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A rotor ship is a type of ship designed to use the Magnus effect for propulsion. The ship is propelled, at least in part, by large powered vertical rotors, sometimes known as rotor sails. German engineer Anton Flettner was the first to build a ship that attempted to tap this force for propulsion. "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." NASA web page
Ships using his type of rotor are sometimes known as Flettner ships.
The Magnus effect is a force acting on a spinning body in a moving airstream, which produces a force perpendicular to both the direction of the airstream and the axis of the rotor.
Due to the arrangement of forces, a rotor ship is able to sail closer to the wind than a conventional sailing ship. Other advantages include the ease of control from sheltered navigation stations and the lack of furling requirements in heavy weather.
If the ship changes tack so that the wind comes from the other side, the direction of rotation must be reversed; the ship would otherwise be propelled backwards.
Sailing ships, including rotor ships, often also have a small conventional propeller to provide ease of manoeuvrability and forward propulsion at slow speeds and when the wind is not blowing or the rotor is stopped. In a hybrid rotor ship the propeller is the primary source of propulsion, while the rotor serves to offload it and thus increase overall fuel economy.Gilmore, C.P. (1984). "Spin Sail: Harnesses Mysterious Magnus Effect for Ship Propulsion," Popular Science (January), pp. 70-73, see [2], accessed 13 October 2015. Rotor sails have been reported to generate 5-20% fuel savings.
Buckau sailed from Danzig to Scotland across the North Sea in February 1925. The ship could tack (sail into the wind) at 20–30 degrees, hence the rotors did not give cause for concern in stormy weather. The ship was renamed Baden Baden after the Baden-Baden and on 31 March 1926 was sailed to New York via South America, arriving in New York Harbor on 9 May.
Some sources claim that the ship had proved inefficient on these voyages, that the power consumed by spinning 15-metre tall drums was disproportionate to the propulsive effect when compared with conventional propellers.
That view stands in contrast to others that claim that due to the impressive performance, Buckau was put into service to carry bulk cargo across the North Atlantic and the Baltic sea. On 31 March 1926, Buckau, now renamed Baden-Baden sailed to New York via South America, the 6,200 nautical mile voyage across the Atlantic used only 12 tons of fuel oil, compared with 45 tons for a motor ship of the same size without rotors (Nuttall & John, 2016), arriving in New York harbor on 9 May (History of Flettner Rotor, n.d.)."
The latter assessment seems to be more accurate, as the outcome of the Buckau experiment, resulted in the development of the next rotor ship, Barbara.
Enercon launched the hybrid rotor ship E-Ship 1 on 2 August 2008. From 2010, it has been used to transport the company's turbine products and other equipment. Enercon claim "operational fuel savings of up to 25% compared to same-sized conventional freight vessels."
The University of Flensburg is developing the Flensburg catamaran or Uni-Cat Flensburg, a rotor-driven catamaran.
In 2007, Stephen Salter and John Latham 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 propelled the vessel stably through the water at a speed of six knots.
In 2009, Wärtsilä proposed a cruiseferry that would use Flettner rotors as a means of reducing fuel consumption. The Finnish ferry operator Viking Line adopted the idea, with MS Viking Grace built in 2011–2012, initially without rotors. A rotor system was retrofitted in 2018.
In 2014 and 2015, Norsepower installed twin rotor sails on Finnish shipping company Bore's RoRo vessel M/V Estraden. In May 2018, the 1996 built cargo ship Fehn Pollux of the German-based Fehn Shipmanagement (Leer) was fitted with an 18-metre long Flettner rotor of the EcoFlettner type at the front. With Flettner's wind power. In: Hansa International Maritime Journal, 9/2018, Hamburg 2018, p. 58/59
In 2018, Norsepower deployed rotor sails with the world's biggest shipping company, Maersk. The Maersk Pelican, an LR2 class tanker, has been fitted with two Norsepower Rotor Sails.
The MV Afros (IMO 9746803) bulk carrier has operated four movable rotors over a year with positive results.
In 2021, Norsepower installed five tilting rotor sails onto a Vale-operated iron ore carrier; the tilting design intended to allow maneuvering below bridges.
Scandlines operates two hybrid ferries with rotorsail, M/F Copenhagen and M/F Berlin.
In October 2023 Airbus announced that it had commissioned six ships with Flettner rotors for entry into service in 2026 to transport aircraft sections to its US assembly line.
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