Science of fins helps athletics of surfers

(Ed. Note: this is the second of a two-part series).

Surfboard designers typically look to three main sources for inspiration and innovation: aeronautics, hydrodynamics, and nature. Looking at the wide variety of fins currently in use, we see silhouettes resembling the dorsal fins of dolphins, boat keels and airplane wings. All are ultimately designed with one goal in mind … to generate and maintain speed through turns.

There are seven standard properties to a fin that give it not only its unique characteristic and shape, but determine its performance in the water as well. Some are used singularly, others as part of a cluster. Fins are selected as a complement to the board’s overall shape, however, in this day of interchangeable fins, additional factors are considered such as the type of waves to be ridden and the individual surfer’s style, size and ability.

The fin “template” refers to the outline shape of the entire fin, which determines how the board will function through turns and its resistance against the force of moving water.

“Depth” measures how tall the fin is from top to bottom, or conversely, how far the fin penetrates into the water. Less depth means less resistance. With a deeper fin, the board will move faster through the water, but will have less holding power when turning. More depth will increase a surfer’s “hold” in the water, but will feel stiffer and more difficult to turn.

“Base Length” is the distance measured of the fin where it sits on the surfboard. Increasing the base length can give the board added drive forward, but will also stiffen the board’s turning radius.

A fin’s “rake” is the distance from which the tip of the fin extends beyond the trailing edge of the base. For example, a boat keel has little to no rake, while a fin more representative of a dorsal fin will have more curve, or rake. More rake adds traction and allows for longer drawn-out turns, while less rake makes for tighter, snappier turns.

“Foil” gives the fin its three-dimensional quality, or shape. Like an airplane wing, the foil creates lift, allowing surfers to gain speed through their turns. Middle fins will have a symmetrical, horizontal curve, while side fins will have curve on their outer edge, and a straight profile on its inner edge. Therefore, on a thruster, if you were to put the two outer fins together, they would create a single-fin silhouette, meeting flush on the inside, with the curve apparent on either outer edge.

The “tip” is considered the upper third of the fin. More tip area increases the board’s holding power while turning; less tip makes the board pivot better in the pocket.

Finally, one needs to consider the fin’s “flex.” This determines the fin’s pliability. Hold the fin in your hand, with the tip going away from you. Wrap your fingers tightly around the foil, and with your thumb, push on the tip. How much movement or play in the fin’s tip determines its flex. Rigid fins, exhibiting less resistance against the water (like against the thumb), go faster. However, too rigid, and the rail will “lock” into its line, making it difficult to change direction at any speed. Too much flex, and the board will succumb to the water pressure. Drive is drastically reduced and the board will simply “flop” in the water. Much like a well-stringed tennis racket, or a good golf club, the right amount of flex gives the board a lively, positive, springing feeling, helping to wrap the board around after a turn.

The board shape will also determine the proper flex to use in a fin. Surfboards with more “vee” in the bottom (like the bottom of a speedboat) already offer resistance against the water, so surfers should consider a more flexible fin. Boards with a concave bottom give less resistance against the water so a stiffer fin is more desirable.

According to La Jollan Tyler Callaway, director of business development at Fin Control Systems (FCS), fin design is and must continue progressing alongside surfboard innovation and athletic performance. “For the past 5-6 years, surfing has moved in an ‘aerial direction.’ This has pushed innovation towards surfboards that can generate more speed. To that end, we’re becoming more interested in foil design and how that can continue to progress this element of the sport.”

Continues Tyler, “The surfboard industry is particularly unique in that we have three areas consistently working together to create a vision of the future in surfing: performance (athletic influence), design (boards and fins working together) and technology (engineering, materials and integrated construction). We’ve only scratched the surface of what’s to come in terms of materials used and influences to draw from.”

If you’d like to feel your board perform differently, contact FCS, 858-300-2640 and ask for the nearest “Test Drive Center,” found in local surfshops. There is no fee required, only a deposit.