FCS II Modern Keel Twin Performance Glass Surfboard Fins - Medium/Natural AlpineUpright keel template designed for traditional fish shapes. Overview Upright keel template designed for traditional fish shapes. Lower sweep (rake) than most conventional, wider based keels which allows it to pivot in a really tight radius. High area and depth not only delivers a feeling of control when pushed harder on the open face, but helps to maintain tremendous speed through roundhouse cutbacks. Board Types Designed to fit the FCS II Fin System.