Saturday, August 17, 2013

Scuba fins: split or paddle?

Scuba Fins and are generally the first piece of equipment a new diver will buy.

This purchase is usually made before the diver has ever entered the water, making it difficult to make and informed decision on what type of fin you'll need.

Dive shops advocate split fins these days, and claim they require less effort while diving, and while this is a true statement, in practice a diver will expend more energy diving a split fin over the course of a dive.

Here's the science:

A split fin is designed to do one thing very well, and that is high-speed flutter kicking.  The split causes a propeller-like action, the pressure differential generated moves the diver forward with less effort (see Bernoulli's Principle).  The trick is, while diving, a high-speed flutter kick is generally not the best kick to use.  If you are trucking along at full speed the amount of energy you are expending and gas you are breathing (even with split fins) is excessive.  You will tire quickly and not have an enjoyable dive.
paddle fin

Scuba is a slow sport. Remaining still, or using a slow speed kick is the goal.  Exploring a coral reef is not done at 90 mph, and diving in advanced, overhead environments requires precision and power on demand, not marathon speed.  Here is where the split fins weaknesses become apparent.  The split itself reduces the power the fins can generate from full stop.  This makes turning and pivoting in the water more difficult.

Frog kicks, excellent for letting a diver rest, and required for any type of technical diving, are of little worth in a split fin.  The limited initial power of a split fin does not allow for good propulsion from a frog kick.

Back kicks, essentially a backwards frog kick, are equally crippled by split fins, causing a diver to work twice as hard to reverse through the water.

The full flutter is also the kick most often responsible  for silting up dive sites, quickly dropping the visibility for surrounding divers.  The repeated strong downward motion of the kick propels water towards the seafloor causing the silt to disperse in the water.  If you've ever been in a crowded swim-though, you've likely had this experience.  To use any other means of propulsion, a traditional paddle fin is ideal.

A Modified Flutter Kick accomplishes a similar strong forward propulsion of the full flutter, but aims the fins upward, preventing the diver from disturbing the silty bottom.

If you are interested in a pair of paddle fins, it turns out the design was perfected some 50 years ago.  The Scubapro Jet Fin is the de facto standard, and with good reason.  They deliver excellent thrust, and set of these solid rubber fins will likely outlive you.

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