Abstract: A highly efficient sailboard shape has a full displacement form for efficient light and upwind sailing and has an efficient planing form for high wind sailing with the conversion from displacement to planing forms caused by the buoyance reaction to aftward weight shift.

Abstract: A low drag and high lift sail has a fabric skin suspended by an edge tension device able to control forward and trailing edge tension to tune and reverse the airfoil section. The fabric skin is double, with a windward and lee section of different curvatures giving the airfoil section thickness. The sail is supported by a mast and a curved boom located between the two fabric sections and thus is out of the impinging air stream. The ends of the boom are used for the sail support, usually with an additional external spar or spars on the windward side. The mast includes a foot which is either fixed or attached by a universal joint to a craft for motive power.