Somewhere between Finland and Sweden, a ship surges through the icy Baltic Sea with a strange white tower protruding, totem-like, from its deck. It may not look like it, but this tall spindle is a sail: the same winds buffeting people about on board channel through the 24-metre-high tower, providing clean, auxiliary power, just like the canvas sails of yesteryear.

Tuomas Riski, the man behind it all, stands at the base of the totem, introducing his invention to a group of note-scribbling journalists. He wears a light, navy suit, seemingly oblivious to the blasting Baltic winds. Above him the tower whirrs in the wind: at its peak it can reach 225 rotations per minute, pushing the ship past the tiny, pine-sprouting granite islands that pepper the Archipelago Sea. “You don’t think it’s making too much noise?” Riski asks, briefly furrowing his brow. In any case, the humming of this slender sail seems a small price to pay for the promise that it will cut fuel use by 300 tons a year, and significantly reduce the ship’s emissions in the process – helping to make this one of the cleanest passenger vessels in the world.

Called the Viking Grace this 2,800-person passenger ferry runs daily between Turku in Finland and Stockholm in Sweden across the Baltic’s Archipelago Sea: the 25th of April marked only its 13th day travelling with the sail, which is known as a Flettner Rotor Sail. Riski, the CEO of Finnish cleantech company Norsepower, has spent the last six years fine-tuning its design to make it worthy of this ship. But this modern sail has roots in an idea that’s actually almost 100 years old: Norsepower is the first company to successfully resurrect the historic concept for the modern age. Now, as pressure intensifies for the global shipping industry to decarbonise, Norsepower plans to bring back these fuel-saving mechanical sails to the decks of huge tankers that roam the seas today.


Riski’s sails are just one among a growing arsenal of inventions designed to transform the future of shipping. The vessels that traverse our seas enable 90 per cent of global trade, but shipping is also a disproportionately polluting industry. Ships produce just over 2 per cent of global carbon dioxide emissions, but they also sputter out between 13 and 18 per cent of global sulphur dioxide and nitrogen oxide emissions. These are key ingredients in bunker fuel, the low-grade, cheaper oil that ships typically use, and they’ve been linked to pollution that has driven a global increase in deaths from lung cancer and cardiovascular disease. “Looking forward to 2020, if we don’t do anything global shipping is going to be one of the major emitters,” says Andrew Scott, programme manager from the UK-based Energy Technologies Institute, which has partnered with Norsepower to put rotor sails on ships. By 2050, shipping is expected to make up 17 per cent of global emissions.

But change is afoot. In April this year, the United Nations’ International Maritime Organisation (IMO) set groundbreaking targets for global shipping companies to halve their greenhouse gas emissions by 2050. Ships are also having to navigate an increasing array of Emissions Control Areas, stretches of ocean where tighter regulations limit the amount of sulphur and nitrogen oxide that vessels can expel. That’s driving worldwide interest in rotor sails – and although Rolls Royce briefly entertained the idea of developing them for British ships, it’s green, sailing-obsessed Finland where the idea is making headway.

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Norsepower founder Tuomas Riski: “When we first started the company, having a rotor sail installed onboard a cruise ferry seemed like a distant dream.” Norsepower

On the ninth floor of the Viking Grace, Riski sits beside a large sunlit window: he’s imposingly tall, with ice-blue eyes, blondish hair tucked behind his ears, and the demeanour of someone at home on the prow of a ship, wind-whipped and scanning the horizon. Norsepower’s founder does in fact spend a large chunk of his time riding ocean swells on his 35-foot sailing boat, which he and his crew race competitively. As a teen he also grew up working in Finnish shipyards, and had a stint in the navy. So for most of his life, he says, he’s had a connection to the sea.


But it was only after a few years in his first job as a partner in an IT company, that Riski realised he yearned for that maritime element in his professional life as well. So, when in 2012 he had a chance meeting with famous Finnish naval architect Kai Levander, Riski was quickly enchanted by the Levander’s idea that a failed shipping invention from the early 1900s, called the Flettner Rotor, could be revamped for modern ships. “I think it was a combination of my background hobby as a sailor, and my understanding of physics. Those things combined made me believe that if this worked it would be quite splendid,” Riski says. Six months later, the duo launched Norsepower as a startup to manufacture rotor sails, with Levander working part-time and Riski as its only official employee.

Riski and Levander’s enthusiasm for the project stemmed in part from understanding precisely why the Flettner Rotor had failed so catastrophically, almost a century ago. First invented in the 1920s by a Finn named Sigurd Savonius, the rotor sail was designed to harness the Magnus Effect: the phenomenon wherein air that moves past a spherical spinning object (in the rotor’s case, a rotating metal cylinder) creates a pressure difference on either side. That imbalance generates a lifting force perpendicular to the direction of the wind, and powerful enough to thrust a ship forward.

In 1925 a German engineer named Anton Flettner built and tested out Savonius’s rotor sail on a schooner called the Buckau: he wanted to prove it could be used as an alternative to the costly fabric sails that still adorned many ships. The Buckau sailed across the Atlantic Ocean without a hitch. But industry at the time was heading in a different direction: “Diesel engines coming to the market, combined with cheap fuels, destroyed Flettner’s idea,” Riski says.

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Today, the exact reverse is true, and rising fuel costs and the pressure to slash emissions have become the perfect incubator for Flettner’s original concept: fortuitously, the forward-thrust of the rotor sail creates an additional push that allows modern-day ships to throttle back the engines and save on fuel.


Norsepower wasn’t the first to see an opportunity. Back in 2008 German wind turbine manufacturer Enercon fitted four rotor sails on to a carrier ship, to transport its green energy cargo more efficiently across the sea. Since then a handful of other rotor projects have sprung up – but modern mechanical sails have mainly been confined to studies that have proved their effectiveness in purpose-built wind tunnels. “A lot of studies have been made on Flettner Rotors, but there was no evidence on how it really was performing at full scale,” Riski says. While Enercon’s project did show fuel savings, Norsepower has provided the most convincing results under real-world conditions out at sea.

That comes down partly to superior design: Norsepower’s mechanical sails are made from carbon and glass fiber materials that make it lighter, meaning it requires less electricity to spin the rotor that enables the Magnus Effect. That, Riski reckons, has been their greatest design challenge, worthy of patents that have given Norsepower a competitive edge. To streamline the machine’s performance, they’ve also embedded sensors in the rotor that detect wind speed and tightly control the number of rotations to maximise the benefits of the wind’s power.

Norsepower first tested its idea on the Estraden, an 18,000 ton Finnish cargo ship. The single 18-metre-high rotor sail, installed there in 2014, has since led to a six per cent annual reduction in fuel use. That’s 400 tons of fuel – and 1200 tons of CO2 that’s been prevented from escaping into the atmosphere. Next came the 24-metre installation on the Viking Grace: simulations suggest that after a year on the deck it will preserve 300 tons of the LNG fuel the Viking Grace runs on, equivalent to an annual €180,000. Throttling back the engines will also save 900 tons of CO2.

This seems almost at odds with a ship that gives every appearance of excess. Boarding the 12-storey Viking Grace feels like entering a towering, luxury condo that just happens to be afloat. Modelling itself on a cruise ship, the ferry comes complete with a panoramic glass-fronted restaurant, a spa, several bars, a floor dedicated to tax-free shopping, and two venues where crooning bands serenade a floor of waltzers, awash in the twinkling light of a disco ball. But beyond this glitzy facade, below deck the ferry also reclaims waste heat from the engine for transformation into electricity, uses seawater to cool the engines and the vessels’ ventilation air, and relies on LNG fuels to cut greenhouse gas emissions by 15 per cent.

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“This is the only wind-power LNG hybrid ship in the world,” says Kaj Takolander, head of marketing and sales for Viking Lines, the company that runs the Viking Grace. “You could go as far as to say that this is the most environmentally-friendly passenger ship in the world.”

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Down on the bridge, the ship’s control centre, Captain Henrik Grönvik – a stern, considered man man wearing a suit decked in brass buttons – is more cautiously optimistic about the rotor sail technology that adorns his ship. Around him, crew members sit silently behind a bank of blinking neon screens that show the ferry’s route between the thousands of rocky isles that make the Archipelago Sea appear almost unnavigable.

It was this complex landscape that initially made Grönvik sceptical about the rotor sail: he was concerned that its angled thrust would cause a tilt in the ship, making it harder to steer – especially in the narrow island channels that dominate its route. “When we started we had a lot of questions,” he admits. Despite Norsepower’s record of success so far – which has since convinced him that the sail is safe – he emphasises that the rotor’s maiden voyage on the Viking Grace is still a test-run. Asked how it affects the ship’s operation, Grönvik says, “I frankly cannot say. It’s only been two weeks. We need some time now to evaluate the results.”

A larger question is whether rotor sails can make enough of a dent in global shipping emissions, considering the magnitude of the problem. The UK Chamber of Shipping, for instance, holds the view that true change can only happen through the discovery of and investment in new fuels. “When it comes to zero emissions we strongly believe we are going achieve this is with alternative fuels,” says Anna Ziou, the trade association’s policy director. “I don’t think that in the next 30 years we will have a technology that is so radical that it’s going to provide the option of zero-emissions transport.”

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Regardless, the allure of Norsepower’s slim mechanical sails is growing for shipping companies feeling mounting pressure to go green. Riding this wave of opportunity, “we could probably make this a mainstream product for certain ships,” Riski reckons. Viking Lines has already opted to fit its new ferry, now under construction in China, with two of Norsepower’s sails. And now, Norsepower is turning its gaze to a new challenge: fitting the ocean’s fuel-guzzling, behemoth tankers with its mechanical sails.

This year Norsepower has partnered with Maersk Tankers to fit two 30-metre rotors to a 100,000-ton ship: “It will be the first tanker ever with a mechanical sail,” Riski says. They’re projected to save 10 per cent of the tanker’s fuel annually – but up to 20 per cent on shipping routes with optimal wind conditions. The UK’s Energy Technologies Institute will provide up to £3.5 million to support Norsepower, with energy giant Shell managing the project.

“The reason we are doing this project is that we want to accelerate the deployment of rotors. And by having Maersk Tankers and Shell, we’ve got two of the biggest operators of ships in the world, now seriously working on [it],” says Scott. The tanker trial will run until the end of 2019, by which time Maersk will have unprecedented data on Flettner Rotors’ effectiveness.

Out on the blustery deck, Riski – who rarely smiles – beams proudly as he gazes up at his mechanical sails rotating industriously: “When we first started the company, having a rotor sail installed onboard a cruise ferry seemed like a distant dream.” Now, he says, that dream has been upgraded to seeing them as a standard feature on tankers around the world.

Even then, this invention won’t solve all of shipping’s ills. But, says Scott, “This is fundamentally about saying, if we’re serious about reducing greenhouse gases we’ve got to start doing things like this.”

Want to know about the future of transport?

This article is part of our WIRED on Transport series where we explore the challenges and solutions in transport, such as the future of borders after Brexit, the new race to make supersonic travel work and the hover train that never was.


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