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Carbon Based Life Forms Call Home

I prefer bifins. Always have, always will. We go back a long, long way, and while I’ve no objection to an occasional romp with my monofin, it just isn’t me. Some of my very dearest friends are devoted monofinners. All perfectly fine, but it’s just not what I do.

My earliest childhood ‘flippers’ were made of some sort of rubber, I think, and were open-heel. Elvis would have liked them, but he was too busy rising to stardom to have any time for me. Like Elvis , my rubber flippers were most notable for an extreme flexibility, an ability to be deformed into all kinds of amazing shapes.

Fast forward to the 1990’s. By this time, the skin-diving of my misspent youth had been reborn as ‘freediving’, and several of the world’s dive equipment manufacturers were in the market niche populated by the readers of this column and our less literary friends and colleagues. Everybody knew that freediving fins are supposed to have long, long blades, and most customers and manufacturers had figured out that the open-heel design isn’t really the way to go. It all has something vaguely to do with power, or so we suppose. Freedivers need powerful fins, fins that make a lot of power.

Plastics had come a long way, too. Cheap, strong, easy to blow, mold, cut and shape.

By the year 2000, I was able to buy a pair of perfectly adequate longblade fins by a perfectly reputable manufacture at a K-Mart, and for less than $US 100.

Perfectly adequate. Black. Comfortable. Get you down, get you back up. Cheap, so one doesn’t worry when they get a little scratched as one wriggles through crevices in the lava deep down in Hawai’ian waters (try that with a monofin, Bucko!).

It was impossible not to notice, though, that all of my top-end freediving buddies were on a different meal plan. They were going deeper, to be sure, and seemingly expending considerably less effort than I over the course of a 3- 4 hour session. Since I cannot make myself 20 years younger, and don’t have Zeus’s permission to actually train myself into good physical condition, I’m inclined to attribute 100% of my performance deficit to my equipment. I must need carbon fiber blades, I reasoned, just like the champions use.

I set out to study the properties of carbon fiber freediving blades.

The first property that made itself apparent was the price. Fellow divers and only friends, these things are not cheap. They cost a small integer multiple of their basic plastic counterparts. Ballpark is 2 -4 times as much.

So, the matter is reduced to a simple question: worth it, or not ?

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.

I conducted a semi-scientific test of the efficiency differences between C4 carbon 40’s and my trusty plastic blades. The test was deliberately designed to stack the deck against finding any difference – it was based on dynamic apnea swimming in a pool. Two experienced local freedivers were tasked with swimming repeat 25 meter underwater lengths. Lots of them. The divers were asked to make a good-faith effort to maintain constant technique and water speed. Blades were swapped in and out.

The results ? One diver experienced a consistent 10% gain in efficiency with the C4 blades, as reflected in fewer kick cycles per 25 meter length. The other diver experienced a similar gain, but only for about half of the trials. However, this guy was showing shorter lap times for the trials in which his kick cycle count was the same as with the plastic fins. He was moving faster with the C4’s, and, when he was moving faster, he was doing that body twisting thing I’d noticed on my first dive with C4’s. He had not adjusted to the greater through-put of the C4’s.

I was pretty impressed by this finding. 10% may not seem like a lot, but given that the measuring method was deliberately insensitive, it speaks volumes. There is no doubt about the superior efficiency of carbon blades as propulsion devices for the freediver. Efficiency is what freediving is all about. Maximizing the potential efficiency gains offered by carbon fiber blades does, in my opinion, require some attention to optimizing technique, but this is something we should all be doing anyway. As a consumer, the only question you face is whether carbon blades are worth the considerably greater expense over regular plastic.

Carbon fiber does have some well-known disadvantages. It is unspeakably strong in some ways (e.g., tensile strength) but surprisingly fragile in others. When carbon fiber masts began to replace aluminum in the windsurfing world, we quickly learned that these fabulous new spars did not take well to being chucked from the roof rack to the parking lot surface. Ultraviolet light is not friendly to carbon fiber, either. Things that scratch and bang are best avoided. That said, I have many friends and colleagues who pack their C4’s in soft bags and submit them to the gentle hands of airline baggage handlers on a weekly basis, with no known casualties to date.

I, personally, have to have carbon fiber blades. My C4 40’s are an essential tool in my freediving kit. They quickly and easily mount and dismount in the footpockets that came with my plastic fins. I use the C4’s for most down-and-up the line freediving, and swap in the plastic blades for the rough stuff on the reef, the wreck or for shore dives involving surfy or rocky entry/exit and relatively shallow diving.

C4 blades, while still costly, are becoming easier to acquire. Contact Marco at for direct orders or for a distributor in your corner of the world. C4 also builds blades with higher carbon fiber content ( even better, even more fragile, even more expensive) than the 40’s, and is applying carbon fiber technology to spear guns as well

Paul Kotik
Paul Kotik
Paul Kotik has been a Staff Writer and Freediving Editor for He lives in Florida, USA with his family.


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