Abstract: A slot-forming foil enhances the performance of sailing yachts without jibs. A two-part foil is provided, including a forward foil section and an aft section pivoted to the forward section and having alternate, toggled working positions. In either working position, the two-part assembly forms a foil of principally convex airfoil contours on the leeward side and principally concave airfoil contours on the windward side. The entire assembly forms a slot in conjunction with the luff of a working sail of the vessel, improving performance and tacking angle.