NOVELTY - A rigid main sail (20) for extending in a vertical plane is supported for pivoting movement about a vertical axis (34). The main and auxiliary secondary airfoils (42a, 42b) are mounted to the main sail so that the airfoils are spaced outwardly from the plane of main sail on opposite sides of main sail. The vertical shafts are arranged for selectively pivoting the airfoils in two different directions relative to a main plane of the main sail, so that the airfoils react with wind passing over to exert a force tending to pivot the main sail in different directions about vertical axis.    USE - Steerable type wing-type sail system of wind powered vessel for use on autonomous unmanned surface vessel (AUSV).    ADVANTAGE - The secondary airfoils are at an elevation close to the vertical center of effort of the main sail, and thus experience the same wind velocities and wind directions as the wing itself. A difference in the apparent angle of the wind to the direction of the vessel's movement is created at different heights above the water. The lateral displacement of the secondary airfoils removes them from the disturbed downwash air that results from the main wing producing lift. The secondary airfoils are able to produce lift much more efficiently, thus permitting smaller and lighter airfoils to be used, and they are also able to produce a smoother, more consistent pivoting action. The forces of drawing the ends of the booms together are selected to be greater the anticipated wind loads, so that the cables can never develop slack during operation. The preloading provides a bracing that eliminates the flexing that can otherwise occur in a cantilever situation. The vertical shafts that support the secondary airfoils are located as near as possible to the aerodynamic centers of the airfoils, thus reducing steering cable tensions and motor control requirements. The pivot shafts are mounted to crossbars, which have ends that extend generally laterally on either side of the airfoils. The crossbars preferably extend perpendicular to the support booms rather than to the secondary airfoils themselves, to simplify the arrangement of the cables and controls. The amount of the turning force exerted on the main sail can be adjusted by increasing or decreasing the angle of the secondary airfoils as desired, e.g., a greater degree of inclination can be used to turn the wind rapidly to make major changes in alignment, or to overcome resistance due to environmental or mechanical conditions, while a lesser degree of inclination can be used for fine adjustments or minor corrections in alignment.    DETAILED DESCRIPTION - An INDEPENDENT CLAIM is included for wind powered vessel.    DESCRIPTION OF DRAWING(S) - The drawing shows an end, elevational view of the vessel and steerable wing-type sail system.    Main sail (20)    Vertical mast (30)    Vertical axis (34)    Main secondary airfoil (42a)    Auxiliary secondary airfoil (42b)