Editor’s Note: Welcome to our new series, “By Design” with Sam George that examines the genius, and sometimes the mystery, of surfing’s storied design history. Sam has been writing about surfing for more than three decades and is the former Editor-in-Chief of SURFER magazine. He won an Emmy for his work on the 30 for 30 documentary, Hawaiian: The Legend of Eddie Aikau. Today, Sam looks at fin configurations and how they work on a surfboard.
For centuries our Polynesian and West African predecessors rode waves for fun on boards with no fins, as did 20th Century surfers up until the 1940s. For years local kids at Sandy Beach in Hawaii have been pulling into deep barrels riding pilfered McDonalds lunch trays, and anyone lucky enough to watch Mike Stewart ride a bodyboard at Pipeline in the 1980s and ’90s would admit that lack of a directional rudder is no hindrance to phenomenal performance. But while most surfers today will agree that having a fin or fins on the bottom of their boards is a good thing, very few of them can tell you exactly why – meaning very few can tell you how a particular fin or fin setup affects their board’s performance.
I intend to change that with these simple explanations of how your fin(s) work. I stress the ‘how’, not the ‘why’—you’ll get no mention of Bernoulli’s Principle, Newton’s Third Law or any references to arcane elements of hydrodynamic flow patterns. Rather just a basic description of the performance qualities likely to be experienced with today’s most common fin configurations. Feel free to click on your preferred fin manufacturer’s website for more detailed (read: sometimes head-scratching) analysis.
Apparently, Simon Anderson got it right the first time — since the Australian shaper/designer first introduced his original three-fin cluster in 1981 the placement pattern and standard template of the three similarly shaped fins (roughly 4.5” high, with the same length base) has remained virtually unchanged. So here’s all you really need to know: Fins with a broader base and tip template offer more surface area to push against, translating to more drive out of your turns. Better for bigger surfers. Fins with a more vertical rake (distance from leading edge of base to trailing edge of tip) will pivot quicker up the face and out of the lip. Fins with a longer rake and narrower template will draw turns out more, aiding down-the-line speed. Fins with more cant (outward tilt) turn up the face better but with increased drag they slow the board down. Plenty of tiny variations out there to choose from, but these are the essential differences.
There’s a complicated hydrodynamic equation that illuminates the performance characteristics of the four-fin (two thruster-size fins on the rails, two smaller fins offset behind) but the digest version reads like this: without any center fin causing drag they go really fast, and with two fins on the rail they really hold into the face, making them perform well in hollow waves. Popular mega-wave board designs for all the above reasons (make sure to take one next time you surf Peahi or Nazarè) in more mortal conditions shorter quads don’t pivot like a thruster and tend to draw your turns out, which can be a disadvantage in tight pocket, peaky conditions.
Canted significantly, generally deeper (approximately 5.0”) with a wider base (4.5”), flat-foiled and with less rake than a thruster or four-fin, the twin-fin is designed to pivot. With no center fin to cause drag and only one fin at a time fully engaged during a turn, the result is a board that’s super loose and easy to turn. This maneuverability, however, comes at the cost of some aspects of control. Modern twin keel fins (meaning those with a base longer than their height) offer more control and down-the-line drive, but are not as loose. NOTE: The keel fins found on traditional fish designs differ in that they’re set without any cant and are not toed-in toward the nose. Built purely for drive, they’ll really draw your turns out — just don’t try to go anywhere near vertical.
The standard configuration for performance longboards (and some popular mid-lengths), this set-up sees a deeper, center fin (7.5” to 8.0” for longboards, 6.5” to 7.0” for mid-lengths) with smaller (approximately 4”) offset fins on the rail. This provides the pivot qualities of a single fin, with added bite and drive off the side fins. Ideal configuration aligns the leading edge of the side fin base with the trailing edge of the center fin base. For optimum performance the center fin should be placed well up in the box. Naturally, a center fin with a narrower template and more rake will be looser. Cutaway or hatchet fins (narrow base, wider tip) combine quick turning capabilities with added drive.
The classic set up, what the good ‘ol single-fin lacks in lift and hold in the face, it makes up in trim speed and pivot. For longboards (8.5” to 10” deep) a narrower template with more rake will loosen the board up, helping it turn quicker, while a fin with more surface area and vertical template will be stiffer in the turns, but facilitate better noseriding. In both cases, the closer to the tail, the stiffer the board becomes to turn. For single-fin mid lengths, see the above 2+1 suggested size, minus the side bites. Groovy surfers riding old school single fins will no doubt be stoked with the standard Brewer broad-base template (7.5” depth, 5.75” base), which has been holding winged-pintails into steep wave faces since 1971. Forget about any tail-slides, though…