A surfboard fin is a foil (see Foil (fluid mechanics) ), specifically, a hydrofoil that is mounted near the tail of a surfboard such that it is more or less perpendicular to the bottom of the board. The fin provides lateral lift (See Lift (force))opposed to oncoming water as a surfer rides a shoaling ocean wave, and also stabilizes the surfboard's trajectory, and as a result of the effects of the foil, fins are used (along with the bottom of the surfboard) as control surfaces by the rider. Surfboard fins were thus an important advancement in the maneuvering performance of surfboards. Surfboard fins may be arrayed in various number and configuration, and many different shapes, sizes, and materials are and have been made and used.
Surfboard Fins were invented in Hawaii, along with the surfboard itself. They are now more or less universally used on surfboards.
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Glass on fins[1] are fins that are permanently connected to the surfboard through fiberglass. This type of fin was mainly used on older model surfboards. Glass on fins are broken easily and are hard to repair. You rarely see these types of fins today because a different type of fin has replaced them.
Removable Fin Systems[2] The most common types of fins used today, removable fins are surfboard fins that can be unscrewed from the surfboard and be replaced by different fins or be moved about the board for a different setup in maneuverability and stability.
Flexible fins [3] fins are used on most rental boards because of liability. These fins are much safer than a hard fin because they cannot cut you. However it does lose some of the performance.
Tom Blake[4](One of surfing most influential fathers) invented the first fin used on a surfboard. Although Blake’s first fin was most like attaching a keel from a boat to the bottom of the board, Blake’s finding started the development of the fins in use today.
From Blake’s first fin, people, perhaps most famously Bob Simmons and George Greenough, have modified and invented new types of surfboard fins. Simmons was apparently the first to use more than one fin on a surfboard. Greenough made the fin flexible and took inspiration from the fins of fish(allegedly tuna) and dolphins. Bob Simmons used a twin-keel design on innovative wooden boards of his own design and manufacture in the 9'-10' range, which he rode in large surf at Windansea in California.
In the 1970s, multi-fin systems became much more widely-used, in competition and by average surfers, as top professionals like Larry Bertlemann and Mark Richards enjoyed competitive success maneuvering shorter boards with twin fins in smaller surf and tighter radius turns.
It wasn’t till the 1980s that Simon Anderson invented the popular thruster set-up (three fins - two on the rail 10-12 inches from the tail end, one center fin 3-5 inches up from the tail) which stabilized the board compared to the twin-fin set-up, and provided more control and lifting surfaces in an effective configuration. The design was an immediate competitive success for Anderson, inasmuch as he immediately won 2 very famous surf contests using "thrusters," and the entire surfing world quickly followed his lead. The thruster is the dominant fin configuration to this day, in both recreational and competition surfing.
The single fin setup is the original fin setup. Single fin setups are common on long boards. They are usually long and wider than other fins, which make the board controllable with only the one fin.
The twin fin setup has two smaller fins mounted near the rail. This setup provides extra speed and easier turning.
The most common setup, the "thruster" is a tri-fin. All the fins are the same size, with two semi-parallel (slightly toed-in, usually, and slightly canted outward, usually) fins mounted near the rails 10-12 inches forward of the tail and a middle fin at 3-5 inches.
The 2+1 denotes a larger center fin (for reference, larger than a thruster center fin) with 2 small to medium-small fins at a position close to thruster rail fin positions. The "sidebites" contribute some lift, control, and stability to the board when it is "on rail," arcing through turns. Typically, "sidebites" are removable, so the surfer can take them out for use in smaller waves, which gives less drag and freer turning. The 2+1 is a popular configuration for mid length to long boards.
The quad setup is four fins, two on each side, in a similar position to the rail fins on a thruster. The fronts are typically larger than the rears but this is not always the case. The rears are nearly always inboard and aft of the fronts . The exact measurements and configuration of the quad set-up can vary pretty widely. This setup is often used in short boards and provides more lift and control surface near the rail. There is no center fin.
The Twinzer is a design by Wil Jobson and similar to the Campbell brothers' "Bonzer," the fin set-up is held to be functionally integral and synergistic with the bottom contours of the board, specifically a "bat-tail" with an integral convex/double-channel. The fin set-up itself is four fins, two on each side, in a similar position to the rail fins on a thruster. The fronts are smaller than the rears, often roughly 1/3 the size, mounted ahead and outboard of the fronts, with ~8 degrees of outward cant, and notably, the fins' trailing edges are behind the leading edges of the main fins. The water coming off the trailing edge of the "canards" becomes part of the flow "behind" the main fins. This fact is held to enhance the lift and speed of the set-up, because of the "slot effect." The exact measurements and configuration of the twinzer are basically standardized by Jobson, but some variation is seen amongst different builders.
See Tunnel fin.
The Bonzer is a 3- or 5- array invented by the Campbell brothers in Oxnard, California in the early 1970s for the powerful waves of a well-known wave near their home. The Bonzer array is an approximately 7" center fin aft and either two or four delta-shaped fins ("runners") mounted near the rails in somewhat similar fashion to other rail fins, but they are substantially lower aspect and aggressively canted outward. The Bonzer array is firmly held to be an integral part of the Campbell brothers' overall board design featuring double concave bottom contours out the tail.