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At last, rotor sails are back

The future of shipping sailing 100 years in the making

After almost 100 years, a long-promising invention might finally change the industry. The first rotor sail-powered vessel crossed the Atlantic in the 1920s. Now, almost 100 years later, the technology is bringing valuable savings to an industry searching for ways to reduce its carbon footprint.

In February 1924, a brand-new ship called the Buckau left Danzig harbor, bound for Edinburgh. The journey, in many respects, was altogether ordinary: 13 crewmembers, two passengers, a load of lumber. But the Buckau was anything but ordinary. It was a sailing ship that had no sails—at least not conventional ones.

Rather than thin masts and billowing white sheets, the Buckau had two huge cylinders that rose from its deck and spun. Picture a couple gargantuan barber’s poles. The spinning poles generated lift, and thus thrust, thanks to something called the Magnus Effect.

The Magnus Effect is a term that describes the pressure differential that forms around a spinning object. It’s why a tennis ball hit with topspin seems to float longer in the air—the spinning ball is generating lift. And it’s why the ball bent in Bend it like Beckham.

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The rotor sails, the brainchild of German engineer Anton Flettner, were seen at the time as the future of shipping. The Buckau could sail at up to 10 knots, and it tacked more easily than conventional sailing vessels. And though the Buckau reportedly did well in difficult weather and even made it to New York, the technology never took hold.

Rotor ships: a new beginning

Why the Flettner’s invention didn’t revolutionize the shipping industry in the 1920s is a question that has a one-word answer: oil. The low cost and abundance of oil meant sailing was no longer a cost-effective means of transporting goods.

The question of why rotor sails are making a comeback now is also largely about oil.

The shipping industry is under pressure to reduce emissions, which is largely an exercise in finding more efficient means of propulsion. In 2012, a group of Finnish engineers had an idea: why not put some rotor sails on conventional ships—not to power them entirely but to supplement their engines and lower their fuel burn?

Modern rotor sails

That team of Finnish engineers started a company called Norsepower. Norsepower produces rotor sails, the biggest of which measure 5 by 30 meters. The sails, which use SKF roller bearings, spin at around 200 rpm. SKF lubrication systems and seals protect against corrosion and the wear and tear of constant motion—of the sails and the sea.

The Norsepower rotors are already in use on a handful of vessels. In 2008, the company installed a single rotor sail on a Viking Line ferry, M/S Viking Grace. Extensive testing has shown that sail reduced the vessels carbon output by about 900 tons per year, equivalent in power consumption to between 207-315 kW.

The technology has value beyond ferries: In October 2019, Norsepower’s rotor sails completed a 2-year trial with Maersk Tankers. In the trial, two sails were positioned aboard the Maersk Pelican, a ship with a gross tonnage of 61,724. The sails resulted in fuel savings of 8.2%, or about 1,400 tonnes of CO2.

The impressive results could change the industry. Maersk is one of the largest shipping companies in the world, and last year Norsepower’s CEO Tuomas Riski told Forbes he thought as many as 20,000 ships could benefit from the technology.

It took almost 100 years, but an invention that began with such promise might finally have come full circle.

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