A small boat comprises a steering wheel and a steering angle sensor that detects a steering angle of the steering wheel. A plurality of propulsion units are mounted to a transom of the boat. Electrically operable steering devices are coupled with the respective propulsion units. A control unit controls an output of each of the propulsion units. The controller adjusts the output, a trim angle or a height of a propeller of the propulsion units in accordance with the steering angle and a running condition of the boat to control a total thrust and a total running direction of the respective propulsion units.