>Not surprisingly, the way we drive depends on the vehicle we're driving. Trying to push my three-quarter-ton pickup through the corners is bound to end in disappointment, as would an attempt by my neighbor to back his BMW down the ramp to haul out a 20-foot Whaler. The way we measure performance has everything to do with the task at hand. So it is with dive fins. The way we outfit our feet depends mostly on where we're going and what we're doing.
>Dive fins come in a broad spectrum of shapes, sizes, styles and stiffness; the particular form of our underwater footwear shapes the performance we can expect. Let's start with the most basic division: full-foot style versus heel-strap. For snorkeling in warm water, nothing is more comfortable than a full-foot fin that slips on over bare skin. But when suiting up in full Jersey-coast wreck-diving gear there is no doubt we'll want a heel-strap fin that fits over some nice, warm booties.
>Variations on a Theme
>Length and flexibility are also important. We can think of our fins like bicycle gears. Smaller and more flexible is like low gear: We won't go too fast, but there won't be a lot of leg strain. Longer and less flexible equates to a higher gear: We work those leg muscles harder and enjoy the speed that comes with our effort. It's the same with our fins: What we're doing makes a difference. Longer and more rigid fins will give us the propulsion we need when fully equipped for fighting currents on cold-water wreck dives. Lightly loaded for a leisurely roam on the reef, however, we might find we can easily get the power we need with a shorter fin.
>Other features also play a part in fin performance. Slotted-fin designs have been the propulsion backbone of the dive business for decades. The slots are said to relieve some of the pressure on the backstroke and provide a boost in hydrodynamic efficiency on the power stroke.
>About 14 years ago split fins hit the recreational diving market. Unlike conventional "paddle fins," split fins sport a cleft that allows them to assume a propeller-blade configuration during the power stroke. The force of the blades against the water causes them to bend into a foil shape, which designers claim reduces drag while increasing the suction or lifting force to enhance propulsion. Many divers find that these fins make them feel like they're "pedaling in a lower gear" and moving more quickly. They find these fins great when it comes to "highway driving" or cruising along the reef. The downside for some divers is difficulty adapting some advanced kicking techniques (e.g., the "helicopter turns" or "backward kicks" used by cave divers) to the split fins. Others find that different techniques such as "frog kicks" can be readily used when wearing split fins. Maybe it's just a matter of taking our Ferraris and Porsches to the track and sorting out our driving techniques.
>An evaluation of fins reported in Undersea and Hyperbaric Medicine (Pendergast DR et al., "Evaluation of Fins Used in Underwater Swimming," UHM 2003, Vol. 30 No. 1) found that divers' perceptions of fin performance are not always accurate. According to the authors, "divers invariably ranked the stiff fins as the best and the flexible fins as the worse, which did not correlate with the objective evaluation of these fins." In other words, when using more flexible fins divers commonly attained speeds greater than they perceived.
>Still, scientific data on fin efficiency does not indicate a clear winner in terms of true fin performance. As Pendergast concludes, "It is clear that the venturis, vents, trauths [and] splits in the tested fins did not improve the performance of the fin." Pendergast found that different strokes are needed for different types of fins and performance may vary with the type of kick used. Tests conducted by Diver magazine focused primarily on the ability of divers to achieve a high speed when swimming against a current, and these led to a similar conclusion. Among the results was the fact that split fins respond best to a shallow, high-speed kick. Again, we need to adjust our technique to the type of fin we're using, just as we adjust driving technique to the type of car we're driving.
>Finding the best-performing fin may be as difficult as finding the best-performing car. Is the Chevy Volt better than the Camaro or the Silverado pickup? The answer depends on where we're going and what we're doing. Will we cruise a Caribbean reef, explore the jungles of an underwater kelp forest, penetrate a cave system or photograph whale sharks off the Costa Rican coast? For my next trip, maybe I'll pack two pairs of fins — just in case.
>Diameter: Larger diameters make it easier to breathe, especially when we're working hard.
>Comfortable mouthpiece: Make certain it fits well and doesn't chafe the gums.
>Purge feature: A purge can make it easier to keep the snorkel clear.
>Attachment: Both security and ease of removal are important.
>© Alert Diver — Summer 2012