A Flat Foil refers to an even levelled surface on the inner side of the fin. The use of a traditional flat foiled fin when formulated with the convex shape of the outer side of the fin provides a well balanced combination of acceleration, pivot, drive, quick release and hold. The flat foil suits the majority of surf conditions and the most common preference between surfboard shapers and pro surfers.
A inside foil refers to the curvature of the inside face of a fin and the leading rounded tip of the fin. An inside foil increase the dynamics of water flow over the fin surface, in doing so creates a tighter turn arc and fast transition between turns.
A 50/50 Foil is most commonly used in rear quads and centre thruster fins. A 50/50 foil is a symmetrical curve on both sides of the fin, the foil evenly distributes the flow of water that creates smooth feely ride, add stability and control.
An 80/20 or 70/30 foils are generally used in side fins (2+1 set ups) in longboards or quad rear fins. The foils offer a smooth transition between turns and rail-to-rail transition that suit a variety of surf conditions.
The base is the area between the front and the back of the fin. The amount of base determines the amount of drive and acceleration. The longer the base the more drive, acceleration and hold a fin will provide
Depth refers to how much a fin penetrates the water and determines a board’s directional control. More drive and hold through turns is achieved through greater fin depth whilst shorter depth will accentuate speed and release.
Sweep is also referred to as “Rake”; it is the measuring of how far the lead edge (Front) of the fin is curved backwards. The amount of rake influences the length (or arc) of a turn, where less sweep allows for tight pivotal turns and an increased sweep allows the board to sustain longer turns.
Flex refers to the amount of fin that is distorted from its original position, which occurs during a manoeuvre. Flex is influenced by the characteristic of the stiffness; a stiffer fin will creates drive and allows for a progressive flex pattern which alters acceleration, speed and release.