Abstract: A controller that executes engine output control that a throttle is closed when a boat is navigated at a predetermined speed or higher and the output of an engine is gradually increased up to predetermined output when a steering system is steered right or left at a predetermined angle or more is provided. Thus, an overshoot phenomenon that the engine speed is held at a predetermined engine speed after the engine speed once increases up to the predetermined engine speed or higher when the engine speed is increased in deceleration can be avoided. As a result, the body of the boat can be prevented from sliding laterally to a great extent at the beginning of turning and the turning performance of the body can be enhanced.

Abstract: A personal watercraft designed to advance suitably in a forward direction, to prevent an influence of side waves, and to incline to the turning center side when being steered by an operator from a forward direction to a turned direction. The personal watercraft includes a keel provided at a middle portion in the widthwise direction of the bottom of the body and extending from the bow to the stern. The keel is formed in an arc in the widthwise direction of the body. The keel is configured such that, at the rear half portion of the body, the center of the arc of the keel substantially coincides with the position G of the center of gravity of the body. On the other hand, at the front half portion of the body, the radius R2 of the arc of the keel gradually decreases in the forward direction.

Abstract: a control unit is provided for closing the throttle when the engine has been rotated for more than a prescribed time period at more than a prescribed number of revolutions, and the throttle has been opened for more than a prescribed time period at more than a prescribed opening. The control unit increases the number of engine revolutions to a predetermined number of revolutions irrespective of the throttle and maintains the same for a predetermined retention time when the steering handle is turned to the left or the right by more than a prescribed angle. The time to start controlling the number of engine revolutions may be delayed by providing a delay time for delaying the time to start controlling the engine revolutions. The number of engine revolutions may be controlled after the hull is underwater. As a consequence, the amount of sideslip of the jet propulsion boat can be improved.

Abstract: To provide a jet propulsion watercraft that allows a step, a vent hole, and the like to be easily provided on a bottom surface thereof. A ride plate of a jet propulsion watercraft is a member, which is formed into a substantially rectangular shape in compliance to an opening in a bottom surface of a hull bottom. The ride plate is provided with a lock tab at a front edge thereof, and bolt holes are made in a right and left end portion thereof. The ride plate is further provided with a step portion that forms part of a general bottom surface, since it is flush with the general bottom surface, a higher level surface that forms a flat surface higher than the step portion by a predetermined distance, and a pair of vent holes that pass vertically through the higher level surface at a position therein closer to the step portion.