Pervasive Fallacy about Split Fins

[Rick Murchison]

 

[mdb]

Rick: Thank you for the stress reduction kit. I've used it already and it seems to be working.

 

[under water]

 

[BKP]

I think the only way to empirically solve this question is on a machine that produces the exact same force and rate of stroke so that the result of the fin and not the fin wearer can be measured. That being said, I like each type for certain diving condition. Can you really own only one pair? That don't make no sense!

You're right.

I own two pair.

They're both splits...

 

[djanni]

Don, I think I'll do that. We have a MEGA Dive-O-Rama coming up here in 2 weeks at Puerto Galera and I'm going to rent a pair. I take pictures and dive pretty slow. I also frog kick almost all the time to keep the sand where it should be, on the bottom, so it will be interesting to see how they work for my style of diving.

Great. Good luck with them. I hope they're a decent pair of splits.

Wish I was going to be there.

Don

 

[djanni]

Rick: This isn't stessful. Its fun.

 

[Temple of Doom]

Do the SEALS use split fins? Therein lies the answer.

Granted this is from the site of the company that holds the split-fin patent, and have a vested interest in getting you to buy split-fins, but it's still anecdotally worthwhile.

While I think you should take the testimonials with a grain of salt. I'm sure they may be a little overly-enthused, holding splits up as the Best Fin Ever™. However, I do think that the soldiers and officer listed (who agreed to have their name and rank next to their testimonial) did not outright lie about their personnel's use of the fins. And perhaps that this is a credible answer to the above quoted question.

http://split-fins.com/press.htm
(look at the bottom: Military Testimonials)

So I think it's safe to say that at least some Special Forces personnel (including SEALS), have used and like split-fins. Further, the SEAL who talks about extensive testing he had done (including VO2 Max) warrants at least some interest.

Craig

 

[radinator]

You're absolutely right that a kick with paddle fins requries more work, and thus requires more energy to do it.

You almost finish that thought to prove my point. I'll take up where you left off:

As you said, the paddle requires more work and less times. And that the split fin requires less work, but more times. Can you see where I'm going now? They balance each other out.

That's a big assumption on your part. They may balance each other out, they may not. It depends on the actual values.

Let me try an analogy. I pay taxes and use government services. Do they balance each other out? How can you say they do until you know exactly how much I pay in taxes and how much government services I actually use. They may balance out for me, or I may use more than I pay, or I may pay more than I use. Just because the 'value' flows both wayd does NOT mean they balance each other out.

Do you honestly believe that the energy output of your body is changing depending on the fin you're using? Are your legs able to metabolize sugars any more because you have a different piece of plastic/rubber on the end of your feet?

Of course not.

Do you honestly believe that the energy output of your body is independent of how much work you are doing? So you have the same energy expended whether you are sitting in a recliner or climbing a mountain?

Tell me, have you ever felt cold on a dive? Have you ever found that by doing a bit more work (kicking harder) you warm up? How do you think that is happening other than expending more energy?

When swimming your hardest (or swimming at your max sustainable rate), your body is outputting a certain amount of energy. Whether you're in bare feet, paddles, or splits will change the velocity and effort of each kick, but the energy coming out of your body is the same.

As I said, things don't automatically 'balance out', and saying they are the same doesn't make it so.

An aside: Who does a dive at their 'maximum sustainable rate'? I certainly don't. Where's the fire?

The harder/less or faster/more ratio of fins doesn't really matter, it's their efficiency. How much of your body's energy is turned into thrust. One could easily tweak split fins to be as efficient as padles (I think adding some generators to charge your light and reduce the efficiency down to paddles would work nicely ). If you did that you would find that both fins would have the same thrust and speed through the water.

Efficiency is what I'm talking about. In fact, the incorrect use of the term is what got me into this discussion.



I don't really have a horse in this race. I really don't care what type of fin you choose to use. Why do you care so much what I use? What is the point of this thread? Who are you trying to convince that they should use split fins?

 

[Tigerman]

Also to remember when you question what equipment a military unit use;
Military purchases are based not only on performance but also on price.
The military also purchases large quantums of the items in question, and plan their use for many years ahead. Replacing old technology for new technology is also normally a process that involve ages of bureaucracy..
Even if all the paperwork for replacing the old equipment with new equipment was made today, the change dont happen over night..

 

[Temple of Doom]

I don't really have a horse in this race. I really don't care what type of fin you choose to use. Why do you care so much what I use? What is the point of this thread? Who are you trying to convince that they should use split fins?

I'm not trying to convince anybody to use splits. I've said it a dozen times, I'm attempting to correct the fallacy that splits don't output more thrust than paddles while flutter kicking (whether in current or high-drag situations), and thus are more efficient than paddles for that type of swim.

Splits have a lot of negatives as well as their positive traits. Some of those are subjective, some are objective. Far too many people state an objective falsehood about splits (they don't work as well in current, or they don't work when you have high-drag). It's important to point out those falsehoods.

As a physicist, maybe you should think about physiology a bit. I'm still not certain we're disagreeing with each other. Do you disagree with the following statement?

A diver kicking their hardest will generate the same amount of energy regardless of what is on thier feet. How much of the diver's energy is translated into thrust is dependant on the efficiency of the fin.

If you disagree with that statement, then I'm not sure if there's a way to convince you otherwise. A diver can only output as much energy as a diver can output (did I have to just say that?). The max output of the diver is invarialbe (under the same physiological conditions), as a result, with different fins, the power relationship between harder/fewer and easier/more must ballance out. The speed the diver is going is based on the max energy output (all things being equal except fin). With fins of the same efficiency, you will go the same speed. With a more efficient fin, you will go faster for that same energy output.

Now if you want to say that a diver trying harder to swim with paddles is generating more energy than a diver trying less hard with splits, then obviously the energy generated will be greater for a diver with paddles. However, we're talking about the same overall effort from the diver.

Of course substitue any energy output level for the max energy in the above paragraphs, and it holds true. Of course you won't be swimming your fastest throughout the dive, but one truth is that if you have a more efficient fin, you will exert less energy to move the same way.

Craig