About 15 years ago, I became aware of the Flettner rotor in a book about “forgotten inventions”. Anton Flettner invented a rotor ship, equipped with the rotors named after him. The rotors use the Magnus effect, named after Heinrich Gustav Magnus. Two ships were built in the 1920s, the Buckau, renamed Baden-Baden, even sailed from Germany to America and back.

The second ship, the Barbara, was equipped with two diesel engines and three rotors and has been used as a commercial freighter in the Mediterranean. With wind force 5, it ran at 13.5 kn operating with diesel engines (which powered the ship propeller) and rotors simultaneously. Without operating the rotors, running with the diesel engines only, it ran at 10 kn. Using the rotors only, without diesel engines, it was almost as fast at 9.5 kn. This means the rotors were able to achieve almost the same ship velocity as the diesel engines.

In the single rotor operating condition, the Barbara gained almost the same speed as the single diesel engine operating condition. The economic crisis, cheap oil and the increasing performance of the diesel engines, with which these kind of sails could no longer compete, unfortunately sealed the end of this technology in the 1930s.