A structural element, usually made of wood or fiberglass, attached to the bottom of a surfboard to aid maneuverability. Fins were first introduced in 1935 by Tom Blake, who fastened a speedboat keel to the tail of his board. The modification, which prevented the board from haphazardly sliding down a wave’s face, led to modern surfing as we know it.
Perhaps more than any other factor, it’s the number, angle, base width, and rake of a surfboard’s fins that determine how it rides. In the late 1940s, Bob Simmons stuck two parallel fins on the bottom of his board, creating a looser, more squirrelly ride. Three decades later, in 1981, Australian Simon Anderson assembled the first “thruster” setup by adding a third fin behind two forward fins, combining the best of single- and twin-fin approaches. Today it’s by far the most popular design.