Patent Publication Number: US-2023136043-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. 2021-180212 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 that each perform motorized forward-rearward movement to move a hull along a forward-rearward direction by driving an auxiliary propulsion device without generating a thrust from a main propulsion device. 
     2. Description of the Related Art 
     A marine vessel that performs motorized forward-rearward movement to move a hull along a forward-rearward direction by driving an auxiliary propulsion device without generating a thrust from a main propulsion device is known in general. Such a marine vessel is disclosed in Japanese Patent Laid-Open No. 2019-199148, for example. 
     Japanese Patent Laid-Open No. 2019-199148 discloses a marine vessel including a hull, a plurality of propulsion units to provide a propulsive force for the hull, and a control device to control driving of the plurality of propulsion units. In the marine vessel described in Japanese Patent Laid-Open No. 2019-199148, the plurality of propulsion units include a first propulsion unit (main propulsion device) driven by an internal combustion engine and second propulsion units (auxiliary propulsion devices) each having a maximum output smaller than that of the first propulsion unit and driven by an electric motor. In the marine vessel described in Japanese Patent Laid-Open No. 2019-199148, the control device performs a control to drive only the second propulsion units of the plurality of propulsion units when a vessel operator performs an operation to select a second drive mode. Thus, in the second drive mode, motorized forward-rearward movement is able to be performed to drive the second propulsion units without generating a thrust from the first propulsion unit. The second drive mode is used when exhaust gas and noise from the internal combustion engine cause problems. In the marine vessel described in Japanese Patent Laid-Open No. 2019-199148, the same number of second propulsion units are provided on the port side and the starboard side in consideration of the right-left balance of the propulsive force of the hull. 
     Although not described in Japanese Patent Laid-Open No. 2019-199148, in a conventional marine vessel as described in Japanese Patent Laid-Open No. 2019-199148, auxiliary propulsion devices may be provided to one side in a right-left direction. In such a case, when motorized forward-rearward movement is performed by the auxiliary propulsion devices that are provided to one side of a hull in the right-left direction without generating a thrust from a main propulsion device, the hull is rotated due to the auxiliary propulsion devices being provided to one side of the hull in the right-left direction. That is, the motorized forward-rearward movement is not performed as intended by a vessel operator. Therefore, it is desired to perform the motorized forward-rearward movement by the auxiliary propulsion devices provided to one side of the hull in the right-left direction of the hull without generating a thrust from the main propulsion device, as intended by the vessel operator. In this description, the terms “the hull is rotated”, “rotation of the hull”, “rotate 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. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide marine propulsion systems and marine vessels that each perform motorized forward-rearward movement by auxiliary propulsion devices provided to one side of hulls in a right-left direction without generating thrusts from main propulsion devices, as intended by vessel operators. 
     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, including an engine to drive a main thruster to generate a thrust, and operable to rotate in a right-left direction to change a direction of the 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, and having a maximum output smaller than a maximum output of the main propulsion device, an operator, and a controller configured or programmed to control driving of the main propulsion device and the auxiliary propulsion device based on a predetermined operation on the operator. The auxiliary propulsion device is provided to one side of the hull in the right-left direction, and the controller is configured or programmed to perform a rudder angle change control to change a rudder angle of the auxiliary propulsion device by a predetermined angle to one side in the right-left direction of the hull with respect to a forward-rearward direction of the hull so as to move the hull along the forward-rearward direction without rotating the hull when motorized forward-rearward movement is performed to move the hull along the forward-rearward direction 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 the rudder angle change control to change the rudder angle of the auxiliary propulsion device by the predetermined angle to one side in the right-left direction of the hull with respect to the forward-rearward direction of the hull so as to move the hull along the forward-rearward direction without rotating the hull when the motorized forward-rearward movement is performed to move the hull along the forward-rearward direction by driving the auxiliary propulsion device that is provided to one side of the hull in the right-left direction without generating a thrust from the main propulsion device. Accordingly, the rudder angle change control is performed when the motorized forward-rearward movement is performed by the auxiliary propulsion device that is provided to one side of the hull in the right-left direction without generating a thrust from the main propulsion device such that check helm is automatically performed to prevent rotation of the hull due to the auxiliary propulsion device being provided to one side of the hull in the right-left direction. Consequently, the motorized forward-rearward movement is performed as intended by a vessel operator by the auxiliary propulsion device that is provided to one side of the hull in the right-left direction without generating a thrust from the main propulsion device. 
     A marine propulsion system according to a preferred embodiment of the present invention performs the motorized forward-rearward movement to move the hull along the forward-rearward direction without rotating the hull by driving the auxiliary propulsion device including the electric motor without generating a thrust from the main propulsion device including the engine. Accordingly, unlike the engine, the electric motor does not directly emit carbon dioxide, and thus a preferable device structure is achieved from the viewpoint of SDGs (Sustainable Development Goals). 
     In a marine propulsion system according to a preferred embodiment of the present invention, the controller is preferably configured or programmed to perform a calibration control to adjust the predetermined angle 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. Accordingly, the calibration control is performed such that the predetermined angle by which the rudder angle of the auxiliary propulsion device is turned to move the hull along the forward-rearward direction when the motorized forward-rearward movement is performed is adjusted according to the shape of the hull, size of the hull, and/or the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc. 
     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 perform the motorized forward-rearward movement while a rudder angle of the main propulsion device is maintained in the forward-rearward direction of the hull. Accordingly, it is not necessary to change the rudder angle of the main propulsion device each time the motorized forward-rearward movement is performed, and thus the hull is prevented from turning due to a change in the rudder angle of the main propulsion device. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the operator preferably includes a joystick, and the controller is preferably configured or programmed to perform the rudder angle change control when the joystick is tilted in the forward-rearward direction in an electric drive mode in which the motorized forward-rearward movement is possible. Accordingly, the operating direction (forward-rearward direction) of the joystick is the same as the moving direction (forward-rearward direction) of the hull, and thus in the electric drive mode, the joystick is operated in an intuitively easy-to-understand state to move the hull along the forward-rearward direction. 
     In such a case, the controller is preferably configured or programmed to perform a control to shift to the electric drive mode when the joystick is in a neutral state in a joystick mode in which the driving of the main propulsion device and the auxiliary propulsion device is controlled based on an operation on the joystick, or when a non-joystick mode is on in which the driving of the main propulsion device and the auxiliary propulsion device is controlled based on an operation on the operator other than the joystick. Accordingly, the marine propulsion system shifts to the electric drive mode only when the joystick is not operated, and thus erroneous transition to the electric drive mode during control of driving of the main propulsion device and the auxiliary propulsion device based on an operation on the joystick is prevented. 
     A marine propulsion system according to a preferred embodiment of the present invention preferably further includes a battery to supply power to the electric motor of the auxiliary propulsion device, and the controller is preferably configured or programmed to not perform a control to shift to an electric drive mode in which the motorized forward-rearward movement is possible when a remaining amount of the battery is smaller than a predetermined threshold. Accordingly, transition to the electric drive mode in a state in which the motorized forward-rearward movement is performed only for a relatively short time due to low battery or in a state in which the motorized forward-rearward movement is not possible is prevented. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the operator preferably includes a joystick, and the controller is preferably configured or programmed to perform a control to move the hull laterally and diagonally by driving both the main propulsion device and the auxiliary propulsion device when the joystick is tilted laterally and diagonally in an electric drive mode in which the motorized forward-rearward movement is possible, respectively. Accordingly, the operating direction (lateral direction and diagonal direction) of the joystick is the same as the moving direction (lateral direction and diagonal direction) of the hull, and thus in the electric drive mode, the joystick is operated in an intuitively easy-to-understand state to move the hull laterally and diagonally. 
     In such a case, the controller is preferably configured or programmed to not perform a control to move the hull laterally and diagonally even when the joystick is tilted laterally and diagonally when the engine is stopped in the electric drive mode. Accordingly, in the electric drive mode, the engine is stopped when a control to move the hull laterally and diagonally is not performed as in a case of the motorized forward-rearward movement. 
     In a marine propulsion system including the controller configured or programmed to not perform a control to move the hull laterally and diagonally when the engine is stopped in the electric drive mode, the controller is preferably configured or programmed to perform a control to notify a vessel operator that the engine is stopped when the engine is stopped in the electric drive mode. Accordingly, when the engine is stopped in the electric drive mode, the vessel operator easily recognizes from the notification that the hull is not able to be moved laterally and diagonally even when the joystick is tilted laterally and diagonally. 
     In a marine propulsion system according to a preferred embodiment of the present invention, the operator preferably includes a joystick, and 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 when the joystick is rotated in an electric drive mode in which the motorized forward-rearward movement is possible. Accordingly, the operating direction (rotating direction) of the joystick is the same as the moving direction (rotating direction) of the hull, and thus in the electric drive mode, 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 the engine to drive a main propeller corresponding to the main thruster 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 in which the main propulsion device and the auxiliary propulsion device are an engine outboard motor and an electric outboard motor, respectively, the motorized forward-rearward movement is performed as intended by the vessel operator by the auxiliary propulsion device that is provided to one side of the hull in the right-left direction without generating a thrust from the main propulsion device. 
     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, including an engine to drive a main thruster to generate a thrust, and operable to rotate in a right-left direction to change a direction of the 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, an operator, and a controller configured or programmed to control driving of the main propulsion device and the auxiliary propulsion device based on a predetermined operation on the operator. The auxiliary propulsion device is provided to one side of the hull in the right-left direction, and the controller is configured or programmed to perform a rudder angle change control to change a rudder angle of the auxiliary propulsion device by a predetermined angle to one side in the right-left direction of the hull with respect to a forward-rearward direction of the hull so as to move the hull along the forward-rearward direction without rotating the hull when motorized forward-rearward movement is performed to move the hull along the forward-rearward direction 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 the rudder angle change control to change the rudder angle of the auxiliary propulsion device by the predetermined angle to one side in the right-left direction of the hull with respect to the forward-rearward direction of the hull so as to move the hull along the forward-rearward direction without rotating the hull when the motorized forward-rearward movement is performed to move the hull along the forward-rearward direction by driving the auxiliary propulsion device that is provided to one side of the hull in the right-left direction 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, the motorized forward-rearward movement is performed as intended by a vessel operator by the auxiliary propulsion device that is provided to one side of the hull in the right-left direction without generating a thrust from the main propulsion device. 
     A marine vessel according to a preferred embodiment of the present invention performs the motorized forward-rearward movement to move the hull along the forward-rearward direction by driving the auxiliary propulsion device including the electric motor without generating a thrust from the main propulsion device including the engine. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, a preferable device structure is achieved from the viewpoint of SDGs. 
     In a marine vessel according to a preferred embodiment of the present invention, the controller is preferably configured or programmed to perform a calibration control to adjust the predetermined angle 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. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the calibration control is performed such that the predetermined angle by which the rudder angle of the auxiliary propulsion device is changed to move the hull along the forward-rearward direction when the motorized forward-rearward movement is performed is adjusted according to the shape of the hull, the size of the hull, and/or the attachment positions of the main propulsion device and the auxiliary propulsion device to the hull, etc. 
     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 perform the motorized forward-rearward movement while a rudder angle of the main propulsion device is maintained in the forward-rearward direction of the hull. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, the hull is prevented from turning due to a change in the rudder angle of the main propulsion device. 
     In a marine vessel according to a preferred embodiment of the present invention, the operator preferably includes a joystick, and the controller is preferably configured or programmed to perform the rudder angle change control when the joystick is tilted in the forward-rearward direction in an electric drive mode in which the motorized forward-rearward movement is possible. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, in the electric drive mode, the joystick is operated in an intuitively easy-to-understand state to move the hull along the forward-rearward direction. 
     In such a case, the controller is preferably configured or programmed to perform a control to shift to the electric drive mode when the joystick is in a neutral state in a joystick mode in which the driving of the main propulsion device and the auxiliary propulsion device is controlled based on an operation on the joystick, or when a non-joystick mode is on in which the driving of the main propulsion device and the auxiliary propulsion device is controlled based on an operation on the operator other than the joystick. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, erroneous transition to the electric drive mode during control of driving of the main propulsion device and the auxiliary propulsion device based on an operation on the joystick is prevented. 
     A marine vessel according to a preferred embodiment of the present invention preferably further includes a battery to supply power to the electric motor of the auxiliary propulsion device, and the controller is preferably configured or programmed to not perform a control to shift to an electric drive mode in which the motorized forward-rearward movement is possible when a remaining amount of the battery is smaller than a predetermined threshold. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, transition to the electric drive mode in a state in which the motorized forward-rearward movement is performed only for a relatively short time due to low battery or in a state in which the motorized forward-rearward movement is not possible is prevented. 
     In a marine vessel according to a preferred embodiment of the present invention, the operator preferably includes a joystick, and the controller is preferably configured or programmed to perform a control to move the hull laterally and diagonally by driving both the main propulsion device and the auxiliary propulsion device when the joystick is tilted laterally and diagonally in an electric drive mode in which the motorized forward-rearward movement is possible, respectively. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, in the electric drive mode, the joystick is operated in an intuitively easy-to-understand state to move the hull laterally and diagonally. 
     In such a case, the controller is preferably configured or programmed to not perform a control to move the hull laterally and diagonally even when the joystick is tilted laterally and diagonally when the engine is stopped in the electric drive mode. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, in the electric drive mode, the engine is stopped when a control to move the hull laterally and diagonally is not performed as in a case of the motorized forward-rearward movement. 
     In a marine vessel including the controller configured or programmed to not perform a control to move the hull laterally and diagonally when the engine is stopped in the electric drive mode, the controller is preferably configured or programmed to perform a control to notify a vessel operator that the engine is stopped when the engine is stopped in the electric drive mode. Accordingly, similarly to the marine propulsion systems according to preferred embodiments of the present invention described above, when the engine is stopped in the electric drive mode, the vessel operator easily recognizes from the notification that the hull is not able to be moved laterally and diagonally even when the joystick is tilted laterally and diagonally. 
     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 diagram illustrating an engine drive mode and an electric drive mode in a marine propulsion system according to a preferred embodiment of the present invention. 
         FIG.  8    is a schematic view showing movement along a forward-rearward direction in an electric drive mode of a marine propulsion system according to a preferred embodiment of the present invention. 
         FIG.  9    is a schematic view showing movement along a forward-rearward direction in an electric drive mode of a marine propulsion system according to a comparative example 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 , a controller  50 , a display  60 , and a battery  70 . The operator  40 , the controller  50 , the display  60 , and the battery  70  are provided on or 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 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 a control performed by the controller  50 . The SCU  29  controls driving of the steering  27  based on a control performed 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 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 , and no auxiliary propulsion device is provided to the R 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 preferably 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 supplied from the battery  70  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 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 auxiliary propulsion device  30  is steerable by about 70 degrees to each of the L side and the R side. That is, 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 a control performed by the controller  50 . The SCU  35  controls driving of the steering  33  based on a control performed 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 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, “tilting the lever  43   b ” and “rotating the lever  43   b ” are referred to as “tilting the joystick  43 ” and “rotating the joystick  43 ”, respectively. 
     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 . That is, the controller  50  controls driving of the main propulsion device  20  and driving of the auxiliary propulsion device  30  based on a predetermined operation on the operator  40 . The controller  50  includes a control circuit including a CPU, for example. The marine propulsion system  100  includes an engine drive mode in which the hull  10  is moved in the forward-rearward direction by driving the main propulsion device  20  corresponding to an engine outboard motor, and an electric drive mode in which the hull  10  is moved in the forward-rearward direction by driving the auxiliary propulsion device  30  corresponding to an electric outboard motor. 
     As shown in  FIG.  7   , when the joystick  43  is operated to move the hull  10  along the forward-rearward direction (the joystick  43  is tilted in the forward-rearward direction) in the engine drive mode, the controller  50  controls driving of the main propulsion device  20  to move the hull  10  along the forward-rearward direction. On the other hand, when the joystick  43  is operated to move the hull  10  along the forward-rearward direction in the electric drive mode, the controller  50  controls driving of the auxiliary propulsion device  30  to move the hull  10  along the forward-rearward direction. That is, when the joystick  43  is operated to move the hull  10  along the forward-rearward direction in the electric drive mode, motorized forward-rearward movement is performed to move the hull  10  along the forward-rearward direction by driving the auxiliary propulsion device  30  without generating a thrust from the main propulsion device  20 . The motorized forward-rearward movement is described below in detail. 
     When the joystick  43  is operated to move the hull  10  laterally and diagonally (the joystick  43  is tilted laterally and diagonally) in each of the engine drive mode and the electric drive mode, the controller  50  controls driving of the main propulsion device  20  and driving of the auxiliary propulsion device  30  to move the hull  10  laterally and diagonally. That is, the controller  50  performs a control to move the hull  10  laterally and diagonally by driving both the main propulsion device  20  and the auxiliary propulsion device  30  when the joystick  43  is tilted laterally and diagonally in the electric drive mode in which the motorized forward-rearward movement is possible, respectively. 
     When the engine  22  is stopped, the controller  50  does not perform a control to move the hull  10  laterally and diagonally even when the joystick  43  is tilted laterally and diagonally in the electric drive mode. Specifically, when the joystick  43  is tilted laterally and diagonally in the electric drive mode, the controller  50  determines whether or not the engine  22  is stopped. When the engine  22  is stopped, the controller  50  does not perform a control to move the hull  10  laterally and diagonally. On the other hand, when the engine  22  is operating, the controller  50  performs a control to move the hull  10  laterally and diagonally. The controller  50  performs a control to notify a vessel operator that the engine  22  is stopped when the engine  22  is stopped in the electric drive mode. The notification that the engine  22  is stopped may be displayed on the display  60 , or may be made by generating a sound, for example. 
     When the joystick  43  is operated to rotate the hull  10  (the joystick  43  is rotated) in each of the engine drive mode and the electric drive mode, the controller  50  controls driving of the auxiliary propulsion device  30  to rotate the hull  10 . That is, the controller  50  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  when the joystick  43  is rotated in the electric drive mode in which the motorized forward-rearward movement is possible. 
     The controller  50  performs a control to switch between the engine drive mode and the electric drive mode when an operation is performed to switch between the engine drive mode and the electric drive mode. For example, the display  60  (see  FIG.  1   ) may be a touch panel, and a button (hereinafter referred to as a mode switching button) displayed on the display  60  may be touched to switch between the engine drive mode and the electric drive mode. Alternatively, a mode switching button may be provided on the joystick  43  and be operated to switch between the engine drive mode and the electric drive mode. 
     Alternatively, a mode switching button may be provided in the vicinity of or adjacent to a vessel operator&#39;s seat of the hull  10  and be operated to switch between the engine drive mode and the electric drive mode. 
     The controller  50  performs a control to shift to the electric drive mode when the joystick  43  is in a neutral state in the joystick mode or when the non-joystick mode is on. Specifically, when an operation is performed to switch between the engine drive mode and the electric drive mode in the engine drive mode, the controller  50  determines whether or not the marine propulsion system  100  (see  FIG.  1   ) is in the joystick mode and the joystick  43  is in the neutral state. When the marine propulsion system  100  is in the joystick mode and the joystick  43  is in the neutral state, the controller  50  performs a control to shift from the engine drive mode to the electric drive mode. On the other hand, when the marine propulsion system  100  is not in the joystick mode or the joystick  43  is not in the neutral state, the controller  50  does not perform a control to shift from the engine drive mode to the electric drive mode. The marine propulsion system  100  performs a similar control when the electric drive mode is switched to the engine drive mode. 
     The controller  50  does not perform a control to shift to the electric drive mode in which the motorized forward-rearward movement is possible when the remaining amount of the battery  70  (see  FIG.  1   ) is smaller than a predetermined threshold. Specifically, when an operation is performed to switch between the engine drive mode and the electric drive mode in the engine drive mode, the controller  50  determines whether or not the remaining amount of the battery  70  is smaller than the predetermined threshold. When the remaining amount of the battery  70  is smaller than the predetermined threshold, the controller  50  does not perform a control to shift from the engine drive mode to the electric drive mode. On the other hand, when the remaining amount of the battery  70  is equal to or larger than the predetermined threshold, the controller  50  performs a control to shift from the engine drive mode to the electric drive mode. 
     As shown in  FIG.  8   , the controller  50  (see  FIG.  1   ) performs a rudder angle change control to change the rudder angle A 2  of the auxiliary propulsion device  30  by a predetermined angle α to one side (L side) in the right-left direction of the hull  10  with respect to the forward-rearward direction of the hull  10  so as to move the hull  10  in the forward-rearward direction when the motorized forward-rearward movement is performed. Specifically, as shown in  FIG.  9   , the auxiliary propulsion device  30  is provided to one side (L side) in the right-left direction of the hull  10 , and thus the hull  10  is turned when a thrust is generated in the forward-rearward direction from the auxiliary propulsion device  30 . Therefore, as shown in  FIG.  8   , the rudder angle change control is performed to change the rudder angle A 2  of the auxiliary propulsion device  30  by the predetermined angle α to one side (L side) in the right-left direction of the hull  10  with respect to the forward-rearward direction of the hull  10  such that the rudder angle A 2  of the auxiliary propulsion device  30  is changed to generate a thrust from the auxiliary propulsion device  30  so as to move the hull  10  along the forward-rearward direction without rotating the hull  10 . The controller  50  performs the rudder angle change control when the joystick  43  is tilted in the forward-rearward direction in the electric drive mode in which the motorized forward-rearward movement is possible. 
     The predetermined angle α that causes the auxiliary propulsion device  30  to generate a thrust to move the hull  10  along the forward-rearward direction varies depending on the shape and size of the hull  10 , the attachment position of the auxiliary propulsion device  30  to the hull  10 , etc. Therefore, the controller  50  (see  FIG.  1   ) performs a calibration control to adjust the predetermined angle α according to the hull  10 . 
     Specifically, in the marine vessel  110  in which the calibration control is not performed, the vessel operator tilts the joystick  43  (see  FIG.  1   ) to move the hull  10  in the forward-rearward direction. At this time, the tilting direction of the joystick  43  is deviated from the forward-rearward 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 forward-rearward direction, the vessel operator performs an operation (pressing a calibration button, for example) to memorize the tilting direction of the joystick  43  in which the hull  10  moves in the forward-rearward direction. After that, when the joystick  43  is tilted in the forward-rearward direction, the controller  50  (see  FIG.  1   ) controls the rudder angle A 2  of the auxiliary propulsion device  30  to move the hull  10  in the forward-rearward direction. The calibration control may be performed at the time of the initial operation of the marine propulsion system  100 , or after the attachment position of the auxiliary propulsion device  30  to the hull  10  is changed, for example. 
     When the motorized forward-rearward movement is performed, the rudder angle A 1  of the main propulsion device  20  is maintained at zero. That is, the controller  50  performs a control to perform the motorized forward-rearward movement while the rudder angle A 1  of the main propulsion device  20  is maintained in the forward-rearward direction of the hull  10 . 
     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 the rudder angle change control to change the rudder angle A 2  of the auxiliary propulsion device  30  by the predetermined angle α to one side in the right-left direction of the hull  10  with respect to the forward-rearward direction of the hull  10  so as to move the hull  10  along the forward-rearward direction when the motorized forward-rearward movement is performed to move the hull  10  along the forward-rearward direction by driving the auxiliary propulsion device  30  that is provided to one side of the hull  10  in the right-left direction without generating a thrust from the main propulsion device  20 . Accordingly, the rudder angle change control is performed when the motorized forward-rearward movement is performed by the auxiliary propulsion device  30  that is provided to one side of the hull  10  in the right-left direction without generating a thrust from the main propulsion device  20  such that check helm is automatically performed to prevent rotation of the hull  10  due to the auxiliary propulsion device  30  being provided to one side of the hull  10  in the right-left direction. Consequently, the motorized forward-rearward movement is performed as intended by the vessel operator by the auxiliary propulsion device  30  that is provided to one side of the hull  10  in the right-left direction without generating a thrust from the main propulsion device  20 . 
     According to a preferred embodiment of the present invention, the marine propulsion system  100  performs the motorized forward-rearward movement to move the hull  10  along the forward-rearward direction by driving the auxiliary propulsion device  30  including the electric motor  32  without generating a thrust from the main propulsion device  20  including the engine  22 . Accordingly, unlike the engine  22 , the electric motor  32  does not directly emit carbon dioxide, and thus a preferable device structure is achieved from the viewpoint of SDGs. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform the calibration control to adjust the predetermined angle α according to the hull  10 . Accordingly, the calibration control is performed such that the predetermined angle α by which the rudder angle A 2  of the auxiliary propulsion device  30  is turned to move the hull  10  along the forward-rearward direction when the motorized forward-rearward movement is performed 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. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to perform the motorized forward-rearward movement while the rudder angle A 1  of the main propulsion device  20  is maintained in the forward-rearward direction of the hull  10 . Accordingly, it is not necessary to change the rudder angle A 1  of the main propulsion device  20  each time the motorized forward-rearward movement is performed, and thus the hull  10  is prevented from swinging due to a change in the rudder angle A 1  of the main propulsion device  20 . 
     According to a preferred embodiment of the present invention, the operator  40  includes the joystick  43 . The controller  50  is configured or programmed to perform the rudder angle change control when the joystick  43  is tilted in the forward-rearward direction in the electric drive mode in which the motorized forward-rearward movement is possible. Accordingly, the operating direction (forward-rearward direction) of the joystick  43  is the same as the moving direction (forward-rearward direction) of the hull  10 , and thus in the electric drive mode, the joystick  43  is operated in an intuitively easy-to-understand state to move the hull  10  along the forward-rearward direction. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to shift to the electric drive mode when the joystick  43  is in the neutral state in the joystick mode in which driving of the main propulsion device  20  and the auxiliary propulsion device  30  is controlled based on an operation on the joystick  43 , or when the non-joystick mode is on in which driving of the main propulsion device  20  and the auxiliary propulsion device  30  is controlled based on an operation on the operator  40  other than the joystick  43 . Accordingly, the marine propulsion system  100  shifts to the electric drive mode only when the joystick  43  is not operated, and thus erroneous transition to the electric drive mode during control of driving of the main propulsion device  20  and the auxiliary propulsion device  30  based on an operation on the joystick  43  is prevented. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to not perform a control to shift to the electric drive mode in which the motorized forward-rearward movement is possible when the remaining amount of the battery  70  that supplies power to the electric motor  32  of the auxiliary propulsion device  30  is smaller than the predetermined threshold. Accordingly, transition to the electric drive mode in a state in which the motorized forward-rearward movement is performed only for a relatively short time due to low battery or in a state in which the motorized forward-rearward movement is not possible is prevented. 
     According to a preferred embodiment of the present invention, the operator  40  includes the joystick  43 . The controller  50  is configured or programmed to perform a control to move the hull  10  laterally and diagonally by driving both the main propulsion device  20  and the auxiliary propulsion device  30  when the joystick  43  is tilted laterally and diagonally in the electric drive mode in which the motorized forward-rearward movement is possible, respectively. Accordingly, the operating direction (lateral direction and diagonal direction) of the joystick  43  is the same as the moving direction (lateral direction and diagonal direction) of the hull  10 , and thus in the electric drive mode, the joystick  43  is operated in an intuitively easy-to-understand state to move the hull  10  laterally and diagonally. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to not perform a control to move the hull  10  laterally and diagonally even when the joystick  43  is tilted laterally and diagonally when the engine  22  is stopped in the electric drive mode. Accordingly, in the electric drive mode, the engine  22  is stopped when a control to move the hull  10  laterally and diagonally is not performed as in a case of the motorized forward-rearward movement. 
     According to a preferred embodiment of the present invention, the controller  50  is configured or programmed to perform a control to notify the vessel operator that the engine  22  is stopped when the engine  22  is stopped in the electric drive mode. Accordingly, when the engine  22  is stopped in the electric drive mode, the vessel operator easily recognizes from the notification that the hull  10  is not able to be moved laterally and diagonally due to the engine  22  being stopped even when the joystick  43  is tilted laterally and diagonally. 
     According to a preferred embodiment of the present invention, the operator  40  includes the joystick  43 . 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  when the joystick  43  is rotated in the electric drive mode in which the motorized forward-rearward movement is possible. 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 in the electric drive mode, 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 and provided on the centerline  91  of the hull  10  in the right-left direction. 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  91  of the hull  10  in the right-left direction. Accordingly, in a structure in which the main propulsion device  20  and the auxiliary propulsion device  30  are an engine outboard motor and an electric outboard motor, respectively, the motorized forward-rearward movement is performed as intended by the vessel operator by the auxiliary propulsion device  30  that is provided to one side of the hull  10  in the right-left direction without generating a thrust from the main propulsion device  20 . 
     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, and the auxiliary propulsion device  30  is preferably an electric outboard motor in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, 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  without generating a thrust from the main propulsion device  20  when the joystick  43  is rotated in the electric drive mode in which the motorized forward-rearward movement is possible in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of 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 when an operator other than the joystick is operated to rotate the hull in the electric drive mode in which the motorized forward-rearward movement. 
     While the controller  50  preferably performs a control to notify the vessel operator that the engine  22  is stopped when the engine  22  is stopped in the electric drive mode in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, the controller may not perform a control to notify the vessel operator that the engine is stopped when the engine is stopped in the electric drive mode. 
     While the controller  50  preferably does not perform a control to move the hull  10  laterally and diagonally even when the joystick  43  is tilted laterally and diagonally when the engine  22  is stopped in the electric drive mode in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, the controller may alternatively perform a control to move the hull laterally and diagonally when the joystick is tilted laterally and diagonally even when the engine is stopped in the electric drive mode. 
     While the controller  50  preferably performs a control to move the hull  10  laterally and diagonally by driving both the main propulsion device  20  and the auxiliary propulsion device  30  when the joystick  43  is tilted laterally and diagonally in the electric drive mode in which the motorized forward-rearward movement is possible, respectively, in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, the controller may alternatively perform a control to move the hull laterally and diagonally by driving both the main propulsion device and the auxiliary propulsion device when an operator other than the joystick is operated to move the hull laterally and diagonally in the electric drive mode in which the motorized forward-rearward movement is possible, respectively. 
     While the controller  50  preferably performs a control to shift to the electric drive mode when the joystick  43  is in the neutral state in the joystick mode in which driving of the main propulsion device  20  and the auxiliary propulsion device  30  is controlled based on an operation on the joystick  43 , or when the non-joystick mode is on in which driving of the main propulsion device  20  and the auxiliary propulsion device  30  is controlled based on an operation on the operator  40  other than the joystick  43  in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, the controller may alternatively perform a control to shift to the electric drive mode when the joystick is not in the neutral state in the joystick mode or when the joystick mode is not on. 
     While the controller  50  preferably performs the rudder angle change control when the joystick  43  is tilted in the forward-rearward direction in the electric drive mode in which the motorized forward-rearward movement is possible in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, the controller may alternatively perform the rudder angle change control when an operator other than the joystick is operated to move the hull along the forward-rearward direction in the electric drive mode in which the motorized forward-rearward movement is possible. 
     While the controller  50  preferably performs a control to perform the motorized forward-rearward movement while the rudder angle A 1  of the main propulsion device  20  is maintained in the forward-rearward direction of the hull  10  in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, the controller may alternatively perform a control to perform the motorized forward-rearward movement while the rudder angle of the main propulsion device is turned with respect to the forward-rearward direction of the hull. 
     While the controller  50  preferably performs the calibration control to adjust the predetermined angle α according to the hull  10  in preferred embodiments described above, the present invention is not restricted to this. In a preferred embodiment of the present invention, the controller may not perform the calibration control to adjust the predetermined angle according to the hull. In such a case, the rudder angle of the auxiliary propulsion device may be manually set by the vessel operator when the auxiliary propulsion device is driven to move the hull along the forward-rearward direction, for example. 
     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 a preferred embodiment of 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 a preferred embodiment of 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 a preferred embodiment of 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. 
     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 a preferred embodiment of the present invention, the auxiliary propulsion device may alternatively be steerable by an angle other than about 70 degrees to each of the left side and the right side 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.