Patent Publication Number: US-2021188409-A1

Title: Apparatus and method for steering control of marine vessel able to automatically reduce chine walk, and marine vessel

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2019-231652 filed on Dec. 23, 2019. 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 apparatuses and methods for steering control of a marine vessel that are able to automatically reduce chine walk, and the marine vessels. 
     2. Description of the Related Art 
     In some marine vessels, there may be cases where what is called chine walk occurs in which a hull rocks from side to side. Chine walk is caused by a decrease in stability arising from a decrease in the area of contact between the hull and water, and tends to mainly occur during high-speed sailing. 
     To properly reduce or eliminate chine walk, counter steering needs to be performed in accordance with rocking of the hull, but such counter steering is not easy for ordinary vessel operators. According to a technique disclosed in Japanese Laid-open Patent Publication (Kokai) No. 2014-180954, when the angle of a hull with respect to the water surface becomes greater than a predetermined angle, a motor control means changes the angle of a propulsion device with respect to the hull. 
     The technique disclosed in Japanese Laid-open Patent Publication (Kokai) No. 2014-180954, avoids an increase in the pitch angle of the hull, but it does not reduce or eliminate chine walk. Moreover, Japanese Laid-open Patent Publication (Kokai) No. 2011-5888 and Japanese Laid-open Patent Publication (Kokai) No. 2010-162965 disclose techniques about counter steering used for heading a marine vessel to a destination. However, neither of the techniques disclosed in Japanese Laid-open Patent Publication (Kokai) No. 2011-5888 and Japanese Laid-open Patent Publication (Kokai) No. 2010-162965 automatically controls counter steering when chine walk has occurred, and thus does not reduce or eliminate chine walk. 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide marine vessels, and apparatuses and methods for steering control of the marine vessels, that are each able to automatically reduce chine walk. 
     According to a preferred embodiment of the present invention, a steering control apparatus for a marine vessel includes a processor configured or programmed to perform the following operations. The processor obtains behavior information on a hull, including one or more of a behavior relating to a shift of the hull in a roll direction, a shift of the hull in a yaw direction, a shift of the hull in a crosswise direction, a steering load, and a helm operation load. The processor judges whether or not one or more conditions to change a steering mode to a counter steering mode in which counter steering is performed are satisfied. The processor changes the steering mode to the counter steering mode upon judging that the one or more conditions are satisfied. In the counter steering mode, the processor controls steering of the marine vessel by performing counter steering so as to reduce at least some of one or more of the behaviors of the hull based on the obtained behavior information. 
     According to a preferred embodiment of the present invention, a steering control apparatus controls steering of a marine vessel as follows. Behavior information on a hull is obtained for use in the steering control, in which the behavior information includes one or more of a behavior relating to a shift of the hull in a roll direction, a shift of the hull in a yaw direction, a shift of the hull in a crosswise direction, a steering load, and helm operation load. It is judged whether or not one or more conditions to change a steering mode to a counter steering mode, in which counter steering is performed, are satisfied. When judging that the one or more conditions are satisfied, the steering mode is changed to the counter steering mode. In the counter steering mode, steering of the marine vessel is controlled by performing counter steering in the direction to reduce at least some of one or more of the behaviors of the hull based on the obtained behavior information. 
     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 top view of a marine vessel to which a steering control apparatus is provided. 
         FIG. 2  is a side view of a lower portion of an outboard motor. 
         FIG. 3  is a side view of a trim tab unit attached to a hull. 
         FIG. 4  is a block diagram of a maneuvering system. 
         FIG. 5  is a flowchart of a steering process. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. 
       FIG. 1  is a top view of a marine vessel to which a steering control apparatus according to a preferred embodiment of the present invention is provided. The marine vessel  11  includes a hull  13 , an outboard motor  15  which defines and functions as a marine propulsion device mounted on the hull  13 , and a plurality of trim tab units (for example, a pair of trim tab units  20 A,  20 B in  FIG. 1 ). A central unit  10 , a steering wheel  18 , and a throttle lever  12  are provided in the vicinity of a cockpit in the hull  13 . 
     In the following description, a fore-and-aft direction, a crosswise direction, and a vertical direction refer to a fore-and-aft direction, a crosswise direction, and a vertical direction, respectively, of the hull  13 . For example, as shown in  FIG. 1 , a centerline C 1  extending in the fore-and-aft direction of the hull  13  passes through the center of gravity G of the marine vessel  11 . The fore-and-aft direction is the direction along the centerline C 1 . Fore or front refers to the direction toward the upper side of the view along the centerline C 1 . Aft or rear refers to the direction toward the lower side of the view along the centerline C 1 . The crosswise direction is defined based on a case in which the hull  13  is viewed from the rear. The vertical direction is vertical to the fore-and-aft direction and the crosswise direction. 
     The outboard motor  15  is mounted on the hull  13 . The outboard motor is mounted on the hull  13  via a mounting unit  14 . The outboard motor  15  includes an engine  16  which is preferably an internal combustion engine. The outboard motor  15  generates a propulsive force to move the hull  13  by using a propeller  28  ( FIG. 2 ) that is turned by a driving force of the engine  16 . 
     The mounting unit  14  includes a swivel bracket, a clamp bracket, a steering shaft, and a tilt shaft (none of which are illustrated). The mounting unit  14  further includes a power trim and tilt mechanism (PTT mechanism)  23  ( FIG. 4 ). The PTT mechanism  23  turns the outboard motor  15  about the tilt shaft. This makes it possible to change an inclination angle (the trim angle or tilt angle) of the outboard motor  15  with respect to the hull  13 , and thus a trim adjustment is carried out, and the outboard motor  15  is tilted up and down. Moreover, the outboard motor  15  is able to turn about a turning center C 2  (about the steering shaft) with respect to the swivel bracket. Operating the steering wheel  18  causes the outboard motor  15  to turn about the turning center C 2  in the crosswise direction (direction R 1 ). Thus, the marine vessel  11  is steered. 
     The pair of trim tab units  20 A and  20 B are mounted on the stern on the port side and the starboard side. To distinguish the two trim tab units  20 A and  20 B from each other, the one located on the port side is referred to as the “trim tab unit  20 A”, and the one located on the starboard side is referred to as the “trim tab unit  20 B”. The trim tab units  20 A and  20 B include a tab  21 A (port side posture control tab) and a tab  21 B (starboard side posture control tab), respectively. 
       FIG. 2  is a side view of a lower portion of the outboard motor  15 . The outboard motor  15  transmits a rotational driving force to a propeller shaft  29  via gears, which are not illustrated, causing the propeller  28  to turn about a turning center C 4 . 
       FIG. 3  is a side view of the trim tab unit  20 A attached to the hull  13 . The trim tab units  20 A and  20 B have the same construction, and thus a construction of only the trim tab unit  20 A will now be described as a representative example. The trim tab unit  20 A includes a trim tab actuator  22 A and a tab  21 A. The tab  21 A is attached to the rear of the hull  13  such that it is able to swing about the swing axis C 3 . For example, the proximal end of the tab  21 A is attached to the rear of the hull  13 , and the free end of the tab  21 A swings up and down (in a swinging direction R 2 ) about the swing axis C 3 . The tab  21 A is an example of a posture control tab that changes its position up and down (in the vertical direction) to control the posture of the hull  13 . 
     The trim tab actuator  22 A is disposed between the tab  21 A and the hull  13  such that it connects the tab  21 A and the hull  13  together. The trim tab actuator  22 A actuates the tab  21 A to swing it with respect to the hull  13 . It should be noted that the tab  21 A indicated by a chain double-dashed line in  FIG. 3  is at a position where its free end is at the highest level (a position at which the amount of lowering of the tab  21 A is 0%), and this position corresponds to a retracted position. The tab  21 A indicated by a solid line in  FIG. 3  is at a position where its free end is at a lower level than a keel at the bottom of the marine vessel  11 . It should be noted that a range in which the tab  21 A is able to swing is not limited to the one illustrated in  FIG. 3 . The swinging direction R 2  is defined with reference to the swing axis C 3 . The swing axis C 3  is perpendicular or substantially perpendicular to the centerline C 1  and parallel or substantially parallel to, for example, the crosswise direction. It should be noted that the swing axis C 3  may extend diagonally so as to cross the turning center C 2 . 
       FIG. 4  is a block diagram of a maneuvering system. The maneuvering system includes a steering control apparatus for a marine vessel according to the present preferred embodiment. The marine vessel  11  includes a controller  30 , a throttle position sensor  34 , a steering angle sensor  35 , a hull speed sensor  36 , a hull acceleration sensor  37 , a posture sensor  38 , a receiving unit  39 , a display unit  9 , and a setting operation unit  19 . The marine vessel  11  also includes a steering load sensor  40 , an operation load sensor  27 , an engine rpm detector  17 , a turning actuator  24 , the PTT mechanism  23 , the trim tab actuators  22 A and  22 B. The marine vessel  11  further includes a throttle sensor  25  and a valve opening controller  26 . 
     The controller  30 , the throttle sensor  25 , the valve opening controller  26 , the steering angle sensor  35 , the hull speed sensor  36 , the hull acceleration sensor  37 , the posture sensor  38 , the receiving unit  39 , the display unit  9 , the setting operation unit  19 , and the operation load sensor  27  are included in the central unit  10  or located in the vicinity of the central unit  10 . The turning actuator  24  and the PTT mechanism  23  are provided for the outboard motor  15 . The throttle position sensor  34  and the engine rpm detector  17  are provided in the outboard motor  15 . The steering load sensor  40  is provided in the turning actuator  24 . The trim tab actuators  22 A and  22 B (port side actuator and starboard side actuators) are included in the trim tab units  20 A and  20 B, respectively. 
     The controller  30  includes a CPU  31 , a ROM  32 , a RAM  33 , and a timer which is not illustrated. The ROM  32  stores control programs. The CPU  31  loads the control programs stored in the ROM  32  into the RAM  33  to implement various types of control processes. The RAM  33  provides a work area for the CPU  31  to execute the control programs. 
     Results of detection by the sensors  25 ,  27 ,  34  to  38 , and  40  and the engine rpm detector  17  are supplied to the controller  30 . The throttle lever  12  is a throttle operator to manually control the throttle opening. The throttle sensor  25  detects the position of the throttle lever  12 . The throttle position sensor  34  detects the opening of a throttle valve, which is not illustrated. The valve opening controller  26  controls the opening of the throttle valve. During normal control, the CPU  31  controls the valve opening controller  26  based on the position of the throttle lever  12 . It should be noted that the position of the throttle lever  12  and the actual opening of the throttle valve do not always correspond to each other. 
     The steering angle sensor  35  detects the turning angle of the steering wheel  18 . The hull speed sensor  36  and the hull acceleration sensor  37  detect the speed (vessel speed V) and acceleration, respectively, of the marine vessel  11  (the hull  13 ) while it is traveling. The CPU  31  obtains the vessel speed V from the hull speed senor  36 . It should be noted that the CPU  31  may obtain the shift speed of the hull  13  from a GPS signal. 
     The posture sensor  38  includes, for example, a gyro sensor, a magnetic direction sensor, and so forth. Based on a signal output from the posture sensor  38 , the controller  30  calculates a roll angle, a pitch angle, and a yaw angle of the hull  13 . It should be noted that the controller  30  may calculate the roll angle and the pitch angle based on a signal output from the hull acceleration sensor  37 . The receiving unit  39  includes a GNSS (Global Navigation Satellite Systems) receiver such as a GPS and includes a function of receiving GPS signals and various types of signals as positional information. A signal received by the receiving unit  39  is supplied to the CPU  31 . The controller  30  may obtain shift accelerations of the hull  13  in multiple directions including the acceleration of a shift of the hull  13  in the crosswise direction based on a signal output from the hull acceleration sensor  37 . It should be noted that the shift accelerations of the hull  13  may also be obtained from a GPS signal received by the receiving unit  39 . 
     The steering load sensor  40  detects a steering load that is applied onto the turning actuator  24  which is an element of a steering system. The steering load arises from a force which the outboard motor  15  has received from the water. The operation load sensor  27  detects a helm operation load applied onto the steering wheel  18  that is being operated. The helm operation load corresponds to a force which a vessel operator who is operating the steering wheel  18  feels via the steering wheel  18 . 
     The engine rpm detector  17  detects the number of revolutions of the engine  16  per unit time (hereafter referred to as “the engine rpm N”). The display unit  9  displays various types of information. The setting operation unit  19  includes an operator that a vessel operator uses to perform operations relating to maneuvering, a PTT operating switch, a setting operator that a vessel operator uses to make various settings, and an input operator that a vessel operator uses to input various types of instructions (none of which are illustrated). 
     The turning actuator  24  turns the outboard motor  15  about the turning center C 2  with respect to the hull  13 . Turning the outboard motor  15  about the turning center C 2  changes the orientation of the turning center C 4  of the propeller shaft  29  around the turning center C 2 . As a result, the turning actuator  24  changes a direction in which a propulsive force acts with respect to the centerline C 1  of the hull  13 . The PTT mechanism  23  tilts the outboard motor  15  with respect to the clamp bracket by turning the outboard motor  15  about the tilt shaft. The PTT mechanism  23  is operated in response to, for example, operation of the PTT operating switch. As a result, the PTT mechanism  23  changes the inclination angle of the outboard motor  15  with respect to the hull  13 . 
     The trim tab actuators  22 A and  22 B are controlled by the controller  30 , more specifically, by a processor in the CPU  31  within the controller  30 . For example, the trim tab actuators  22 A and  22 B operate in response to the controller  30  outputting control signals to them. In response to the operation of one of the trim tab actuators  22 A and  22 B, a corresponding tab swings. It should be noted that actuators used for the PTT mechanism  23  and the trim tab actuators  22 A and  22 B may be either hydraulic or electric. 
     It should be noted that the controller  30  may obtain results of detection by the engine rpm detector  17  via a remote control ECU, which is not illustrated. The controller  30  may also use an outboard motor ECU (not illustrated) provided in the outboard motor  15 , to control the engine  16 . 
     A signal output from the posture sensor  38  is also used for detection of a turning state of the hull  13 . The signal output from the posture sensor  38  includes a yaw rate (yaw rotational angular velocity) which is an angular velocity of rotation around a yaw axis. Based on the yaw rate output from the posture sensor  38 , the CPU  31  judges the direction that the hull moves in, in other words, judges whether or not the hull  13  moves straight. When the yaw rate is equal to or smaller than a predetermined value, the CPU  31  judges that the hull  13  moves straight, and when the yaw rate is greater than the predetermined value, the CPU  31  judges that the hull  13  is turning. It should be noted that based on time-series data on the yaw angle obtained from the magnetic direction sensor of the posture sensor  38 , the CPU  31  may judge whether or not the direction that the hull  13  moves in has changed. 
     When the throttle opening of the engine  16  of the outboard motor  15  is increased from a stopped state of the hull  13 , and the speed (vessel speed V) of the hull  13  reaches a high speed, the hull  13  shifts from a hump state (non-planing state) into a planing state in the end. If the ship speed V further increases, chine walk may occur. A vessel speed at which chine walk occurs (hereafter referred to as the predetermined speed V 1 ) is well known although it varies with vessels. The predetermined speed V 1  is determined in advance based on a lower limit to the vessel speed at which it is assumed that chine walk occurs (for example, 50 miles/h). The predetermined speed V 1  is greater than a speed at which the hull  13  shifts from a non-planing state to the planing state (i.e., a speed at which planing starts). Information indicating the predetermined speed V 1  is stored in the ROM  32 . 
     In the present preferred embodiment, the CPU  31  estimates occurrence of chine walk, and when it is estimated that chine walk has occurred, the CPU  31  changes a steering mode to a counter steering mode, and performs counter steering in the counter steering mode so as to automatically reduce chine walk. Details of the counter steering mode will be described with reference to  FIG. 5 . 
       FIG. 5  is a flowchart of a steering process. This process is implemented by the CPU  31  loading a control program stored in the ROM  32  into the RAM  33  and executing the same. This process starts when, for example, the maneuvering system is activated. In the processes illustrated in  FIG. 5 , the CPU  31  defines and functions as an obtaining unit, a judgment unit, and a control unit of the steering control apparatus. 
     In step S 101 , the CPU  31  carries out “other processes”. As the other processes, processes are carried out according to, for example, settings made and operations performed with the setting operation unit  19 . As an example of the other processes, a process that ends this flowchart is carried out in response to an instruction to stop the maneuvering system. In step S 102 , the CPU  31  judges whether or not one or more conditions (mode changing conditions) to change the steering mode to the counter steering mode have been satisfied. The mode changing conditions are satisfied when the direction that the hull  13  moves in is straight, and the vessel speed V is equal to or greater than the predetermined speed V 1  (straight movement and V 1 ≤V). 
     Here, the judgement whether or not the direction that the hull  13  moves in is straight is made from the yaw rate as discussed above. It should be noted that the judgement whether or not the mode changing conditions are satisfied may be made only from the relationship between the vessel speed V and the predetermined speed V 1  without making the judgement whether or not the direction that the hull  13  moves in is straight. 
     As a result of the judgment in the step S 102 , when it is judged that the mode changing conditions are not satisfied, the process proceeds to step S 109  and the CPU  31  in turn sets the steering mode to the normal mode and controls steering of the marine vessel  11 . In a case in which the previous steering mode was the counter steering mode, the CPU  31  changes the steering mode to the normal mode. It should be noted that in a case in which as of the judgment in the step S 102 , the steering mode was the counter steering mode, and the CPU  31  has provided notification that the steering mode was the counter steering mode, the CPU  31  cancels this notification in the step S 109 . It should be noted that the normal mode in the step S 109  is a manual steering mode. The steering control apparatus may be configured such that an automatic steering mode is set in accordance with a user&#39;s instruction. In the automatic steering mode, the CPU  31 , for example, creates a planned sea route from the current location to a destination and controls steering of the marine vessel  11  so as to head for the destination by the planned sea route. After the CPU  31  completes the step S 109 , the process returns to the step S 101 . 
     As a result of the judgment in the step S 102 , when it is judged that the mode changing conditions are satisfied, the process proceeds to step S 103 , and the CPU  31  in turn controls steering of the marine vessel  11  in the counter steering mode. Thus, in a case in which the previous steering mode was the normal mode, the CPU  31  changes the steering mode to the counter steering mode. The CPU  31  also provides notification that the steering mode is set to the counter steering mode. This notification is provided by, for example, displaying a message on the display unit  9  or using an audio or voice output. 
     Then, in step S 104 , the CPU  31  obtains behavior information on the hull  13 . The behavior information includes information (behaviors of the hull  13 ) relating a shift of the hull  13  in one or more of the roll direction, the yaw direction, and the crosswise direction. In the present preferred embodiment, the CPU  31  obtains all the behaviors as the behavior information. The CPU  31  further obtains a speed and an acceleration of the hull  13  in each of the directions as the information or behaviors relating to shifts of the hull  13  in the directions. As the information or behaviors relating to shifts of the hull  13  in the roll direction and the yaw direction, the CPU  31  further obtains differences of the yaw angle and the roll angle from respective target values. In addition, the CPU  31  obtains the steering load and the helm operation load discussed above and their amounts of change per unit time as the behavior information. How these elements of the behavior information are used will be described below with reference to step S 108 . 
     In step S 105 , the CPU  31  judges whether or not the behavior of the hull  13  has become excessive. To make this judgment, a first threshold value and a second threshold value are provided for each of the elements of the behavior information such as shifts in the roll direction, yaw direction, and crosswise direction of the hull  13 , the steering load, and the helm operation load. The second threshold value is greater than the first threshold value. The first threshold value is a judgment threshold value to judge whether or not to perform counter steering. When at least one of the elements has become greater than the corresponding first threshold value, counter steering is performed (described below with reference to steps S 106  to S 108 ). On the other hand, the second threshold value is a judgment threshold value to judge whether or not to perform forced deceleration on the hull  13 . When at least one of the elements has become greater than the corresponding second threshold value, the CPU  31  judges that the behavior of the hull  13  has become excessive, and performs forced deceleration on the hull  13  (described below with reference to steps S 110 ). Forced deceleration forcefully decreases the speed of the hull  13 . The reason for performing forced deceleration is that when the behavior of the hull  13  has become excessive, it is determined that excessive chine walk has occurred and hence it cannot be controlled by counter steering. 
     As a result of the judgment in the step S 105 , when it is judged that the behavior of the hull  13  has become excessive, the process proceeds to the step S 110 , and the CPU  31  in turn forcefully decreases the speed of the hull  13  and also provides notification that forced deceleration is performed because the behavior of the hull  13  has become excessive. As the forced deceleration, the CPU  31  closes the throttle valve (or decreases the throttle opening) of the engine  16  by a predetermined amount. At this time, the throttle valve may be fully closed. Alternatively, as the forced deceleration, the CPU  31  may control the trim tab actuators  22 A and  22 B to lower both of the tab  21 A and the tab  21 B by a predetermined amount. At this time, both of the tab  21 A and the tab  21 B may be lowered to the lowermost position. It should be noted that decreasing the throttle opening and lowering the tabs  21 A and  21 B may be done in combination for the forced deceleration. After the CPU  31  completes the step S 110 , the process returns to the step S 101 . 
     As a result of the judgment in the step S 105 , when it is judged that the behavior of the hull  13  has not become excessive, the process proceeds to step S 106 , and the CPU  31  in turn judges whether or not it is necessary to perform counter steering. As described above, the CPU  31  judges that it is necessary to perform counter steering when at least one of the elements of the behavior information such as shifts of the hull  13  in the roll direction and other directions has become greater than the corresponding first threshold value. When the CPU  31  judges that it is not necessary to perform counter steering, the process returns to the step S 101 . Thus, counter steering is not performed when changes in the behavior are small, and excessive steering control is avoided. Judging that it is necessary to perform counter steering can be considered substantially synonymous with judging that chine walk has substantially occurred. It should be noted that it is not absolutely necessary to execute the steps S 105 , S 106 , and S 110  (to make judgements using the first and second threshold values). 
     When the CPU  31  judges in the step S 106  that it is necessary to perform counter steering, the process proceeds to step S 107 , and the CPU  31  in turn calculates correction values. In step S 108 , the CPU  31  performs counter steering based on the correction values calculated in the step S 107 , and in the case in which the CPU  31  has performed counter steering, it provides notification thereof continuously for a predetermined period of time. It should be noted that the period of time during which the notification is continued may be a period of time during which counter steering is performed. After the CPU  31  completes the step S 108 , the process returns to the step S 101 . A description will now be given of how the correction values are calculated and counter steering is performed in the steps S 107  and S 108 . 
     When the CPU  31  judges that it is necessary to perform counter steering, it controls steering of the marine vessel  11  by performing counter steering so as to reduce at least some of one or more of the behaviors of the hull  13  based on the obtained behavior information. For example, counter steering includes an operation to change the orientation of the propeller shaft  29 . Counter steering also includes an operation to change the angle of at least one of the tabs  21 A and  21 B. It should be noted that the CPU  31  may perform counter steering by changing the orientation of the propeller shaft  29  and/or changing the angles of the tabs  21 A and  21 B. A description will now be given of how the orientation of the propeller shaft  29  is changed so as to control counter steering. 
     The CPU  31  calculates a total counter-steering acceleration BB and a total counter-steering target amount AA as described below. The CPU  31  changes the orientation of the propeller shaft  29  about the turning center C 4  by a target amount, which is represented by the total counter-steering target amount AA, to an orientation that will reduce the behaviors of the hull  13 . In mathematical expressions below, Ay, Ar, and As represent correction values for the target amount to control the posture of the hull  13  in directions opposite to shifts of the hull  13  in the yaw, roll, and crosswise directions (hereinafter, referred to as correction values for the counter-steering target amount). Also, By, Br, and Bs represent correction values for the acceleration to control the posture of the hull  13  in directions opposite to shifts of the hull  13  in the yaw, roll, and crosswise directions (hereinafter, referred to as correction values for the counter-steering acceleration). Au and Bu represent correction values for the counter-steering target amount and the counter-steering acceleration, both relating to the steering load and the helm operation load. It should be noted that y1 to y6, r1 to r6, s1 to s4, u1 to u8, ky1, kr1, ks1, ku1, ky2, kr2, Ks2, and ku2 are coefficients. 
     As the correction values relating to the yaw direction, the CPU  31  calculates the correction value Ay for the counter-steering target amount and the correction value By for the counter-steering acceleration from the expressions (1) and (2), respectively. It should be noted that a yaw angle in the expressions is a difference between a target yaw angle and an actual yaw angle. The target yaw angle is a center of an amplitude of the actual yaw angle. 
         Ay =yaw angle× y 1+yaw rate× y 2+yaw acceleration× y 3  (1)
 
         By=yaw angle×y 4+yaw rate× y 5+yaw acceleration× y 6  (2)
 
     As the correction values relating to the roll direction, the CPU  31  calculates the correction value Ar for the counter-steering target amount and the correction value Br for the counter-steering acceleration, from the expressions (3) and (4), respectively. It should be noted that a roll angle in the expressions is a difference between a target roll angle and an actual roll angle. The target roll angle is a center of an amplitude of the actual roll angle. 
         Ar =roll angle× r 1+roll speed× r 2+roll acceleration× r 3  (3)
 
         Br =roll angle× r 4+roll speed× r 5+roll acceleration× r 6  (4)
 
     As the correction values relating to the shift in the crosswise direction of the hull  13 , the CPU  31  calculates the correction value As for the counter-steering target amount and the correction value Bs for the counter-steering acceleration from the expressions (5) and (6), respectively. 
         As =shift speed× s 1+shift acceleration× s 2  (5)
 
         Bs =shift speed× s 3+shift acceleration× s 4  (6)
 
     As the correction values relating to a helm and steering, the CPU  31  calculates the correction value Au for the counter-steering target amount and the correction value Bu for the counter-steering acceleration from the expressions (7) and (8), respectively. 
         Au =[steering load× u 1+the amount of change in steering load× u 2]+[helm operation load× u 3+the amount of change in helm operation load× u 4]  (7)
 
         Bu =[steering load× u 5+the amount of change in steering load× u 6]+[helm operation load× u 7+the amount of change in helm operation load× u 8]  (8)
 
     Then, the CPU  31  calculates the total counter-steering target amount AA and the total counter-steering acceleration BB from the expressions (9) and (10), respectively. 
         AA =( Ay×ky 1)+( Ar×kr 1)+( As×ks 1)+( Au×ku 1)   (9)
 
         BB =( By×ky 2)+( Br×kr 2)+( Bs×ks 2)+( Bu×ku 2)   (10)
 
     It should be noted that the correction values may be weighted. To weight the correction values, the values ky1, kr1, ks1, ku1, ky2, kr2, ks2, and ku2 may be set to respective desired values. Moreover, it is not absolutely necessary to completely correct the behaviors (such as shifts) of the hull  13 , but the behaviors of the hull  13  may be corrected partially. Thus, in the expression (9), the coefficients other than at least one of the coefficients ky1, kr1, ks1, and ku1 may be set to zero. Likewise, in the expression (10), the coefficients other than at least one of the coefficients ky2, kr2, ks2, and ku2 may be set to zero. 
     As described above, when performing counter steering in the counter steering mode, the CPU  31  controls the amount by which the orientation of the propeller shaft  29  is changed (the total counter-steering target amount AA) and the acceleration at which the orientation of the propeller shaft  29  is changed (the total counter-steering acceleration BB) based on the behavior information. 
     It should be noted that in a case in which the angles of the tabs  21 A and  21 B are changed during controlling counter steering, the CPU  31  may use only the total counter-steering target amount AA without using the total counter-steering acceleration BB. In this case, the CPU  31  lowers an appropriate one of the tabs  21 A and  21 B by an angle corresponding to the total counter-steering target amount AA, in such a direction as to reduce the shifts of the hull  13 . In other words, in the counter steering mode, the CPU  31  determines one of the tabs  21 A and  21 B to be actuated based on the obtained behavior information, and controls a corresponding one of the trim tab actuators  22 A and  22 B so as to change a position of the determined tab. For example, the CPU  31  lowers one of the tabs  21 A and  21 B which is on the side opposite to the yaw direction. Moreover, the CPU  31  may calculate the total counter-steering target amount AA from the following expression (11) instead of the expression (9). 
         AA =( Ay×ky 1)−( Ar×kr 1)  (11)
 
     It should be noted that the second term in the expression (11) is opposite in sign to the one in the expression (9). This is because moving the tab in such a direction as to correct for yawing will have an adverse effect from the viewpoint of reducing the displacement in the roll direction. 
     According to the present preferred embodiment, when judging that the mode changing conditions are satisfied, the CPU  31  changes the steering mode to the counter steering mode, and based on the obtained behavior information, the CPU  31  controls steering of the marine vessel  11  by performing counter steering so as to reduce at least some of one or more of the behaviors of the hull  13 . According to the steering control, chine walk is automatically reduced even if the vessel operator is not an advanced level operator. 
     Moreover, since the CPU  31  forcefully decreases the speed of the hull  13  when judging that one or more of the behaviors of the hull  13  becomes excessive, it quickly reduces the behaviors that cannot be dealt with by counter steering. 
     The CPU  31  obtains the behavior information including one or more of the information elements relating to shifts of the hull in the roll direction, the yaw direction, and the crosswise direction; the steering load; and the helm operation load. The CPU  31  performs the counter steering so as to reduce at least some of one or more of the behaviors indicating the above-described information elements. It allows the steering control apparatus to deal with complex changes in behavior of the hull  13  and properly reduce chine walk. It should be noted that the CPU  31  may obtain and use one or more of the behavior of the hull  13  in the roll direction, the behavior in the yaw direction, the behavior in the crosswise direction, the steering load, and the helm operation load, as the behavior information. 
     It should be noted that counter steering may include changing an operation position of a helm (the steering wheel  18 ), which is operated by a vessel operator to control the direction that the hull  13  moves in, in addition to changing the orientation of the propeller shaft  29  and/or changing the angles of the tabs  21 A and  21 B. Alternatively, the CPU  31  performs the counter steering by changing an operation position of the helm without changing the orientation of the propeller shaft  29  or changing the angles of the tabs  21 A and  21 B. The helm for use in these cases is not limited to the steering wheel  18  but may be, for example, a joystick. 
     It should be noted that as the posture control tabs, interceptor tabs may be used in place of the tabs  21 A and  21 B. In this case, each of the interceptor tabs changes its position in the water from a position at which it projects from a bottom surface (the vessel bottom) of the hull  13  to a position which is above the bottom surface of the hull  13 . The CPU  31  lowers the interceptor tabs instead of lowering the tabs. Alternatively, the CPU  31  may change the positions of both the tabs  21 A and  21 B and the interceptor tabs. 
     It should be noted that two or more outboard motors  15  may be mounted on the hull  13 . Marine vessels to which preferred embodiments of the present invention are applicable are not limited to those equipped with one or more outboard motors, but the present invention is also applicable to marine vessels equipped with other types of marine propulsion devices such as inboard/outboard motors (stern drive, inboard motor/outboard drive). 
     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.