Fin Specs and Technical Terms

We have created a brief compilation of the various technical terms used in surfboard fins technical lingo, to help learning about surfing fins technology.  To learn about not only the lingo and terms used in the industry but also how those terms that translates on the way a surfboard behaves, and how is affecting you to choose your equipment.

Remember that how a surfboard behaves does not only depend on its fins but it also depends on the combination of many elements like: the shape of the board, its size, the shape of the bottom of the board, how you surf, what kind of wave you surf.

Here is a few terms just about the fins´ part of the puzzle.

PHYSICS & FORCES INVOLVED IN SURFBOARD FINS

Drive

Drive is said to how much the fins help you accelerate out of turns if you put enough pressure on them against the water. While fins by definition will produce drag for a surfboard going straight, the water surging against a fin in mid turn will produce a feeling of acceleration. This is known as drive. 

Lift

Is the force that acts sideways on the fin as air would on an airplane wing but instead of vertically it acts horizontally. It´s direction is forward and sideways. The lift depends on the shape of the fin. The greater the lift, the greater the hold a fin will have in a waves face.

Hold

Hold prevents a surfboard from sliding out during turns. It is a sideways force and it is part of the combination of forces a fin when surfing and having water pressuring on the fin.

Drag

Is the force slowing you down form the friction with the water.

SIZE & SHAPE OF THE FIN

Area

Measures the area of a fin in square millimeters, base by height. Larger surfers will need more area (bigger size fins) to provide the necessary hold, while smaller area will result in a looser board. It is important to experiment with area and the size of waves you ride to find a fin that will hold in the wave while also being loose enough for your liking it with that size of waves.

Base

Is the length of the fin on the part that is on the board. Fin base directly affects the Area of the fin and thus the drive of the board, the hold, the drag.... etc. The longer the base, the more surface area a surfer has to push against the wave, producing more drive, and making it more difficult (harder) to turn. Better for higher and faster waves where the turns are more rounded. Fins with a smaller base will have a shorter turning arc, being better for smaller waves.

Depth

Is the other component that affects the Area of a fin along with the Base size. It measures how deep a fin goes in the water. Depth as the base size influences drive, hold, drag... etc. A fin with shorter depth will offer less resistance to turning, so you can turn the board easier and the surfboard will feel more loose. A longer depth will produce more hold, better for bigger and faster waves.

Flex

Flex is how much the fin will bend from the straight position when a certain amount of pressure s applied (for instance when you do a bottom turn). A fin with more flex will be more forgiving while surfing, loosening the board a bit on slides and turns. On the other hand 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.

Sweep

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.

Template

This is the outline of a fin's shape. It includes the depth, area, base, and sweep of the board.

Foil

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.

Toe Angle

The angle of the side fins in relation to the stringer.

Cant

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.