Wind-powered rotor ships were the maritime breakthrough of the 20s — according to the March 1925 issue of Popular Mechanics:
With a proven record of supplying clean, natural energy to mariners ever since they first took sails to sea, wind power is an attractive — if inconsistent — alternative to diesel engines, which consume gallons of oil. In March 1925, Popular Mechanics featured an innovation called the “rotor ship,” invented by German engineer Anton Flettner. The vessel was hailed as “the first new development in sailing ships since the earliest navigators discovered they could utilize the wind’s power.” Buckau, the first of the rotor ships, featured two hollow towers of steel, 10 ft. in diameter and 65 ft. tall, mounted on pivots powered by 9-hp motors. The towers utilized the Magnus effect—wind currents striking a rotating cylinder exert a force approximately at right angles to the direction of the wind. After an initial jumpstart from the motors, the cylinder’s motion caused the ship to advance, PM reported. Its designers claimed the vessel outran other sailing ships as well as freight steamers.
More than 80 years after the rotor ship’s birth and demise — engines proved most practical at the time — engineers are searching for modern methods of harnessing the winds to propel cargo ships. The Association for Innovative Propulsion Concepts is now testing the SkySail parafoil, a type of kite that supplements the engines of a cargo ship — and that’s caught PM’s attention once again.
I’ve mentioned kite-like sails before. Now Popular Mechanics has an entire article on how kite power could finally pull global shipping to the green side:
To operate, the captain would first raise a telescoping mast to launch the kite, which waits for use folded like an accordion. Twenty minutes later, the kite would be high enough to unfurl completely. The entire process is automated: Computer-controlled steering compensates for wind direction, speed and bearing. Steering the sail is akin to steering a paraglider or parachute — the “autopilot” pod flying just under the kite shortens one side to dump wind and turn. A piloting program using weather updates and a schedule could help captains plan the optimum route, officials with the company that designed the system say.
During 27 test cruises of the research ship Beaufort, owned by the Association for Innovative Propulsion Concepts, a sail of 80 square meters produced pulling power of 7 tons at wind forces up to 25 mph — strong enough to form whitecaps. Towing kites of twice the size could be employed on the Beaufort, which, according to the researchers, could save up to 2400 liters of marine gas oil per day.