Wind-Assisted Propulsion: Rotors, Wings and Kites
Wind-assisted propulsion reduces a ship's fuel use by harnessing wind through systems such as rotors, wings or kites.
Wind-assisted propulsion reduces a ship's fuel use by harnessing wind through systems such as rotors, wings or kites. The wind does not carry the ship alone, it takes load off the main engine. On 1 June 2026 more than 100 large commercial ships worldwide had these systems fitted. Reported savings on retrofits mostly fall between 5% and 20%.[6]
Sail Leaves the Merchant Fleet
For most of history sail was how ships moved. Early steamers in the 19th century burned so much coal that they could work only short routes, carrying mail and passengers, while sail held the advantage on long passages. The Suez Canal opened in 1869, around the same time as more fuel-efficient steamers appeared. In the 1880s the triple-expansion engine let steam compete with sail on every major route. Sailing ships held on for a time on long runs such as Australia to Europe, because they needed no coal bunkers or boiler water. The last commercial sailing ships stopped trading around 1960.[8]
Flettner's Rotor
The first modern experiment came before sail had fully gone, in the 1920s. Anton Flettner was born in Eddersheim, Germany, in 1885. He began as a village teacher and went on to teach mathematics and physics in Frankfurt. In the First World War he worked on remote-control systems for the German War Ministry and developed the forerunner of the trim tab still used on aircraft.[9] The Magnus effect, by which a spinning cylinder in the wind produces a sideways force, was already known. Flettner wanted to try it on a ship and got help from the aerodynamicists Betz, Ackeret and Prandtl.[1]
A rotor does not catch the wind as a sail does. A vertical cylinder spun by an electric motor produces a sideways force through the Magnus effect, and when the wind is on a suitable bearing part of that force pushes the ship ahead. If the wind moves to the other side, the rotation reverses.[1] Flettner's Buckau was converted from a sailing ship at Germaniawerft in October 1924. It had two rotors about 15 metres tall and 3 metres across, driven by a 50-horsepower system. In February 1925 it sailed from Danzig to Scotland.[1]
Renamed Baden-Baden, it set out for America on 31 March 1926 and reached New York via South America on 9 May. It had burned 12 tons of fuel over about 6,200 nautical miles, against an estimated 45 tons for a similar motor ship without rotors. The figure has been disputed ever since, with some sources saying the gain vanishes once the rotors' electricity is counted.[1]
A.G. Weser in Bremen built the three-rotor freighter Barbara in 1926, and the ship worked in the Mediterranean until 1929. In 1928 Flettner had orders for six more of the type.[1]
The 1929 crash and cheap diesel ended it. Payback periods grew very long and the orders fell away.[1] Flettner founded an aircraft company in 1926 and moved into helicopters. He was taken to the United States after the Second World War and died in New York in December 1961.[9] The rotor idea sat on the shelf for half a century.
The Oil Crises and a Japanese Tanker
The subject came back when fuel prices rose. After the oil crises of the 1970s, the Japan Marine Machinery Development Association (JAMDA) and Nippon Kokan began working on it in Japan. The result was the 1,475 dwt tanker Shin Aitoku Maru, which began its maiden voyage on 1 August 1980. It had two polyester sails on steel frames. A microcomputer set the sail angle to suit the wind and reduced engine power at the same time. The owner estimated fuel savings of US$50,000 a year.[10]
Other trials followed. A 1981 study for the US government estimated savings of 15% to 25% for a small freighter with a wingsail.[2] Jacques Cousteau's Alcyone was launched at La Rochelle in 1985, with two turbosails supporting its diesel engines, and was built to test that system.[11] The bulk carriers Aqua City and Usuki Pioneer received wind equipment in 1984 and 1985, but these trials did not spread through the fleet.[2]
Climate Rules and the Comeback
The next wave came with a different motive. In Germany SkySails developed a kite tethered to a cargo ship. The wind turbine maker Enercon launched E-Ship 1 on 2 August 2008, and since 2010 the ship has carried the company's own turbine parts. Enercon reports savings of up to 25% against similar freighters, a manufacturer's figure.[1] The US Military Sealift Command chartered the Beluga SkySails in 2009 to test the kite.[2]
The measured trial that did more to persuade the industry came in 2018. In August Norsepower fitted two rotors to the tanker Maersk Pelican, and the trial ran from 1 September 2018 to 1 September 2019. The result was an 8.2% fuel saving, or about 1,400 tonnes of CO2. Lloyd's Register's ship performance group reviewed the data. Maersk Tankers kept the rotors on the ship.[3]
That same year rotors reached passenger ships. The ferry Viking Grace, built without them in 2011 and 2012, was fitted in 2018 and became the first passenger ship with a rotor. MV Afros got rotors the same year.[1][2]
Rigid Wings: Wind Challenger, Pyxis Ocean and Oceanbird
Alongside rotors there are now rigid wing sails, suction sails and kites. A rigid wing resembles an aircraft wing and turns to suit the wind. A suction sail uses a fan to draw air across its surface and raise lift. A kite is tethered at the bow and catches the stronger wind higher up.[2]
On the wing side Japan was again early. The 100,422 dwt coal carrier Shofu Maru, of Mitsui O.S.K. Lines and Tohoku Electric, was delivered in October 2022 with a single telescoping Wind Challenger sail. Eighteen months of measurement showed average savings of 5% to 8% per voyage and up to 17% on the best days. Lloyd's Register verified the method. In a headwind the sail produces no thrust.[12]
Pyxis Ocean came the following year. This Kamsarmax bulk carrier, chartered by Cargill, was fitted with two BAR Technologies WindWings and began its trial in August 2023. The companies had projected an annual average saving of 3 tons of fuel a day, about 14%, and reported that the first six months came within 10% of that. On the best days the saving passed 11 tons. These figures come from the companies themselves.[4]
Another step came in June 2026. Oceanbird's Wing 560, 46 metres tall and 14 metres wide, was fitted at the Damen yard in Rotterdam to Wallenius Wilhelmsen's 230-metre car carrier Tirranna, and on 2 July acceptance tests were announced as complete. The wing can tilt for bridges and port cranes. The company projects savings of up to 10% for an existing ship on a suitable route. An Oceanbird team is sailing with the ship and collecting data in real conditions, so measurement has only just begun.[5]
The Fleet Today
The International Windship Association (IWSA) counted more than 230 installed systems on large commercial ships on 1 June 2026, on more than 100 vessels: 37 tankers, 24 bulk carriers, 24 passenger ro-ros and 19 cargo ships. Its secretary general, Gavin Allwright, expects about 200 within 12 months.[6] Much of the savings data still comes from makers and owners. The range is wide because results depend on route, wind frequency, ship speed and the number of units. An owner doing fuel management works the sums voyage by voyage.
Rules and the Sums
Regulation is a large part of today's interest. Under FuelEU Maritime, which took effect in the EU in 2025, wind is the only technology with a reward factor, and it lowers the greenhouse gas intensity calculated for the energy used on board. Under the EU ETS less fuel means fewer allowances, and the CII rating improves along with fuel use.[13] Globally the Net-Zero Framework has still not been adopted. MEPC 84, which ended on 1 May 2026, took no decisions on design, with members divided especially over the fund. Draft guidelines supporting the framework include how to monitor energy from wind propulsion.[7] MEPC 85 meets from 30 November to 3 December 2026, and members are due to decide on the framework at the resumed extraordinary session on 4 December.[14]
Cost and deck space are the obvious barriers. Structures above deck affect the view from the bridge, port cranes and air draught under bridges. The WindWings on Pyxis Ocean cost about 1,590 tonnes of deadweight.[13] Every ship with rotors or wings still takes bunkers in port. The question on the owner's desk is the one Flettner could not answer after 1929: how many years before the equipment pays for itself. The price of fuel and the cost of carbon set the two sides of that sum.
Frequently asked questions
What is wind-assisted propulsion?
Wind-assisted propulsion reduces a ship's fuel use by harnessing wind through systems such as rotors, wings or kites.
How does a rotor sail work?
A vertical cylinder spun by an electric motor produces a sideways force through the Magnus effect. When the wind is on a suitable bearing, part of that force pushes the ship ahead.
How much fuel can wind-assisted propulsion save?
Reported savings on retrofits mostly fall between 5% and 20%. Measurement on Maersk Pelican showed 8.2%, and Shofu Maru showed 5% to 8% per voyage. The result depends on route and wind.
How many ships have wind-assisted systems?
The IWSA counted more than 230 systems on more than 100 large commercial ships on 1 June 2026.
Sources
- Wikipedia. Rotor Ship.
- Wikipedia. Wind-Assisted Propulsion.
- Norsepower. Norsepower Rotor Sails Confirmed Savings of 8.2% Fuel and Associated CO2 in Maersk Pelican Project, 24 October 2019.
- Maritime Executive. Cargill Reports Encouraging Results from 6-Month Sail Test on Bulker, March 2024.
- Oceanbird. Oceanbird Completes Installation and Successful Sea Trial With Wing560 on Tirranna, July 2026; Wallenius Lines, 2 July 2026.
- ENGINE. Wind-Assisted Propulsion Fleet Crosses 100-Vessel Mark: IWSA, 2 June 2026.
- DNV. IMO MEPC 84: Revisiting the Net-Zero Framework, 4 May 2026.
- Wikipedia. Sailing Ship.
- Wikipedia. Anton Flettner.
- Wikipedia. Shin Aitoku Maru.
- Wikipedia. Alcyone (1985 ship).
- SWZ Maritime. Wind Challenger Saves Fuel for Coal Carrier Shofu Maru, 23 May 2024.
- gCaptain. Business Case for Wind Propulsion Improves as Decarbonisation Rules Kick In, 26 November 2024.
- Ammonia Energy Association. MEPC84: Support for Net Zero Framework Stabilizes Ahead of Key Decision Point in Late 2026.
