Efficiency evidence: frog vs flutter?

[MikkelBC]

Well then maybe a physics refresher on kinetic energy is needed. Kinetic energy - Wikipedia

The energy to accelerate a mass depends on the mass and rate of change. Which is why jackrabbit starts are less efficient than gradual starts and why trains take a long time to get up to speed. It takes 4x energy to double speed. Once at velocity it takes zero energy to maintain it, absent external forces. In practice, when maintaining you are only accelerating against the frictional drag.

Common sense should tell you that accelerating to a higher velocity AND against friction is greater than simply accelerating against friction alone.

The force you need to apply to maintain the speed is equal to the force from the flow resistance.
To counter the flow resistance, you can either apply a force from swimming (expending more energy), or you can spend your stored kinetic energy and replenish it later. That is not a waste, since you would have to expend energy against the flow resistance in any case. Total energy expended will be the same (assuming the force from the flow resistance was constant, which it is not. It increases with the square of the speed).

 

[Doc Harry]

I used to dive solo a lot just to log a lot of bottom time. One time I set up a marked, measured course, and spent a couple of hours measuring my gas consumption while trying a variety of kicks at different speeds (lazy, normal speed, mild exertion, maximal speed).

I was in a dry suit with Turtle fins, and double steel 130s.

The course was at about 30-35 feet, about 100 yards around, and I did laps. I rested in between the exertion tests by exploring other parts of the lake at a lazy speed.

A lazy flutter gave me the furthest distance travelled per PSI of gas consumed.

The frog was not even close to the flutter in efficiency. (My primary kick is the frog.)

Your results may differ.

 

[CT-Rich]

I used to dive solo a lot just to log a lot of bottom time. One time I set up a marked, measured course, and spent a couple of hours measuring my gas consumption while trying a variety of kicks at different speeds (lazy, normal speed, mild exertion, heavy exertion).

I was in a dry suit with Turtle fins, and double steel 130s.

The course was at about 30-35 feet, about 100 yards around, and I did laps.

A lazy flutter gave me the furthest distance travelled per PSI of gas consumed.

The frog was not even close to the flutter in efficiency. (My primary kick is the frog.)

Your results may differ.

That makes sense if you accept the two posits, at low speed resistance to water is low and second, both up and down strokes in a flutter kick are providing forward thrust.

 

[Landau]

So why are there no fins optimized for a frog kick? I think asymmetric fins with the blades tilted would frog kick more efficiently. There are special fins for competitive swimmers to practices the breast stroke "Whip" kick and they look very different. All the fins we use (even stiff ones with thick sidewalls) are optimized for up and down movements (Flutter or dolphin kick) - not pushing backwards. I'd think some frog kick optimized fins would interest cave and wreck divers or anyone else when silting is going to be an issue for most of the dive.

For the record I use flutter when silting is not an issue, frog (Or sometimes scissor kick) when silting is an issue. And dolphin for getting somewhere quickly

 

[dmaziuk]

So why are there no fins optimized for a frog kick?

a) A very niche market,
b) how would you do it? All I can think of is turning the blade 45 degrees so it's vertical during the "clap" phase. However, that also increases drag during recovery phase and makes the fin useless for other kicks.

Breaststroke fins have their "blade" under the foot where it doesn't interfere with the wind-up much, and are 100% useless for flutter and dolphin kicks.

 

[ronscuba]

I used to dive solo a lot just to log a lot of bottom time. One time I set up a marked, measured course, and spent a couple of hours measuring my gas consumption while trying a variety of kicks at different speeds (lazy, normal speed, mild exertion, maximal speed).

I was in a dry suit with Turtle fins, and double steel 130s.

The course was at about 30-35 feet, about 100 yards around, and I did laps. I rested in between the exertion tests by exploring other parts of the lake at a lazy speed.

A lazy flutter gave me the furthest distance travelled per PSI of gas consumed.

The frog was not even close to the flutter in efficiency. (My primary kick is the frog.)

Your results may differ.

Your results confirm what free divers know. The flutter kick is the best choice for the combination of distance traveled, time and energy efficiency.

 

[northernone]

I used to dive solo a lot just to log a lot of bottom time. One time I set up a marked, measured course, and spent a couple of hours measuring my gas consumption while trying a variety of kicks at different speeds (lazy, normal speed, mild exertion, maximal speed).

I was in a dry suit with Turtle fins, and double steel 130s.

The course was at about 30-35 feet, about 100 yards around, and I did laps. I rested in between the exertion tests by exploring other parts of the lake at a lazy speed.

A lazy flutter gave me the furthest distance travelled per PSI of gas consumed.

The frog was not even close to the flutter in efficiency. (My primary kick is the frog.)

Your results may differ.

Exactly what I was hoping someone has done! Thanks for sharing what you discovered.