Help me understand the effects of current on fins

[Susanne]

Correlations between fish and scuba divers are essentially useless. They swim at entirely different speeds and Reynolds numbers, their (fish) entire body provides propulsion, they have a slime coating, their design is optimized by millions of years of competitive evolution not marketing quackery. N

If you conduct a google search for - science magazine how fish move - abstracts for a number of fundamental flow studies and others that involve various types of bodies moving through water will be listed. Some are very relevant, many are very interesting, and all are educational.

Yes, we are different than fish. Fish are generally symmetrical. Our legs have more strength kicking forward than when pulling a fin back. Another reason flat fins of any configuration make no sense. They are neither aquatic nor designed for a human leg. Acknowledging that bio-dynamic difference is the reason that Force Fins are curved and snap in the direction relative to your legs that they do.

I think we all have to agree, the more fish like we are, the better we will move through water.

One of my favorite dives of all time was in Fiji. At an outer Island there are 2 pinnacles sitting next to one another in about 70' of water, but they rise from a very deep Ocean bottom. Because the currents running between the pinnacles are very strong, the protocol for this dive is to stay in the lee of the pinnacle upon which you are dropped and enjoy the little critters encrusting it.

I like to move about in the water. My interest was sparked by the fish that were enjoying hovering in the current that runs between the 2 pinnacles, so I inched my way out into the open chasm, and found it most enjoyable to kick in place alongside them for the entire dive. I tried my best to mimic their attitude, if not their profile, and I do believe they enjoyed having a diver in their midst. They certainly reacted with what appeared to be curiosity.

 

[meesier42]

If you used a normal flutter kick with splits, it would make you really slow...which is seems to have done.

You consider a 3.5-3.7 knots slow??

 

[Nemrod]

I think we all have to agree, the more fish like we are, the better we will move through water.

I guess I am not agreeing, y'all agree with yourselves, I don't. We are not "fish like" at all and flapping our feet around with split fins, Forcer Foolers or any manner of paddle fins and hand mits and flip tuna tails, turbo vents or other manner of Tom Foolery we can stick on a diver, he/she is not very fish like at all. I don't do science by Google. Garbage in, garbage out.

Some of the monofin free divers come about as close to emulating a human fish as can probably get as they use their entire body during the effort.

N

 

[DaleC]

Excellent discussion for the most part about fins and technique. It's what I like best about SB.

Puffer, I'd like to see some video too. I'm not doubting what you say but I have never heard of that kick before. I visualize a movement simular to that of a person on a stairmaster and can't help but think it would be fatiguing (in relation to a flutter kick) and would create some counter resistance from the up stroke of the returning knee. I also realise I could have what you are saying wrong.

My thoughts with the flutter is that it is a very powerful kick at any speed but most people don't have the muscle development in their core to sustain it for long. I train in the pool doing straight legged flutters (from the hips) and even with that after a while it degrades into something of a modified flutter. While I have good form I can maintain an excellent speed/exertion ratio.

If I understand Dan correctly he is saying that when doing a flutter kick paddles hold their integrity longer than the more flexible splits so that, as the kick speed is intensified, blades produce more forward thrust. The splits lose their form sooner and thus their ability to produce thrust.

I am also reminded of arm strokes in swimming. Propulsion is a product of both the exertion and recovery strokes with a glide phase in between. Speed is achieved (after a point) not by repetition as much as the seamless transition between the three. There is a point at which faster stokes do not yeild more speed as the arm movements actually interfere with forward momentum (visualize a strong smooth front crawl compared to someone thrashing forward more wildly). Perhaps the same phenomenon occurs with splits. Because they provide less resistance, could there be a point wherein the rapid back and forth movement of the fins actually counters the forward thrust they are trying to exert. With paddles it is almost impossible to "overdrive" the fin if one maintains correct form. The usual result is fatigue as indicated in para 1 or degradation of the stroke.

I think of spits like the low gear on a mountain bike. Easier to pedal at low intesity but not effective at higher speeds. Paddles require more effort at low intesities but beyond a certain point propel the bike faster with less effort.

Though, according to puffer, it could be a case of comparing apples to oranges.

 

[thanksforallthefish]

I believe what Dan says is true, that he has had to drag divers using splits because they have trouble in current, however as Puffer said it is due to the fact that they are not finning correctly, I doubt it has anything to do with the fact they are using splits.

I have used splits in current, and automatically start finning as you would in paddles ie put more effort into the stroke, consequently you go nowhere.
As soon as you start finning correctly (for splits) you start to move again.

I have dived splits for the last 5 years, the 14 years before that i used paddles.

Just my AU0.02c

 

[ickis]

i dont know, during current dives ive only used the simplest of paddles and i did just fine...
about splits, i suppose its common sense to assume that you need a diferent finning technique from the paddles to use them during current due to their increased flexibility and the fact theyre split down the middle.
i guess the current has some sort of effect on the water moving in the split or on the blades and it disrupts the kick or the motion.

 

[danvolker]

I guess I am not agreeing, y'all agree with yourselves, I don't. We are not "fish like" at all and flapping our feet around with split fins, Forcer Foolers or any manner of paddle fins and hand mits and flip tuna tails, turbo vents or other manner of Tom Foolery we can stick on a diver, he/she is not very fish like at all. I don't do science by Google. Garbage in, garbage out.

Some of the monofin free divers come about as close to emulating a human fish as can probably get as they use their entire body during the effort.

N

Nemrod,
I took what Suzanne said about "fishlike" just to mean low drag..since she was certainly not talking about swimming with side to side body motions
Basics I think both you and Suzanne would agree with:
* A freediver with slick wetsuit and virtually no drag ( compared to scuba divers) will glide through the water much more efficiently than a scuba diver, and will also require less thrust to do so...an even bigger issue from this is the idea of being able to glide/coast between kicks..like a fish...for a diver, a long glide makes a huge difference in far lower heart rate and better muscle efficiency.

*A scuba diver with a slick wetsuit, and ultra slick backplate and wing , with nothing hanging and dragging in the current, will be able to GLIDE/coast after a big kick. A scuba diver with stuff hanging everywhere, with nasty rough wetsuit( surface drag) , with tank hanging at poor angle, and with weighting/trim off badly so that they must swim head up, and feet down( too much weight on weight belt instead of upper torso) and basically pushing a bow wave....will have almost no glide/coasting between kicks, and largely because they will never benefit from the previous kicks ( almost like starting from scratch on each kick) can never attain much speed, must use a far higher turnover or kick speed, and will be breathing at a much higher rate( than if there was no drag, etc at given speed). The high drag and no coasting also will make this scuba diver feel finning is easier, if the fins use what you could call very low gearing--so that you push less water with each kick, and don't tire the legs out as much. To me, this ties in with the ability of the split fin propaganda to get average divers to try splits--since most dive shops have configurted their students to be very high-drag divers, typically with poor trim( head up and feet down swimming). The splits ( like a mountain bike in the granny gear) get the high drag diver to move with less muscle fatigue. Most diving does not call for a scuba diver to swim really fast, so most dives put the split fin wearer at no fin based disadvantage ( that they can discern).
* Exagerate the low drag issue, by putting each of the fins on a ultra slick freediver who can glide huge distances between kicks. Both splits and force will require more turnover than freedive blades, but the splits will be far inferior to the force fins--the split fin diver will not be able to do drops to as deep as the Force fin wearing diver ( of course this relates mostly to the efficiency of swimming back up to the surface, not the 3/4ths of the drop where you are just falling--though the beginning of a drop DOES require the fins to make a couple of big pushes).
*Optimal freedive fins, like the C4's, can be used in dolphin kick and come very close to the same or better performance than many monofins--as several posters have said, the individual's kick technique is crucial to how well the kick will propel the diver. And yes, this kick style does require fitness training beyond just walking and talking---cyclists are well set up for using both the down and upward thrust required, along with the sine curved body actions necessary to sustain the kick--for a competitive cyclist with good core strength, this kick can be sustained easily for several hours--however, a diver with no training beyond walking would not be able to sustain this for more than a few minutes...so much for the Rodales testers

If a fin can allow a big glide, to be combined with thrust that can be maintained at higher speeds ( previous kicks serve to make substantial cumulative rise in speed) , the fin will be efficient at much higher top cruising speeds for a scuba diver. Splits fail at this, Force Fins do far better than you would expect on this( almost like a gearing change they get at higher speeds), and the better freedive fins do great at this . The problem with normal Jets is the fatigue factor of high speed turnover with them--too stiff for most diver legs to sustain an optimal bend , particularly with a high turnovr ( meaning no rest for muscles between kicks, and poorer bloodflow because of constant contractions)

Regards,
Dan

 

[meesier42]

*Optimal freedive fins, like the C4's, can be used in dolphin kick and come very close to the same or better performance than many monofins--as several posters have said, the individual's kick technique is crucial to how well the kick will propel the diver. And yes, this kick style does require fitness training beyond just walking and talking---cyclists are well set up for using both the down and upward thrust required, along with the sine curved body actions necessary to sustain the kick--for a competitive cyclist with good core strength, this kick can be sustained easily for several hours--however, a diver with no training beyond walking would not be able to sustain this for more than a few minutes...so much for the Rodales testers

I don't think there is any debate that a clean drag free is more efficient and will require less thrust to move. to go as far as a slick skin wetsuit I think is pointless when you have a big @$$ tank on your back.

in scuba applications I really think monofins are nearly useless. I've tried it and its flat out ugly, maneuverability is nonexistant, at least without significant use of your hands. So in a scuba application freedive fins would be better, but yet maneuverability is still limited (no back kick for example) not to mention that in confined spaces or near fragile coral they are simply not appropriate. In specific environments (sandy bottom areas, or wall dives, not the least of which) they can be good. I owned a pair of C4 Falcons for a while (2-3 months) and although they were much much better than the Spetton's they replaced, I found that I didn't care for them all that much and sold them before they lost value. But to say that they can be as fast as monofins, as I showed earlier, the best trained fin swimmers, wearing the fastest fins in the world are a full 1.4 knots slower wearing bi-fins.

But all that said. absolute top speeds have nothing to do with scuba diving. The ability to maintain a high speed for an individual during a scuba dive when you HAVE TO is dependent on a few factors
1) the fitness and strength of the diver
2) the comfort of the diver wearing the fins on his/her feet

will any fin fail? I doubt it, will the diver using the fin fail? YES
each and every diver needs to identify the fin that works best for them, in the conditions that they intend to use them. For me, diving both dry and wet, warm, temperate, and cold waters, great and zero viz, high current and no current, shore diving and boat diving. Basically, if it water, I'll dive and probably have. For me there is no better fin, that works in all conditions, all the time, everytime. Its a ForceFin, for me its the Excellerating Force Fin, but I used the Pro for years.

 

[Nemrod]

This is like some of the bike forums that go on and on about aerodynamics. Finally one engineer for a top company said the difference between the two pieces of equipment they were arguing over was about equal to riding with the mouth open vs riding with the mouth closed in terms of drag. That is how all of this emulation of fish by scuba divers and fins strikes me, esoteric at best, foolish at worst. If I can swim faster in a pool with splits then I can swim faster with them in the ocean and it matters not if the current is zero or twenty knots.

Unlike bike equipment, where there are at least a few engineers and aero people involved, I think most scuba equipment is market design driven by what looks cool or what gimmick can catch the consumers eye.

The difference in drag between a slick skin suited scuba diver A vs shark skinned suited scuba diver B, identical equipment otherwise, is probably about equal to swimming with a buzz cut vs a mullet.

A couple of years ago, inspired by a fellow diver who had done a swim fin test, I did my own. I swam a variety of fins and even split some fins and taped with Duct tape other splits closed. I swam Jets and then I taped their turbo vents over, you know what, after several months of furious testing, I found nothing, well, I did get a cardio boost. As an ex long distance swimmer, I am pretty good at monitoring my output. I believe FF Pro gave me the fastest top speed over a 1/8 mile swim. Tapping the splits over did virtually nothing to measure, splitting several old sets of fins did very little unless I split them deeply and then it slowed them down, Jet Fins actually seem to go a bit faster, maybe, with the vents tapped over. But, you go grab a dozen different fins, spend a few months swimming them and then see for yourself, YRMV.

N