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A new age of sail begins

Posted on June 25, 2024

By harnessing wind power, high-tech sails can help cut marine pollution

Excerpt from article in The Economist:

A return to sail has been heralded before as a way to cut pollution. It has led, in recent years, to renewed interest in Flettner rotors as well as other wind technologies, including rigid sails, giant kites and tall structures called suction sails. Yet the marine industry, like many of its vessels, can take a long time to change course. After a period in which progress was limited to fanciful sketches and small-scale trials, shipowners are now starting to place orders to retrofit existing cargo ships and build wind-assisted vessels. A new age of sail may be in the offing.

Wind is particularly suitable as a form of auxiliary power for larger deep-sea vessels. Battery technology cannot at present power much beyond small craft operating on short routes. And though alternative fuels made via green processes, such as biofuels, hydrogen and ammonia, have the necessary oomph, little infrastructure exists to make and distribute them. Initially, at least, they will be expensive. Hence, even for ships that use alternative fuels, harnessing the wind will help reduce costs and emissions further.

Blast from the past

Flettner rotors remain an attractive solution. As the wind flows around the revolving cylinders, the rotation creates an area of high air pressure on one side and lower pressure on the other. Thanks to a phenomenon known as the Magnus effect (which also helps spinning balls curve), this pressure differential creates a force at right angles to the wind direction. On a horizontal aircraft wing, it generates lift. On a vertical rotor, it helps push a ship forward. The rotors can be turned at different speeds and in different directions allowing them to be “trimmed” to the prevailing wind conditions. All this is done automatically, so no additional crew are needed.

Among the companies supplying modern-day Flettner rotors is Norsepower, a firm based in Finland. Earlier this year it won what it says is the biggest ever wind-propulsion deal, with an order to fit six 35-metre rotors to each of three new cargo ships being built for Louis Dreyfus Armateurs, a French shipping owner. The vessels will be chartered to Airbus, a European aerospace group. Each will carry enough partially constructed aircraft, made up of fuselages, wings and tails, to be assembled into six a320 airliners at Airbus’s factories in America.
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