Deutsches Technikmuseum Berlin - Flettner-Rotor

Rotor ship E-SHIP 1 under construction, December 2009 in Emden, Photo: Onno K. Gent, http://filapper.de

A Rotating Substitute for Sail

The launch of the world’s first rotor ship, the BUCKAU, on 7 November 1924 in Kiel caused quite a splash. Never before had the world seen such a vessel, with its two silently rotating columns rising tall from the deck. The new fuel-saving auxiliary propulsion system was named after its inventor Anton Flettner (1885–1961), a trained mathematics teacher and self-taught engineer.

Inside the exhibition. Photo: Kirchner, SDTB

The Flettner rotor deflects the wind to one side, using the resulting forces to propel the ship forward in a similar way to a sail. But unlike conventional sails, the rotors can be operated by one person on their own. Despite successful trials on a second larger ship, the BARBARA, the rotor never took off. But now, in an age of increasing environmental awareness and rising fuel costs, Flettner’s idea of a rotating substitute for sail is gaining ground again. Perhaps its time has come?

Using photographs, documents and a contemporary film, the exhibition relates the ups and downs of this nautical innovation. A 1:50 functioning model of the BUCKAU made in 2001 illustrates the proportions of the rotors and offers an opportunity to approach the subject from the perspective of a model-builder.

The second rotor ship, the BARBARA, in the Port of Hamburg, shortly before setting off on a long voyage, 1926. Photo: SDTB Archive

From Idea to Reality

The Flettner rotor was based on a much earlier breakthrough made in 1851 in Berlin. The physicist Heinrich Gustav Magnus (1802–1870) discovered a hitherto unknown force that arises when air flows over a rotating body. This came to be known as the Magnus effect. Flettner came up with his idea for a ship-powering rotor in 1923 after hearing about the research of Professor Ludwig Prandtl (1875–1953), Director of the Aerodynamic Research Institute in Göttingen. The young science of aerodynamics supplied Flettner with the necessary engineering data and backed up his argumentation concerning the practicability of the rotor drive. This was enough to convince his sponsors at the Germania Shipyard in Kiel, and the first prototype, the BUCKAU, was launched in 1924. A second, larger, rotor ship, the BARBARA, followed two years later.

The Flettner-Rotor in the Great Depression

The two prototypes proved that the drive functioned reliably, and the BARBARA served as a normal freighter in the Mediterranean between 1926 and 1929. But no new orders for rotor ships followed, not even from the United States where Flettner sent the BUCKAU in 1926 for demonstration purposes. Fuel was so cheap at that point that the savings achieved by the rotor were too small for shipping companies to recoup the investment quickly enough. Flettner’s attempt to enthuse yachtsmen and women for his rotor fared no better.

In the aftermath of the Great Crash of 1929 and the slump in world trade that followed, the charter operator handed the BARBARA back to its owner, the German Navy, in 1931. The Navy in turn sold the ship on to a new owner who dismantled its three rotors and used only its engines. The history of the rotor ship had come to an end for the moment.
Flettner himself went off on a different tack, turning his talents for example to designing helicopters and inventing a rotating air vent for vehicles that is still in production today.

Experimental vessel UNIKAT (2006) with Flettner rotor (loan from Flensburg University). Photo: Kirchner, SDTB

A 21st-Century Renaissance?

When fuel prices spiked after the oil crisis of 1973 shipping companies were hit too, and they began looking for savings. Flettner’s idea was dusted off and the Hamburg shipbuilders Blohm & Voss drew up plans to install rotors on a chemical tanker. But the idea was dropped in 1986 when the oil price fell again.

Today, as oil prices threaten to rise and increasing importance is placed on renewable forms of energy, the rotating sail is gaining in relevance again. In 2006 Flensburg University built a Flettner catamaran, which is on show in the exhibition. The E-SHIP 1 – the first rotor-powered freighter since the BARBARA – is scheduled for completion this year at a shipyard in Eastern Friesland. When it goes into operation this vessel could open up a new chapter in the history of shipping.