Definition: Fins act as keels under a surfboard. They dictate both direction and maneuverability. Fins can be made of fiberglass or plastic and can be glassed in as a permanent fixture or screwed in with a special system that allows removal at your discretion. The most basic configurations for fins are in groups of four, three, two, or even as a single entity. Some fins are flexible and allow more play as a surfer turns his surfboard while other fins are rigid and keep the surfboard on a more true trajectory. Surfboard fins come in different lengths and shapes.
Also Known As: skegs
When the surf is really small, I take out my third fin, so my board turns more quickly.