to drive both of the propulsion devices that have different maximum outputs and are asymmetrical to each other in the right-left direction of the hull in the control to rotate the hull, and thus the control by the controller to rotate the hull is effectively prevented from being complex. 
     In such a case, the controller is preferably configured or programmed to control an output of the auxiliary propulsion device and a rudder angle of the auxiliary propulsion device such that a rotational moment to rotate the hull counterclockwise is equal or substantially equal to a rotational moment to rotate the hull clockwise. Accordingly, even when the auxiliary propulsion device is provided to one side of the centerline of the hull in the right-left direction, the rotational moment to rotate the hull counterclockwise and the rotational moment to rotate the hull clockwise are equalized such that the rotating speed of the hull at the time of rotating the hull counterclockwise and the rotating speed of the hull at the time of rotating the hull clockwise are equalized or substantially equalized. Consequently, even when the auxiliary propulsion device is provided to one side of the centerline of the hull in the right-left direction, the hull is rotated without reducing the maneuverability. 
     In a marine propulsion system including the controller configured or programmed to control the output of the auxiliary propulsion device and the rudder angle of the auxiliary propulsion device such that the rotational moment to rotate the hull counterclockwise is equal or substantially equal to the rotational moment to rotate the hull clockwise, the controller is preferably configured or programmed to perform a control to make the output and the rudder angle of the auxiliary propulsion device to rotate the hull counterclockwise different from the output and the rudder angle of the auxiliary propulsion device to rotate the hull clockwise such that the rotational moment to rotate the hull counterclockwise is equal or substantially equal to the rotational moment to rotate the hull clockwise. Accordingly, the output of the auxiliary propulsion device and the rudder angle of the auxiliary propulsion device are easily controlled such that the rotational moment to rotate the hull counterclockwise is equal or substantially equal to the rotational moment to rotate the hull clockwise. 
     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 rotate the hull by driving the auxiliary propulsion device without generating the thrust from the main propulsion device and with a rudder angle of the main propulsion device changed to a same side in the right-left direction as a rudder angle of the auxiliary propulsion device. Accordingly, the hull is rotated while the direction of the thrust of the auxiliary propulsion device and the orientation of a portion of the main propulsion device located in the water are relatively aligned with each other, and thus a resistance generated in the portion of the main propulsion device located in the water when the hull is rotated is reduced or prevented. Consequently, the hull is rotated smoothly. 
     In such a case, the controller is preferably configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device without generating the thrust from the main propulsion device and with the rudder angle of the main propulsion device changed to the same side in the right-left direction as the rudder angle of the auxiliary propulsion device up to an end of the steering angle range of the main propulsion device. Accordingly, the rudder angle of the main propulsion device is aligned with the rudder angle of the auxiliary propulsion device as much as possible, and thus a resistance generated by the portion of the main propulsion device located in the water when the hull is rotated is further reduced or prevented. Consequently, the hull is rotated more smoothly. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the auxiliary propulsion device preferably has a maximum value of a power range when generating a thrust for forward movement larger than that when generating a thrust for rearward movement, and the controller is preferably configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device to generate the thrust for forward movement. Accordingly, as compared with a case in which the auxiliary propulsion device is driven to generate a thrust for rearward movement, the rotational moment to rotate the hull is increased to improve the rotating speed of the hull. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the steering angle range of the auxiliary propulsion device is preferably about 60 degrees or more and about 80 degrees or less in each of clockwise and counterclockwise directions. Accordingly, the auxiliary propulsion device is steered to a rudder angle sufficient for only the auxiliary propulsion device to rotate the hull, and thus a structure in which the hull is rotated by driving the auxiliary propulsion device without generating a thrust from the main propulsion device is easily achieved. 
     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 rotate the hull by driving the auxiliary propulsion device when a joystick corresponding to an operator to operate the hull is rotated. Accordingly, the operating direction (rotating direction) of the joystick is the same as the moving direction (rotating direction) of the hull, and thus the joystick is operated in an intuitively easy-to-understand state to rotate the hull. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the main propulsion device is preferably an engine 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. Accordingly, in a structure including a plurality of propulsion devices having different maximum outputs, the main propulsion device of which is an engine outboard motor provided on the centerline of the hull in the right-left direction and the auxiliary propulsion device of which is an electric outboard motor provided to one side of the centerline of the hull in the right-left direction, the hull is rotated while the control by the controller is prevented from being complex. 
     A marine propulsion system according to a preferred embodiment of the present invention includes a main propulsion device to be 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 to be attached to the stern, operable to rotate in the right-left direction to change a direction of a thrust, having a maximum output smaller than a maximum output of the main propulsion device, and having a steering angle range wider than a steering angle range of the main propulsion device, and a controller configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device without generating the thrust from the main 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 rotate the hull by driving the auxiliary propulsion device having a maximum output smaller than a maximum output of the main propulsion device and having a steering angle range wider than a steering angle range of the main propulsion device without generating the thrust from 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 a plurality of propulsion devices having different maximum outputs, the hull is rotated while the control by the controller is prevented from being complex. 
     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, having a maximum output smaller than a maximum output of the main propulsion device, and having a steering angle range wider than a steering angle range of the main propulsion device, and a controller configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device without generating the thrust from the main 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 rotate the hull by driving the auxiliary propulsion device having a maximum output smaller than a maximum output of the main propulsion device and having a steering angle range wider than a steering angle range of the main propulsion device without generating the thrust from 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 a plurality of propulsion devices having different maximum outputs, the hull is rotated while the control by the controller is prevented from being complex. 
     In a marine vessel according to a preferred embodiment of the present invention, the controller is configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device including the electric motor to drive the auxiliary thruster to generate a thrust without generating a thrust from the main propulsion device. 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 rotated, 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, the control by the controller to rotate the hull is effectively prevented from being complex. 
     In such a case, the controller is preferably configured or programmed to control an output of the auxiliary propulsion device and a rudder angle of the auxiliary propulsion device such that a rotational moment to rotate the hull counterclockwise is equal or substantially equal to a rotational moment to rotate the hull clockwise. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, even when the auxiliary propulsion device is provided to one side of the centerline of the hull in the right-left direction, the hull is rotated without reducing the maneuverability. 
     In a marine vessel including the controller configured or programmed to control the output of the auxiliary propulsion device and the rudder angle of the auxiliary propulsion device such that the rotational moment to rotate the hull counterclockwise is equal or substantially equal to the rotational moment to rotate the hull clockwise, the controller is preferably configured or programmed to perform a control to make the output and the rudder angle of the auxiliary propulsion device to rotate the hull counterclockwise different from the output and the rudder angle of the auxiliary propulsion device to rotate the hull clockwise such that the rotational moment to rotate the hull counterclockwise is equal or substantially equal to the rotational moment to rotate the hull clockwise. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the output of the auxiliary propulsion device and the rudder angle of the auxiliary propulsion device are easily controlled such that the rotational moment to rotate the hull counterclockwise is equal or substantially equal to the rotational moment to rotate the hull clockwise. 
     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 rotate the hull by driving the auxiliary propulsion device without generating the thrust from the main propulsion device and with a rudder angle of the main propulsion device changed to a same side in the right-left direction as a rudder angle of the auxiliary propulsion device. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the hull is rotated smoothly. 
     In such a case, the controller is preferably configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device without generating the thrust from the main propulsion device and with the rudder angle of the main propulsion device changed to the same side in the right-left direction as the rudder angle of the auxiliary propulsion device up to an end of the steering angle range of the main propulsion device. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the hull is rotated more smoothly. 
     In a marine vessel according to a preferred embodiment of the present invention, the auxiliary propulsion device preferably has a maximum value of a power range when generating a thrust for forward movement larger than a maximum value of a power range when generating a thrust for rearward movement, and the controller is preferably configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device to generate the thrust for forward movement. 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 is driven to generate a thrust for rearward movement, the rotational moment to rotate the hull is increased to improve the rotating speed of the hull. 
     In a marine vessel according to a preferred embodiment of the present invention, the steering angle range of the auxiliary propulsion device is preferably about 60 degrees or more and about 80 degrees or less in each of clockwise and counterclockwise directions. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, a structure in which the hull is rotated by driving the auxiliary propulsion device without generating a thrust from the main propulsion device is easily achieved. 
     In a marine vessel according to a preferred embodiment of the present invention, the controller is preferably configured or programmed to perform a control to rotate the hull by driving the auxiliary propulsion device when a joystick corresponding to an operator to operate the hull is rotated. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the joystick is operated in an intuitively easy-to-understand state to rotate the hull. 
     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 a power range of an engine of a main propulsion device and a 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 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 rearward 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 rearward movement state, a driving force is transmitted from the engine  22  to the main propeller  21  to generate a rearward 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 angle 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 on 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 rearward 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 steering angle range of the auxiliary propulsion device  30  is wider than that of the main propulsion device  20 . The steering angle range of the auxiliary propulsion device  30  is about 60 degrees or more and about 80 degrees or less in each of clockwise and counterclockwise directions.  FIG.  2    shows an example in which the auxiliary propulsion device  30  is steerable by about 70 degrees to each of the L side and the R side. That is,  FIG.  2    shows an example in which a steering angle 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 . In the auxiliary propulsion device  30 , the maximum value T 21  of the power range T 20  at the time of generating a thrust for forward movement is larger than the maximum value T 21  of the power range T 20  at the time of generating a thrust for rearward movement. 
     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 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 rearward 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, “rotating the lever  43   b  ” is referred to as “rotating 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 rotate the hull  10  by driving the auxiliary propulsion device  30  having a steering angle range wider than that of the main propulsion device  20  without generating a thrust from the main propulsion device  20 . When the joystick  43  is rotated, the controller  50  performs a control to rotate the hull  10  by driving the auxiliary propulsion device 
     Specifically, when the marine propulsion system  100  is in the joystick mode and the joystick  43  (see  FIG.  1   ) is rotated, the controller  50  (see  FIG.  1   ) controls the output T 2  and the rudder angle A 2  of the auxiliary propulsion device  30  such that the hull  10  is rotated in a direction (counterclockwise or clockwise) corresponding to the rotating direction of the joystick  43  and at a rotating speed corresponding to the amount of rotation of the joystick  43 .  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.  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. Al 2  is equal (in magnitude) to A 11 , as described below. A 22  may be equal to or different from A 21 . 
     The controller  50  (see  FIG.  1   ) performs a control to rotate the hull  10  by driving the auxiliary propulsion devices  30  to generate a thrust for forward movement from the auxiliary propulsion device  30 . 
     As shown in  FIGS.  7  and  8   , the controller  50  (see  FIG.  1   ) controls 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 rotational moment to rotate the hull  10  counterclockwise is equal or substantially equal to the rotational moment to rotate the hull  10  clockwise. Specifically, the controller  50  performs a control to make the output T 2  and the rudder angle A 2  of the auxiliary propulsion device  30  to rotate the hull  10  counterclockwise different from the output T 2  and the rudder angle A 2  of the auxiliary propulsion device  30  to rotate the hull  10  clockwise such that the rotational moment to rotate the hull  10  counterclockwise is equal or substantially equal to the rotational moment to rotate the hull  10  clockwise. 
     More specifically, as shown in  FIG.  7   , when the hull  10  is rotated counterclockwise, the controller  50  (see  FIG.  1   ) controls the auxiliary propulsion device  30  to steer to the L side and generate the output T 2  (see  FIG.  5   ) to the FWD side. The cross product (vector product) of the output vector V 1  of the auxiliary propulsion device  30  and the position vector X 1  from the center of gravity  81  of the hull  10  to the point of action  92  of the output vector V 1  becomes the rotational moment M 1  to rotate the hull  10  counterclockwise. As shown in  FIG.  8   , when the hull  10  is rotated clockwise, the controller  50  controls the auxiliary propulsion device  30  to steer to the R side and generate the output T 2  to the FWD side. The cross product (vector product) of the output vector V 2  of the auxiliary propulsion device  30  and the position vector X 2  from the center of gravity  81  of the hull  10  to the point of action  93  of the output vector V 2  becomes the rotational moment M 2  to rotate the hull  10  clockwise. When the amount of counterclockwise rotation of the joystick  43  to rotate the hull  10  counterclockwise is equal or substantially equal to the amount of clockwise rotation of the joystick  43  to rotate the hull  10  clockwise, the rotational moment M 1  is equal or substantially equal to the rotational moment M 2 . 
     As shown in  FIGS.  7  and  8   , the controller  50  (see  FIG.  1   ) performs a control to rotate the hull  10  by driving the auxiliary propulsion device  30  without generating a thrust from the main propulsion device  20  with the rudder angle A 1  of the main propulsion device  20  changed to the same side in the right-left direction as the rudder angle A 2  of the auxiliary propulsion device  30  up to the end of the steering angle range A 10  (see  FIG.  2   ) of the main propulsion device  20 . Specifically, as shown in  FIG.  7   , when the hull  10  is rotated counterclockwise, the controller  50  controls the auxiliary propulsion device  30  to steer the auxiliary propulsion device  30  to the L side and controls the main propulsion device  20  to steer the main propulsion device  20  to the L side by about 30 degrees. As shown in  FIG.  8   , when the hull  10  is rotated clockwise, the controller  50  controls the auxiliary propulsion device  30  to steer the auxiliary propulsion device  30  to the R side and controls the main propulsion device  20  to steer the main propulsion device  20  to the R side by about 30 degrees. That is, the rudder angle A 1  (A 11  (see  FIG.  7   )) of the main propulsion device  20  obtained when the hull  10  is rotated counterclockwise and the rudder angle A 2  (A 12 ) of the main propulsion device  20  obtained when the hull  10  is rotated clockwise are equal to each other in magnitude. 
     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 rotate the hull  10  by driving the auxiliary propulsion device  30  having a maximum output smaller than that of the main propulsion device  20  and a steering angle range wider than that of the main propulsion device  20  without generating a thrust from the main propulsion device  20 . Accordingly, although the main propulsion device  20  and the auxiliary propulsion device  30  have different maximum outputs, the auxiliary propulsion device  30  is driven without generating a thrust from the main propulsion device  20  in the control to rotate the hull  10 , and thus as compared with a case in which a thrust is generated from the main propulsion device  20  and the auxiliary propulsion device  30  is driven, the control by the controller  50  to rotate the hull  10  is prevented from being complex. Furthermore, the auxiliary propulsion device  30  has a steering angle range wider than that of the main propulsion device  20 , and thus even when a thrust is not generated from the main propulsion device  20 , the hull  10  is easily rotated by driving the auxiliary propulsion device  30 . Consequently, in a structure including a plurality of propulsion devices having different maximum outputs, the hull  10  is rotated while the control by the controller  50  is prevented from being complex. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to rotate the hull  10  by driving the auxiliary propulsion device  30  including the electric motor  32  to drive the auxiliary propeller  31  that generates a thrust without generating a thrust from the main propulsion device  20 . 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 rotated, 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. Furthermore, the auxiliary propulsion device  30  is provided to one side of the centerline of the hull  10  in the right-left direction. Accordingly, it is not necessary to drive both of the propulsion devices that have different maximum outputs and are asymmetrical to each other in the right-left direction of the hull in the control to rotate the hull  10 , and thus the control by the controller  50  to rotate the hull  10  is effectively prevented from being complex. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to control the output T 1  of the auxiliary propulsion device  30  and the rudder angle A 2  of the auxiliary propulsion device  30  such that the rotational moment to rotate the hull  10  counterclockwise is equal or substantially equal to the rotational moment to rotate the hull  10  clockwise. Accordingly, even when the auxiliary propulsion device  30  is provided to one side of the centerline of the hull  10  in the right-left direction, the rotational moment M 1  to rotate the hull  10  counterclockwise and the rotational moment M 2  to rotate the hull  10  clockwise are equalized such that the rotating speed of the hull  10  at the time of rotating the hull  10  counterclockwise and the rotating speed of the hull  10  at the time of rotating the hull  10  clockwise are equalized or substantially equalized. Consequently, even when the auxiliary propulsion device  30  is provided to one side of the centerline of the hull  10  in the right-left direction, the hull  10  is rotated without reducing the maneuverability. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to make the output T 1  and the rudder angle A 2  of the auxiliary propulsion device  30  to rotate the hull  10  counterclockwise different from the output T 1  and the rudder angle A 2  of the auxiliary propulsion device  30  to rotate the hull  10  clockwise such that the rotational moment to rotate the hull  10  counterclockwise is equal or substantially equal to the rotational moment to rotate the hull  10  clockwise. Accordingly, the output T 1  of the auxiliary propulsion device  30  and the rudder angle A 2  of the auxiliary propulsion device  30  are easily controlled such that the rotational moment to rotate the hull  10  counterclockwise is equal or substantially equal to the rotational moment to rotate the hull  10  clockwise. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to rotate the hull  10  by driving the auxiliary propulsion device  30  without generating a thrust from the main propulsion device  20  and with the rudder angle A 1  of the main propulsion device  20  changed to the same side in the right-left direction as the rudder angle A 2  of the auxiliary propulsion device  30 . Accordingly, the hull  10  is rotated while the direction of the thrust of the auxiliary propulsion device  30  and the orientation of a portion of the main propulsion device  20  located in the water are relatively aligned with each other, and thus a resistance generated in the portion of the main propulsion device  20  located in the water when the hull  10  is rotated is reduced or prevented. Consequently, the hull  10  is rotated smoothly. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to rotate the hull  10  by driving the auxiliary propulsion device  30  without generating a thrust from the main propulsion device  20  and with the rudder angle A 1  of the main propulsion device  20  changed to the same side in the right-left direction as the rudder angle A 2  of the auxiliary propulsion device  30  up to the end of the steering angle range A 10  of the main propulsion device  20 . Accordingly, the rudder angle A 1  of the main propulsion device  20  is aligned with the rudder angle A 2  of the auxiliary propulsion device  30  as much as possible, and thus a resistance generated in the portion of the main propulsion device  20  located in the water when the hull  10  is rotated is further reduced or prevented. Consequently, the hull  10  is rotated more smoothly. 
     According to a preferred embodiment of the present invention, the auxiliary propulsion device  30  has the maximum value T 21  of the power range T 20  when generating a thrust for forward movement larger than that when generating a thrust for rearward movement. Furthermore, the controller  50  is configured or programmed to perform a control to rotate the hull  10  by driving the auxiliary propulsion device  30  to generate a thrust for forward movement. Accordingly, as compared with a case in which the auxiliary propulsion device  30  is driven to generate a thrust for rearward movement, the rotational moment to rotate the hull  10  is increased to improve the rotating speed of the hull  10 . 
     According to a preferred embodiment of the present invention, the steering angle range A 20  of the auxiliary propulsion device  30  is about 60 degrees or more and about 80 degrees or less in each of the clockwise and counterclockwise directions. Accordingly, the auxiliary propulsion device  30  is steered to a rudder angle sufficient for only the auxiliary propulsion device  30  to rotate the hull  10 , and thus a structure in which the hull  10  is rotated by driving the auxiliary propulsion device  30  without generating a thrust from the main propulsion device  20  is easily achieved. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to rotate the hull  10  by driving the auxiliary propulsion device  30  when the joystick  43  corresponding to an operator to operate the hull  10  is rotated. Accordingly, the operating direction (rotating direction) of the joystick  43  is the same as the moving direction (rotating direction) of the hull  10 , and thus the joystick  43  is operated in an intuitively easy-to-understand state to rotate the hull  10 . 
     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 a main thruster that generates a thrust and provided on the centerline  91  of the hull  10  in the right-left direction. Furthermore, the auxiliary propulsion device  30  is an electric outboard motor including the electric motor  32  to drive the auxiliary propeller  31  corresponding to an auxiliary thruster and provided to one side of the centerline of the hull  10  in the right-left direction. Accordingly, in a structure including a plurality of propulsion devices having different maximum outputs, the main propulsion device  20  of which is an engine outboard motor provided on the centerline  91  of the hull  10  in the right-left direction and the auxiliary propulsion device  30  of which is an electric outboard motor provided to one side of the centerline of the hull  10  in the right-left direction, the hull  10  is rotated while the control by the controller  50  is prevented from being complex. 
     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 rotate the hull  10  by driving the auxiliary propulsion device  30  when the joystick  43  corresponding to an operator to operate the hull  10  is rotated 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 rotate the hull by driving the auxiliary propulsion device when an operation is performed on an operator other than the joystick to rotate 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 side and the right side of the hull as long as the steering angle range of the auxiliary propulsion device is wider than the steering angle range of the main propulsion device. 
     While the steering angle range A 20  of the auxiliary propulsion device  30  is preferably about 60 degrees or more and about 80 degrees or less in each of the clockwise and counterclockwise directions in preferred embodiments described above, the present invention is not restricted to this. In the present invention, the steering angle range of the auxiliary propulsion device may alternatively be less than about 60 degrees or more than about 80 degrees in each of the clockwise and counterclockwise directions as long as the steering angle range of the auxiliary propulsion device is wider than the steering angle range of the main propulsion device. 
     While the controller  50  preferably performs a control to rotate the hull  10  by driving the auxiliary propulsion device  30  to generate a thrust for forward movement 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 rotate the hull by driving the auxiliary propulsion device to generate a thrust for rearward movement. 
     While the controller  50  preferably performs a control to rotate the hull  10  by driving the auxiliary propulsion device  30  without generating a thrust from the main propulsion device  20  with the rudder angle A 1  of the main propulsion device  20  changed to the same side in the right-left direction as the rudder angle A 2  of the auxiliary propulsion device  30  up to the end of the steering angle range A 10  of the main propulsion device  20  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 rotate the hull by driving the auxiliary propulsion device without generating a thrust from the main propulsion device and with the rudder angle of the main propulsion device changed to the same side in the right-left direction as the rudder angle of the auxiliary propulsion device up to some point between the beginning and the end of the steering angle range of the main propulsion device. 
     While the controller  50  preferably performs a control to rotate the hull  10  by driving the auxiliary propulsion device  30  without generating a thrust from the main propulsion device  20  with the rudder angle A 1  of the main propulsion device  20  changed to the same side in the right-left direction as the rudder angle A 2  of 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 alternatively perform a control to rotate the hull by driving the auxiliary propulsion device without generating a thrust from the main propulsion device in a state in which the rudder angle of the main propulsion device is not changed to the same side in the right-left direction as the rudder angle of the auxiliary propulsion device. 
     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 centerline 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 centerline of the hull in the right-left direction, and 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 preferred embodiments of the present invention have been described above, it is to be understood that 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.