A boat has a propulsion unit and a steering system. The steering system includes a steering device actuated by an electric actuator. A steering wheel operated by an operator is electrically connected to the actuator. Detectors collect data regarding one or more of operation status of the steering wheel, running status of the boat, status of the propulsion unit, status of the electric actuator, and the like. In certain situations, the electric actuator may not be capable of providing a quick steering response. A controller weighs detected data to identify such situations and controls a propulsive force of the propulsion unit so as to restrain the propulsive force if necessary to maintain good steering response.