Surfboards may have any number of fins, usually 1 or 3, and there are valid design points (and fans) for the different combinations and designs. Without a fin a surfboard would slide sideways and be almost uncontrollable. A fin creates resistance to the water allowing the surfboard to be turned and to travel across the face of the wave without sideslipping.
Single Fin are mainly used on beginners surfboards where control and not performance is the main criteria. Single fins are also used on modern longboards and on some big wave guns. The deeper the fin and the larger its area the more control the rider has. However if the fin is too big it will cause drag and may eventually make the surfboard harder to turn. An optimum size would be 6″ – 10″ deep with a 6″ – 8″ base. Upright fins allow the surfboard to be pivoted around them in a turn whilst raked fins provide better control at higher speeds. Single fins are generally 6″ – 8″ from the tail of the surfboard (to the rear of the base) and are foiled to present excess drag.
Twin (2 Fins)
Twin fins are usually used on retro style surfboards. Twin fins tend to make the surfboard very loose but difficult to control in certain situations, especially in large waves.
Thruster (3 Fins)
Thruster is used in the vast majority of surfboards. Thruster design has been found to perform best for most people, on most surfboard designs, in most surf conditions. The 3 Fin set up gives good manoeuvrability, holds in well and makes the surfboard feel very stable. Generally the fins are about 4″ deep with a 3″ – 4″ base. The forward fins have their bases angled towards the nose of the surfboard and their tips further apart than their bases. These features enhance the speed and manoeuvrability of the surfboard and prevent the surfboard tracking. The rear fin is foiled normally but the front fins have flat inside faces to improve drive whilst turning.
Quad (4 Fins)
Quad fins are excellent on Fish surfboards and have the characteristics of thruster and twin fins being that they are relatively stable and also easy to maneuver. Perfect for performing circus stunts, great for the trickster.
With a 5 fin setup most people do not have all 5 fins at once fitted in their surfboards at one time. Suited for the surfer who can not make up his/her mind what style of surfboard they would like. Many surfboards have this option due to not being able to decide on the surfboard style and wave conditions. Yet to be convinced of its merits.