MikeFerrara once bubbled...
As for a frog being better fo scuba divers...Not much fluttering going on in a cave (even in big tunnels with rock bottoms where silting isn't an issue) where penetration didtance is often the goal. In order to get the didtance you need to take max advantage of a fixed air supply and just carrying more is not the answer because there is a cost to that also.
My limited understanding is that the most important reason cave divers train to use the frog kick for its anti-silting properties. Divers tend to use whatever technique they are in the habit of using, so my guess would be they would tend to stick to the familiar frog kick. If you train your muscles to use one type of kick, it may become the most efficient kick for you. However, that doesn't mean you wouldn't achieve higher efficiency if you switched to a different kick and trained yourself to use it effectively.
I can't think of a diving example off hand so I'll use a non-diving one I'm familiar with. Hockey players are fast ice skaters and they have a certain style of skating, mostly pushing to the back. They are nowhere near as fast as speedskaters who use a different more efficient technique. You could teach a hockey skater the speedskating style (and I've seen it done many times) but until he has trained to really use it his old style will remain the most efficient (fastest) for him.
MikeFerrara once bubbled...
I could tell you of my personal air consumption but thats not a scientific study. I could tell of the consumption rates of my students but again I did not design an experiment specificly to prove this point.
It's not a controlled study, but it would at least be interesting. Have you compared a series of dives flutter kicking to a series of dives frog kicking (similar conditions and speeds of course) and seen a difference in air consumption? Just hearing a low SAC rate doesn't tell anyone much. You could train some students to use the flutter kick and some to use the frog kick and compare SAC rates. After experimenting with several classes, you might be able to form a preliminary conclusion. Remember my previous point, any unfamiliar kick is likely to produce mediocre results.
MikeFerrara once bubbled...
I do have one idea though practice and use a frog for a while and let me know if it helps you as much as others.
Unfortunately, I have very limited flexibility and the frog kick never works that well for me. I've learned to use it a bit, but it will never be my main kick. Also, I've had a hip problem in the past from too much whip kicking and egg beaters during my swimming days. Constant frog kicking is likely to bring it back.
MikeFerrara once bubbled...
You don't even need to measure the sac, the difference is so significant you can see it by watching bubbles.
That's just silly. I've been around enough frog kickers to know you can't tell the difference from the bubbles. I've trained myself to breathe deep and slow, are you suggesting I'd breathe less deeply using a frog kick?
MikeFerrara once bubbled...
There is also the mechanics of it. With every flutter you are also putting out the flaps (brakes). Doesn't the outward position of a flutter look just like the flaps on a plane? Your giving gas and brakes at the same time.
Many people use too wide a flutter kick, a narrow quick kick is more efficient than a slow wide kick with most fins, both paddle and split. No real point in comparing bad flutter technique just to try to make a point. The blades extend out to the side in a frog kick too, it's not drag free. It's not clear to me that there is any real advantage here.
The flutter kick allows a fairly steady input of power, maintaining a relatively constant speed. The frog kick uses a push and glide, you lose momentum on each glide and have to use energy to overcome the inertia again and again with each new kick. Flutter kicking you only fight the inertia when you come up to speed, after that drag is the only opposing forcer.
MikeFerrara once bubbled...
You are also pushing water (and thrust)up and down. We divers are not allowed to break the laws of energy conservation so that means less to the rear. If you dont believe that watch under and behind someone using a flutter when they are anywhere near a silty bottom.
Again not necessarily correct. While a flutter kick may push more water up or down it
might also push more water back,
if it pushes more water overall. Notice I say might. I haven't measured it nor have I read a report by anyone who has measured it so I have no idea how much water is pushed in any direction by either kick. The frog kick does have a slower turnover than the flutter kick, limiting the total amount of water that can be pushed.
Oh and back to the original split fin topic, the goal isn't to move water around, the goal is to generate forward thrust. The split fins generate additional forward thrust by increasing the lift produced by the blade, which increases thrust without shoving more water around.
My point is the hydrodynamics and physics of kicking is too complex to simply tell what is more efficient by looking at it, you need actual measurements to obtain a meaningful result.
Ralph
