Abstract: An apparatus for improving the flow of air past the headsail (5) of a sailboat including an airfoil (41) which is oval-shaped in cross-section, the leading edge of the sail being secured in a groove (45) along one side thereof. A portion (37 or 39) of the curved surface of the airfoil (41) extends into the wind, with the surface (37 or 39) curving toward the inner side of the sail, forming a wide leading edge for the sail. The airfoil (41) may be rotated about the leading edge of the headsail as necessary, depending on the direction of the boat relative to the wind.