Patent Publication Number: US-11383802-B2

Title: Trim tab control system for a ship and a ship with the trim tab control system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2019-077955 filed Apr. 16, 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 a trim tab control system for a ship and a ship with the trim tab control system. 
     2. Description of the Related Art 
     The prior art discloses a configuration in which a trim tab is attached to a rear portion of a ship body. For example, in Japanese Patent Application Laid-Open No. 2009-262588, a trim tab is swingably attached to the rear portion of the ship body. The trim tab generates a lifting force on the ship body by swinging from the ship body toward a water surface and landing on the water surface. 
     Generally, in the prior art, the trim tab swings at a constant swing speed from the ship body toward the surface of the water surface and lands on the water surface. In this case, when the trim tab lands on the water surface, there is a possibility that the ship attitude changes by the resistance acting on the trim tab. In other words, the attitude of the ship body may change to an attitude different from the attitude intended by the designer during operation of the trim tab in the prior art. 
     SUMMARY OF THE INVENTION 
     In view of the above-described problems, preferred embodiments of the present invention provide trim tab control systems for ships and ships including the trim tab control systems, each of which is able to stably change a ship attitude during operation of the trim tab. 
     A trim tab control system according to a preferred embodiment of the present invention includes a trim tab and a controller. The trim tab is swingable on a ship body. The controller is configured or programmed to swing the trim tab at the first swing speed when the trim tab is not at the time of landing on the water based on the operation state data indicating the operation state of the ship. The controller is configured or programmed to swing the trim tab at a second swing speed less than the first swing speed when the trim tab is at the time of landing based on the operation state data. 
     According to preferred embodiments of the present invention, it is possible to stably change a ship attitude during operation of the trim tab in a trim tab control system for the ship. 
     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 ship according to a preferred embodiment of the present invention. 
         FIG. 2  is a side view of a propulsion device. 
         FIG. 3  is a side view of a trim tab attached to a ship body. 
         FIG. 4  is a schematic diagram showing a configuration of the trim tab control system. 
         FIG. 5A  is a figure for explaining the change of the operation state data at the time of landing of the tab body. 
         FIG. 5B  is a figure for explaining the change of the operation state data at the time of landing of the tab body. 
         FIG. 5C  is a figure for explaining a swing speed of the tab body. 
         FIG. 6A  is a flowchart showing processes performed by a trim tab control system. 
         FIG. 6B  is a flowchart showing processes performed by a trim tab control system. 
         FIG. 6C  is a flowchart showing processes performed by a trim tab control system. 
         FIG. 7  is a figure for explaining the change of the operation state data at the time of landing of the tab body in a variation of a preferred embodiment of the present invention. 
         FIG. 8A  is a side view of a tab body in a variation of a preferred embodiment of the present invention. 
         FIG. 8B  is a figure for explaining the change of the operation state data at the time of landing of the tab body in a variation of a preferred embodiment of the present invention. 
         FIG. 9  is a flowchart showing processes performed by the trim tab control system according to another preferred embodiment of the present invention. 
         FIG. 10A  is a schematic diagram showing a configuration of the trim tab control system according to another preferred embodiment of the present invention. 
         FIG. 10B  is a schematic diagram showing a configuration of the trim tab control system according to another preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments will be described with reference to the drawings. The ship  1  includes a ship body  3  and at least one trim tab  7 . Specifically, the ship  1  includes a ship body  3 , a propulsion device  5 , and a plurality of trim tabs  7  (for example, a pair of trim tabs  7 ). The ship  1  includes a trim tab control system  31 . 
     An example in which one propulsion device  5  is provided is illustrated, but a plurality of propulsion devices  5  may be provided. Further, the number of trim tabs  7  may be one or three or more. 
     In the following description, the front, rear, left, right, up, and down directions mean the front, rear, left, right, up, and down directions of the ship body  3 , respectively. For example, as shown in  FIG. 1 , a center line C 1  extending in the front-rear direction of the ship body  3  passes through the center of gravity G of the ship body  3 . The front-back direction extends along the center line C 1 . The forward direction extends upward along the center line C 1  in  FIG. 1 . The rear direction extends downward along the center line C 1  in  FIG. 1 . 
     The left-right direction (the width direction) is perpendicular to the center line C 1  in  FIG. 1 . The left direction is perpendicular to the center line C 1  and on a left side of the center line C 1  in  FIG. 1 . The right direction is perpendicular to the center line C 1  and on a right side of the center line C 1  in  FIG. 1 . The vertical direction is perpendicular to the front-rear direction and the left-right direction. 
     As shown in  FIG. 2 , the propulsion device  5  is, for example, an outboard motor. The propulsion device  5  generates a thrust to propel the ship body  3 . The propulsion device  5  is attached to the stern of the ship body  3 . For example, the propulsion device  5  is disposed between the pair of trim tabs  7 . 
     The propulsion device  5  includes an engine  9 , a drive shaft  10 , a propeller shaft  11 , a shift mechanism  13 , an engine cover  15 , a housing  17 , and a bracket  29 . 
     The engine  9  applies the thrust to the ship body  3 . The engine  9  is a power source to generate the thrust of the ship body  3 . In the present preferred embodiment, an example in which the engine  9  is used as the power source is illustrated, but a motor may be used as the power source. The engine  9  is disposed inside the engine cover  15 . The engine  9  includes a crankshaft  21 . The crankshaft  21  extends in the vertical direction. 
     The drive shaft  10  is connected to a crankshaft  21 . The drive shaft  10  extends downward from engine  9 . The propeller shaft  11  extends in a direction intersecting the drive shaft  10 . The propeller shaft  11  extends in the front-rear direction. The propeller shaft  11  is connected to the drive shaft  10  via the shift mechanism  13 . A propeller  23  is connected to the propeller shaft  11 . 
     The housing  17  is disposed below the engine cover  15 . The drive shaft  10 , the propeller shaft  11 , and the shift mechanism  13  are disposed in the housing  17 . The shift mechanism  13  is driven by a shift actuator  27  via a shift member  25 . The shift mechanism  13  switches the rotation direction of the power transmitted from the drive shaft  11  to the propeller shaft  12 . Thus, the rotation direction of the propeller  23  is switched to the forward direction or the reverse direction. 
     The bracket  29  is used to attach the propulsion device  5  to the ship body  3 . The propulsion device  5  is detachably fixed to the stern of the ship body  3  via the bracket  29 . The bracket  29  includes a steering shaft  30 . The propulsion device  5  is supported by a bracket  29  so as to be rotatable around the steering shaft  30 . 
     As shown in  FIG. 1 , the pair of trim tabs  7  are attached to the stern of the ship body  3 . For example, each of the pair of trim tabs  7  is swingably attached to the stern of the ship body  3 . Specifically, the pair of trim tabs  7  are swingably attached to the stern of the ship body  3  on the left and right sides of the propulsion device  5 . Each of the pair of trim tabs  7  is attached to the stern of the ship body  3  so as to be swingable around a swing axis C 2 . 
     As shown in  FIG. 3 , each of the trim tabs  7  includes a trim actuator  34  and a tab body  47 . 
     The trim actuators  34  are used to swing the tab bodies  47  with respect to the ship body  3 . The trim actuators  34  are attached to the tab bodies  47  between the tab bodies  47  and the ship body  3 . 
     Each of the tab bodies  47  is swingably attached to the stern of the ship body  3 . For example, the base end of each of the tab bodies  47  is attached to the stern of the ship body  3  so as to swing around the swing axis C 2 . When each of the trim actuators  34  operates, each of the tab bodies  47  swings in a swing direction R. 
     As shown in  FIG. 3 , the swing direction R is defined based on the swing axis C 2 . In the present preferred embodiment, the swing axis C 2  extends in a direction perpendicular or substantially perpendicular to the center line C 1 . For example, the swing axis C 2  extends in the left-right direction. The swing axis C 2  may extend obliquely so as to intersect the steering shaft  30 . 
     Hereinafter, when each of the tab bodies  47  swings in a direction away from the ship body  3 , for example, when each of the tab bodies  47  swings from the ship body  3  toward the water surface, the swing direction R of each of the tab bodies  47  is described as a first swing direction R 1 . 
     When each of the tab bodies  47  swings in a direction approaching the ship body  3 , for example, when each of the tab bodies  47  swings from the water surface (underwater) toward the ship body  3 , the swing direction R of each of the tab bodies  47  is described as a second swing direction R 2 . The “swing direction R” broadly includes the first swing direction R 1  and the second swing direction R 2 . 
     The ship  1  is equipped with a trim tab control system  31 . As shown in  FIG. 4 , the trim tab control system  31  includes the trim tabs  7  and a controller  33 . The trim tab control system  31  includes a ship speed sensor  35 , a rotation detection sensor  37 , and an attitude sensor  39 . 
     Each of the trim tabs  7  includes the trim actuator  34  and the tab body  47  as described above. Each of the trim actuators  34  is controlled by the controller  33 . Each of the tab bodies  47  swings due to the operation of each of the trim actuators  34 . Each of the trim actuators  34  may be a hydraulic actuator or an electric actuator. 
     The operation amount data corresponding to the operation amount of the trim actuator  34  is stored in a memory  33   b  (described below) during the operation of the trim actuator  34 . For example, when the trim actuator  34  is the hydraulic actuator, the operation amount data corresponding to the operation amount of a piston is stored in the memory  33   b . When the trim actuator  34  is the electric actuator, the operation amount data corresponding to the operation amount of the rod and/or the rotation amount of the motor is stored in the memory  33   b.    
     The controller  33  includes a processor  33   a  and a memory  33   b . The processor  33   a  includes, for example, a CPU (Central Processing Unit). The processor  33   a  executes processes to control each device and each sensor based on a program stored in the memory  33   b . For example, the processor  33   a  executes the process to control each of the trim actuators  34  based on the program stored in the memory  33   b . The description of “the process executed by the controller  33 ” may be interpreted as “the process executed by the processor  33   a”.    
     The memory  33   b  includes a volatile memory such as a RAM. The memory  33   b  includes a nonvolatile memory such as a ROM. The memory  33   b  stores programs and data to control each device and each sensor. For example, the memory  33   b  stores programs and data to control each of the trim actuators  34 . 
     The controller  33  may include an auxiliary storage device such as a hard disk and/or an SSD. Further, an external storage device (not shown) such as a hard disk and/or an SSD (not shown) may be connected to the controller  33 . 
     For example, the memory  33   b  stores operation state data indicating the operation state of the ship  1 . Specifically, the memory  33   b  stores the operation state data as time-series data. The operation state data includes at least one of ship speed data indicating the speed of the ship body  3 , attitude data indicating an attitude of the ship body  3 , and rotation speed data indicating the rotation speed of the engine  9 . In the present preferred embodiment, an example is shown in which the operation state data includes the ship speed data, the attitude data, and the rotation speed data. 
     The operation state data further includes tab position data indicating the position of the tab body  47  with respect to the ship body  3 . The tab position data is detected by a tab position sensor  40  (see  FIG. 4 ). The tab position sensor  40  is mounted on the ship body  3 . Specifically, the tab position sensor  40  is mounted on the ship body  3  so as to face the tab body  47 . 
     The tab position data is able to be calculated by the controller  33  based on the operation amount data of the trim actuator  34 . The tab position sensor  40  outputs the tab position data indicating the position of the tab body  47  to the controller  33 . 
     The operation state data may include a first swing speed V 1  (described below) of the tab body  47 . 
     The memory  33   b  stores landing determination data to set the time of landing before the tab body  47  lands on the water. The landing determination data indicates a correspondence relationship between the first condition data (the ship speed data, the rotation speed data, the attitude data, and the tab position data) and the time of landing. For example, the landing determination data includes data such as table data and map data and the like. 
     For example, a flag corresponding to the first condition data is defined in the landing determination data. The flag includes a first flag (for example, 0) indicating that the tab body  47  is not at the time of landing, and a second flag (for example, 1) indicating that the tab body  47  is at the time of landing. 
     The first flag or the second flag is determined by comparing the operation state data (the ship speed data, the rotation speed data, the attitude data, and the tab position data) acquired by the controller  33  with the first condition data (the ship speed data, the rotation speed data, the attitude data, and the tab position data) of the landing determination data. 
     The memory  33   b  stores speed setting data to set a second swing speed V 2  (described below) of the tab body  47 . The speed setting data indicates the correspondence relationship between the second condition data (the ship speed data, the rotation speed data, the attitude data, the tab position data), and the second swing speed V 2  of the tab body  47 . For example, the speed setting data includes data such as table data and map data and the like. 
     The second swing speed V 2  of the tab body  47  is determined by comparing the operation state data (the ship speed data, the rotation speed data, the attitude data, and the tab position data) acquired by the controller  33  with the second condition data (the ship speed data, the rotation speed data, the attitude data, the tab position data) in the speed setting data) of the speed setting data. 
     The memory  33   b  stores first table data indicating the relationship between the attitude data and a target tab position of each of the tab bodies  47 . The first table data is used to set the target tab position to adjust the ship attitude of the ship  1 . 
     The memory  33   b  stores the swing speed of each of the tab bodies  47  which is set based on the landing determination data. The swing speed V includes the first swing speed V 1  and the second swing speed V 2  that is less than the first swing speed V 1  (see  FIG. 5C ). Preferably, the first swing speed V 1  and the second swing speed V 2  are set based on the operation state data (the ship speed data, the attitude data, the rotation speed data, the tab position data). 
     Specifically, the first swing speed V 1  and the second swing speed V 2  are preferably changed based on at least one of the ship speed of the ship body  3 , the ship attitude of the ship body  3 , the rotation speed of the engine  9 , and the tab position of the tab body  47 . Each of the first swing speed V 1  and the second swing speed V 2  may be interpreted as an average swing speed of the tab body  47 . 
     The memory  33   b  stores a threshold to determine when the tab body  47  lands on the water. The threshold is preferably set based on the operation state data (the ship speed data, the attitude data, the rotation speed data, the tab position data). Specifically, the threshold is preferably set to a predetermined value for each of the ship speed of the ship body  3 , the ship attitude of the ship body  3 , and the rotation speed of the engine  9 . 
     In this case, the memory  33   b  stores second table data indicating the relationship between the operation state data (the ship speed data, the attitude data, the rotation speed data, the tab position data) and the threshold. The second table data defines thresholds respectively corresponding to the ship speed data, the attitude data, the rotation speed data, and the tab position data. 
     The ship speed sensor  35  detects the ship speed data indicating the ship speed of the ship body  3 . The ship speed sensor  35  is attached to the ship body  3 . For example, the ship speed sensor  35  includes a GPS receiving unit. The ship speed sensor  35  receives time series data of a ship body position from a GPS satellite. GPS is an abbreviation of Global Positioning System. 
     The GPS receiving unit calculates the ship speed data with the time series data of the ship body position and outputs the ship speed data to the controller  33 . The ship speed data is stored in the memory  33   b . The GPS receiving unit is able to output the time series data of the ship body position to the controller  33  and the controller  33  is able to calculate the ship speed data based on the time series data of the ship body position. 
     The rotation detection sensor  37  detects the rotation speed data indicating the rotation speed of the engine  9 . For example, the rotation detection sensor  37  detects the rotation speed data indicating the rotation speed of the crankshaft  21 . The rotation detection sensor  37  is attached to the engine so as to face the crankshaft  21 . The rotation detection sensor  37  outputs rotation number data to the controller  33 . The rotation speed data is stored in the memory  33   b  as time-series data. The rotation detection sensor  37  may include a sensor such as an electromagnetic sensor and an optical sensor and the like. 
     The attitude sensor  39  detects the attitude data indicating the ship attitude of the ship body  3 . The attitude sensor  39  is attached to the ship body  3 . For example, the attitude sensor  39  includes a gyro sensor. The attitude data includes roll data around a roll axis, pitch data around a pitch axis, and yaw data around a yaw axis. The attitude sensor  39  outputs the attitude data to the controller  33 . The attitude data is stored in the memory  33   b  as time-series data. The attitude sensor  39  may be another sensor such as an acceleration sensor. 
     The controller  33  operates each of the tab bodies  47  by controlling each of the trim actuators  34 . For example, the controller  33  sets the swing speed V of each of the tab bodies  47  by controlling each of the trim actuators  34 . The swing speed V includes the first swing speed V 1  and the second swing speed V 2 . The controller  33  sets the first swing speed V 1  to a predetermined swing speed stored in the memory  33   b.    
     The controller  33  preferably sets the second swing speed V 2  such that an elapsed time from when the tab body  47  lands on the water and the water pressure acting on the tab body  47  are in a proportional relationship. Specifically, the controller  33  preferably sets the second swing speed V 2  so that the elapsed time elapsed from when the tab body  47  lands on the water and the vertical force acting on the tab body  47  are in a proportional relationship. The vertical force may be a substantially vertical force. 
     In this case, the controller  33  sets the second swing speed V 2  based on the operation state data (the attitude data, the ship speed data, the tab position data). Specifically, the controller  33  sets the second swing speed V 2  corresponding to the operation state data (the attitude data, the ship speed data, the tab position data) based on the speed setting data. 
     In the present preferred embodiment, the controller  33  sets the second swing speed V 2  based on the operation state data (the ship speed data, the rotation speed data, the attitude data, the tab position data). In this case, the controller  33  sets the second swing speed V 2  corresponding to the operation state data (the ship speed data, the rotation speed data, the attitude data, the tab position data) based on the speed setting data. 
     In the speed setting data, the second swing speed V 2  is defined so that the elapsed time from when the tab body  47  lands on the water and the water pressure acting on the tab body  47  are in a proportional relationship. 
     The controller  33  determines the current position of the tab body  47  with respect to the ship body  3  based on the tab position data. The controller  33  is able to determine the current position of the tab body  47  with respect to the ship body  3  based on the tab position data. In this case, the controller  33  calculates the current tab position data of the tab body  47  based on the tab position data. The controller  33  determines the current position of the tab body  47  based on the tab position data. 
     The controller  33  acquires the attitude data from the attitude sensor  39 . The controller  33  operates each of the trim actuators  34  based on the attitude data. For example, the controller  33  sets the target tab position of each of the tab bodies  47  based on the attitude data. The controller  33  operates each of the trim actuators  34  toward the target tab position. 
     In the present preferred embodiment, the tab position is set to a reference tab position, for example, 0 (degree), when the tip of the tab body  47  is located at the uppermost position. The target tab position is set based on the reference tab position. The “tab position” and “target tab position” may be interpreted as “the tab position data” and “target tab angle”. 
     The controller  33  acquires the ship speed data from the ship speed sensor  35 . The controller  33  acquires the attitude data from the attitude sensor  39 . The controller  33  acquires the rotation speed data from the rotation detection sensor  37 . The controller  33  acquires the tab position data. 
     The controller  33  operates each of the trim actuators  34  based on the ship speed data, the attitude data, the rotation speed data, and the tab position data. For example, the controller  33  determines the flag (the first flag or the second flag) corresponding to the ship speed data, the attitude data, the rotation speed data, and the tab position data based on the landing determination data. 
     When the controller  33  determines the first flag is set, the controller  33  swings each of the tab bodies  47  at the first swing speed V 1 . Specifically, the controller  33  operates each of the trim actuators  34  such that each of the tab bodies  47  swings at the first swing speed V 1 . 
     When the controller  33  determines the second flag is set, the controller  33  swings each of the tab bodies  47  at the second swing speed V 2 . For example, the controller  33  swings each of the tab bodies  47  at the second swing speed in a predetermined time range including the time when the tab bodies  47  lands on the water. Specifically, when the controller  33  determines the second flag is set, the controller  33  operates each of the trim actuators  34  such that each of the tab bodies  47  swings at the second swing speed V 2  in the above-described predetermined time range. 
     When at least one of the pair of tab bodies  47  swings toward the water in order to adjust the ship attitude of the ship body  3 , the controller  33  sets the time of landing of the tab body  47  based on the operation state data before the tab body  47  lands on the water. 
     For example, when the controller  33  causes the tab body  47  to swing toward the water, the controller  33  estimates the time of landing of the tab body  47  based on at least one of the ship speed data, the rotation speed data, the attitude data, and the tab position data. 
     Here, the controller  33  estimates the time of landing of the tab body  47  based on the ship speed data, the rotation speed data, the attitude data, and the tab position data. For example, the controller  33  sets the time of landing of the tab body  47  based on the landing determination data (table data or map data) stored in the memory  33   b.    
     The controller  33  refers to the landing determination data. The controller  33  determines that the tab body  47  is at the time of landing when the flag corresponding to the rotation speed data, the attitude data, and the tab position data is the first flag. The controller  33  determines that the tab body  47  is not at the time of landing when the flag corresponding to the rotation speed data, the attitude data, and the tab position data is the second flag. 
     When at least one of the pair of tab bodies  47  swings toward the water in order to adjust the ship attitude of the ship body  3 , the controller  33  determines the landing of the ship body  3  based on the operation state data. For example, when the controller  33  causes the tab body  47  to swing toward the water, the controller  33  determines the landing of the ship body  3  based on at least one of the ship speed data, the rotation speed data, the attitude data, and the tab position data. 
     Specifically, as shown in  FIGS. 5A and 5B , each of the ship speed data, the rotation speed data, and the attitude data changes before and after the landing of the tab body  47 .  FIGS. 5A and 5B  show an example in which the tab body  47  lands on the water in a state where the ship speed is constant, for ease of explanation. The landing time of the tab body  47  is described as “to” in  FIGS. 5A and 5B . 
     For example, as shown in  FIG. 5A , the ship speed data is stable at the first data value D 1  until the tab body  47  lands on the water (T&lt;to). After the tab body  47  lands on the water (T≥to), for example, immediately after the tab body  47  lands on the water, the ship speed data decreases from the first data value D 1 . In other words, the ship speed data greatly changes before and after the first data value D 1 . 
     Similarly, the rotation speed data is stable at the second data value D 2  until the tab body  47  lands on the water (T&lt;to). After the tab body  47  lands (T≥to), for example, immediately after the tab body  47  lands on the water, the rotation speed data decreases from the second data value D 2 . In other words, the rotation speed data greatly changes before and after the second data value D 2 . 
     Similarly, as shown in  FIG. 5B , the attitude data is stable at the third data value D 3  until the tab body  47  lands on the water (T&lt;to). After the tab body  47  lands on the water (T≥to), for example, immediately after the tab body  47  lands on the water, the attitude data decreases from the third data value D 3 . In other words, the attitude data greatly changes before and after the third data value D 3 . 
     Thus, amount of change of the operation state data (the ship speed data, the rotation speed data, the attitude data) differs before and after the landing of the tab body  47 . Therefore, the controller  33  is able to determine the time of landing of the tab body  47  by monitoring the amount of change of the operation state data by the controller  33 . 
     Further, the controller  33  is able to determine the time of landing of the tab body  47  by assuming that the tab body  47  lands on the water when the tab position (the current tab position) of the tab body  47  is at the predetermined tab position. 
     The controller  33  calculates the amount of change of the operation state data based on the time series data of the operation state data (the ship speed data, the rotation speed data, the attitude data). 
     For example, the absolute values |K 1 |, |K 2 |, |K 3 | of the inclinations K 1 , K 2 , K 3  of the operation state data are used as the amounts of change of the operation state data respectively. The inclinations K 1 , K 2 , K 3  of the operation state data are calculated based on the time-series data of the operation state data shown in  FIGS. 5A and 5B . 
     As shown in  FIGS. 5A and 5B , the amount of change of the operation state data is evaluated by the absolute values, since the inclinations K 1 , K 2 , and K 3  of the operation state data have negative inclinations. 
     Here, an average value of the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data in a predetermined time range is preferably used as the amount of change |K 1 |, |K 2 |, |K 3 | of the operation state data. 
     For example, there is a possibility that the tab body  47  instantaneously lands on the water due to a change of the water surface state. In this case, the controller  33  may determine that the tab body  47  lands on the water. However, the controller  33  is able to appropriately estimate the time of landing by using the average value of the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data as the amount of change of the operation state data. 
     The controller  33  sets a threshold based on the operation state data. For example, the controller  33  sets a threshold corresponding to the operation state data (the ship speed data, the attitude data, the rotation speed data, the tab position data) based on the second table data. 
     The controller  33  preferably changes the threshold according to the ship speed of the ship  1  and the rotation speed of the engine  9  based on the second table data. For example, the controller  33  preferably changes the threshold according to the first data value D 1  of the ship speed data and/or the second data value D 2  of the rotation speed data shown in  FIG. 5A . The controller  33  is able to change the threshold according to the third data value D 3  of the attitude data shown in  FIG. 5B . 
     Further, the controller  33  preferably changes the threshold according to the tab position of the tab body  47  based on the second table data. As shown in  FIGS. 5A and 5B , the time of landing of the tab body  47  may be estimated based on the tab position. The time of landing corresponding to the tab position, for example, the deceleration start time (ts) and the landing time (to) is defined in the second table data. 
     The controller  33  determines the time of landing of the tab body  47  based on the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data. For example, the controller  33  determines that the tab body  47  does not land on the water when the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data are less than the threshold. When the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data are equal to or greater than the threshold, the controller  33  determines that the tab body  47  lands on the water. 
     The amount of change of the operation state data is at least one of the amount of change |K 1 | of the ship speed data, the amount of change |K 2 | of the rotation speed data, and the amount of change |K 3 | of the attitude data. 
       FIGS. 6A to 6C  are flowcharts showing processes performed by the trim tab control system  31 . The controller  33  constantly monitors the operation state of the ship  1  (S 1 ). For example, the controller  33  acquires operation state data, for example, at least one of the ship speed data, the attitude data, the rotation speed data, and the tab position data. In the present preferred embodiment, the controller  33  acquires the ship speed data, the attitude data, the rotation speed data, and the tab position data. 
     Thus, the controller  33  determines the speed of the ship  1 , the attitude of the ship  1 , the rotation speed of the engine  9 , and the swing angle of the tab body  47 . The operation state data, for example, the ship speed data, the attitude data, the rotation speed data, and the tab position data are stored in the memory  33   b  as time-series data. 
     The controller  33  sets the threshold based on the operation state data (S 2 ). For example, the controller  33  sets the threshold corresponding to the operation state data (the ship speed data, the attitude data, the rotation speed data, and the tab position data) based on the second table data. 
     The controller  33  determines whether it is necessary to adjust the ship attitude of the ship body  3  based on the attitude data (S 3 ). For example, the controller  33  determines whether or not the tab body  47  needs to be operated based on the attitude data. Specifically, the controller  33  determines that the controller  33  needs to operate the tab body  47  when the amount of change of at least one of the roll data, the pitch data, and the yaw data exceeds a predetermined value stored in the memory  33   b.    
     When the controller  33  determines that the ship attitude of the ship body  3  needs to be adjusted (Yes in S 3 ), the controller  33  causes the trim actuator  34  to activate based on the attitude data. Further, the controller  33  sets the target tab position of the tab body  47  based on the attitude data (S 4 ). Further, the controller  33  sets the swing speed V of the tab body  47  to the first swing speed V 1  (S 5 ). 
     The controller  33  outputs an operation start signal to the trim actuator  34  so that the tab body  47  operates toward the target tab position at the first swing speed V 1 . Accordingly, the tab body  47  starts operating at the first swing speed V 1  in the first swing direction R 1  (S 6 ). When the controller  33  determines that the ship attitude of the ship body  3  does not need to be adjusted (No in S 3 ), the controller  33  continues the process of step  3  (S 3 ). 
     In a state where the trim actuator  34  operates at the first swing speed V 1 , the controller  33  determines whether or not the tab body  47  is at the time of landing based on the operation state data (S 7 ). 
     For example, the controller  33  determines whether the operation state data satisfies a predetermined condition. Specifically, the controller  33  determines whether or not the ship speed data, the attitude data, the rotation speed data, and the tab position data satisfy the predetermined condition respectively. 
     The controller  33  calculates the average value of each of the ship speed data, the attitude data, and the rotation speed data at predetermined time intervals with the time-series data of each of the ship speed data, the attitude data, and the rotation speed data. The controller  33  determines whether or not the current tab position data and the average value of each of the ship speed data, the attitude data, and the rotation speed data satisfy the predetermined condition. 
     The determination of whether or not the operation state data satisfies the predetermined condition, for example, the determination of whether or not the above data satisfies the predetermined condition, is performed based on the above-described landing determination data. 
     For example, the landing determination data includes the table data stored in the memory  33   b . The table data indicates a correspondence relationship between the first condition data (the ship speed data, the rotation speed data, the attitude data, and the tab position data) and the flag indicating whether or not the tab body  47  is at the time of landing. 
     The controller  33  compares the current ship speed data, the current attitude data, the current rotation speed data, and the current tab position data with the first condition data with reference to the table data. Due to this comparison, the controller  33  determines whether or not the tab body  47  is at the time of landing. 
     Here, an example is shown in which the first condition data includes all of the ship speed data, the rotation speed data, the attitude data, and the tab position data. However, the first condition data is required for including at least one of the ship speed data, the rotation speed data, the attitude data, and the tab position data. 
     When the controller  33  determines that the operation state data does not satisfy the predetermined condition (No in S 7 ), the controller  33  determines that the tab body  47  is not at the time of landing. In this case, the controller  33  outputs an operation signal to the trim actuator  34  so that each of the tab bodies  47  operates at the first swing speed V 1 . In other words, the controller  33  operates the trim actuator  34  such that the swing speed V of the tab body  47  is maintained at the first swing speed V 1 . Thus, the tab body  47  swings at the first swing speed V 1  (S 8 ). In this case, the controller  33  continues the process of Step  7  (S 7 ). 
     When the controller  33  determines that the operation state data satisfies the predetermined condition (Yes in S 7 ), the controller  33  determines that the tab body  47  is at time of landing. The controller  33  stores the time when the controller  33  determines that the tab body  47  is at the time of landing as the deceleration start time (ts) in the memory  33   b.    
     In this case, the controller  33  outputs an operation signal to the trim actuator  34  so that each of the tab bodies  47  operates at the second swing speed V 2 . In other words, the controller  33  operates the trim actuator  34  so that the swing speed V of the tab body  47  becomes slower than the first swing speed V 1 . Thus, the tab body  47  swings at the second swing speed V 2  (S 9 ). The swing speed V of the tab body  47  is changed to the second swing speed V 2  before the tab body  47  lands on the water. 
     Here, the second swing speed V 2  is set as described above. For example, the controller  33  refers to the speed setting data (the ship speed data, the rotation speed data, the attitude data, the tab position data). The controller  33  sets the second swing speed V 2  corresponding to the operation state data (the ship speed data, the rotation speed data, the attitude data, the tab position data). 
     The controller  33  determines whether or not the tab body  47  actually lands on the water based on the operation state data (S 10 ). For example, whether or not the tab body  47  actually lands is determined based on the amount of change corresponding to at least one of change of the ship attitude and change of the ship speed. 
     Whether or not the tab body  47  actually lands is preferably determined based on the amount of change corresponding to at least one of the change of the ship attitude, the change of the ship speed, and the change of the rotation speed of the engine  9 . In the present preferred embodiment, whether or not the tab body  47  actually lands is determined based on the amount of change corresponding to each of the change of the ship attitude of the ship  1 , the change of the ship speed, and the change of the rotation speed of the engine  9 . 
     For example, when the amount of change of the inclination of the ship  1  in the predetermined time is equal to or greater than a first threshold, the controller  33  determines that the tab body  47  actually lands on the water because the ship attitude is changed by the water pressure acting on the tab body  47  when the tab body  47  actually lands on the water. 
     Also, when the speed reduction amount of the ship  1  in the predetermined time is equal to or greater than the second threshold, the controller  33  determines that the tab body  47  actually lands on the water because the ship speed is reduced by the water pressure acting on the tab body  47  when the tab body  47  actually lands on the water. 
     Further, when the reduction amount of the rotation speed of the engine  9  in the predetermined time is equal to or greater than the third threshold, the controller  33  determines that the tab body  47  actually lands on the water because the rotation speed is reduced by the water pressure acting on the tab body  47  when the tab body  47  actually lands on the water. 
     Specifically, the controller  33  determines whether or not each of the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data is less than the above threshold. It is able to be determined whether or not at least one of the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data is less than the above threshold. 
     Here, when each of the amounts of change |K 1 |, |K 2 |, and |K 3 | of the operation state data is equal to or larger than the above threshold (Yes in S 10 ), the controller  33  determines that the tab body  47  lands on the water. The time point of the determination corresponds to the landing time (to). In this case, the controller  33  executes the process of Step  11  (S 11 ). 
     When the controller  33  determines that the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data is less than the above threshold (No in S 10 ), the controller  33  determines that the tab body  47  does not land on water. In this case, the controller  33  executes the process of Step  10  (S 10 ) until the tab body  47  lands on the water. 
     The controller  33  determines whether or not the predetermined time (td 1 ) has elapsed from the landing time (to) (S 11 ). The predetermined time (td 1 ) is stored in the memory  33   b.    
     When the controller  33  determines that the predetermined time (td 1 ) has elapsed (Yes in S 11 ), the controller  33  outputs the operation signal to the trim actuator  34  so that each of the tab bodies  47  operates at the first swing speed V 1 . In other words, the controller  33  operates the trim actuator  34  such that the swing speed V of the tab body  47  returns to the first swing speed V 1 . Thus, the tab body  47  swings again at the first swing speed V 1  after the deceleration end time (te=to+td 1 ) in  FIG. 5C  (S 12 ). 
     When the controller  33  determines that the predetermined time (td 1 ) has not elapsed (No in S 11 ), the controller  33  continues the process of step  11  (S 11 ). 
     The controller  33  determines whether the tab position of the tab body  47  has positioned the target tab position (S 13 ). For example, the controller  33  determines whether the tab position of the tab body  47  has positioned the target tab position based on the operation amount data of the trim actuator  34 . The controller  33  is able to determine whether the tab position of the tab body  47  has positioned the target tab position based on the tab position data. 
     Here, when the controller  33  determines that the tab position of the tab body  47  has positioned the target tab position (Yes in S 13 ), the controller  33  stops the operation of the trim actuator  34 . In other words, the operation of the tab body  47  stops (S 14 ). When the controller  33  determines that the tab position of the tab body  47  has not positioned the target tab position (No in S 13 ), the controller  33  continues to operate the trim actuator  34  and executes the process of step (S 13 ). 
     As described above, in the trim tab control system  31 , the time of landing of the tab body  47  is estimated based on the operation state data. When the tab body  47  is at the time of landing, the swing speed V of the tab body  47  is changed from the first swing speed V 1  to the second swing speed V 2  (&lt;first V 1 ). Thus, the increase of lift force is reduced when the tab body  47  lands on the water. In other words, the trim tab control system  31  is capable of stably changing the ship attitude of the ship body  3  when the tab body  47  operates. 
     The trim tab control system  31  described above includes the following features. 
     In the above-described preferred embodiments, the ship speed data, the attitude data, the rotation speed data, and the tab position data are used as the operation state data in order to determine the time of landing of the tab body  47 . The time of landing of the tab body  47  is able to be determined by using at least one of the ship speed data, the attitude data, the rotation speed data, and the tab position data without using all of the ship speed data, the attitude data, the rotation speed data, and the tab position data. Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     In the above-described preferred embodiments, examples in which the controller  33  determines the current tab position data based on the operation amount data of the trim actuator  34  have been described. Instead of this, the current tab position data may be estimated based on the ship speed data and the attitude data. 
     In this case, the memory  33   b  stores third table data indicating a relationship between the ship speed data and the tab position data and/or a relationship between the attitude data and the tab position data. The third table data is used to estimate the tab position data based on the ship speed data and the attitude data. 
     The controller  33  estimates the current tab position data based on the current ship speed data and the current attitude data. For example, the controller  33  determines the current tab position data corresponding to the current ship speed data and the current attitude data by referring to the third table data. 
     Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     In the above-described preferred embodiments, an example in which the swing speed V of the tab body  47  is returned to the first swing speed V 1  in step  12  (S 12 ) based on the landing time (to) is described. 
     Instead of this, as shown in  FIG. 7 , after the predetermined time (td 2 ) has elapsed with reference to the deceleration start time (ts) (when the time of landing is set), the swing speed V of the tab body  47  is returned to the first swing speed V 1  in step  12  (S 12 ). 
     In this case, the process of step  10  (S 10 ) is omitted and the process of step  11  (S 11 ) is performed. In step  11  (S 11 ), the controller  33  determines whether or not the predetermined time (td 2 ) has elapsed with reference to the deceleration start time (ts). Subsequent processes are the same as in the above-described preferred embodiments. 
     Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     In the above-described preferred embodiments, an example is shown in which the second swing speed V 2  is constant as shown in  FIG. 5C . Instead of this, the second swing speed V 2  may be changed in a state where the second swing speed V 2  is less than the first swing speed V 1 . 
     For example, when the tip of the tab body  47  is curved as shown in  FIG. 8A , the second swing speed V 2  is preferably changed as shown in  FIG. 8B . In this case, the second swing speed V 2  gradually decreases from the deceleration start time (ts) to the landing time (to). Thereafter, as time elapses from the landing time (to), the second swing speed V 2  gradually increases toward the first swing speed V 1 . 
     The control of the second swing speed V 2  is executed by the controller  33 . In this case, the process of steps  10 ,  11 , and  12  (S 10 , S 11 , S 12 ) is omitted. In step  9  (S 9 ), the controller  33  controls the second swing speed V 2  of the tab body  47  with reference to the deceleration start time (ts) as shown in  FIG. 8B . 
     Here, as described above, the controller  33  sets the second swing speed V 2  so that the elapsed time from when the tab body  47  lands on the water and the water pressure acting on the tab body  47  are in the proportional relationship. 
     For example, the controller  33  sets the second swing speed V 2  corresponding to the operation state data (the ship speed data, the rotation speed data, the attitude data, the tab position data) based on the speed setting data which satisfies the above proportional relationship. 
     Further, the controller  33  is able to control the second swing speed V 2  of the tab body  47  based on the speed control function. The speed control function is stored in the memory  33   b . In this case, the speed control function has operation state data (the ship speed data, the rotation speed data, the attitude data, the tab position data) as variables. The speed control function derives a second swing speed V 2  corresponding to the variables. 
     Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     The trim tab control system  31  described above may be configured as follows. 
     In the above-described preferred embodiments, an example in which the swing speed V of the tab body  47  is changed to the second swing speed V 2  before the tab body  47  lands on the water is described. Instead of this, the swing speed V of the tab body  47  is changed to the second swing speed V 2  when the tab body  47  lands in a state where the tab body  47  swings toward the water to adjust the ship attitude of the ship body  3 . 
     In this case, first, the controller  33  executes the process of step  1  (S 1 ) to step  6  (S 6 ) of the above-described preferred embodiments in the same manner as the above-described preferred embodiments (see  FIG. 6A ). Next, as shown in  FIG. 9 , the controller  33  determines whether or not the tab body  47  lands on the water based on the operation state data (S 7   a ). The operation state data includes, for example, the ship speed data and the attitude data. In the present preferred embodiment, the operation state data further includes the rotation speed data. 
     Specifically, the controller  33  calculates the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data based on the time series data of the operation state data (the ship speed data, the rotation speed data, the attitude data). The controller  33  determines whether or not the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data are less than the threshold. The process of step  7   a  (S 7   a ) is performed in the same manner as step  10  (S 10 ) of the above-described preferred embodiments. 
     Here, when the amounts of change |K 1 |, |K 2 |, |K 3 | of the operation state data are less than the threshold (No in S 7   a ), the controller  33  determines that the tab body  47  has not landed. In this case, the controller  33  swings the tab body  47  at the first swing speed V 1  (S 8   a ). 
     When the amounts of change |K 1 |, |K 2 |, and |K 3 | of the operation state data are equal to or larger than the threshold (No in S 7   a ), the controller  33  determines that the tab body  47  is at the time of landing. In this case, the controller  33  swings the tab body  47  at the second swing speed V 2  (S 9   a ). 
     Subsequently, the controller  33  determines whether or not the predetermined time (td 1 ) has elapsed from the landing time (to) (S 10   a ). When the controller  33  determines that the predetermined time (td 1 ) has elapsed (Yes in S 10   a ), the controller  33  returns the swing speed V of the tab body  47  to the first swing speed V 1  (S 11   a ). When the controller  33  determines that the predetermined time (td 1 ) has not elapsed (No in S 10   a ), the controller  33  continues the process of Step  10   a  (S 10   a ). 
     The process of step  10   a  (S 10   a ) and step  11   a  (S 11   a ) is performed in the same manner as the process of step  11  ( 11 ) and step  12  (S 12 ) of the above-described preferred embodiments. 
     After the process of step  11   a  (S 11   a ) is executed, the controller  33  executes the process of steps  13  (S 13 ) to  14  (S 14 ) of the above-described preferred embodiments in the same manner as the above-described preferred embodiments (see  FIG. 6C ). 
     Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     The operation state data of the above-described preferred embodiments may include strain data detected by a strain sensor  50 . The strain data indicates the strain of the tab body  47 . The operation state data of the above-described preferred embodiments may include load data detected by the load sensor  51 . The load data indicates the load detected by the load sensor  51 . 
     When the operation state data includes the strain data, as shown in  FIG. 10A , the trim tab control system  31  includes the strain sensor  50  to detect the strain of the tab body  47 . The strain sensor  50  is provided on the tab body  47 . The strain sensor  50  includes, for example, a strain gauge. The strain sensor  50  outputs the strain data to the controller  33 . 
     When the operation state data includes the load data, as shown in  FIG. 10A , the trim tab control system  31  includes the load sensor  51  to detect a load transmitted from the trim tab  7  to the ship body  3 . The load sensor  51  is disposed between the ship body  3  and the trim tab  7 . Specifically, the load sensor  51  is disposed between the ship body  3  and the trim actuator  34 . The load sensor  51  detects the load transmitted from the trim actuator  34  to the ship body  3 . The load sensor  51  outputs the load data to the controller  33 . 
     When the operation state data includes the strain data and/or when the operation state data includes the load data, the controller  33  determines whether the tab body  47  lands on the water based on the strain data and/or the load data in the above step  7   a  (S 7   a ). 
     Before and after the landing of the tab body  47 , the time-series data of the strain data and the load data changes such as the case of  FIGS. 5A and 5B . Therefore, the controller  33  is able to determine whether or not the tab body  47  lands on the water based on the time-series data of the strain data and/or the load data. 
     Here, for example, the controller  33  determines whether or not the amount of change of the strain data and/or the amount of change of the load data is less than a threshold. 
     Each of the amounts of change is calculated in the same manner as in the above-described preferred embodiments. When the amount of change of the strain data and/or the amount of change of the load data is less than the threshold, the controller  33  determines that the tab body  47  has not landed on water. When the amount of change of the strain data and/or the amount of change of the load data is equal to or greater than the threshold, the controller  33  determines that the tab body  47  is at the time of landing. 
     Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     In the case where the trim actuator  34  of the above-described preferred embodiments is the hydraulic actuator or the electric actuator, the determination of the time of landing can be performed as follows. 
     When the trim actuator  34  is the hydraulic actuator, as shown in  FIG. 10B , the trim actuator  34  has a hydraulic pressure sensor  60  that detects the pressure of the hydraulic fluid. The operating state data includes pressure data which is detected by the hydraulic pressure sensor  60 . The hydraulic pressure sensor  60  outputs the pressure data to the controller  33 . 
     When the trim actuator  34  is the electric actuator, as shown in  FIG. 10B , the trim actuator  34  includes a load sensor  61  that detects a load acting on the motor of the trim actuator  34 . The operation state data includes load data which is detected by the load sensor  61 . The load sensor  61  outputs the load data to the controller  33 . 
     When the operation state data includes the pressure data and/or when the operation state data includes the load data, the controller  33  determines whether the tab body  47  is at the time of landing based on the pressure data and/or the load data in step  7   a  (S 7   a ). 
     Before and after the landing of the tab body  47 , the time series data of the pressure data and the load data changes such as the case of  FIGS. 5A and 5B . Therefore, the controller  33  is able to determine whether or not the tab body  47  lands on the water based on the time-series data of the pressure data and/or the load data. 
     Here, for example, the controller  33  determines whether the amount of change of the pressure data and/or the amount of change of the load data is less than a threshold. 
     Each of the amounts of change is calculated in the same manner as in the above preferred embodiments. When the amount of change of the pressure data and/or the amount of change of the load data is less than the threshold, the controller  33  determines that the tab body  47  has not landed on water. When the amount of change of the pressure data and/or the amount of change of the load data is equal to or larger than the threshold, the controller  33  determines that the tab body  47  is at the time of landing. 
     Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     In Step  10  (S 10 ) of the above-described preferred embodiments, an example in which the time of landing of the tab body  47  is determined based on the amount of change of the ship speed data, the amount of change of the rotation speed data, and the amount of change of the attitude data is described. 
     Instead of this, the determination of the landing of the tab body  47  in step  10  (S 10 ) can be performed by using the amount of change of the strain data and/or the amount of change of the load data in (B 2 ). Further, the determination of the landing of the tab body  47  in step  10  (S 10 ) can be performed by using the amount of change of the pressure data and/or the amount of change of the load data in (B 3 ). 
     Even if this configuration is used, the same advantageous effects as in the above-described preferred embodiments are obtained. 
     According to the preferred embodiments of the present invention, it is possible to stably change a ship attitude during operation of the trim tab in a trim tab control system for the ship. 
     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.