Captain Fin: CF Keel Twin Fin (Twin Tab) - Yellow The CF Keel is a house made design that blends a balanced approach for retro twin trimming. The wider base and lightly swept outline creates hold, drive and makes for fast, smooth arcs on an open face. DETAILS: Template: Drive—perfect, balanced template for any retro twin. Construction: Fiberglass Flex: Stiff Compatibility: Compatible with Captain Fin Snap-In fin system without screws and FCS II using the provided screws. Fin Specification Area 25.99" Height 5.35" Base 6.2" Foil Flat