History of Flettner Rotors
Birth of the Flettner Rotor
In 1922, Anton Flettner first patented the Flettner rotor which harnessed the Magnus effect using a vertically rotating, deck-mounted cylinder to provide propulsive energy (Nuttall & John, 2016). With assistance from Albert Betz, Jakob Ackeret, Ludwig Prandtl, and Albert Einstein, he constructed an experimental rotor vessel named Buckau in October 1924 at the Friedrich Krupp Germania werft (History of Flettner Rotor, n.d.).
The vessel was a retrofitted schooner carrying two rotors roughly 15 meters in height and 3 meters in diameter, with the rotors being powered by an electrical propulsion system. 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 were successful on the maiden voyage with no main cause for concern even in high wind and sea states (History of Flettner Rotor, n.d.).
Due to the impressive performance, the Buckau was put into service to carry bulk cargo across the North Atlantic and the Baltic sea (Seufert & Seufert, 1983). On 31 March 1926, the 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.).
Flettner Rotor and the Great Depression
Impressed with the Buckau’s success, Weser shipyards in Bremen was commissioned in order to build a new, larger rotor ship on a proven full design. The Barbara was then launched in 1926 with three rotors that were taller and wider but very similar in construction and weight to the Buckau. The rotors produced an additional power of close to 450kW at wind speeds of 11-14 m/s. Test rides at these wind speeds led to a top speed of 24km/h when both combustion motors were running at full power (Seifert, 2012).
The two prototypes proved that the technology functioned reliably, and the Barbara served as a normal freighter in the Mediterranean between 1926 and 1929. By 1928, Flettner had secured orders for six new ships of the Barbara class. However, in 1929, two main events stunted the growth and progression of the Flettner technology. Firstly, there was a global economic crash causing a decrease in consumer buying confidence. In addition to this, Marine Diesel Oil (MDO) and the related engine technology to required to utilize it became readily and cheaply available (Nuttall & John, 2016). Fuel prices at that point meant that any savings achieved by the rotor were too small for shipping companies to consider the investment due to the lengthy payback period. In the aftermath of the Great Crash of 1929 and the slump in world trade that followed, the Barbara was returned to its owner, the German Navy. The ship was then sold on to a new owner who dismantled its three rotors and used only its engines (History of Flettner Rotor, n.d.).
Recent Development of Flettner Rotor
In recent time, the interest in flettner rotor technology has peaked due to high fuel prices and the potential regulation of shipping emissions due to global warming. On the 2nd of August 2008, The German wind-turbine manufacturer Enercon launched and christened its new rotor ship, E-Ship 1 (History of Flettner Rotor, n.d.). The ship uses conventional diesel power but it is assisted by four Flettner rotors to harness wind energy and to cut down fuel costs and reduce emissions. Enercon uses the ship to haul wind turbines parts. E-Ship 1 uses four Flettner rotors that 25m in height and 4m in diameter. It has an overall length of 130m and a top speed of 17.5 knots. Besides the rotor sail, E-Ship 1 uses two diesel engines that deliver a total power of 3.5 MW. The exhaust gas boilers are connected to a downstream steam turbine, which in turn drives the Flettner rotors (Baltateanu, DriveMag Boats , 2017). Following an initial trial voyage from Germany to Ireland, E-Ship 1 had travelled 170,000 sea miles by 2013 and averaged 25% overall fuel savings, of which 15% are directly attributable to the use of the rotors (Nuttall & John, 2016).
M/S Viking Grace is first large-scale passenger ferry to be powered by liquefied natural gas (LNG) as well as being fitted with a rotor sail. This cruise ferry is owned by Finland-based, ‘Viking Line’ and it took service on 13 January 2013. The cylindrical rotor sail unit installed on M/S Viking Grace is 24m in height and 4m in diameter and is a modernized version of the Flettner rotor. The technology is fully automated and senses whenever the wind is strong enough to deliver fuel savings, at which point the rotors start automatically (Baltateanu, DriveMag Boats, 2018).
LNG gives the ferry higher engine efficiency and lower fuel consumption. The new technology which is a hybrid usage of LNG and wind power is called Rotor Sail Solution and it is developed by a Finnish company called Norsepower. It has proved its economic efficiency by allowing a fuel savings of up to 20% in favorable wind conditions (Anon, 2017). In addition to the installation onboard the M/S Viking Grace, Viking Line will also install two Norsepower rotor sails onboard a newbuild cruise ferry vessel which is currently being built in China and is due to be operational in 2020 (Baltateanu, DriveMag Boats, 2018).
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Nuttall, P., & John, K. (2016). The Magnus Effect and the Flettner Rotor: Potential Application for Future Oceanic Shipping. The Journal of Pacific Studies, 36(2), 161.
Seifert, J. (2012). A review of the Magnus effect in aeronautics. Progress in Aerospace Sciences, 55, 17-45.
Seufert, W., & Seufert, U. (1983, March 10). Critics in a spin over Flettner's Ships. New Scientist, 97(1348), 656-659.