Fin Specs and Performance
This is a brief review of the various characteristics of surfboard fins and how they impact the way a surfboard handles.
Goals of Surfboard Fins
Simply said, fins will help you accelerate out of turns if you put enough pressure against them. While fins produce drag for a board going straight, the water surging against a fin in mid turn will produce a feeling of acceleration. This is known as drive. The best analogy to use is a swimmer approaching a pool wall, preparing to hit the wall and catapult in the opposite direction. Springing off the wall is similar to laying into a turn and applying a lot of pressure against the fins. Both actions will accelerate the athlete out of the turn. This is drive.
This is the force on a fin that provides vertical lift. Fin cant increases fin lift. The greater the lift, the greater the hold a fin will have in a waves face.
Hold prevents a surfboard from sliding out during turns.
Characteristics of Surfboard Fins
Measures the two-dimensional area of a fin in square millimeters. Larger surfers will need more area to provide necessary hold, while smaller area will result in a looser board. It is important to experiment with area to find a fin that will hold in the wave while also being loose enough for your liking in the water.
The length of the fin where it meets the board. Fin base affects the drive of the board. The longer the base, the more surface area a surfer has to push against the wave, producing more drive. Fins with a smaller base will have a shorter turning arc.
Measures how far a fin penetrates the water. Depth influences drive and hold. A fin with shorter depth will offer more slide to a surfer. Longer depth will produce more hold. This is especially true of center fins.
This is a fancy way of identifying how far the fin curves backward. The degree is measured between a vertical line extending straight upward from the midpoint of the fin's base to the line connecting the midpoint of the base to the fin's highest point. A higher degree sweep produces longer arcing turns while less sweep allows more of a pivot movement.
Flex is the amount a fin will bend from the straight position. A fin with more flex will be forgiving loosening the board while a stiffer fin will respond better, improve speed and drive. A fin with a stiff base with a more flexible tip is an ideal setup.
This is the outline of a fin's shape. It includes the depth, area, base, and sweep of the board.
This is the shape of the fin if you were to look at it upside down, staring at the bottom of the fin. Some foils are totally symmetrical, where the inside surface and outside surface are curved exactly the same. Other foils are asymmetrical, having one surface shaped differently than the other. Foil affects the lift and drag of a fin similar to how an airplane wing’s foil creates lift.
The angle of the side fins in relation to the stringer.
This measures the degrees in which a fin leans away from being totally perpendicular to the board's bottom surface. Picture the fin leaning toward the outside rail or toward the middle of the board.
Angle of Attack
The fin's angle in relation to the water moving around it.