High Quality Content by WIKIPEDIA articles! A surfboard fin is a foil (see Foil (fluid mechanics) ), specifically, a hydrofoil that is mounted near the tail of a surfboard such that it is more or less perpendicular to the bottom of the board. The fin provides lateral lift (See Lift (force))opposed to oncoming water as a surfer rides a shoaling ocean wave, and also stabilizes the surfboard`s trajectory, and as a result of the effects of the foil, fins are used (along with the bottom of the surfboard) as control surfaces by the rider. Surfboard fins were thus an important advancement in the maneuvering performance of surfboards. Surfboard fins may be arrayed in various number and configuration, and many different shapes, sizes, and materials are and have been made and used.