A rotor ship, or Flettner ship, is a ship designed to use the Magnus effect for propulsion. To take advantage of this effect, it uses rotorsails which are powered by an engine. The Magnus effect is a force acting on a spinning body in a moving airstream, which acts perpendicularly to the direction of the airstream. German engineer Anton Flettner was the first to build a ship which attempted to tap this force for propulsion.
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Flettner's spinning bodies were vertical cylinders; the basic idea was to use the Magnus effect. The idea worked, but the propulsion force generated was less than the motor would have generated if it had been connected to a standard marine propeller.[1] These types of propulsion cylinders are now commonly called Flettner rotors.
His first idea was to produce the propulsion force by using a belt running round two cylinders. Later Flettner decided that the cylinders would be better rotated by individual motors. Flettner applied for a German patent for the rotor ship on 16 September 1922.
Assisted by Albert Betz, Jacob Ackeret and Ludwig Prandtl, Flettner constructed an experimental rotor vessel, and in October 1924 the Germaniawerft finished construction of a large two-rotor ship named Buckau. The vessel was a refitted schooner which carried two cylinders (or rotors) about 15 metres (50 ft) high, and 3 metres (10 ft) in diameter, driven by an electric propulsion system of 50 hp (37 kW) power.
Following completion of its trials, the Buckau set out on her first voyage in February 1925, from Danzig to Scotland across the North Sea. The rotors did not give the slightest cause for concern in even the stormiest weather, and the rotor ship could tack (sail into the wind) at 20-30 degrees, while the vessel with its original sail rig could not tack closer than 45 degrees to the wind.
On 31 March 1926, the Buckau, now renamed Baden Baden after the German spa town, sailed to New York via South America, arriving in New York harbor on 9 May.
However, it was found that the rotor system was less efficient than conventional engines. Flettner turned his attention to other projects and the rotors were dismantled. Baden Baden was destroyed in a Caribbean storm in 1931.
Several types of rotor ships can be distinguished, similar to sailing ships. Both rotor sail-assist (hybrid) ships exist, as well as rotor sail only ships. Wind Ship Development Corporation has also worked out two types of sail assist setups, for use with different ships sizes.[2]
Most rotor ships have a system with an electric engine which allows the stopping or initial starting of the rotor by the sailor. This allows the sailor to control the rotor's RPM and direction of spin.
The University of Flensburg is developing the Flensburg catamaran or Uni-cat Flensburg, a rotor-driven catamaran.
The German wind-turbine manufacturer Enercon launched and christened its new rotor-ship E-Ship 1 on the 2nd of August 2008. The ship will be used to transport turbines and other equipment to locations around the world. The maiden delivery of turbines for Castledockrell Windfarm arrived in Dublin Port on 11th Aug 2010.[3]
In 2009 the Finland-based maritime engineering company Wärtsilä unveiled a concept for a cruiseferry that would utilise flettner rotors as means of reducing fuel consumption. This concept has been linked with the Finnish ferry operator Viking Line,[4] who have stated they will make a decision on whether or not they'll order new ships during 2010.[5]
Stephen H. Salter and John Latham recently proposed the building of 1,500 robotic rotor-ships to mitigate global warming. The ships would spray seawater into the air to enhance cloud reflectivity.[6][7] A prototype rotor ship was tested on Discovery Project Earth. The rotors were made of carbon fibre and were attached to a retrofitted trimaran and successfully propelled the vessel stably through the water at a speed of six knots. The focus of the experiment was based on the ability for the boat to move emissions free for a specialized purpose leaving it unclear whether or not the efficiency of the rotors was on parity or superior to conventionally propelled vessels.
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