The turbosail or French is a marine propulsion system using a sail-like vertical surface and a powered boundary layer control system to improve lift across a wide angle of attack. This allows the sail to power the boat in any direction simply by moving a single flap at the back of the sail, unlike conventional sails which have to be continually adjusted to react to changes in the relative wind. The turbosail was first developed in a large scale application by Jacques-Yves Cousteau who commissioned the Alcyone to test the concept in production. The larger Calypso II was also designed to use a turbosail, but that design was not built. Technical design Concept In 1980, Jacques Cousteau dreamed of creating a ship with a modern engine that would be powered, at least in part, by the wind, a clean, free, renewable energy source. Aerodynamics Cousteau and his associates, Professor Lucien Malavard and Dr. Bertrand Charrier, used a fixed cylinder that looked like a smokestack and functioned like an aeroplane wing. It consists of an airfoil, vertical and grossly ovoidal tube, with a mobile flap which improves the separation between the intrados and extrados. An aspiration system pulls air into the tubes, and is used to increase the depression on one side of the sail; a reaction force occurs as the result of the pressure difference. In this way, the sails act as wings, creating both lift and drag. A movable, flap-like trailing-edge shutter and a fan-drawn aspiration system are used for control and increase the magnitude of the maximum reaction force. As a result of this design, the turbosail provides a reaction force, a component of which, thrust, is available for the direction of travel. Just like an unpowered sail, thrust cannot be obtained when making headway directly into a headwind, nor can it be obtained without wind. However, the use of fan-drawn aspiration, which requires engine power, increases the generated reaction force compared to the unpowered device. Propeller-based propulsion can be used in conjunction with the turbosails. These traditional engines, together with the angles, and suction power of the sails, can be coordinated with computers to control the ship. Engineering analysis According to the Cousteau Society, "when compared to the thrust coefficient of the best sails ever built (Marconi or square types, i.e. ships of the American Cup [sic] or the Japanese wind propulsion system) that of the turbosail