A Guide to Surfboard Fins.

Similar in form and theory to the keel on a boat, the fin helps to give a surfboard stability, drive, and manoeuvrability. And like the keel, how much of each it provides depends on both the design of the fin and its arrangement. Below is a brief and simple guide to fin design, fin arrangement, and fin types.

(Note: how useful you find this guide will depend on your ability; if you are a beginner surfer, this information, for the meantime, will be largely academic; if you are an intermediate surfer, this information should serve as a starting point for your own research.)

Fin design.

The main terms that relate to fin design are: toe, cant, foil, rake, flex, base length, and height.

Toe. Toe refers to the angle of a board’s side fins in the relation to the board’s stringer ( the stringer is the strip of wood that runs through the middle of a board, from nose to tail, to give the board strength). Most side fins are set with their front angled inward toward the stringer (known as toe-in). Toe-in causes water to pressure the fin’s outside surface, which helps make the board easier to manoeuvre.

Cant. Cant refers to the angle of a board’s side fins in the relation to the board’s base contour. If a fin is set perpendicular to the base it has no cant; if it angles toward the board’s rail it has cant (imagine the fin as the hand on a clock: either side of 12 and the fin has cant). Cant effects a board’s manoeuvrability and drive; more cant means more manoeuvrability but less drive, while less cant means less manoeuvrability but more drive.

Foil. Foil refers to the aerodynamic shape of the fin. Most fins are foiled (curved), so that the thickest part of the fin is in the middle, while the thinnest part of the fin is around the edges. Typically, side fins are foiled on their outside surface (the surface facing away from the stringer) and flat on their inside surface, while centre fins are foiled on both sides. The idea is to create lift under the surfboard and help propel it most effectively in different wave conditions. The more pronounced the foil, the more lift it will provide. Unfortunately, this also causes more drag on the board, which slows it down.

Rake. Rake refers to how far back the fin curves in relation to its base. To find a fin's rake, imagine a flat line continuing out from the base of the fin; next imagine a line that extends from the back of the fin base to the very tip of the fin. The angle that these two lines form where they intersect at the back of the fin base is the rake. A fin’s rake affects both drive and manoeuvrability; fins with small rakes offer more drive but less manoeuvrability, whereas fins with large rakes offer more manoeuvrability but less drive.

Flex. Flex refers to how flexible (or how stiff) a fin is. A fin’s flex affects stability and manoeuvrability; a fin with less flex will offer a board more stability but will make a board harder to manoeuvre, whereas a fin with more flex will offer a board less stability but will make a board easier to manoeuvre.

Base length. As the name suggests, base length refers to the length of the fin’s base. As with most of the terms above, a fin’s base length affects drive, stability and manoeuvrability; a fin with a long base offers a board more drive and stability but less manoeuvrability, whereas a fin with a short base offers a board less drive and stability but more manoeuvrability.

Height. Another self-explanatory term, height refers to the fin’s height. A fin’s height affects a board in much the same way that a fin’s base length does.

Fin arrangements/setups.

Below are the three most widely used fin arrangements/setups.

Single Fin (one fin). A single fin setup is typically found on longboards. The fin itself will usually be much larger than the fin’s used in a multi-fin setup. This setup offers more stability but less manoeuvrability.

Twin-fin (two fins). A twin-fin setup consists of two side fins only. Typically, the fins in a twin-fin setup will be larger than the fins in a thruster setup (more on that next). This setup makes a board much easier to manoeuvre than a single fin setup; however, the absence of a middle fin means that the board is much harder to control.

Thruster (three fins). The thruster setup combines, in a sense, the single fin and twin-fin setups (albeit with much smaller fins than both setups). It provides a more equal balance between stability and manoeuvrability. It is the most common fin setup.

Fin types.

There are two types of fins: Glassed-in and Removable.

Glassed-in. Glassed-in fins are laminated to the board permanently, making them structurally more sound than removable fins. However, in a practical sense, their benefit is also their drawback: you will never need to attach your fins before a surf; however, you will never have the option of changing your fins. Glassed-in fins also make a surfboard more susceptible to damage when travelling or storing.

Removable. As the name suggests, removable fins can be removed (or attached) to a board. Removable fins offer a surfer more options in terms of fin combinations, as well as making a surfboard less susceptible to damage when travelling or storing. The drawback of removable fins is that they are much more easily dislodged than glassed-in fins.