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Gearmiester answers your questions about FINS...

"Fins to the left, fins to the right "

Recently we covered the ins and outs of masks and snorkels ( more info.) This month, we’ll finish off the basics by talking about fins, our “underwater propulsion.” (And even though  I call them “dive fins,” everything applies to fins you’d use for snorkeling as well..)

Here's the problem: look at your feet and compare them to a dolphin’s tail. It’s not hard to see that humans are at a distinct disadvantage when it comes to moving around. in the water. Soultion:  the dive fin.

Fin Mechanics 101
When you kick (using a nice straight leg, right?), your fin displaces water. Ideally, that water flows directly behind the fin, providing propulsion in the opposite direction. Any water that spills over the side edge of the fin uses your energy but doesn’t really provide any propulsion – it’s a waste of energy. Most fins have a rail of some sort along the edge of the fin (and sometimes down the interior) to minimize “side spillage."

Is stiffer better?
All fins have a degree of flex in them. The stiffer the fin, the more water it can move. But, it takes a lot of leg strength to move a really stiff fin. If you can’t efficiently kick the fin, it doesn’t do you any good. Find the stiffest fin you can easily kick for your size, strength, and condition. This will give you the optimum power for your kicking effort.

The other aspect of fin flex is what happens on the up stroke. Early fins were really designed to push water on the down stroke and relax on the up stroke by bending and spilling the water for less resistance. Today’s top quality fins allow power transmission on both the up stroke and down stroke by using. a combination of foot pocket angle and combinations of materials. Again, more “bang for your kick.”

Is longer better?
The longer the fin, the more water it moves in each kick. The downside - it takes a lot of strength and fitness to kick a long fin for a long time. Consider the extremely long fins that free divers use. Free divers need to get down quickly but only for a relatively short time. Long fins allow them maximum power while swimming, but that’s usually followed by a rest period between dives. Long fins aren’t well suited to the more constant kicking of scuba divers and snorkelers.

How about split fins?
The idea here is that water spilling through the center of the fin would create a vortex and offer power and propulsion with less kicking effort. For easy to moderately hard kicking, this works as advertised and is the favorite of many divers. However, when kicking hard, the split tends to open too wide and spill too much water which means wasted effort. So, if you often dive where there is current, they may not work for you.

To get around this problem (while keeping the benefitof a split fin), many solid blade fins now use a more flexible material down the center of the fin which allows it to cup and push more water out the back. This accomplishes the same thing as the split fins without the disadvantage when kicking hard.

Another consideration with a split fin - some people have a problem doing different types of kicks with a this type of fin. If you need to do a frog kick or something other than a straight leg kick, make sure you can do it with this type of fin before you’ve committed your money.

Sooo many choices…
Looking at the wall of fins in your typical dive shop, which fin is right for you? For a weekend of casual snorkeling, just about anything on the wall will work without spending much money. However, if you’re going to scuba dive or do serious skin diving, you really want to invest in a good quality, comfortable, well-performing pair of fins. After all, you’re going to use them on every dive.

Here's some things to think about:

Full foot or open heel? (booty or no booty)

Think terrain and water temperature.

If you dive in cold water, you'll need a neoprene booty for warmth. Do you walk across rocks and coral to reach the water? You'll want to wear booties. So you'll need an open heel fin that you can wear over your booties.

Dive only in warm water and don't need a booty for terrain? Full foot fins are a great choice. Today’s top quality full foot fins have a very comfortable foot pocket, thanks to several different kinds of silicone. In lower quality full foot fins, the user can  use a lycra sock to prevent chafing.

What can I power?.
This will determine the length and flexibility of the fins you can use.

Does it fit?
This is much more important in a full foot fin since it fits just like a shoe. An open-heel fin provides some leeway since most will accommodate your foot with a variety of booty thicknesses. But you should try on the fin with the booty that you will typically use

Now you can get to the details. Is the rail along the edge high enough to keep the water from spilling over the edge? Do the materials allow the fin to cup on both the up and down stroke so that water is pushed out the back of the fin? Or do you want a split fin?.

After that, it’s just the nice-to-haves – what kind of strap and buckle system, what color, and so on.

More info on the top rated fins of 2007-08 in Sport Diver Magazine (Dec 2007 issue.)