Among the variety of water-jet-pump-propulsion type small watercraft, personal watercraft (PWC) are the most popular. Personal watercraft generally have a water jet pump impeller that rotates counterclockwise when seen from a rear of the watercraft when the watercraft travels forward. During forward travel, the watercraft tends to bank to the right due to a reactive force of impeller rotation; thus, the watercraft tends to turn to the right.
The water jet pump is configured so that its thrust direction can be changed by horizontally swinging a steering nozzle arranged behind the impeller and, thus, the watercraft makes a turn. Because of this configuration, it is more difficult to steer the watercraft when a throttle is in a fully-closed state.
U.S. Pat. No. 6,159,059, Canada patent No. 2,207,938, and U.S. Pat. No. 6,124,809 disclose a steering assist technique addressing the above difficulties. The disclosed steering assist technique is to make steering easier by controlling thrust when a throttle is in a fully-closed state and the steering is not easy to operate. The thrust is controlled so as to be increased independently of throttle operation.
However, the above disclosed technique has a drawback in that steering to the right and steering to the left does not work the same even if the thrust is increased in the same manner for both cases, due to a reactive force of impeller rotation.