The Alcyone - an experimental turbosail boat operated by the Cousteau Society.
Turbosails work on the Magnus effect:
An object spinning in fluid (or air) creates a whirlpool that results in a force perpendicular to the stream around the object:
This exact effect is responsible for the curved trajectory of spinning footballs or golf balls.
Turbosails - as a supplementary propulsion to diesel engines - improve the fuel efficiency of the vessel by 15-30%.