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Fins and Boots


Fins provide your propulsion underwater. Water is about 300 times as dense as air, so it takes a lot more force to move through it than it does to move across its surface. A good set of fins gives you all the thrust you need for very little effort on your part. Note that fins are almost never referred to as “flippers.” Reduced to their essence, fins have a foot pocket and a blade. The foot pocket holds them on you, the blade does the work of propulsion. Before we start looking at fins in detail, let’s consider why you might (or might not) want to have boots as well.

Why Boots?

There are two basic classes of fin: open-heel and full-foot. Full-foot fins have a soft molded foot pocket which pulls over your bare foot. Open-heel fins have a heel strap and are designed to take a rubber or neoprene boot, also called a “bootie.”

Full-foot fins are generally lighter-weight than open-heel fins. They are good for diving in warm water, especially if you’re diving from a boat. Open-heel fins are necessary for cold-water diving, as your feet need the insulation of dive boots. Open-heel fins are also useful for warm-water shore diving, because the walk into the water and out to where you’re actually swimming can involve a number of hazards: hot sand, sharp rocks, slippery algae, and so on. A pair of boots helps keep you safe in those situations.

And there is a compromise, which is to wear neoprene socks and use full-foot fins. Neo socks are made from wetsuit material, so they provide some cushioning and some chafe protection while finning.

Boots come in a range of stiffness, from very soft to very rugged with hard molded soles, ideal for climbing down to a dive site over rough terrain. Of course, choosing an open-heel fin and a boot involves checking that the boot fits into the foot pocket. If the bottom of the foot pocket covers most of your instep, the match is good. The bottom of the fin should not come all the way to your heel or you’ll have trouble getting the strap to hold it securely.

Straps

If you’re using full-foot fins, straps are obviously not a concern. But full-foot straps are an important item. Many divers carry a spare strap on dive trips, just in case one breaks. The straps usually feed into buckles with a spring-loaded clip that allows you to adjust their length (very much the same as a mask strap). And the clips often end in quick-release snaps that can make getting the fins off much easier.

A few years ago, spring straps became available for most makes of open-heel fin. Spring straps are made from stainless steel springs in a range of lengths. They never need adjustment: you simply pull the spring back, insert your boot, and let the spring hold your foot in. They make donning and removing fins much, much easier.

Fin Designs

Scuba fins vary widely in design. Two basic styles are the paddle and the split fin. The paddle is the traditional single blade, sometimes with vents or ribs. The split features a cut in the middle, turning each fin into two separately-flexing surfaces.

Split fins have become popular in recreational diving because they require much less effort to move you through the water. In low-current locations where you are unlikely to have to move quickly, split fins can be ideal.

In general, paddle fins require more muscle strength than split fins, although they are available in a wide range from supple to very stiff. The advantage of a paddle fin is that you can generate more thrust to move faster, for example when fighting a current.

There are also some innovative fin designs outside the paddle-versus-split camp. One is the line of Force Fins, which look very different from other fins and are based on somewhat different propulsion principles. A recent innovation is a fin with blades that fold up to lie along the front of your shin while your foot stays in the pocket. This approach makes walking out through the surf on a shore dive much easier.

Donning Fins

Donning your fins can be done sitting, if you’re limber. It can be done standing, if you have a rail or a buddy to lean on, using the “figure-four” method of raising one leg and crossing it away from your support side to make a figure four. Or it can be done while you’re floating with BC inflated and regulator in your mouth. Again, some limberness helps.

On boats, fins are always donned last. On larger dive boats they’re often stored back on the swim deck to prevent anyone trying to shuffle across the decks with fins on.

If you’re using open-heel fins with standard fin straps, adjust the straps so they’re just loose enough that you can pull the strap over your boot. Do this before you assemble and don your gear, because otherwise this step tends to get forgotten until you’re standing on one leg trying to don the fin.

Using Fins

The first thing new divers notice is that fins provide so much propulsion, there’s no need to use your hands to swim. In fact, any time you have your arms out you are increasing your drag and your air consumption. Relaxed divers typically keep their hands together, near their waist or (if using wrist-mounted gauges) slightly out in front where they can see the gauges.

As stated before, your leg strength and cardio fitness will make some designs better for you than others. You should also consider the conditions in which you’ll dive, especially current. Most divers don’t care to work hard continuously underwater, and a current of one knot (1.1 mile per hour) is about as much current as you’ll find comfortable to work against.

Most beginning divers learn the flutter kick. The key to an efficient and relaxed flutter is to keep the knees almost straight. Legs should be long and the kick a small movement. The wider you spread your legs on a kick, the more drag you’re creating. Try a small kick, then bring your feet together and try gliding. If you’re just cruising, looking for interesting life, there’s usually no need to kick continuously.

As you near the bottom, of course, it’s important to look down and back to your fins to see how close to the bottom you’re kicking. It’s possible to stir up sand and silt from the bottom even if you’re not touching it, because the down-current from your flutter kicks will extend two feet or more beneath you. For this reason many divers learn alternative non-silting kicks, such as the Frog Kick. This is a great kick to use whenever the bottom is soft, to prevent stirring it up and reducing your visibility. Divers bend their knees to a right angle. They rotate the fins away from each other and bring them together in a move that feels like you’re trying to clap the soles of your feet together. The resulting propulsion is directed straight back, not down, so you don’t stir up the bottom.

Finally, as the fins were the last item you donned before entering the water, they are the first item you should remove. For boat dives you can remove them after you have hold of the ladder, or you can float your feet up and let the crew pull them off. For shore dives, removing them in waist-deep water outside the surf zone, with a buddy’s support, is ideal. In really bad shore conditions you can leave everything on and the regulator in your mouth and just crawl out of the water. There is no shame in that, and you won’t be knocked down repeatedly while trying to shuffle out.

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