The Rotor Driven Flettner Ship
The rotor drive or Flettner ship, so called because it was designed by the German Flettner, uses vertical cylindrical rotors. When these rotate in the wind, the rotation acts to create a force which can be made to propel the boat through the water.
The original design used only 12 m tall two cylinders, 2.7 m in diameter, each powered by a 15 hp motor. With these the ship could reach a speed of 14.3 km/hr and sail much closer to the wind than ordinary sailing vessels. Later vessels added more funnels and reached higher speeds. A modern rotor driven boat is shown below.