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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.
Flettner's spinning bodies were vertical cylinders; the basic idea was to use the Magnus effect. 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, thus avoiding power losses from the main engine. Flettner applied for a German patent for the rotor ship on 16 September 1922.
Assisted by Albert Betz, Jakob 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. In 1926, a larger ship with three rotors, the Barbara, was built by the shipyard A.G. Weser in Bremen.
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.
It was found at the time that the rotor system could not compete economically with the diesel engines that were also being developed for ships in this era. Flettner turned his attention to other projects and the rotors were dismantled. Baden Baden was destroyed in a Caribbean storm in 1931. Due to the rising cost of fossil fuels, as well as environmental concerns, there has been renewed interest in the concept in the later 20th century, starting with Jacques-Yves Cousteau's Alcyone in 1983.
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.
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 German wind-turbine manufacturer Enercon launched and christened its new rotor-ship E-Ship 1 on 2 August 2008. The ship was 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. On 29 July 2013, Enercon provided a press release claiming a potential for "operational fuel savings of up to 25% compared to same-sized conventional freight vessels." after 170,000 sea miles  Actual performance figures were not provided.
The THiiiNK organizations web site displays detail of an improved version of the Flettner Rotor, that is retractable and supplemented by an additional control surface.  The page claims that "The system has been developed and tested both in tank tests and in full-scale sea trials." The design improvement claims include: 1) improved rotor performance by 50% or more and 2) an internal rate of return (IRR) of up to 55% compared to a standard rotor.
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, (the ship, M/S Viking Grace, was built 2011–2012, without the rotors).
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. 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, inferior to, or superior to conventionally propelled vessels.
- Flettner rotor bomblet
- Turbosail — used to propel Jacques-Yves Cousteau's Alcyone
- Windmill ship
- Rotor sail assist and rotor sail only ships
- State-of-the-art cargo ship to dock with haul of wind turbines. Siliconrepublic. Posted: August 10, 2010.
- "Thiiink Flettner rotor". Thiiink. Retrieved 21 January 2014.
- "Thiiink Retractable Rotor". Thiiink. Retrieved 6 May 2014.
- Reinikainen, Kari (2009-06-22). "Wind and lng power Wartsila’s cruise ferry design". Cruise Business Online. Retrieved 2010-01-19.
- Latham, John (15 February 2007). "Futuristic fleet of 'cloudseeders'". BBC. Archived from the original on 2012-07-25. Retrieved 2012-07-25.
- Salter, Stephen; Sortino, Graham; Latham, John (2008-11-13). "Sea-going hardware for the cloud albedo method of reversing global warming". Phil. Trans. R. Soc. A 366 (1882): 3989–4006. Bibcode:2008RSPTA.366.3989S. doi:10.1098/rsta.2008.0136. PMID 18757273. Retrieved 2009-07-27.
|Wikimedia Commons has media related to Rotor ships.|
- Center for the Study of Technology article
- Photograph of Baden Baden in NY harbour
- Enercon press release for the launch of E-Ship 1
- Winchester, Clarence, ed. (1937), "Rotor ships", Shipping Wonders of the World, pp. 398–399 illustrated description of rotor ships