C4 Monofin!

You are right, Spaghetti. The American Indian tribes from this region prepared a delicious slurry made with petoskey stones, the secretions of female bobcats, certain mosses and some type of weevil. It is said the were able to fly to the Pleiades after imbibing it, where they would consult with the beings living there; mostly about recipes and fashion.

However the fin itself may be at this juncture - the idea of those footpockets on a mono pretty much rocks.

Fondueset said:

You are likely right - but doesn't all that depend on how stiff the blade is - and where the stiffness is concentrated?

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No, not really. Or rather, you could fix the trailing edge angle by changing the stiffness but that would make a large portion of the blade redundant. The first half of the blade below the feet would need to be almost rigid.

Of course I have a lot of faith in C4's engineering ability. It's simply the shape of the blade I have doubts about and I'm sure they will improve it if it doesn't stand up to testing.

Mullins said:

No, not really. Or rather, you could fix the trailing edge angle by changing the stiffness but that would make a large portion of the blade redundant. The first half of the blade below the feet would need to be almost rigid.

Of course I have a lot of faith in C4's engineering ability. It's simply the shape of the blade I have doubts about and I'm sure they will improve it if it doesn't stand up to testing.

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You could offer to help them test it...

Also, you are well aware of the disadvantages of wide monofins without stiff blades. The convex flexing on your new mono was fairly acute, judging by the vid of your dive in Sharm. What's the solution? Stiffer material on the edges?

I'd be more than happy to test it - if it did turn out to be a winner I'd eat my words and be first in line to use it in competition

Yeah I'm guessing it's the material limitations that prevent fins getting shorter and wider. That said, the footpocket and/or wing design on the hypers seems to be largely responsible for the folding action, as regular footpocket/blade combinations of the same dimensions (eg waterway) don't seem to fold at all. However the hyper configuration seems to bring other benefits that make up for the 'washout' or whatever you want to call it.

To clarify why I think current monofin design is inherently dodgy and longer monofins even more so: there should be one optimal angle of attack for a blade surface to propel a diver forwards. However with monofins (and even more so with bifins) a large blade area is flexed progressively, so only a small part of the blade surface is being held at the optimal angle at any one time during the kick cycle. I'm sure somebody who is actually an engineer (Phil?) will quickly correct me if I'm wrong here, but this seems wildly inefficient to me. The top two thirds of the blade's surface area exist solely to flex appropriately under load in order to put the bottom third (very approximately) at the correct angle to do its work. I think those top two thirds would themselves provide negligible forward thrust.

Ideally, I think you need to do away with long blades and their hugely variable angle of attack (which goes all the way from 0 to 90 degrees!) and stick with a single rigid surface that 'sets' at a single angle of attack for the up and down strokes. Or at least sticks to a much narrower range either side of optimum. I haven't seen a lunocet and have no idea how well they work, but I expect they have the potential to work very well. The design concept seems spot-on to me.

In my mind the ideal monofin would be akin to a windsurfing sail with battens/cambers that induce the optimal angle of attack on both upstroke and downstroke (which would likely need to be asymmetrical). So on each stroke the fin (which would be a solid fixed shape so that there would be no distortion of the angle of attack/lift profile) would snap into the optimal position. Think of changing tacks on a modern race windsurfing sail, for all you boardheads out there.

And also the "fin" would have a higher aspect ratio (unlike the C4 monofin) and the camber/foil shape would be progressively trimmed towards the ends to minimize drag, as is done in a windsurfing sail or a marlin's tail. I think that windsurfing has made tremendous leaps in sail design that far outstrip what's going on in monofins. An application of that approach would yield really interesting results.

I think another big problem with current monofins is that the leading edge of the monofin is subjected to very disturbed and turbulent water as it flows around the body and it is part of the footpocket. An idea I've had for a long time is to have a "fin" at the end of a arced shaft that project out in front of the body (anterior, I think) so that the leading edge of the foil has clean laminar flow.

I thought once of trying to build such a monofin but quickly realized I didn't have the financial reserves to build a prototype.

For those of you who don't windsurf, this is what I'm talking about: Catalogue - Sail design - NEILPRYDE-WINDSURF - NauticExpo Click on the small thumbnails for a rough idea of common design features of a sail)

Anyone want to loan me $75,000 to get started...?

I realize that much of this design has parallels in that amazingly weird foil swimming device that trux found a while back (I think) and the lunocet. But I think that my design idea would yield a very low stroke rate, much like that of a cruising whale that would be very efficient as getting up to speed and then maintaining the speed with minimal effort once optimal velocity has been reached. that's the main strength of modern windsurfing sails- incredible range, ability to minimize drag when suddenly loaded with force (ie. a big gust) and still powerful enough at low winds to generate lift.

I very very briefly tried one of those C4 fins and...(drumroll)...The impression was "meh". I mean it did carry me forward, but not in any significant way better than a normal fin. Sprinting with it was very very hard, but I think it's best used in slow travel (I was almost 5 sec slower with that on 50m sprint than my own fin, but 50m in "dynamic competition speed" was in the same ballpark - but felt harder). Granted I could not tie the footpockets properly, which probably makes a big difference in faster speeds.

Probably it needs a completely different technique than normal monos and I'm not saying it couldn't work if you had some time with it. But that short experience did not leave me hungry for more.

Now the lunocet, that's an interesting design. Among the other features, the specs mention "dynamic angle of attack". Not sure what that means in practice, ie is it actively or passively dynamic. Meaning can you control the angle or does it just adjust it self? It could as well turn out to be rubbish, but I'd sure like to try one...

AIDA doesn't currently enforce any rules on fin construction and dimension (at least I'm not aware of such)? Maybe it's time to think about that too. For example in finswimming it is controlled very very closely.

jome said:

AIDA doesn't currently enforce any rules on fin construction and dimension (at least I'm not aware of such)? Maybe it's time to think about that too. For example in finswimming it is controlled very very closely.

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This might be off-topic, but anyway... why?

So it doesn't turn into a test of technology.

Fair enough, as far as it goes. A level playing field is very important. But the next question is, why would this (or any) particular point in the evolution of monofins be one we want to stick to?

I'd think you'd want to re-evaluate from time to time - probably on a yearly basis.

$75,000 anyone...anyone...

laminar said:

$75,000 anyone...anyone...

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Yes, you can count on me - I accept any amount of cash anytime. Just send it my way

Fondueset said:

So it doesn't turn into a test of technology.

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That's actually the wrong way. What I expect from competitions is the same I expect from F1 races - technology improvements. Competitions are the best place to test inventions and see what technological modifications lead to better results. So artificially limiting the dimensions, shape or other aspects of the fin makes no sense to me. If a better fin can bring me farther or is faster, why would we ban it from competitions? That makes no sense to me.

jome said:

I very very briefly tried one of those C4 fins and...(drumroll)...The impression was "meh"....

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Well, I just came back from the training where I asked Cedric Genin who also briefly tested the C4 monofin in Italy, and his comments were even much more negative. He did not like it at all. He did not even like the foot pockets - they may look cool, but do not seem to be well suited for the use on monofins. His comments were very negative and almost not publishable, but I realize that they were very subjective and based on only a very brief experience, without the chance to experiment with it and trying to find a more optimal kicking style.

Unlike what Spaghetti wrote, Cedric told me that C4 introduced the monofin as a finished product, not a prototype, and also mentioned price of some €600 (which might have been also a reason of his very critical view)

Mullins said:

To clarify why I think current monofin design is inherently dodgy and longer monofins even more so: there should be one optimal angle of attack for a blade surface to propel a diver forward.

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Me too, I believe that the current monofins are very far in efficiency from what they could be. However, the hydrodynamics is little bit more complicated, so just having a fin with ideal angle of attack is not all. There are several aspects in the flow, not only the angle of attack. It is quite complex, so I would no reject long fins completely. They may not be ideal for speed swimming, but may offer some advantages for slow swimmers. The long fin (if correctly designed) allows for more relaxed, steady / continuous kick with little turbulences. At the kick the pushing edge is only part of the time in the optimal attack angle - there are rather big "dead" motions bringing only little propulsion if you have a type of fin you described. In contrary, the long fin (together with your body), moves in a sinusoid, and propulses you smoother, and possibly more efficiently - there are really far too many factors involved to tell it without testing that long monofins are not well suited for freediving. In animal world you can finally also find both wide short and narrow long fins, and they seem to have withstand millions of years of evolution, so both probably have some advantage.

Well, I am not expert in hydrodynamics, but we have a university professor in fluids flow in our club, so I may try to get an expert view on the topics from him. We also discussed that he could propose his students some research jobs related to freediving and to swimming fins - they might try some software simulations of different types, shapes, and length of fins.

Trux, I agree with what you've said above. My thinking is that new technologies should be incorporated in a way that still keeps the emphasis on athletic performance - not by imposing an artificial limitation.

"the leading edge of the monofin is subjected to very disturbed and turbulent water"
That might be good since the front of all blades (mono and bi-fin) is trying to produce thrust in the opposite direction according to my flow model.
"have a "fin" at the end of a arced shaft that project out in front of the body"
That appears to be the best solution. Combine it with a thin symmetrical foil that is very stiff except for 20-30% at the trailing edge and we're on the same track. $75k is overkill, I figured less than $750 for mod 1, a total disaster, mod 2, to fix all the problems and mod 3 that might actually work, just like all new designs. The money is easy to find, it's the 3-400 hours of labor by a skilled model builder that is holding me back.
About rules. We don't need no stinking rules except to cover length, width, chemical assist, atomic power, etc., etc.

I am categorically opposed to the use of nuclear power in constant ballast.

Fondueset said:

I am categorically opposed to the use of nuclear power in constant ballast.

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Luddite! rofl
j/k

Well, I said maybe time to think about it, not time to enforce it. I don't want too much limitation either. But in F1 there is certainly thousands and thousands of pages of just restrictions on what you can and can not do.

Just an off the wall example. Is it currently banned by the rules to use an external power source on a monofin? I mean we would need to have at least some general guidelines on what is a fin and what is a scooter? Well ok, it is kind of obvious, no power sources. How about a contrapiton that has a propellor and you paddle it like a bi-cycle? Taking it really far - is Ted's "muscle powered submarine" allowed? It's constant in weight, it's muscle powered...

Is a "merman suit" a fin? I mean a suit with a trailing "fin" going all the way through the body (kind of like an eel). Or should "with fins" be restricted to "something that is attached to the feet". So is attaching to the knee ok?

I know I know, I already see it coming "we have enough rules already!"...I'm simply pointing out that currently there is pretty much no definition of what "with fins" actually means...And it's currently not a problem because everyone pretty much has the same type of fin - nothing else is available. But things might change in the future...

Well I hope at least someone catches on to the playful tone I'm intending to have in this post, but it's sometimes hard to express in writing

trux said:

Well, I just came back from the training where I asked Cedric Genin who also briefly tested the C4 monofin in Italy, and his comments were even much more negative. He did not like it at all. He did not even like the foot pockets - they may look cool, but do not seem to be well suited for the use on monofins. His comments were very negative and almost not publishable, but I realize that they were very subjective and based on only a very brief experience, without the chance to experiment with it and trying to find a more optimal kicking style.

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Almost not publishable? Was his impression that negative? That amazes me that someone would be that violently opposed to a monofin

I've also been known to swear a bit at products I don't like