FCS FCS ARC tri fins are known for exceptional drive and maneuverability. The FCS ARC fins are great for long arcs, down the line surfing, or in boards with wider tails and a lot of rocker. With Inside Foil Technology, these fins are geared towards medium and smaller surfers. Performance core material and construction is designed to deliver the feeling of a traditional glass fin with the added performance of reduced weight. The result is a lightweight fin with remarkable flex, a smooth feel and an impressive aesthetic.