Viking Line Installs Rotor Sail on Cruise Ferry

Image courtesy Viking Line

Published Apr 11, 2018 4:44 PM by The Maritime Executive

Viking Line has installed a Norsepower rotor sail unit on the cruise ferry Viking Grace, making her the world's only working passenger vessel with a modernized Flettner rotor. 

Viking says that the 80-foot-tall rotor will allow the Grace to save up to 900 tonnes of fuel annually on her run between Turku, Finland and Stockholm, Sweden. A newbuild Viking Line cruise ferry currently under construction in China will also receive two of the Norsepower rotors. 

"The last traditional windjammers in the world were owned and operated by shipping companies based in [Åland, Finland], so it’s only fitting that Åland-based Viking Line should be a forerunner in launching modern auxiliary sail technology," said Norsepower CEO Tuomas Riski. "The completion of this project is a great moment for all those involved.”

A technology long in the making

The history of the Flettner rotor dates back to 1924, when engineer Anton Flettner installed two of his newly invented rotors on the converted schooner Buckau. The Buckau showed promise, with high reliability and efficiency, but the availability of cheap fuel and the onset of the Great Depression sunk the technology's chances at widespread adoption.

Flettner rotors depend upon an aerodynamic phenomenon known as the Magnus effect. When wind contacts a rotating cylinder, it flows at different relative speeds as it passes on each side. That speed difference translates into a pressure difference, creating force at a right angle to the wind direction - an effect similar to that of a traditional cloth sail. Unlike a sail, though, the Flettner rotor needs no furling, reefing or line-tending. The Buckau's performance also suggested that rotor-driven ships could sail closer to the wind than traditional sailing vessels.  

In a 1925 editorial, Albert Einstein used the example of the Flettner rotor to criticize the pace of technological innovation. "Even when the external and scientific conditions for the formation of an idea have long been present, an external incentive is mostly needed for its emergence; the subject must be right in front of a person's nose, so to speak, for the thought to arrive," the world's most famous scientist complained. "One nice example of this banal and, for us, hardly flattering truth is the Flettner ship . . . The scientific basis for Flettner's invention is actually already about 200 years old." 

93 years later, Flettner's idea has reemerged, and it appears to be gaining traction. In addition to the Viking Grace, Norsepower has installed its equipment on the freight ro-ro Estraden, and it has an agreement with Maersk Tankers for the installation of two rotors on an LR2 product tanker. 

The Norsepower rotor sail is an update on the original Flettner design, with several notable improvements. It is built of lightweight composite materials, and it is fully automated: its control equipment senses whenever the wind is strong enough to deliver fuel savings, at which point the rotor starts on its own (with full control available to the crew). The firm says that it can deliver fuel savings of five to 20 percent, and is suitable for vessels with high utilization, open deck space, and trading routes in areas with favorable wind conditions.