C4 Monofin!

[Mullins]

More travel but at a very low angle of attack at the fin tip. You get equal travel plus a better angle of attack if you have a shorter active (flexed) area placed further from the feet by a rigid spar that has very little water resistance (if you WANT more travel that is, which is debatable. Currently it's only required because material limitations have meant fin makers haven't been able to increase the blade surface laterally). In the case of this C4 fin the entire surface all the way from the toes to the tip of the blade is being flexed and only a small part of it (the trailing edge) will be at an angle sufficient to provide thrust. Not very efficient.

Sorry for the rant, just trying to put some detail around what I see as a key element of fin design... This is why I think the lunocet - a product of the opposite design approach - is such a good idea. I'll go out on a limb and say I'm reasonably sure a fin with the dimensions shown above will be rubbish

[Fondueset]

You are likely right - but doesn't all that depend on how stiff the blade is - and where the stiffness is concentrated? It may be they've tried to make a mono based on the same logic that governs the c4 flap fins - which would seem to be dubious.

[Pastor]

Hard to imagine a company like that launching something that is both ugly and rubbish. I guess time will tell

[spaghetti]

Quiet boys, that's just a prototype, a starting point. The few people who tried it so far said the same things that have been said here, and mister C4 took it as a feedback for developping further steps of the project.
By the way, and this is curious, I read a debate on the forum of Apnea Academy website (Pelizzari's organization) and one of the guys commented that, being made like it is, this type of mono "would be interesting to try with a Mullins' style double stroke slippering kick" (I'm just just reporting and translating what he said)...
Fondueset: yes please. I'm sure they (petoskey stones) are delicious!

[whucash]

It looks tatally different that all other.. Wow it give so much question Waitnig for the official presentation

[Fondueset]

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.

[Mullins]

Originally Posted by Fondueset

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

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.

[chrismar]

Originally Posted by Mullins

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.

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?

[Mullins]

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.

[laminar]

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.

[jome]

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.

[NotSoDeep]

Originally Posted by jome

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.

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

[Fondueset]

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

[Mullins]

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?

[Fondueset]

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