New Equipment - DOL Fin WebSite

[Grant Smith]

The Web site for the DOL Fin is now available in a preliminary form. The URL is http://smithaerospace.us/
This fin was developed over a long period of time specifically for improved free diving experience and performance. It is also applicable to SCUBA applications. I have experience diving with this fin and find it to have a significant performance advantage over conventional dive fins. I will limit my comments to that since I am not an independent evaluator. I am related to the designer and have followed its development since inception.

You will see that this monofin takes a fresh approach to dive fin technology with its low area, high aspect ratio extruded aluminum hydrofoil and patented suspension system.

 

[Mullins]

Interesting, thanks for the link Grant. Have you had any freedivers test the DOL Fin?

To be honest, I think you may be doing yourself a disservice putting those videos up as the performance they show is very poor. The guy in the pool has a very high kick rate to speed ratio. For reference, I've just checked a couple of technique review videos I have lying around, and using a soft hyperfin which I didn't particularly like, without making an effort to emphasise anything except technique, my average numbers seem to be:

25m, 11 strokes, 13-14 seconds (1.79 - 1.92 m/s, 2.27 metres per stroke)
Compare that to:
20m, 16 strokes, 13 seconds (1.54 m/s, 1.25 meters per stroke) for the guy in the last video. Both slower AND less distance per kick.

That sort of demo is likely to put most freedivers off the idea. It may largely be a technique thing, but to me it looks like the Dol Fin could afford to be bigger and provide more resistance. Even a novice should get better numbers than those. Despite what the website says about low amplitude, it seems those divers in the videos are actually kicking quite deeply. I think the high aspect ratio just makes it look like narrower kick because there is no long trailing edge whipping around, as there is with bifins and even monos (by comparison). The footpockets are also quite large and not very streamlined. I hope you don't mind the feedback, this is a freediving website after all

And before anybody says 'but Dave always swims really slowly', although I swim at 1m/s in DYN comps I train at a range of speeds and spend a fair bit of time over the 2m/s mark. That way I can at least pretend I'm doing CW

 

[Mullins]

I just had a bit of a play around after training this evening, trying to roughly emulate what that guy was doing with the DOL fin. With a pair of duck-fins, if I did 25m lengths in 16 seconds I was having to do 16-17 kicks. That's 1.56m/s and 1.5 metres per kick.

Of course, there are plenty of variables involved here. But it's quite hard to fake that kick frequency/speed relationship in a video, so I think it is a good performance indicator to use if you want to promote the fin to freedivers. The only thing you would be missing is kicking resistance (i.e. effort input), but you can at least infer that. A good start might be to video a guy bettering my duck-fin performance using a DOL fin. Then you can start chasing down the monofins

 

[Grant Smith]

Interesting, thanks for the link Grant. Have you had any freedivers test the DOL Fin?

You are welcome, and yes. A detailed report is in the works. I anticipate that it will be favorable overall, but with a few negatives, as one may expect.

I agree with your comments on the Video. I have suggested a need for a more typical free diver video. That may require another trip to Hawaii.

I am sure that you recognize the missing factor in your calculations is stroke effort. The effort per stroke is certainly difficult, if not impossible, to assess from a video. But, in general, humans are power limited. If a swimmer can kick one fin at twice the rate of another, it is probably because the fin has half the overall resistance. Low stroke effort is an important factor in eliminating leg and foot cramping. While this may not be significant in most competition environments, it is a factor in recreational diving and sea hiking where divers are sometimes in the water for an extended period.

I have requested a video displaying slower speed operations as would be used in dynamic apnea, but the designer does not currently have suitable video to upload. His unheated pool is too cold at the moment to convince the photographer to record new video. Additional video must remain on the to-do list for now.

 

[Mullins]

I don't suppose the DOL fin requires less effort input than a pair of duck-fins, though? The monofin I used for comparison was also one of the softest on the market, and I've used it for hours on end - although I agree most scuba divers aren't likely to have much dolphin kicking experience or fitness.

All the divers in the videos are maintaining a very high stroke rate. Regardless of the effort required to actuate the fin itself, I don't think that is very efficient (maintaining that kick rate with no fins at all would still consume a lot of energy). If they want good performance, your scuba divers might have to suck it up a bit and do a little bit of training to avoid cramps. After all, if you're going to dolphin kick while on scuba then you've already indicated a commitment to high-speed, straight line performance at the expense of manoeuvrability.

I do like the whole idea of a rigid, pitching foil and I think somebody will eventually get it to work well. Tough job resolving that really complicated ergonomic/fluid mechanics combo, which has previously been done largely through trial and error, but you guys and Ted seem to be on the right track at least.

 

[DivingDane]

hmmmm, not sold, if i had to by a foil me think it would be a lunocet. either way i'm glad to see new technologies being put forward, its just a shame that more experienced freediviers were not involved in the development of such fins, because if they were alot of the obvious (to us) mistakes regarding comfort, hydrodynamics and efficiency for long distance would probably have been solved on paper long before any money had to go into a prototype, for exanmple the foot attachment points on this fin look very basic and i cant imagine they would allow very efficient transfur of energy to the foil.... could be wrong. particularly when it looks like the only way for these to fit comfortably would be with a a pair of Scuba boots which in themselves creates drag and movement between boot and foot.

my question is the weakest part of a person during the fin stroke is the ankles, yet very few fins (if any really) adress this problem by taking the ankles out of the equation. why?

a "leg pocket" which would start above the ankles securing the ankles in a fixed position fit slightly bent with a blade coming off it similar to the high andkle hyper style monos on the market would negate any ankle problems and would allow power to be transfured directly to the fin (much more like a dolphin tail does)

wil have to try and draw what i'm thinking of when i get some time.

DD

dd

 

[Mullins]

I definitely wouldn't be spending any money on a foil-based mono at the moment, but it would be interesting to have a play with one (even a bad one) and see how our impressions actually play out.

 

[laminar]

I have a Dolfin and have been using it in the ocean since last summer. Will post full review soon....

Quick points:
Has potential for performance with a few mods.
Great winter open water device for cold water conditions or long swims.
Excellent with FRC on descent. No resistance. No buoyancy.
Kick and glide works better with thicker suit and more weight. Glide is quite far.
Rugged, solid attachment.
I prefer it to the Lunocet.
Have been to 30m with it.
Have breached to my mid-thigh with it.
Very light and portable (fits in a duffel, snowboard bag)

Drawbacks:
Wide profile not great in surf.
Foot attachment needs some work for non-booted divers.
Does not do efficient speed (sprinting)...yet.
Swimming on your side is not easy.
Sideslipping happens easily until you've used it for a while, but better bindings would help.

I think the approach that Ron used with this design is very sound. But it has a slightly different application. I have talked to him about mods for greater "snap" but that would require more R&D and money.

 

[Mullins]

How does it compare to a decent mono Pete - how far away is it from being a legit alternative for competitive diving? Or is it there already?

Edit: oh right: 'full review coming soon' - I can wait

 

[ahofbauer]

One definite advantage is that
it should fit without fuzz inside
one of those airport x-ray machines.