FF Fat Boys are designed for boards where it is difficult to hold the tail in while turning hard or nose riding. The foil is thick at the base thin in the middle and thick at the tip creating a bulb. The water flowing over the bulb holds the tail of the board in the water more than the conventional foil due to water pressure. :: Unisex > Surf Accessories. Board is held in the water substantially more than a conventional fin due to hydrodynamic\n water resistanceUnique foil and bulb-like tipDesigned for on-rail performance and nose riding Size: one size.