Abstract: A glider sail assembly comprises a center boom with a fore end for directing into a wind and a mount for connecting the center boom generally horizontally at the top of a mast and directed at an upward angle towards the fore end. Each of two side booms has a fore end connected to the center boom near the fore end of the center boom and flexible portions near an aft end of said each side boom. The side booms are extendable to diverge away from each other in a V-shaped arrangement. A generally triangular sail is securable to the booms, so the sail extends between the side booms, and has skirt portions at each side thereof adjacent the flexible portions of the side booms. The skirt portions extend downwardly when the flexible portions of the side booms are deflected downwardly, so one of the skirt portions provides a propulsive force when the center boom is directed into the wind.