Experimental prototype Here is the motor boat used for the tests with leeboards added. The rig is composed of three pieces: - A short mast able to turn of 360° around his axis. A mast of sail board is convenient for this use. - The reels fixed on the mast to store the lines between the sails and the boat with a handle to control the launch. We have built and tested a dozen of different reels. - A spar, called the “grenadier” is also fixed on the mast via a horizontal axis. At the extremity, the main lines of the sail pass through guides. We have tested more than ten different sails. The launch was obtained in two steps: launch of a first sail of limited area called the “pilot” able to launch easily a main sail by supporting it through his attack edge. But due to the poor thinness of the pilot it was not possible to run against the wind. So we have defined a procedure to launch directly and easily a kite-surf sail available on the market up to 22 sq.meters. This sail can be used alone or as a pilot to launch sails up to 100 sq.meters. These sails are not available to-day. The launching Here above is the 22 sq.meters kite-surf sail after inflation. The optimum wind speed for the launch is 10 knots. If the wind speed is not sufficient, the boat is headed into the wind and the motor increases the apparent wind speed. The reels control the raising of the sail. The brake lines are always operational. Sail drive The sails are driven like classical kite-surf sails but the cleats placed in due position are able to stabilise them. Photos during the tests organized for Thomas Coville. - launching. - in operation. - return of the sail. Overturning torque With a kite sail the overturning torque is naturally 2 or 3 times lower than the traditional sails. It is possible to suppress the keeling as shown on the figure with a sufficient length of the grenadier and by using a stay at his free extremity. But this disposition is reserved only in case of research of the maximum speed.