Flettner Rotor

A Flettner rotor is a right circular cylinder, capped with disc end plates, that is spun along its own long axis so that wind passing over it generates lift at right angles to both the wind direction and the rotor axis, an effect called the Magnus effect after the physicist Gustav Magnus and analyzed mathematically by Martin Kutta and Nikolai Zhukovsky. German engineer Anton Flettner developed the rotor sail beginning in the 1920s, and the first rotor-powered ship, the Buckau, later renamed Baden Baden, crossed the Atlantic under rotor power in 1925. Practical marine use then lay dormant for decades until renewed interest during the energy crises of the 2000s; the E-Ship 1, launched in 2008, revived the rotor ship, and rotor sails fitted to modern cargo ships report fuel savings of five to twenty percent under favorable wind conditions, with newer installations able to tilt the rotors to pass beneath bridges.