Scientific American - USA (2020-12)

December 2020, ScientificAmerican.com 23

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ENGINEERING

Rotating Sails

A century-old concept gets a fresh look as shippers cut back on fuel

In 1926 a cargo ship called the Buckau crossed the Atlantic sporting what looked like two tall smokestacks. But these tower- ing cylinders were actually drawing power from the wind. Called Flettner rotors, they were a surprising new invention by German engineer Anton Flettner (covered at the time in Scientific American ). When the wind was perpendicular to the ship’s course, a motor spun the cylinders so their forward- facing sides turned in the same direction as the wind; this movement made air move faster across the front surface and slower behind, creating a pressure difference and pulling the ship forward. The rotating sails provided a net energy gain—but before they could be widely adopted the Great Depression struck, followed by World War II. Like the electric car, the Flettner rotor would be abandoned for almost a century in favor of burning fossil fuel. Now, with shippers under renewed pressure to cut both costs and carbon emissions, the concept is getting another shot. In one notable example, the 12,000-gross-ton cargo vessel SC Connec- tor is adding 35-meter Flettner rotors that can tilt to near horizontal when the ship passes under bridges or power lines. The new rotors need electrical power to spin, but manufacturer Norsepower says they can still save up to 20 percent on fuel con- sumption and cut emissions by 25 percent. The SC Connector is one of a growing

series of rotor-boosted ships expected to be operating in various parts of the world by year’s end, according to SSPA, a Swe- den-based nonprofit research institute. Shipbuilders are also incorporating other wind-propulsion technologies, such as kite-style sails. But Flettner rotors are getting the earliest adoption, says Sofia Wer- ner, a naval architect who leads an SSPA team studying their performance. Ships can easily be retrofitted, literally overnight, with rotors activated by an on/off switch. “It’s a quite simple solution, understand- able and safe,” Werner says. “It’s also very visible, which is good for marketing.” The United Nations International Mari- time Organization has set ambitious de - carb onization goals involving marine fuels, and the European Union is now funding rotor research. Climate pressures and easy installation make wind-power systems an attractive option, according to the Interna- tional Windship Association. “A lot of peo- ple wanted to see wind dead [in the 1920s] because they were making a lot of money off fuel,” says Gavin Allwright, the organization’s secretary-general. “That’s still true today. I can’t sell you a unit of wind. What I am bullish about is that where we’ve got a major decarbonization issue, [alternative fuels] have great potential but are five to 10 years from being proven out. Wind, we could put on a vessel today.” — Lynn Freehill-Maye

Buckau cargo ship’s innovative rotors

GETTY IMAGES

ENGINEERING

Rotating Sails

In 1926 a cargo ship called the Buckau crossed the Atlantic sporting what looked like two tall smokestacks. But these tower- ing cylinders were actually drawing power from the wind. Called Flettner rotors, they were a surprising new invention by German engineer Anton Flettner (covered at the time in Scientific American ). When the wind was perpendicular to the ship’s course, a motor spun the cylinders so their forward- facing sides turned in the same direction as the wind; this movement made air move faster across the front surface and slower behind, creating a pressure difference and pulling the ship forward. The rotating sails provided a net energy gain—but before they could be widely adopted the Great Depression struck, followed by World War II. Like the electric car, the Flettner rotor would be abandoned for almost a century in favor of burning fossil fuel. Now, with shippers under renewed pressure to cut both costs and carbon emissions, the concept is getting another shot. In one notable example, the 12,000-gross-ton cargo vessel SC Connec- tor is adding 35-meter Flettner rotors that can tilt to near horizontal when the ship passes under bridges or power lines. The new rotors need electrical power to spin, but manufacturer Norsepower says they can still save up to 20 percent on fuel con- sumption and cut emissions by 25 percent. The SC Connector is one of a growing

series of rotor-boosted ships expected to be operating in various parts of the world by year’s end, according to SSPA, a Swe- den-based nonprofit research institute. Shipbuilders are also incorporating other wind-propulsion technologies, such as kite-style sails. But Flettner rotors are getting the earliest adoption, says Sofia Wer- ner, a naval architect who leads an SSPA team studying their performance. Ships can easily be retrofitted, literally overnight, with rotors activated by an on/off switch. “It’s a quite simple solution, understand- able and safe,” Werner says. “It’s also very visible, which is good for marketing.” The United Nations International Mari- time Organization has set ambitious de - carb onization goals involving marine fuels, and the European Union is now funding rotor research. Climate pressures and easy installation make wind-power systems an attractive option, according to the Interna- tional Windship Association. “A lot of peo- ple wanted to see wind dead [in the 1920s] because they were making a lot of money off fuel,” says Gavin Allwright, the organization’s secretary-general. “That’s still true today. I can’t sell you a unit of wind. What I am bullish about is that where we’ve got a major decarbonization issue, [alternative fuels] have great potential but are five to 10 years from being proven out. Wind, we could put on a vessel today.” — Lynn Freehill-Maye

GETTY IMAGES

ENGINEERING

Rotating Sails

In 1926 a cargo ship called the Buckau crossed the Atlantic sporting what looked like two tall smokestacks. But these tower- ing cylinders were actually drawing power from the wind. Called Flettner rotors, they were a surprising new invention by German engineer Anton Flettner (covered at the time in Scientific American). When the wind was perpendicular to the ship’s course, a motor spun the cylinders so their forward- facing sides turned in the same direction as the wind; this movement made air move faster across the front surface and slower behind, creating a pressure difference and pulling the ship forward. The rotating sails provided a net energy gain—but before they could be widely adopted the Great Depression struck, followed by World WarII. Like the electric car, the Flettner rotor would be abandoned for almost a century in favor of burning fossil fuel. Now, with shippers under renewed pressure to cut both costs and carbon emissions, the concept is getting another shot. In one notable example, the 12,000-gross-ton cargo vessel SC Connec- tor is adding 35-meter Flettner rotors that can tilt to near horizontal when the ship passes under bridges or power lines. The new rotors need electrical power to spin, but manufacturer Norsepower says they can still save up to 20percent on fuel con- sumption and cut emissions by 25percent. The SC Connector is one of a growing

series of rotor-boosted ships expected to be operating in various parts of the world by year’s end, according to SSPA, a Swe- den-based nonprofit research institute. Shipbuilders are also incorporating other wind-propulsion technologies, such as kite-style sails. But Flettner rotors are getting the earliest adoption, says Sofia Wer- ner, a naval architect who leads an SSPA team studying their performance. Ships can easily be retrofitted, literally overnight, with rotors activated by an on/off switch. “It’s a quite simple solution, understand- able and safe,” Werner says. “It’s also very visible, which is good for marketing.” The United Nations International Mari- time Organization has set ambitious de - carb onization goals involving marine fuels, and the European Union is now funding rotor research. Climate pressures and easy installation make wind-power systems an attractive option, according to the Interna- tional Windship Association. “A lot of peo- ple wanted to see wind dead [in the 1920s] because they were making a lot of money off fuel,” says Gavin Allwright, the organization’s secretary-general. “That’s still true today. I can’t sell you a unit of wind. What I am bullish about is that where we’ve got a major decarbonization issue, [alternative fuels] have great potential but are five to 10 years from being proven out. Wind, we could put on a vessel today.” —Lynn Freehill-Maye

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Scientific American - USA (2020-12)

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