An ordinary displacement type ship, which is composed of three parts, i.e., a hull, a propeller and a rudder in order from the front, is usually advanced with an almost constant speed in a seaway disturbed by waves and winds. Then the ship continues surge, sway, heave, roll, pitch and yaw motions, and is requested at first to be safe from the standpoints of motion and strength, and next to have a main engine on board, whose output is sufficient to maintain a given speed in waves and winds. In this paper, we develop the hydrodynamical method to estimate the required main engine power of a ship with a given speed in given regular waves.
