Abstract: An improved sail for sailboards, small sailboats or the like having an efficient airfoil horizontal cross-section. The sail is formed from a sail panel which is wrapped around the mast and extends co-extensively aft away from the mast. An inflatable bag having a sleeve along one side is positioned within the sail panels with the sleeve over the mast. The sleeve is a narrow panel which wraps around the mast inside the sail and has edges substantially parallel to the mast which extend aft along the inside of the sail. The forward edge of the inflatable bag extends between the sleeve panel edges and is secured thereto such that the forward edge of the bag is pressed firmly against the mast when the bag is inflated. This arrangement prevents concave regions from forming immediately behind the mast when the sail is in use, which adversely affect sail performance.