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The rebirth of the sail?

Shipping companies are mulling a return to tradition, one that stretches back five millennia: the sail. Are they insane, or can shipping really provide capacity for today’s supply chains using this technology?

At around the time Egyptians were writing their first hieroglyphs, the Austronesian peoples, originating in Taiwan, were sweeping across a staggering extent of the Pacific and Indian Oceans. Extraordinary seamanship took them as far as Hawaii, to the east, and the Comoros Islands, to the west. Augmenting the effort of their own muscles was the most important discovery in maritime history – sails.

Today, our most advanced vessels cannot cover the same distance without burning thousands of tonnes of crude oil derivatives. In fairness to them, there is a lot more to carry – around 11 billion tonnes, annually. But now, the age of the neo-sail is upon us, with shipping mulling a return to its 5,000-year tradition.

Returning to tradition

The neo-sail has different iterations, some purporting to replace conventional propulsion almost entirely, some, less so. The Flettner rotor is an example of the latter. It differs from conventional sails, spinning up using electric motors piggybacking on the ship’s main propulsion. Using the Magnus effect, which relies on the friction between the rotating cylinder and the air, it creates a vortex effect, akin to topspin on a tennis ball, exerting a propulsive force on the vessel perpendicular to the wind direction.

Despite running on engine power, and therefore fuel, Flettner rotors have been able to achieve some impressive fuel-saving results. Two Norsepower rotor sails on the deck of LR2 tanker Timberwolf – Maersk Pelican, at the time of the tests – were found to reduce fuel consumption by 8.2%.

Norsepower claims vessels operating on more favourable routes, such as in the North-Atlantic, could achieve anything up to 25% fuel savings using rotor sails. Indeed, this is the company’s expectation for Sea-Cargo ro-ro vessel SC Connector, fitted with Flettner rotors in Q4 2020, due to sail the North Sea and Baltic. The ship would be over a third of the way toward meeting the IMO’s 2050 targets, assuming Norsepower’s projections are correct. In combination with an alt-fuel, for example the biofuel readily available in ports in northern Europe, it could more than meet those criteria today.

“Rotor Sails are particularly well suited to ro-ro vessels,” said Norsepower CEO Tuomas Riski, adding that the sails’ tilting capacity “fits with particular vessel requirements, specifically demonstrating vessels with height restrictions to benefit from the rotor sail solution.”

Not just theory

The Suez Crisis of the 1980s yielded a generation of fuel-saving innovations largely forgotten since, and one of these was the ‘JAMDA’ (Japan Marine Machinery Development Association) sail, comprising canvas stretched over a metal frame. Fitted to vessels operating in the Sea of Japan, it proved capable of between 10 and 30% fuel savings. (In sheer dedication to this principle, JAMDA-fitted Shin Aitoku Maru also burned sludge and its crew’s sewage as fuel.)

Now in the 21st Century, Neoline has proposed a wind-powered car carrier, which would operate between St Nazaire, in France, and the United States. The project gained a vote of confidence when Groupe Renault partnered with Neoline in 2018, calling the move “the latest example of our supply chain’s commitment to reduce its carbon footprint by 6% between 2016 and 2022,” in the words of Jean-François Salles, Alliance Global Director, Production Control, Groupe Renault.

Wallenius has also proposed its own sailing car carrier concept, Oceanbird, along similar lines. Its designer claims that building the vessel as a sailing ship from the keel-up, increasing voyage times from seven days to around 12, and increasing the dimensions of the sails – up to a maximum height of 80m, double the height of today’s tallest sailing ships – will allow much greater efficiencies than previously seen. In fact, both designers purport to be capable of an outlandish 90% reduction in fuel consumption – 30%, while achieved with JAMDA sails, is considered exceptional today.

Scaling back down

It is thought that a major potential benefit of powering ships using sails is defeating the economies-of-scale principle dominating and dictating ship design in recent decades. Harnessing enough free wind energy to offset their fuel use, by using a greater proportion of sail surface area to cargo, fleets of smaller sailing vessels could perform better economically than a single massive one.