Abstract: The sail rig comprises a quadrangular sail. A mast sleeve is arranged through the sail area from head to the foot and a flexible mast of flat cross section is inserted therein. A wishbone or a single-boom is connected at the fore to the luff clew and at the rear to the aft leech clew. Owing to the curvature or camber of the sail, its periphery is subject to higher tension than the remaining surface. Therefore, even after rigging up, the sail will not only curve horizontally, but also vertically. When exposed to wind, the sail will form a harmonic compound shape having its concave side to windward. The mast connected to the sail by the mast sleeve bends in the same direction as the sail. The tension around the periphery produces a triangulation effect in conjunction with the mast, similar to that of stays, thereby preventing the mast head from deflecting to leeward. The tension forces of the sail acting upon the mast are balanced and negligible. It is thus possible to build a lighter and more flexible mast.