Diving's Most Radical Fin DesignBy Bonnie Cardone
-Dive Training Magazine Nov. 1999
It's safe to say Bob Evans' kicks are powered by the thrust of a different fin. The first glimpse of his brand new Extra Force Fin produces a universal reaction: What on earth are those neon yellow things, what do they do and why would I need them?
Creator of the original Force Fin, introduced in 1982, and of the six Force Fin models that evolved from it, Bob is used to questions about his products. After all, none of his brainchildren is exactly your ordinary, everyday dive fin, each is unique If one could be "more unique" than any other ever devised, however, the Extra Force Fin would certainly stand (or swim) alone.
So, exactly what are those neon yellow things? Evans calls them Whiskers but to me they look very much like the wings on Mercury's hat and heels. Mercury, you may recall, was a messenger to the gods. And, like Mercury's wings, they are intended to speed you on you underwater way. The Whiskers are what make the Extra Force Fin, in Bob Evans' words, "The worlds first variable thrust dive fin." Get a thrill from shifting the gears on a super high performance sport car? Wait'll you try shifting into "high" with the Extra Force Fin! Like a sport car, this fin can be "shifted" into first, second and third using the whiskers.
Under normal diving conditions, the Whiskers are aligned with the outside edge of the blade. To increases thrust, turn the Whiskers in one click stop. If that's not enough to counter a current, try one more stop. The third click stop is for strongest currents. According to Evans, turning the Whiskers inward directs the flow of water toward the center of the fin. Since water is noncompressible, the rechanneled water must speed up, creating a "ram jet" effect that increases the thrust/power of the fins.
The Whiskers alone would make the Extra Force Fin uniquely unique but that's just one of its unusual features. Take the bumps on the bottom, for example. Evans calls these "vortex generators." He says that on most fins, the downstroke is what produces the forwards thrust that propels the diver through the water. The upstroke is pretty much a waste of effort but necessary to move the fin into position for the downstroke. The bumps on the bottom of the Extra Force Fin create water turbulence that decreases the effort needed on the upstroke.
The Extra Force Fin is made of the same material as the Tan Delta Force Fin, introduced on these pages in April. This exceptional material- a Uniroyal Chemical liquid-cast prepolymer- is not only as bright and shiny as the finish on the sport car of your dreams but, when bent out of shape, springs back super quick. When used for scuba fins, this property produces propulsion efficiency.
At first your attention will be diverted by the Extra Force Fin's Whiskers and its beautiful material. Eventually, however, you'll get around to noticing the fins graceful shape. According to Evans' literature: "The key to great design is to look at nature and copy it. Nature evolved the V-shaped, fast swimming fish or mammal tail to focus water behind and allow for maneuverability with minimal drag. The V-shape of the force fin is the optimum shape for scuba diving."
All Force Fins have a very comfortable open heel, open toe design. Your feet will never feel cramped and your toes will never be abraded by Force Fin footpockets. The easily adjusted nylon webbing strap has a neoprene sleeve so it won't dig into your heel.
Are Force Fins, especially the Extra Force Fins, for you? Only you can tell. Know that they require a flutter kick as opposed to the long sweeping stroke you may be accustomed to using. Know that, like the sport car of your dreams, they aren't cheap-they cost $475 per pair, a price that guarantees you'll never see them worn by the masses. Also because of their cost, these are not fins you'll see in every dive store. If you want to check out a pair in person, you'll have to contact the company for the name of the Force Fin dealer nearest you.