Science and Technology

Why sailing ships are making waves again

| Updated on January 03, 2021

Sailing ships ruled the oceans for centuries until they were put out of business by steam-powered engines and, later, diesel. But now, thanks to the need to de-carbonise and control costs, they are slowly making a comeback.

But you’re unlikely to see the tall masts and bulging canvases of yore; instead you may find tall, chimney-like, cylindrical spinning towers called Flettner rotors, named after the German engineer who invented them. When air blows at right angles to the rotors — say, from left to right — and the rotors are spinning clockwise, the air that flows along the spin (front) moves faster than the air that flows against the spin (behind). Therefore, the air pressure in the front is less than in the back, causing a forward movement — called Magnus effect.

Although a cargo ship named Buckau did cross the Atlantic in 1926 with Flettner rotors, the idea was given up as diesel engines, which freed up deck space, made more economic sense. But now, there’s a sail redux, with work on mainly in Scandinavia by companies such as Norsepower of Finland and the Swedish ship designer Wallenius Marine in collaboration with SSPA, a Swedish non-profit research institute. Sure, you need power to spin the Flettner rotors, but there is a net energy gain. Wallenius Marine is working on a wind-powered car-carrier that can hold 7,000 cars and can beat a similar diesel ship in emissions by 90 per cent.

Future sailing ships need to overcome obstacles such as deck space (especially in container vessels), ability to pass under bridges and the cost of additional crew to handle the sail systems, but these are no deal-breakers.

Published on January 03, 2021

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