Carbon Based Life Forms Call Home
Posted By Paul Kotik on 21 July 2003
Let's look first at the upside. There is no room for any doubt about carbon fiber's superior performance in this application. It is not a matter of the fin being more powerful - after all, the fins do not output any energy. They are not engines. The diver's body is the engine. Fins are mechanical transducers. Their job is to transform the body's energy output into propulsion. The issue is efficiency: how much of the body's biochemical energy output is translated into propulsion. Centimeters per calorie, or something like that.
The detailed reasons for carbon fiber's superior efficiency are interesting to some, involve lots of cool words like hysteresis and deformation, and have been reported ad nauseum elsewhere. Google it, if you want. Let's keep it simple here. The thing about carbon fiber fin blades is that they turn more of the effort you put into them into a visible and useful result: motion. You go farther for the same amount of effort. Or more farther for more effort.
This is , in my experience, immediately apparent to most divers who try
carbon fiber fins after being accustomed to the common sort of plastic
blades. In my case, it happened during a lunch break back on shore in
Hawai'i, when my buddy mounted his C4's in my Sporasub foot pockets. Back in
the water, on my first dive, it felt a little different. I noticed during
the descent that my kicks were causing a little body rotation, so I cut back
on the effort and twisting stopped. It was immediately clear that I was
getting more propulsion bang for my kicking buck. The big hello, though,
came at turnaround time, somewhere in the 35-40 meter/115 -130 ft range.
With my plastic blades, even at that modest depth it usually seemed to me after turning that I'd overweighted a little, or forgotten to take my vitamin pill that morning: The line would just sit there in front of me , as I kicked away, and only grudgingly would I finally develop a little upward momentum. The C4's produced a very conspicuous improvement in acceleration off the bottom. Snappy.
At more serious depths, the effect is even more pronounced. Our bodies are more negatively buoyant and offer greater inertial resistance to acceleration back up toward that nice breathable stuff. A world record holder friend of mine once did a 70m constant ballast dive he was very proud of, even though this is many, many meters less than his record dives. " Did it with plastic blades !" he bragged.
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