The component of a ship propulsion power plant that converts engine torque into propulsive force or thrust, thus overcoming the ship's resistance to forward motion by creating a sternward accelerated column of water. Early steamship propulsion forms, such as the jet propeller (1782) and the paddle wheel (1801), were gradually replaced by the screw propeller (1804), which since 1860 has been the only propeller type used in ocean transport, mainly because of the evolution of the marine engine toward higher rotative speed.