Water jet propulsion boat and method of maintaining bow-up attitude of water jet propulsion boat

Abstract

A water jet propulsion boat includes a hull, a drive source in the hull, a jet propulsion mechanism to generate a propulsive force for the hull by ejecting a jet of water with a driving force from the driving source, a jet stream changer to change at least one of a jet stream direction and a jet stream force of the jet of water from the jet propulsion mechanism, a tilt detector to output a detection signal according to a tilt angle of the hull, and a controller configured or programmed to execute an angle difference calculation to calculate an angle difference between the tilt angle of the hull and a target angle of the hull for a bow-up attitude based on the detection signal from the tilt detector, and a feedback process to reduce the angle difference by changing at least one of the jet stream direction or the jet stream force by the jet stream changer.

What is claimed is: 
     
         1 . A water jet propulsion boat comprising:
 a hull;   a drive source in the hull;   a jet propulsion mechanism to generate a propulsive force for the hull by ejecting a jet of water with a driving force from the driving source;   a jet stream changer to change at least one of a jet stream direction or a jet stream force of the jet of water from the jet propulsion mechanism;   a tilt detector to output a detection signal according to a tilt angle of the hull; and   a controller configured or programmed to execute:
 an angle difference calculation to calculate an angle difference between the tilt angle of the hull and a target angle of the hull for a bow-up attitude based on the detection signal from the tilt detector; and 
 a feedback process to reduce the angle difference by changing at least one of the jet stream direction or the jet stream force by the jet stream changer. 
   
     
     
         2 . The water jet propulsion boat according to  claim 1 , wherein
 the controller is configured or programmed to execute an angular velocity calculation to calculate an angular velocity of the tilt angle of the hull based on the detection signal from the tilt detector; and   in the feedback process, at least one of the jet stream direction or the jet stream force is changed by the jet stream changer according to the angular velocity of the tilt angle.   
     
     
         3 . The water jet propulsion boat according to  claim 2 , wherein the controller is configured or programmed to increase, in the feedback process, a rate of change of at least one of the jet stream direction or the jet stream force by the jet stream changer as the angular velocity of the tilt angle increases. 
     
     
         4 . The water jet propulsion boat according to  claim 1 , wherein
 the jet stream changer includes a direction changer to change the jet stream direction of the jet of water from the jet propulsion mechanism; and   the controller is configured or programmed to execute, in the feedback process, a jet stream direction control mode to change the jet stream direction with the direction changer to reduce the angle difference.   
     
     
         5 . The water jet propulsion boat according to  claim 4 , further comprising:
 a steering device on the hull; wherein   the jet stream changer is operable to change the jet stream force according to an operation by the steering device to change the jet stream force; and   the jet stream direction control mode includes a first jet stream direction control mode to reduce the angle difference while allowing a change in the jet stream force according to the operation by the steering device.   
     
     
         6 . The water jet propulsion boat according to  claim 5 , wherein
 the jet stream direction control mode further includes a second jet stream direction control mode to reduce the angle difference while prohibiting the change of the jet stream force according to the operation by the steering device; and   the controller is configured or programmed to selectively execute the first jet stream direction control mode and the second jet stream direction control mode in the feedback process.   
     
     
         7 . The water jet propulsion boat according to  claim 4 , further comprising:
 a steering device on the hull; wherein   the direction changer is operable to change the jet stream direction according to an operation by the steering device to change the jet stream direction;   the jet stream direction control mode includes a third jet stream direction control mode to reduce the angle difference while allowing a change in the jet stream direction according to the operation by the steering device, and a fourth jet stream direction control mode to reduce the angle difference while prohibiting a change in the jet stream direction according to the operation by the steering device; and   the controller is configured or programmed to selectively execute the third jet stream direction control mode and the fourth jet stream direction control mode in the feedback process.   
     
     
         8 . The water jet propulsion boat according to  claim 1 , wherein
 the jet stream changer includes a jet stream force changer to change the jet stream force of the jet of water from the jet propulsion mechanism; and   the controller is configured or programmed to executes in the feedback process, a jet stream force control mode to change the jet stream force by the jet stream force changer to reduce the angle difference.   
     
     
         9 . The water jet propulsion boat according to  claim 8 , further comprising:
 a steering device on the hull; wherein   the jet stream force changer is operable to change the jet stream force according to an operation by the steering device to change the jet stream force; and   the jet stream force control mode includes a first jet stream force control mode to reduce the angle difference while allowing a change in the jet stream force according to the operation by the steering device.   
     
     
         10 . The water jet propulsion boat according to  claim 9 , wherein
 the jet stream force control mode further includes a second jet stream force control mode to reduce the angle difference while prohibiting the change of the jet stream force according to the operation by the steering device; and   the controller is configured or programmed to selectively execute the first jet stream force control mode and the second jet stream force control mode in the feedback process.   
     
     
         11 . The water jet propulsion boat according to  claim 8 , further comprising:
 a steering device on the hull; wherein   the jet stream changer further includes a direction changer to change the jet stream direction of the jet of water from the jet propulsion mechanism;   the direction changer is operable to change the jet stream direction according to an operation by the steering device to change the jet stream direction;   the jet stream force control mode includes a third jet stream force control mode to reduce the angle difference while allowing a change in the jet stream direction according to the operation by the steering device, and a fourth jet stream force control mode to reduce the angle difference while prohibiting a change in the jet stream direction according to the operation by the steering device; and   the controller is configured or programmed to selectively execute the third jet stream force control mode and the fourth jet stream force control mode in the feedback process.   
     
     
         12 . The water jet propulsion boat according to  claim 1 , wherein
 the jet stream changer includes a direction changer to change the jet stream direction of the jet of water from the jet propulsion mechanism and a jet stream force changer to change the jet stream force of the jet of water from the jet propulsion mechanism; and   the controller is configured or programmed to execute, in the feedback process, a combined control mode to change the jet stream direction and the jet stream force by the jet stream force changer to reduce the angle difference.   
     
     
         13 . The water jet propulsion boat according to  claim 12 , further comprising:
 a steering device on the hull; wherein   the jet stream force changer is operable to change the jet stream force according to an operation by the steering device to change the jet stream force; and   the combined control mode includes a first combined control mode to reduce the angle difference while allowing a change in the jet stream force according to the operation by the steering device.   
     
     
         14 . The water jet propulsion boat according to  claim 13 , wherein
 the combined control mode further includes a second combined control mode to reduce the angle difference while prohibiting the change of the jet stream force according to the operation by the steering device; and   the controller is configured or programmed to selectively execute the first combined control mode and the second combined control mode in the feedback process.   
     
     
         15 . The water jet propulsion boat according to  claim 12 , further comprising:
 a steering device on the hull; wherein   the direction changer is operable to change the jet stream direction according to an operation by the steering device to change the jet stream direction;   the combined control mode includes a third combined control mode to reduce the angle difference while allowing a change in the jet stream direction according to the operation by the steering device, and a fourth combined control mode to reduce the angle difference while prohibiting a change in the jet stream direction according to the operation by the steering device; and   the controller is configured or programmed to selectively execute the third combined control mode and the fourth combined control mode in the feedback process.   
     
     
         16 . The water jet propulsion boat according to  claim 1 , wherein the controller is configured or programmed to start the feedback process based on the detection signal from the tilt detector if the tilt angle of the hull reaches a trigger angle smaller than the target angle. 
     
     
         17 . The water jet propulsion boat according to  claim 1 , further comprising:
 a steering device on the hull and including a display; wherein   the controller is configured or programmed to cause the display to display tilt-related information according to the tilt angle of the hull based on the detection signal from the tilt detector.   
     
     
         18 . A method of maintaining a bow-up attitude of a water jet propulsion boat including a hull and a jet propulsion mechanism to generate a propulsive force of the hull by ejecting a jet of water, the method comprising:
 calculating an angle difference between a tilt angle of the hull in an upper-lower direction and a target angle of the hull in the bow-up attitude; and   reducing the angle difference in a feedback process by changing at least one of a jet stream direction or a jet stream force of the jet of water from the jet propulsion mechanism.   
     
     
         19 . The method of maintaining a bow-up attitude of a water jet propulsion boat according to  claim 18 , further comprising:
 calculating an angular velocity of the tilt angle of the hull; wherein   in the feedback process, at least one of the jet stream direction or the jet stream force is changed according to the angular velocity of the tilt angle.   
     
     
         20 . The method of maintaining a bow-up attitude of a water jet propulsion boat according to  claim 19 , wherein
 in the feedback process, a rate of change of at least one of the jet stream direction or the jet stream force is increased as the angular velocity of the tilt angle increases.