How base, rake, sweep and other properties affect your fin
The effect of surf fins on the board's riding characteristics depend not only on the number of fins (twin fin, single fin, thruster, ...) and their set-up, but also on the shape of the fin. In the following we explain the main terms that describe the shape of a fin.
Fin Size
The size of the fin influences the performance in the water. In general, a larger fin provides more support and control. While smaller fins are more maneuverable, but lose drive and grip in larger waves.
Height / Depth
Height describes the size of the fins. This is measured from the base to the highest point of the fin. Larger fins provide more grip in the water, so the higher the fin, the less maneuverable it is in the water. Shorter fins offer less grip in the water and therefore more maneuverability / release. Hence, the relatively large single fins are designed for long, smooth turns, while the smaller fins (such as the Thruster) are designed for fast, tight turns.
Base
The base of the fin is measured from the lowest front point to the rearmost point of the fin. It measures the entire surface with which the fin is placed on the surfboard. The length of the base affects the drive that can be achieved by the fin, in the water. A longer base provides more surface area for pushing and therefore more speed / drive but less maneuverability. It is suitable for long drawn out turns. A shorter base, on the other hand, offers less speed but is easier to turn.
Rake / Sweep
Now it gets a little more complicated. Rake is the length of the leading edge of the fin (see graphic). Sweep is the angle from the center of the base to the highest point of the fin. Rake and sweep are measured differently, but are directly related. A smaller rake (i.e. shorter leading edge) provides a very stable feel. The fin looks upright and straight. This shape means less pivot. Pivot describes how well the board turns on a point. A longer rake, on the other hand, makes for more turns and provides a looser feel in the water.
Flex
The flex of a fin also has a great impact on its behavior in the water. The more flexible the fin, the more 'playful' it behaves in the water. Softer fins bounce back faster after a turn, giving this energy into your turn. Less control, more freedom. The feel is closer to a 'skate feel'. Stiffer fins offer more stability and are therefore better suited in high, steep waves. In general, stiffer fins are suitable for beginners as well as advanced riders. While a lot of flex is well suited for fast, progressive surfing. The flex of a fin depends on its material and its shape.
Fin Foil / Finnenprofil
If you look at the wings of an airplane, they are not straight from front to back, but have an aerodynamic shape that provides lift. It is the same with the foil of surf fins. Normally, a fin gets thicker towards the middle and tapers off flatter towards the edges. A 'bulbous' bulge.
Depending on the fin (single fin, twin fin, thrusters, ...) the fin profile differs. Side fins are often flat or slightly curved inward on the inside.
There are several types of fin foils with many variations of each. Side Fins (on Twins, Thrusters, and Quads) are usually flat, sometimes curved inward on the inside, with a foil on the outside. Center Fins usually have the same foil on both sides, this is called symmetrical or 50/50.
Fin Cant
Cant refers to the angle at which the fin is positioned on the board. If the fin is straight on the board (0 degrees cant / angle), this ensures fast straight-line driving. However, the fin behaves less responsive in turns. A larger angle (cant), on the other hand, ensures that the board retains more drive in turns.
That was a lot of information about the geometry and shapes of the fins. Besides the shapes, there are also the different setups of the surf fins, which are suitable for different boards. Should you still be looking for the right fin, check out our sustainable surf fins....