Monofin Bend

[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]

Originally Posted by Mullins

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]

Originally Posted by BennyB

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.

Originally Posted by BennyB

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.

[Walrus]

Just one more thing I remember that is specific to the Hyper fin only that would be adding to the footpocket "bending" effect:-

I've tried out 4 hyper fins so far and I've noticed that with all of them the heel strap is very flexible and has a lot of give. I can actually feel my foot sliding in & out of the footpocket and it is definitely adding to the blade angle. I definitely don't get this with the leaderfins although it is still bending thru the footpocket itself. With the leaderfins the heel strap is probably double the thickness and has far less give, the hyper heel strap feels like a rubber band in comparison. This is something that could be fixed by gluing on and additional rubber support onto the footpocket and heel strap. So might help reduce the footpocket "bending" effect at least a bit.

The hyper style fins are mostly used for long distance in fin swimming. They always allow for a softer more comfortable footpocket for long distance, the sprint fins should have little to no give in the footpocket (and probably very little comfort). With the hyper fins I think they trade off performance for comfort with the footpockets. With the waterway fins I used to custom order the long distance blade with a stiffer middle distance footpocket, and the performance was much better. It felt like a much stiffer fin then a normal LD1, but in reality the normal soft footpockets just had too much give.


Cheers,
Wal

[Walrus]

Despite all the problems it's funny that the Hyper fin still seems to be the most efficient fin for dynamic (quite good for constant too). I wonder if most of it isn't just from the footpocket angle ?
For constant weight the fancy hydrodynamic footpockets really does nothing. For most of the dive the foam is compressed, past 20-30m it's really just squished flat.

When I tried a kicking/gliding style with waterway the gliding was very difficult, need a very large knee bend to avoid putting the brakes on. Even with a classic finswimming technique I think the increased footpocket angle, therefore decreased blade angle is actually decreasing drag a lot. (When it's not bending thru the footpocket )
I wonder how a waterway LD1 would perform if you give it a 30 degree angle ?

Might be a good DIY project. Get a LD1 fin, order the footpocket separate. Make a 30 degree wedge out of very high density foam, like from a kick board. Then glue the wedge in between the footpocket and blade. I think I might have seen an old thread where someone has actually done that.

[BennyB]

Originally Posted by Walrus

Might be a good DIY project...

Who wants to put a wager on that Andy is in the shed tinkering as we speak?

[EdHornby]

Originally Posted by apneaboy

I had no idea it could be bending like that, i'm going to get some videos done.

shout me if you want me to bring my camera to the monday pool

[jome]

Originally Posted by 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. I

Now the question is - is that automatically a bad thing? I mean weren't world records broken with that fin?

Benny - personal observations about lactics (I also seem to be "resistent"):
Most important factors are:
-The amount of ventilation pre-dive
-Warmups
-Speed and kicking style.

Quite simply the biggest lactics I get with no-warmup, no breathup, fast speed. On heavy warmup, slight hyperventilation and slow speed I get nothing.

My personal feeling is also that this has to do with the magnitude of the dive response - ie. some of us simply don't get a really good one in the pool (with max packing especially). I won't get into the whole aerobic vs. anaerobic metabolism thing, but in a nut shell not getting lactics indicates you're not very well vasoconstricted and are probably burning a lot of oxygen to swim. This would make sense since I get pretty good lactics even on a pretty shallow CW dive, which I'd like to think is because the pressure magnifies my response. My personal gut feeling is that this has to do with me being in general more of the "endurance type" physiologically. Mostly just speculation, but that's how I explain my self for sucking at dynamic All the best dyn dives I've done I felt really strong lactic burn, but on average I just "don't get that". This is especially present in bouts of aerobic training, which for me is 95% of the season. When I taper down I start to get lactics and better dynamics too...

Bit of off topic, but still...

[Mullins]

The Leaderfins mono was pretty good, but my dynamics are a lot better now I'm using the Hyperfin. I agree with Wal, this is mainly because of the angle. So the fact that records were set with a fin certainly doesn't make it perfect....

I agree with what you say about the reasons behind lactic buildup

[jome]

Yeah, there's always room for improvement and in fact I dislike it when people get hung up on records - it doesn't always mean that that particular method or fin is for example perfect for them. But I think it can be accepted as an indication that the fin is "good enough" for most uses, or at least average or intermediate divers don't need to worry too much...

I still believe that in 99% of cases, simply having the right stiffness and right footpocket size are the most important characteristics of a fin - and both properties are completely individual. Well yeah, angle is important too - agreed.

[trux]

Originally Posted by jome

Now the question is - is that automatically a bad thing? I mean weren't world records broken with that fin?

Yes, as long as the bending keep the blade in the right angle, or better told as long as it keeps the blade running through the optimal curve, it is not bad, of course. You just need to find the optimal kick style for it, so that the negatives do not overweight the positives.

The V-bending is another cup of tea, though. Although it has also some positives (better directional stability), a big part of the input energy is directly lost on moving water to the wrong direction (sideways instead of backward). So here too, the kick should be adjusted to minimize the V-bend and the resulting energy loss. Strengthening the blade accros the fin under foot-pockets and/or on the trailing edge might help too avoiding the V-bend.

[Mullins]

Just had somebody watch me in the pool tonight. Apparently my fin is doing all sorts of funny things, like v-bending even when I'm gliding.

[trux]

Originally Posted by Mullins

Just had somebody watch me in the pool tonight. Apparently my fin is doing all sorts of funny things, like v-bending even when I'm gliding.

That sounds like the fin is not reinforced under the footpockets and you bend the blade with your feet. Or the reinforcement (often a metalic plate) is bent or broken, or simply too weak. However, when gliding, the V-bend is not bad at all - in fact it stabilizes you. It is only bad when the fin is in action.