To provide a high-speed boat capable of navigating at a lower speed than a boat speed determined by the lowest engine speed of a propulsion engine, and capable of substantially suppressing rolling of a hull.

A left screw 3A and a right screw 3B comprising propellers are provided in the lower part of the bottom of the stern of a high-speed boat 1. A left steering gear 4A and a right steering gear 4B comprising rudders are provided at the rear position of respective screws 3A, 3B. When navigating at a low speed, both steering gears 4A, 4B are steered so as to form a truncated chevron shape in which they gradually approach each other while turning toward the bow. As a result, the slipstream of each screw 3A, 3B is impeded by the steering gears 4A, 4B, thrust is reduced, and resistance is increased. Therefore, navigation at a lower speed than a boat speed determined by the lowest engine speed of a propulsion engine becomes possible. In addition, when the hull rolls, a rolling reducing rudder angle having a reverse phase to cancel it is superimposed over the rudder angle having the truncated chevron shape, and both steering gears 4A, 4B are steered. Thereby, the rolling of the hub can be substantially suppressed.