A design for spinning “rotor sails” could potentially reduce fuel consumption and carbon emissions from ocean ships. The concept was explored earlier in the 20th century, but failed to gain traction with low fuel prices and no environmental regulations.
In early 2018, the new design will be outfitted onto two vessels, including a tanker owned by the Danish transportation giant Maersk, and a passenger ship owned by Viking cruises.
The spinning cylinders are mounted vertically on the decks of ships, towering as high as 10 stories in some cases. Fuel consumption could go down by up to 10 percent, which would save shipping companies hundreds of thousands of dollars, while also reducing carbon emissions by thousands of tons for each trip.
The design relies an aerodynamic principle called the Magnus effect, identified by German physicist Heinrich Gustav Magnus in the 1850s. Magnus observed that spinning objects experience a sideways force as they move through the air, the same force that allows baseball pitchers to throw curveballs.
Scientists have been suggesting this force could be used to propel ships since the early 20th century, and a similar design for a rotor sail was used for a ship, by German engineer Anton Flettner in the 1920s. But with low fuel prices and no environmental regulations, and without lightweight materials like ones used in the modern design, Flettner did not find investors and the design never caught on.
Today, the shipping industry is facing pressure to reduce carbon emissions and fuel consumption. Ninety percent of the world’s goods are shipped via the ocean, and most of these ships use heavy fuel oil which produces not only carbon dioxide, but also soot and sulfur which contribute to acid rain. Now, Helsinki-based clean technology company Norsepower Oy Ltd. has designed a new rotor sail based on early 20th century designs, but taking advantage of modern materials such as carbon and glass fibers that allow for lighter weight, allowing the rotors to spin using far less electricity.
“Our largest rotor sails can provide forward thrust equivalent of up to 3 megawatts of main-engine power while drawing less than 90 kilowatts of electricity,” according to Norsepower CEO Tuomas Riski.
Rotor sails are effective in conditions where wind is faster than 18 kilometers per hour, or about 10 knots, blowing across a ship’s bow at an angle of 20° or more. Such conditions are often faced by ships in the northern Pacific and norther Atlantic oceans. These sails are not intended to replace a ship’s engine, but rather to supplement propulsion.
If the design is shown to be practical on the two ships next year, rotor sails could eventually become widespread, in an effort to reduce fuel costs and carbon emissions in the shipping industry.