Giant inflatable sails could be key to making shipping greener in the future.

(CNN) — Sailing boats date back more than 5,000 years, when the ancient Egyptians floated up and down the Nile in wooden vessels powered by wind and oars. But when steam and diesel engines arrived and globalization increased the need for timely trade, the sails dropped.

Today, they are making a comeback as the shipping industry looks to decarbonize. But the new sails look nothing like those of the past. Tall, white and puffy, the giant inflatable sails designed by tire manufacturer Michelin more closely resemble the Michelin man -- the company's mascot -- than a traditional cloth sail. Made from a flexible material that the company would not reveal, the sails can inflate or deflate at the push of a button. No crew is required to rig them, and they pivot automatically to catch the wind, equipped with sensors that measure the wind direction and speed.

Intended to be retrofitted onto existing cargo ships, the sails will work alongside the ship's engine, reducing its overall reliance on fossil fuels. Michelin estimates fuel savings could be as high as 20%.

"Our aim is to contribute to the decarbonization of maritime transport," says Benoit Dailliez, project leader for the company's wing sail mobility project (WISAMO). He adds that as regulation around carbon emissions increases so will the demand for green alternatives.

Shipping, which is predominantly powered by fossil fuels, accounts for around 3% of global greenhouse gas emissions, according to the International Maritime Organization (IMO).
Decarbonization is proving a slow process, with emissions from shipping rising in the last decade. But modern sails could help to accelerate the transition, according to a report released this year from the Institution of Mechanical Engineers. It urged the industry to take up the technology, noting that "21st century wingsails" could play a significant part in reducing the industry's emissions, especially when retrofitted onto cargo ships.

Wings not sails

Thanks to their size, material and automation, modern sails are able to harness more wind than those of the past. In fact, they are more similar to an aircraft wing than a conventional cloth sail -- designed to generate a lift force perpendicular to wind direction with as little aerodynamic drag as possible.

"These are not sails, these are wings," Dailliez tells CNN. He says that the fact that they can be installed on existing merchant ships makes the technology appeal to the mass shipping market, adding that it's also where the most carbon savings are as older ships tend to be the worst polluters.

However, Michelin's design is still a long way from fruition. The company would not disclose if it had secured any commercial clients, and so far, has only tested a 1,000-square-foot version of the design, hoisting it onto a 40-foot yacht in Switzerland's Lake Neuchatel. While this was a success, says Dailliez, it's a world away from 500-foot-plus bulk carriers or oil tankers. He hopes that the company will test a larger version -- between 3,000 and 5,000 square feet -- on a cargo ship in 2022 before heading into full-scale production.

But Michelin isn't the only company bringing high-tech sails to cargo ships. UK-based BAR Technologies has secured a contract with US shipping giant Cargill to retrofit its "WindWings" onto a bulk cargo ship chartered by the company by 2022.

Based on the same theory as the Michelin design but made of steel, the 150-foot-tall structures not only operate like an airplane wing but look like one too. Instead of inflating or deflating, the wings will sit upright on the deck of a cargo ship and can fold down flat to pass under a bridge or enter a port.

BAR Technologies'

BAR Technologies' "WindWings" (seen here in a rendering) could enter the water by 2022, under a partnership with Cargill.

Courtesy BAR Technologies

The rigid sails look more similar to those on Oceanbird, a 650-foot-long wind-powered transatlantic car carrier designed by Swedish shipbuilder Wallenius Marine, that is due to make its maiden voyage in 2024.

Unlike Oceanbird, which relies solely on wind, BAR Technologies' wings will work alongside the engine -- increasing the vessel's fuel efficiency by between 25% and 30%.

BAR Technologies' CEO John Cooper explains that 100% wind power works for routes with guaranteed wind or in situations where it's acceptable for a ship to be a couple of days late. But he says that isn't an option for most commercial shipping.

While the company would not disclose how much it will sell the wings for, Cooper says it's more about payback than price.

"The obvious economic (incentive) is reduced fuel," he says, "and when you reduce fuel you reduce your greenhouse gas (emissions)." These savings make up for the installation cost, he adds, and would be increased if a global carbon tax is introduced, or if the industry moved to more expensive, low-carbon fuels like hydrogen, ammonia or liquefied natural gas.

Low pressure

However, the shipping industry may need a bigger stimulus to convince it to take up these technologies, says Tristan Smith, associate professor and head of the Shipping Group at University College London.

Wind propulsion has long been seen as an option to reduce shipping's dependence on diesel, he explains. Flettner rotors, a technology that dates back to the 1920s, consisting of vertical cylinders that spin with the wind and create a forward motion, have been deployed on cargo ships, such as the Timberwolf tanker (formerly the Maersk Pelican) and the m/v Afros, reportedly generating fuel savings of more than 10%. Giant kites which fly ahead of the vessel and tow it on a rope have also been proposed, with German company SkySails claiming it could save an average of 10-15% of fuel each year.

But despite these savings, uptake of the technologies hasn't been widespread. "There's a decade of (wind propulsion) designs that look good, that save money, that in theory pay for themselves, that haven't materialized into action," Smith tells CNN. "It's not because they don't save fuel, but clearly because they don't save enough fuel relative to their cost."

Another sticking point is that the charterer, not the shipowner, usually pays for fuel. This means there's less incentive for the shipowner to fork out on fuel-saving technology and similarly the charterer might not lease the ship for long enough to see the payback.

Cooper acknowledges this "conundrum" but believes that as demand rises, charterers will be willing to pay more expensive charter rates as they'll be spending less on fuel.

Regulations need to be changed to encourage the use of wind power, urges Smith. While the IMO has set an industry-wide target to halve emissions in the next three decades, he says it lacks stringent enforcement and regulation, and though the EU has proposed charging ship owners for pollution, this is yet to come into force.

"We're basically missing an opportunity to reduce thousands and millions of tons of greenhouse gas emissions because the regulatory bodies aren't making the right decisions at this point in time," he says.

BAR Technologies' Cooper is more optimistic. "Wind is a free fuel," he says, and as some responsible, climate-conscious companies start installing wingsails, the price of the technology will drop, increasing accessibility and

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