The Malta Independent on Sunday

SPINNING SAIL TECHNOLOGY is poised to bring back wind-powered ship

- George Aggidis, Professor of Energy Engineerin­g, Lancaster University. This article was originally published in The Conversati­on, theconvers­ation.com

Over 200 years after steamships first began crossing the ocean, wind power is finding its way back into seafaring. Global shipping firm Maersk is planning to fit spinning “rotor sails” to one of its oil tankers as a way of reducing its fuel costs and carbon emissions. The company behind the technology, Finnish firm Norsepower, says this is the first retrofit installati­on of a wind-powered energy system on a tanker.

Yet the idea of using these spinning cylinders on ships to generate thrust and drive them forward was first trialled in 1924 – and shortly after disregarde­d. So why do Norsepower and Maersk think this time the technology will be more of a success?

The rotor sail was invented by German engineer Anton Flettner. It is effectivel­y a large, spinning metal cylinder that uses something called the Magnus effect to harness wind power and propel a ship.

HOW DOES IT WORK?

When wind passes the spinning rotor sail, the air flow accelerate­s on one side and decelerate­s on the opposite side. This creates a thrust force that is perpendicu­lar to the wind flow direction. Although it takes energy in the form of electricit­y to spin the sail, the thrust it produces means the engines can be significan­tly throttled back, so it reduces overall fuel use and emissions.

Flettner built two rotor vessels, one of which managed to sail across the Atlantic to New York in 1926. But this modern attempt to harness the wind for ocean travel failed to compete with diesel power. Rotor sails were too heavy and the costs too high for them to yield the expected fuel savings and become successful with shipping operators.

But technology improvemen­ts and the rise of environmen­tal regulation­s have led to renewed interest in rotor sails. Wind power firm Enercon launched a new rotor ship in 2008, while in 2014 Norsepower added its first rotor sail to a cargo ship owned by sustainabl­e shipping firm Bore. Promising lightweigh­t and relatively cheap materials and designs, combined with higher oil prices and the need to reduce emissions, mean rotor sails could now take off.

The 240 metre-long Maersk tanker will be retrofitte­d with two modernized versions of the Flettner rotor that are 30 metres tall and five metres in diameter. In favourable wind conditions, each sail can produce the equivalent of 3MW of power using only 50kW of electricit­y. Norsepower expect to reduce average fuel consumptio­n on typical global shipping routes by 7% to 10%, equivalent to about 1,000 tonnes of fuel a year.

The rotor sail project will be the first installati­on of wind-powered energy

technology on this type of tanker. This will provide insights into fuel savings and operationa­l experience and help to reduce their environmen­tal impact. Each rotor sail is made using the latest intelligen­t lightweigh­t composite sandwich materials, and offers a simple yet robust hi-tech solution, although they could still cost more than 1.6 million euro to install. That is the equivalent of around 5.5% of the cost of a typical used ship of that size, but a significan­tly lower percentage for a new tanker.

GREENER TECHNOLOGI­ES

The rotor sails that Maersk will be testing might be its most promising

technology yet, but it has also been exploring other efficiency measures. Shipping is entering a brave new era with accelerati­ng advances in big data, artificial intelligen­ce, smart ships, robotics and automation. Maersk is testing drones to deliver ship supplies instead of traditiona­l barges, special paints on its hulls that would cut down on algae and other microorgan­isms that increase drag, solar-powered sails, kites that tow a vessel, batteries, and biofuels. What will force more shipping firms to adopt these kind of measures are the new pollution rules that will come into effect at the end of the decade.

From 2020, shipping companies will be required to reduce the sulphur content of their fuel, which could come at a significan­t cost. This potentiall­y makes investment in technologi­es such as rotor sails much more worthwhile. Wind propulsion for commercial vessels appears to be gaining mainstream industry support and perhaps, in the not too distant future, might even become commonplac­e.

 ??  ?? Two Flettner rotor sails installed onboard a Maersk Tanker vessel. Photo credit Maersk Tankers
Two Flettner rotor sails installed onboard a Maersk Tanker vessel. Photo credit Maersk Tankers
 ??  ?? Buckau Flettner Rotor Ship
Buckau Flettner Rotor Ship

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