Surfboard fin

A surfboard fin or skeg is a hydrofoil mounted at the tail of a surfboard or similar board to improve directional stability and control through foot-steering. Fins can provide lateral lift opposed to the water and stabilize the board's trajectory, allowing the surfer to control direction by varying their side-to-side weight distribution. The introduction of fins in the 1930s revolutionized surfing and board design. Surfboard fins may be arrayed in different numbers and configurations, and many different shapes, sizes, and materials are and have been made and used.

History

Traditional Hawaiian surfboards had no fins. On these boards, some amount of control could be achieved through convex hulls and the surfer dragging a foot in the water. A common problem with these early boards was "sliding ass", in which the tail would slip sideways, usually causing a wipeout. The first fixed fin was introduced by surfing pioneer Tom Blake in 1935. In Waikiki, Blake attached a long, deep metal keel from an abandoned speedboat to his surfboard, and was immediately impressed with the results. Around 1936, Woody Brown independently added a fixed fin to his second surfboard design in San Diego, which further popularized the feature.
The stability and control fins allowed revolutionized the sport, though many surfers avoided them for several years. The feature grew more common in the mid-1940s and became the universal industry standard in the 1950s. Experimentation with fin design and configuration increased after 1966 with the popularization of shortboards. Parallel double fins, first introduced in the 1940s by Bob Simmons, became periodically popular. In 1980, Simon Anderson introduced the three-fin "Thruster" design, which has since become standard.

Configurations

In surfing, there are two major types of surfboard fins, and a host of illustrative issues.
Both a skeg and "rail ''fins" stabilize the motion of the surfboard. They also contribute to the desired effect of converting the push of the sloped wave face combined with the rider's mass on the sloped wave face into redirected energy – lift – the surfer deflects his surfboard and fins off the water of the wave face to make forward progress across the wave face, or "down the line," that is, parallel to the wave crest and beach – riding parallel to the crest in this way is known as "trimming." Lift from the board and its fin is what enables all maneuvers in surfing.
A "skeg" typically denotes one centrally mounted stabilizer foil mounted perpendicularly to the riding surface, at the rear of the surfboard.
Smaller surfboard fins mounted near the edge of the surfboard are known as "rail fins" and are seen in multi-fin arrangements. Rail fins enable high-performance surfing, and are most often "single-foiled," with one flat side and one "foiled" side, as seen on an airfoil, for greater lift.
A fin configuration with fins near the edge of the board stabilizes and contributes lift during turning maneuvers, which contributes to the board's ability to "hold" during turning maneuvers. Rail fins are often seen in addition to a central fin, but can be used without a central fin as well. Some of the most popular multi-fin configurations use two rail fins, two rail fins plus a similar-sized central fin mounted further back, or four fins. Rail fins are more or less engaged by the rider's heel and toes as they lean in the desired direction of their turn. As the rider does so, an "inside" rail fin sinks deeper and its angle of attack is increased, as is its lift-induced drag. Rail fins also add lift in trim and with greater holding ability, enable steeper wave faces to be ridden and higher speed "down the line."
Rail fins are typically "toed-in," that is, the leading edge of the fins are oriented toward the centerline of the surfboard, which decreases the angle of attack in trim, which makes it easier to initiate turns. "Toeing in" rail fins also adds drag on the "outside" fin, as its angle of attack is negative during trim or in a turn. These combined factors of toed-in rail fins cause several issues: drag on a toed-in outside rail fin can slow the board down in trim, but it can also give a braking effect during turns that is useful. The inside rail fin can be "pumped," attacked and re-attacked, by swerving up and down the face, causing acceleration down the line, or similarly pumped to achieve a desired trajectory through a multi-stage turn. At higher speeds, the drag off toed-in rail fins can cause surfboards to oscillate and become unstable – a phenomenon known as "speed wobbles".
Most surfboards intended for larger waves are longer, and as most shapers orient the rail fins toward the nose of the board, a longer board inherently results in reduced toe-in of rail fins, therefore less negative angle of attack, less oscillation, greater stability, and higher speeds.
Rail fins also typically have some degree of "cant," that is, are tilted out toward the rail they are adjacent to. This is a significant additional factor in lift at various attitudes, drag, and performance, as are the variables of other foils – including flexibility, thickness, and planform.
Rail fins evolved into being and surged into popularity as riders sought a solution to two major performance issues of a central "single" fin – both related to engagement of the foil: For one, a centrally''-mounted fin is tilted up out of the water as the board is leaned over, and thus it loses more and more of its lift as the lean angle increases – if the lean angle is acute enough, the fin's tip can be the only area left in the water; the tip may then rapidly stall and, having lost its lift, become disengaged from the water, leaving the board's bottom as the only control surface still operating. Before rail fins became popular, this tendency of "single fins" led to riders "nursing" turns – this tendency was a significant limiting factor on performance. The enhanced hold offered by rail fins during turning led to more types of maneuvers being possible.
The other major issue leading to rail fins' use is the fact that a rider can use the lift near the rail to increase speed and performance on smaller waves due to the above effects and abilities of these foils.
Conventional statics fins suffer from the inability to have a camber and attack angle always adapted to variations trajectories. The angles given to rail fins are a compromise generating straight drag and oppositions in maneuvers. The center fin merit of being able to adjust its suction face and its angle with the direction of the turn to avoid the hydrodynamic stall. The fin camber and attack angle needed to accord to the different phases of trajectory. When turning left or right the fins need to adjust the camber and attack angles to avoid hydrodynamic stall, so the Adaptive Dynamic Attack & Camber system brought a solution to this hydrodynamic problem. This surf fin technology introduced adaptable structures with variable geometry inspired by aeronautics and biomimetic in the surf.
In Windsurfing, a derivative of traditional surfing, skegs are also often used as a central stabilizing fin located at the rear of the board. A windsurfer's skeg also has the effect of producing lift, which allows the rider to direct the craft laterally against the lift the sail produces. The skeg has undergone numerous phases of development and, as with other foils, its design is determined by the balance of the pressures it experiences in use, including lift, drag, ventilation and stall.

Types

Glass on fins 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 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. In the early '90s, three Australian surfers invented the fin control system. The system also streamlined the surfboard manufacturing process by making it easier to install fins into boards and repair damaged fins. The leading competitor to FCS fins is Futures fins. Using a single larger fin box, the manufacturer claims the fins provide a stronger connection and more closely approximate the feeling of a glass on fin. Third, there is the US Box system that is still often used for single fin setups.
Flexible fins are used on most rental boards because of liability. These fins are safer than a hard fin because they reduce the risk of injury, although there is a loss of performance.
ADAC System Adaptive Dynamic Attack & Camber fins. bio-mechanics variable geometry fins able to adjust the attack angle and camber according to the various phases of the trajectory.
Materials Used Nowadays fins are normally made in Plastic or Fiber. Fiber fins are combining different materials to obtain better performance, and better weight and flotation ratios like honeycomb cores, bamboo core, and then glassed with fiber and sometimes reinforced with carbon fiber.

Production

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.
Bob Simmons and George Greenough later experimented with new types of surfboard fins. Simmons, regarded as the father of the modern surfboard, introduced multiple fins as one of his numerous innovations. Greenough made the fin flexible and took inspiration from the fins of fish.
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 was not until the 1980s that Simon Anderson invented the popular thruster set-up 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 two 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.