Monofin Bend

[BennyB]

Following on from some of the discussion in this thread :http://forums.deeperblue.net/monofins/75538-waterway-glide-vs-leaderfins-hyper.html

I had a comp this weekend and got some dynamic photos. What do you think of this for a fin bend? This is a Hyperfin.

 

[trux]

Yes, besides the V-bend already discussed earlier, the fin seems to be quite overpowered. Well, both effects are likely related, but the fin definitely does not look very efficient. Perhaps it may work better with a slow relaxed kick. Perhaps you need to stop eating all those steroids! Or does all the power come from beer?

 

[BennyB]

Lately i've changed fuel sources from beer to cider-powered

I do a kick-kick glide style, with the last kick being a bit harder with a bit more knee bend. This style has brought great results in the past but with the Hyperfin everything feels like hard work. I'm thinking of going back to a slow constant kick and keep my speed up, though i'll probably try a few different ways to accommodate it.

 

[trux]

If you can, borrow a stiffer or shorter fin, try with it, to see if it makes any difference. You could also try provisorily reinforcing the blade with some flexible material to see if it helps. Shortening the blade might help too, but that would be irreversible, so probably not something you are willing to experiment with.

 

[jome]

Any chance of getting a video? From the stills it does indeed look overpowered. But to know why, a video would be helpful. Ie. is the mono too soft or are you just abusing it?

 

[trux]

From the stills it does indeed look overpowered.

Yes, indeed it does. Almost the entire blade is bent practically perpendicularly to the axis of motion, hence having practically zero propulsive force at that moment. It only propulses when it flexes back, but on my mind that's not the way a monofin should work. I think that for the optimal propulsive efficiency, the working part of the blade should be (possibly most of the time) in the ideal angle of attack, which is (if I am not wrong) 45° when still, and decreasing with increasing speed. That's why fins for sprint are stiffer (achieving so the lower angle for the maximal propulsive efficiency). If you watch videos of monofin swimmers, the blade practically follows the shape of a rather flat sinusoid. I never saw a fin blade bending so much like in the photo above.

 

[Kars]

Nice photo's Ben! Not discribing the technique and matrial.

In general I think you have overpowerd your fin big time.

Don't write of your kick, kick glide style, just adapt it, tune it a bit to fit your fin. You could stretch the time of your kick (kick slower).

On the otherhand I like the contious stroke, I think kick and glide is helpfull for those who have muscles that acidate quickly, cannot drain that acid fast enough and need recovery-time. I think it's more efficient to have a very stable speed with as little speedchanges as possible.

Appart from efficiency, I much rather see a beautifull contious stroke performes by a flexible person.

Love, Courage and Water,

Kars

 

[Mullins]

Looks very much like my fin, when I swim fast with it. Although mine would have much move V-bend at that point. I guess a kick and glide style is always going to result in the fin bending more, as you're almost doing a standing start each kick.

Although the hyperfins have got the v-flex thing going on, I think all the hyper-style fins bend at the footpockets rather than the blades. My leaderfins certainly did and I've seen pics of Glide fins doing the same. However I'm getting one of these to try so will report back, if the shipping company ever manages to locate it...

 

[trux]

Looks very much like my fin, when I swim fast with it. Although mine would have much move V-bend at that point. I guess a kick and glide style is always going to result in the fin bending more, as you're almost doing a standing start each kick.

It seems then that a shorter/stiffer fin would be better suited for the kick and glide style. Not only it would allow for more powerfull kick from the quasi still stand, and avoid both the V-bend and overpowering, but the shorter blade would also reduce the drag in the glide phase. Did you try experimenting with that, Dave?

 

[Walrus]

Hi Ben,
I agree with Dave, it's bending much more at the footpocket then the blade itself, I have photo's of my medium stiff leaderfins hyper doing the same thing. The new generation fins are prone to this because the footpockets have a lot of rubber or foam between your foot and the blade. Compare this to the old waterway and your foot was sitting directly on top of the fibreglass blade. The bending at the footpocket is going to be worse as the blade is stiffer it puts more load on the footpocket. I haven't seen photo's of my soft leaderfins hyper pro, but it doesn't feel like it's bending thru the footpocket anywhere near as much as the medium stiff one. The leaderfins hyper and pro also has the foot very far back from the blade, this probably makes the problem worse too. To reduce the problem you would need more reinforcement between the footpocket and blade, and perhaps very thick fibreglass on the footpocket side of the blade. They really need to do it at the time of construction, don't think it's an easy DYI fix once you have a fin.

These fins are designed for finswimmers and not freedivers, I think with normal finswimming technique you wouldn't notice the footpocket bending as much. Of the fins I have tried for dynamic the ones that seem to be the most efficient are larger and softer blades. The shorter stiffer fins performed much worse.


Cheers,
Wal

 

[gingko]

Well, I've got a Leaderfins Hyper too, in a "soft" stifness, and I didn't ever saw that bend on mine.
I'm not tall (1m73 / 68kg), and I don't use the same kick-style when I swim with my monofin : I use to have a low amplitude in the mouvement (comming from my back) and medium frequency in the kicking (with quite straight legs), and so the speed is a little bit faster. (I have to say that I'm not a good finswimmer, and I don't manage very long DYN, as some of you.)

As Trux said, I think that the footpocket bend come from a wrong (?) or too hard kick-style. And the fulcrum seems to be only on the blade, instead of be also on the upper-body (and the arms).


.../...

 

[OceanMan]

I have a hard blade hyper from leaderfin and a kershkov monofin (hyperfin like).
They don't bend like Ben's monofin. No v-bend and no footpocket bend even with kick&glide style.

I totally agree with Trux when he says that a monofin should not bend this way for optimal propulsion.

I think it really depends on the design of the fin. For sure, a wide and large blade can only make things worse.

What is weird is that the same fin can either show bad bending or not.
I know glide fins have the problem but recently a guy from my club bought one and the fin has no bad bending.
All hyperfins don't bend the way ben's one does either. I have many videos of freedivers using hyperfins and hyperfins-like monofins (including Pedersen and Stig) and 90% of the fins show no footpocket bending and no v-bending at all.
Why ?

 

[trux]

Why ?

I'd tell that besides the differences among individual fins (they are unavoidable at the hand manufactured fins), it is (as already mentioned in this thread) especially the kicking style. I think it is not such a problem for swimmers with continuous kick like Peter Pedersen, but a bigger issue for the kick and glide style. If it happens even at a continuous kick, then the fin is apparently either overpowered (and you need a stiffer one), or it has a manufacturing problem.

 

[Mullins]

Bending at the footpockets often isn't apparent until you slow down a video. I thought my leaderfins mono was bending pretty well, but it turns out the blade itself hardly flexes and it's all coming from the footpockets. It does this regardless of what type of stroke I use, and is very different from my old waterway MD1: [ame=http://www.youtube.com/watch?v=4BFleRM6nas]YouTube - Dynamic training - leaderfins hyper[/ame]

 

[OceanMan]

I watched your video in slow motion.
Then I re-watched my own videos in slow motion.
It appears you're damn right.

 

[apneaboy]

Amazing. I saw those pics Benny that is a harsh bend and yes it is from the pocket.
Good video, any others?

Is there anyway of stiffening the pockets?
How much propulsion must be lost from that sort of bend in that position?

I have a Leaderfin Hyper and I always thought the footpockets were a bit suspect, my feet are rammed in at the arch and there is loads of movement at the toes, sometimes i tape my feet at the end. I had no idea it could be bending like that, i'm going to get some videos done.

I suppose the stiffer the fin the more likely you will overpower the footpocket?

 

[gingko]

Bending at the footpockets often isn't apparent until you slow down a video. I thought my leaderfins mono was bending pretty well,

Dave, you're right. I've just seen again old vidz, and I saw that (V-bend and footpocket-bend):


You can note the same position (the same 'bad/wrong' mouvement..?) as one of Ben's picture, and the same effect on the blade.
At this time, I was just beginning monofin, so my kicking style was a bit tough.
but I must admit that...

.../...

 

[BennyB]

Thanks for all the comments so far. It's an interesting problem - one big difference between the older style fins and the new hyperfin style is the footpocket placement. On older style fins (eg Waterways Model 1) the blade ends half way up the foot, whereas on the hyperfin style fins the blade ends near the toe, giving an overall more powerful undulation. However the trade off seems to be that this makes the footpocket the weakest point. There is some sort of metal in the base of the footpocket (aluminum I think) that provides some support but not at the toeline where it is needed.

Interestingly I discussed the bend briefly today with a finswimmer and he said that type of bending isn't necessarily a bad thing if you have an energy efficient stroke. Clearly my stroke is a bit too strong for this particular fin, so I think my options are to start playing around with my stroke or get a stiffer fin.

As a sidenote, I never get that lactic on my max dynamics, I wonder if that's a sign of an inefficient stroke?

Cheers,
Ben

 

[ADR]

I dont believe v-bend it's anything to do with footpocket construction/placement or technique but rather blade shape and construction . I have a Hyperfin (does it a little), Waterway Glide Black (does it a lot) and Leaderfin Hyper (does it a fair bit), water way model 1 (no v bend at all)

The reason i believe it is all in the blade is

1. Ant Williams Hyperfin doesn't do it and mine does (that's with both divers using either fin) Only real difference in the fins is the blade shape and construction. His is an older fin with more shoulder area and more layering but same stiffness

2. I cut my Glide footpockets off my (black freediving fin) and put them on a standard waterway model 1 blade. This went from the worst offending v-bend fin to almost perfect no v-bend profile. Again much more shoulder area in the blade and different layering in the fibreglass

Here is pic from a previous thread of the two blades one on top of the other and you can see the shoulder area difference

 

[trux]

Interestingly I discussed the bend briefly today with a finswimmer and he said that type of bending isn't necessarily a bad thing if you have an energy efficient stroke.

Yes, the bending at the foot-pocket is not necessarily bad (though the V-bending definitely is!). It does not really matter if the blade itself does not flex (it could possibly even result in better efficiency). As long as the foot-pocket does not bend more than the optimal angle of attack (45° at still stand and decreasing with speed). If the pocket bends just to the ideal angle of attack and the blade remains flat, there is actually a bigger working square area, and bigger resulting propulsive force, than if the blade flexes nicely in sinusoid. It then works similarly like for example the hydrofoils on Aqueon. The disadvantage of such pointed bending is that there are bigger dead spaces on the end of the kick amplitude. Also turbulences may be higher, but it does not mean that such bending is less efficient than continuous blade flexing (I believe than under circumstances it could be even better). The problem in the cases on the photos is, that the angle is far too big, hence most of the energy of the kick gets lost.

As a sidenote, I never get that lactic on my max dynamics, I wonder if that's a sign of an inefficient stroke?

I'd tell it is more than likely - you are kicking fin up and down, with less resistance and with little resulting propulsion.