The century-old ship sail technology finally catching on

Modern rotors are even more efficient than the ones on Buckau in 1925 because they are made with lighter composite materials such as carbon fibre.

Prof Mehmet Atlar, an expert in hydrodynamics at Strathclyde University, believes there was a lot of initial interest in the design with an order book starting to grow.

A larger ship was launched, called the Barbara, with a further six waiting to be built.

But by the end of the 1920s, those orders were being cancelled and the design concept was shelved.

He said: "In my opinion, nothing is new.

"The need is the most important thing. The need now is there, therefore the Flettner rotor came back."

He said that the lighter materials, combined with more effective motors to drive the rotors, mean it's much more effective than a century ago.