Century-old rotorsail design gets modern makeover

From towing kite propulsion to sails fitted with solar panels, modern engineers have been working hard to find ways to make our increasing reliance on big cargo shipping more energy efficient and environmentally friendly. Finnish company Norsepower has looked to the past for inspiration, finding a solution in a nearly century-old engineering innovation relegated to the annals of quirky mechanical history.

In 1924, German engineer Anton Flettner revealed his first large-scale rotor ship to the public. Named the Buckau, this retrofitted schooner astonished the general public with its large, imposing metal cylinders rising from the deck.

Two years later, the first rotor ship designed from the ground up appeared in a shipyard in Bremen. Inspired by Flettner's prototype, the German naval authorities designed a three-tower rotor ship dubbed, the Barbara.

Both ships employed an innovative new engine design pioneered by Flettner and utilized a process known as the Magnus effect for propulsion. Named after German physicist Heinrich Gustav Magnus who investigated the effect in 1852, the principle was initially used to illustrate how balls or artillery can curve away from their principle flight path depending on the airstream that surrounds the object.

The idea behind the Flettner rotor is that as wind passes a spinning cylinder, the air flow accelerates on one side while decelerating on the other. This creates a thrust perpendicular to the wind direction.

The Flettner rotor-propelled ships of the 1920s were popular at the time as a novelty, but the considerable capital costs and the looming Great Depression caused the design to slip into the oddspot pages of engineering history. As these engines still required traditional fossil-fuel based power to function, the technology wasn't of a great interest to most in the 20th century's age of omnipresent fossil fuels.

In our modern era of environmental concern and shifts towards sustainable energy engineers began to hunt for ways to make current large shipping processes more fuel efficient.

It has been reported that 3.5 to 4 percent of all climate change emissions are caused by the global shipping industry, and one recent study estimated these rates could rise by as much as three times by 2050.

In 2008, German wind-turbine manufacturer Enercon developed the first modern Flettner ship, the E-Ship 1. With its four giant rotorsails, the E-Ship 1 reportedly achieved fuel-savings of nearly 25 percent after several years of testing and 170,000 sea miles (195,633 mi/314,840 km) traveled.

More recently, Finnish company Norsepower has snatched the rotorsail baton, trialling the technology on several large-scale ships. Norsepower initially reported successful results, noting the technology had the potential for fuel savings of up to 20 percent on routes with favorable wind conditions.

The biggest move forward for the technology has been the recent announcement of Norsepower joining forces with shipping giants Maersk and Shell to being testing the rotorsail motors on their giant tanker vessels.

Initial estimates from Maersk and Norsepower expect the rotorsail technology to reduce average fuel consumption by 7 to 10 percent. The collaborative effort between the companies will implement the prototype engines and test the efficiency through to the end of 2019 before analyzing the overall results.

"Our Rotor Sails have the power to reinvent the existing market and make auxiliary wind propulsion a natural choice for merchant shipping," CTO of Norsepower Jarkko Vainamo explained.

Over 50 years after innovative inventor Anton Flettner passed away, one of his earliest designs has finally been rediscovered and it may prove to be a vital step towards a more environmentally sustainable and efficient cargo shipping industry.

Source: Norsepower