Modified Flutter versus Frog Kick (from a different point of view)

[Angelo Farina]

Drag. If you are moving at all, the frog kick blade path results in much higher drag than flutter.


I don't know what "return the energy back to the water" means. Frog's perceived efficiency is almost entirely a byproduct of its low speed. Throttling flutter back to frog speeds results in greater efficiency.

Frog kicks does have advantages, but efficiency is not one of them.

I agree entirely with @lowwall .
When I became a finned swimming instructor I had to make a number of experiments for finding the most efficient kicking style and the corresponding best type of fin(s) for each athlet under my supervision.
The result was invariantly the same with all athlets I worked with: whilst the fastest style is dolphin kick with a monofin, the most efficient style is flutter kick with modest amplitude and long flexible carbon-fiber fins.
This is the way an athlet can travel the longer distance with a single breath.
The optimum efficiency was reached by each athlet at his own optimal speed, and with a personal optimal choice of fin's length, stiffness and angle between blade and foot.
So there is no "best fin for everyone".
Athlets coming to finned swimming after years of frog swimming without fins were often convinced that frog kicking was more efficient also wearing fins. It did usually take me a dozen of hours or more of work in the pool for proofing them wrong.
It is first necessary to teach them how to flutter kick properly. Often people used to good frog kicking have a terrible flutter kick, they use just half of the kick for active propulsion (usually the down kick), using the other part of the movement just as a "recovery".
But there is no recovery in a proper flutter kick (even if modified for keeping the fins away from the bottom): both down and up motions are fully active.

 

[Gandalf-the-Diver]

rog kicks does have advantages, but efficiency is not one of them.

... try following someone who has mastered the "flick" in the kick cycle of a frog kick or mod frog. I tried once, dive buddy only moved his ankles. Nothing else moved, yet I had to break into a full on scissor kick to keep up in parts. His kick was very efficient.

 

[inquis]

Drag. If you are moving at all, the frog kick blade path results in much higher drag than flutter.

Even assuming the frog is less efficient, I don't believe that would be the reason. During the recover phase of the frog kick, the area presented is less than that of the flutter until completion (when they are briefly equal). Furthermore, the recovery is performed when at a slower speed through the water, and drag goes as the square of that speed. During the glide, very little fin area is presented. I see no way for the integrated drag contribution *from the fins & legs* to be higher with a frog kick compared to the mod. flutter.

(Again, I'm specifically addressing the "frog kick blade path" statement. Its an open question how the whole-body drag plays out in conjunction with the variable speed yielded by the frog kick.)

 

[BlueTrin]

@Angelo Farina out of curiosity, what do you think would be the most efficient kick while using Jet Fins style of fins? Would that still be the flutter (I imagine it may be … just don’t have any real life testing)

 

[dmaziuk]

@Angelo Farina out of curiosity, what do you think would be the most efficient kick while using Jet Fins style of fins? Would that still be the flutter (I imagine it may be … just don’t have any real life testing)

Flutter is generally more efficient because your legs and feet are in the streamline, i.e. not exposing extra surfaces and generating extra resistance, and with the right amount of technique and ankle flexibility: it pushes the water directly backwards, i.e. it pushes you forward.

The only exception would be if using these fins, and I don't know if they actually worked as well as advertised: it seems speedo has discontinued them so presumably they weren't selling too many.

 

[Angelo Farina]

@Angelo Farina out of curiosity, what do you think would be the most efficient kick while using Jet Fins style of fins? Would that still be the flutter (I imagine it may be … just don’t have any real life testing)

There are several variants of Jetfins. The original ones were developed and patented by Beuchat in France and were manufactured in different versions and lengths.
The venturi channels were designed and optimised for flutter kicking, with the explicit goal of improving thrust during the downstroke.
In the seventies I purchased a pair of Beuchat Jetfins, the version optimised for free diving: full foot pocket, no strap, medium length.
They were better than Rondine L by Cressi, providing the same thrust with a shorter blade, thanks to the double surface in the area with channels.
Later on, in the eighties, I purchased the Scubapro-licensed version, with half pocket and strap.
In this version, now widespread, the channels did not provide a good venturi effect, resulting in reduced thrust and larger effort than the Beuchat version.
I really do not understand why this inferior Scubapro version was so successfull, whilst the original Beuchat version was not so succesfull.
I also never understood why they became popular among people needing to frog kick inside wrecks or certain types of caves (namely, those without red coral, which instead are the most common ones here in Italy).
The venturi channels only operate when the fin is doing a downstroke, while they are irrelevant or even detrimental during the frog kick.
And fins optimized for frog kicking were available and employed, for example, by military frogmen (Comsubin here in Italy).
Furthermore the development of fins made of composite materials make the Scubapro Jetfins entirely obsolete.
Now we have fins with half pockets, stainless spring strap and composite materials blades which are quite good both for frog kicking and powerful flutter kicking, such as Mares Plana Avanti 4 or similar.
Also Scubapro makes many types of fins, with performances much better than the Jetfin.
They possibly continue being used just for their vintage look.

 

[mcohen1021]

I like the frog kick because I can take a break between movements… plus have you ever seen a frog using the flutter kick? Lol

 

[lexvil]

It all depends on your goal, need to get from point A to point B quickly (military) flutter kick is perfect, need/want to go slow to see what there is to see, frog kick. There are fins optimized for each kind of kick and there are fins that compromise to be good for each in varying degrees.

 

[Nick_Radov]

There are several variants of Jetfins. The original ones were developed and patented by Beuchat in France and were manufactured in different versions and lengths.
The venturi channels were designed and optimised for flutter kicking, with the explicit goal of improving thrust during the downstroke.
In the seventies I purchased a pair of Beuchat Jetfins, the version optimised for free diving: full foot pocket, no strap, medium length.
They were better than Rondine L by Cressi, providing the same thrust with a shorter blade, thanks to the double surface in the area with channels.
Later on, in the eighties, I purchased the Scubapro-licensed version, with half pocket and strap.
In this version, now widespread, the channels did not provide a good venturi effect, resulting in reduced thrust and larger effort than the Beuchat version.
I really do not understand why this inferior Scubapro version was so successfull, whilst the original Beuchat version was not so succesfull.

Scubapro has a larger dealer network, especially in the US, so their products were just more available than Beuchat. The half-pocket fins are also usable with drysuits and wetsuit booties, so they work for all water temperatures as well as shore diving in rough terrain. Along the California coast we're sometimes walking down rocky paths to reach the water; can't do that barefoot or even in thin neoprene socks.

I also never understood why they became popular among people needing to frog kick inside wrecks or certain types of caves (namely, those without red coral, which instead are the most common ones here in Italy).

Jet Fins are relatively short which makes them easy to maneuver in tight spaces. Sometimes this is more important than efficiency. They are also negatively buoyant which helps for achieving good trim in a drysuit without using ankle weights. On many dives we rely on DPVs for propulsion and so the fins are mainly for steering.

The venturi channels only operate when the fin is doing a downstroke, while they are irrelevant or even detrimental during the frog kick.
And fins optimized for frog kicking were available and employed, for example, by military frogmen (Comsubin here in Italy).
Furthermore the development of fins made of composite materials make the Scubapro Jetfins entirely obsolete.
Now we have fins with half pockets, stainless spring strap and composite materials blades which are quite good both for frog kicking and powerful flutter kicking, such as Mares Plana Avanti 4 or similar.
Also Scubapro makes many types of fins, with performances much better than the Jetfin.
They possibly continue being used just for their vintage look.

I have not tried the latest Mares fins. However, the issue with similar fins has been that the blade material wasn't strong and stiff enough for tech divers and would tend to flex too much under heavy load. Any fin material can work well enough for a single tank recreational dive in a wetsuit. But when wearing a drysuit and carrying back mount doubles plus multiple stages and other gear there is so much mass and drag that lesser fins break down and become ineffective when a strong diver kicks with maximum force. As a friend of mine put it, "When you dive the big gear you need the big Jet."

I have no particular attachment to Jet Fins and would be happy to switch to something better. But so far, I haven't seen anything with a superior mix of features. Just being more efficient is not enough.

 

[Angelo Farina]

I fully understand that efficiency is not the most important feature in most cases.
My point is that the Jetfins are fins designed with a peculiar goal and optimised for flutter kicking.
As said, here in Europe we had a long tradition of short, stiff and heavy fins, starting from WW2, some of them carefully optimised exactly for the same kind of usage where US tech divers employ the Scubapro Jetfin.
Simply, they do not have venturi channels, which are useless for frog kicking.
So why carrying an amount of rubber which does not provide any thrust during the active part of the kick and causes drag during the recovery?
For modern tech fins without venturi channels, see for example the Dive Rite XT or the Mares XR Power Plana Tec.
There are many others, of course.
Also consider that legs and kicking styles are different. So each diver should search for the fin with the optimal geometry for her/him, not simply choose the same fins that others use.