Extreme Dolfinism

[laminar]

Hi guys,

I went diving with Eric and friends on Saturday. Unfortunately, I had back spasms all morning before the dive, so my technique was a bit limited - I could not undulate fully or streamline my arms over my head properly.

But some initial observations:

Getting the fin on: No problems at all and way easier than putting on a monofin with thick gloves. I usually destroy my gloves from putting my monofin. As a thumb or forefinger usually gets stuck under the heel strap and I yank it out anyway. Everntually, the gloves tear apart. (Yes, I know I could do it without my gloves on, but sometimes it's a bother) More importantly, with a thick suit on, I didn't have to strain to get the fin on, as is often the case with a monofin - especially with the bulk of a 7mm suit.

My feet stayed very warm: I wore 3mm socks with the size 46 shoes. My socks also had holes in them. (I also bought size 45 shoes for warm weather diving.) Without first going for the 5mm sock, I wanted to see how it felt, how warm my feet stayed and the degree of clean power transfer. I was in for an hour and then a second dive for about 30 minutes and my feet were warm, no numbness. The water was 7-8C.

Surface swimming: My favourite way to swim is on my side. I call it shark swimming. With the X20, the fin tip extends above the surface and actually looks like a fin cutting through the water. I had no issues with doing this and made great progress through the current. Wearing a 7mm suit always makes this more tricky given the added buoyancy in the legs. I look forward to diving with a 5mm or 3mm suit. And no suit, as well.

Surface swimming on my stomach was difficult, but not impossible, but this was because of the high buoyancy in my legs from the suit. I find face down surface swimming with a thick wetsuit tough, with monofin or otherwise. So I usually swim on my side.

I did try swimming freestyle with the X20 stabilizing behind me. The X20 has to be the world's best pull buoy!

Performance:
For my first dive session, my back was acting up, but on the descents and horizontal swimming, the X20 felt responsive, stable and low drag, as I remembered the X18 prototype.

In the second session, I felt a little more loose and I could experiment a little more. The main difference between the X20 and a monofin is that the small surface area of the blade allows for an easy awareness of the upstroke that most monofin freedivers do not achieve. I could feel this especially on the smaller amplitude stroke that can be performed with the ankles alone, but also on large monofin-like amplitude strokes.

I had forgotten about this dimension of the DOL-fin. It's quite interesting. I look forward to exploring the various subtleties of the fin now that I have one for keeps.

I really enjoy the style of diving where a small twitch of your fin can help you change direction, speed up or adjust trim. And the low drag feature of the fin allows that without putting on the brakes.

The glide potential of the X20 is significant for a single stroke. I'm looking forward to testing that further.

Fin Buoyancy: Eric and I talked about the buoyancy of the DOL-fin. It wasn't at all an issue for me with the 7mm suit on. In fact, I would have preferred using less buoyant pants to feel the fin's performance better. But I think there are some easy solutions to this issue. See below.

Any cons for the X20?

Initially, my achilles tendon was a little sore from the flex of my ankle pressing against the back of the shoe. But to trade a little initial soreness with crushed feet in a monofin footpocket, numbness, and loss of blood flow, I'll adjust. I'll see if that persists in the long term.

The bungee cord assembly inside the fin that hold the fin tips (wings) taught on the ends of the fin might be the only part of the fin vulnerable to malfunction or damage. When I was getting the fin ready for transport on my way to the dive site, one of the zap-ties came undone and I had to repair it. It took five minutes and no harm done. But I don't know what happens if they come undone within. I know Eric tends to leave his fin tips in place after diving, whereas I'll be folding them back for storage after each dive.

Drag on the shoe. I don't sense that there is lots of drag over the surface of the shoe. Although there's something I want to try: I saw a triathlete with shoe covers made by Shimano that are made from smoothskin neoprene and attach by elastic tension cords and a velcro strap. Looks like a perfect solution for adding buoyancy, if needed, and reducing drag. And it might fit the X20 shoe interface without any mods. Ron, have you tried that?

Smoothskin socks: I did try to put on the X20 with 5mm socks at home and it was a little more work with the stickiness of smoothskin socks. Nylon 5mm socks would be way easier to use. However, all you have to do is simply open the shoe bindings a little more to get your feet in. It really depends on how snug you it want for a fit.

Sideslipping / Stalling: Unlike the earlier DOL-fin (HP?), I had no issues with strange stalling or twisting movements of the fin. Perhaps it is my experience with the fin, but I think the shoes make it so much easier to use the fin and figure out foot pressure differences from one leg to the other. I think with a little practice, this will become a non-issue. Think of all the pitfalls for the monofin in terms of technique. I'm looking forward to having my girlfriend try it, who has used a monofin maybe three times in her life.

Verdict so far: The X20 delivers what it promises, performance on par or better than a hyperfin for ocean diving and a warm, comfortable, easy to control finning experience. Can't wait for my next dive. :friday

Photos and a little video coming up soon.

Pete

 

[REVAN]

...Initially, my achilles tendon was a little sore from the flex of my ankle pressing against the back of the shoe. But to trade a little initial soreness with crushed feet in a monofin footpocket, numbness, and loss of blood flow, I'll adjust. I'll see if that persists in the long term....

I have not had a problem with this personally. I found out it could be an issue for some people when my wife try on the fin only two weeks ago. It turns out that she has a very shallow heel that causes the back of the shoe to apply uncomfortable pressure on her achilles tendon when her foot is fully extended. For a solution, I'm looking to use a heel lift insert in the shoe. This will reduce the elevation of the back of the shoe relative the heel and alleviate the pressure. The solid material and gel type inserts won't crush with pressure and should be a viable and inexpensive solution. However, I have not had a chance to experiment with it yet, so I can't comment on this beyond introducing the idea.

...The bungee cord assembly inside the fin that hold the fin tips (wings) taught on the ends of the fin might be the only part of the fin vulnerable to malfunction or damage. When I was getting the fin ready for transport on my way to the dive site, one of the zap-ties came undone and I had to repair it. It took five minutes and no harm done. But I don't know what happens if they come undone within. I know Eric tends to leave his fin tips in place after diving, whereas I'll be folding them back for storage after each dive....

This is why the bungees are redundant. If one breaks, there is still one remaining to get you through your dive. If it comes undone inside the foil, it is easily repaired with a wire to pull the bungee assembly through the foil where you can install the new zip tie. Sacrificing a wire cloths hanger will provide an acceptable wire for the job.

...Drag on the shoe. I don't sense that there is lots of drag over the surface of the shoe. Although there's something I want to try: I saw a triathlete with shoe covers made by Shimano that are made from smoothskin neoprene and attach by elastic tension cords and a velcro strap. Looks like a perfect solution for adding buoyancy, if needed, and reducing drag. And it might fit the X20 shoe interface without any mods. Ron, have you tried that?

No I have not. Feel free to experiment, though my intuition tells me any statistically significant improvement is unlikely.

...Sideslipping / Stalling: Unlike the earlier DOL-fin (HP?), I had no issues with strange stalling or twisting movements of the fin. Perhaps it is my experience with the fin, but I think the shoes make it so much easier to use the fin and figure out foot pressure differences from one leg to the other. I think with a little practice, this will become a non-issue. Think of all the pitfalls for the monofin in terms of technique. I'm looking forward to having my girlfriend try it, who has used a monofin maybe three times in her life....

The positive connection of the shoes significantly improve the sensory feedback of what the fin is doing. That make it more easy to control. However, the raked fin tips incorporated on the HP, Orca and the X20, improve the stability of the fin as compared to the rectangular fin of the DOL-Fin Classic that you had tried previously.

...Verdict so far: The X20 delivers what it promises, performance on par or better than a hyperfin for ocean diving and a warm, comfortable, easy to control finning experience. Can't wait for my next dive. :friday

Thanks for reviewing the X20, and I'm glad that your experience on your first dive with it has been positive. :thankyou

 

[laminar]

There's more to come, for sure.

I am looking forward to testing the fin in the pool with classic monofin swimming technique and with DOL-fin specific techniques.

And also with line diving when things warm up here....

The heel elevation is a great idea, I'll try that out. Thanks.

 

[nostres]

Pete,

Are You running trim plate #5? I am currently on setting 5, when I feel fairly good with the fin I'll try settings 3 and 7.


My fin came with strong zip ties but one of them was at the edge of the foil blocking the tip from entering. It was easy to shift so I moved zip ties deep into the foil. This rubber bands even if they'll break over time, they're sure simple enough to fix or replace easily.

 

[cdavis]

"a small twitch of your fin can help you change direction, speed up or adjust trim."

Laminar, could you expound on this? Compared to what? Monofins, bifins?

Thanks

Connor

 

[noa]

it would be fantastic to see some side to side testing of the X 20 with Hyper style monos in regards to line diving, dynamic and surface swimming.
maybe some of the new X 20 ownwers who also have a Hyper can start playing and report findings.
it's becoming more and more apparent that the days of classic monofins are numbered...
i guess simple, cheaper old school monofins will always have their place, but for someone who wants performance, everything is pointing in the direction of the DOLfins.

 

[REVAN]

Will full undulation swimming still have a practical function, or will we see leg only swimming in the future? Esthetically I love to see the full undulation technique.

I'll provide my own opinion on this:

Good monofin technique using full undulation will still tend to lower a swimmer's drag and have some associated performance advantages that will result from using it. What is different with the X20 as compared to a traditional monofin will be the amount of performance degradation that will be experienced by not using this swimming technique.

A traditional monofin can be expected to loose about 25% to 30% of it's performance when using a leg only kick stroke. I think the associated degradation of the same technique when using an X20 will be much less; probably less than 10%. In the long run, the hydrofoil technology will be probably prove to be more forgiving of what is presently considered "poor technique".

As far as overall capability goes, whether full body undulation with it's associated drag reducing properties will prevail over something slightly less efficient from a drag perspective, but which reduces the energy consumption of other muscle groups, remains to be seen. But, it is certainly possible, or even probable, that when we re-write the book on good monofin technique, it will look surprisingly similar to the old book. Natalia's swim with the Orca at the 2010 WC is a demonstration of how good technique can go a very long way with the new technology.

 

[Mullins]

A traditional monofin can be expected to loose about 25% to 30% of it's performance when using a leg only kick stroke.

What do you mean by "performance"? The thrust of the fin only, or the overall efficiency of the diver?

 

[esom]

But, it is certainly possible, or even probable, that when we re-write the book on good monofin technique, it will look surprisingly similar to the old book.

there is an old book about good freedivers´ (not finswimmers) monofin technique?
i´d like to read it to become less sceptical about the use of the term "good technique"

the uncertainty (or is it a freedom?) regarding less drag vs less effort is present without taking a hydrofoil model into acount, isn´t it?

 

[REVAN]

What do you mean by "performance"? The thrust of the fin only, or the overall efficiency of the diver?

I am referring to the apparent thrust efficiency of the fin. Keep in mind that these are my opinions based on me trying to make sense of a complicated dynamic system with inadequate observable data.

The reason I say "apparent" is that I believe the traditional monofin is about 45 to 50 percent thrust efficient. However, this does not take into account that it can be an effective deflector of the swimmer's wake and may therefore recover a portion of the swimmer's drag as drag-neutralizing thrust. The catches are that the swimmer's wake must be delivered to the fin for deflection, and it only works when the fin is being stroked.

The effective delivery of the wake to the fin for deflection requires the full body wave. When done properly, I think efficient monofinners are recovering as much as 25 to 30 percent of their overall drag as thrust. Therefore, a hyper style monofin may be said to have an apparent thrust efficiency in the 65 to 70 percent range for this application, even though the fin itself is only operating in the 45 to 50 percent range.

The performance loss, for leg only kick technique, I am referring to is the difference between the apparent 65% to 70% efficiency for the swimmer utilizing an effective drag recovery technique, and the 45% to 50% efficiency of the fin without this technique.

Again, this is just my opinion.

 

[cdavis]

I am the happy owner of a prototype of the x20, called an x18(thanks Ron). Very similar to the x20, but not quite as efficient. I'm a bifiner who recognizes the advantages of a mono but has never been able to find one versatile enough for the types of diving I do. My experience with normal monos is like “Mary”, when she is good, she is very very good. but when she's bad. . . . . . you don't want to go there. Bifins are like plain Jane, not nearly as good as Mary at her best, but able to do a much wider variety of things reasonably well. I've been looking for years for a mono that will be as good as Mary with Jane's adaptability. I think I found it.

I've only had the fin 3 days, 2 pool sessions. Open water will have to wait awhile, but already I see real potential for this fin to replace my bifins.

The first session, I gotta admit, was a bit disappointing at first. The fin did not instantly transform me into the perfect diver, able to swim at warp speed, clear tall buildings with a single breach, etc etc. The problem clearly was my technique. The fin is very very different from any mono I've used (or any bifin)and it is going to take a while to learn how to move efficiently, and particularly to do so in a relaxed manner. By the second session, I was better relaxed with the needed motions, but still producing slightly more C02 for the same distance as bifins. Long way to go.

As expected, the x18 produces good thrust over an extremely wide range of kick styles and speeds, very versatile. Goes slow much better than any other mono, even the monoflap. My technique is going to have to improve some before I can say much about going fast. By the second session, I was equaling my best bifin speed, but that isn't much. One thing different from other monos that reinforces REVANS comments about undulation and fin efficiency, I don't feel the distinct reduction in effort and speed increase that I get with other monos when I hit the right undulation groove. Something that I dislike about monos is the klutzy discombobulated feeling that they give me between the time I start moving and when I can get the fin into its preferred speed/undulation range. They, very briefly, feel like I'm tied to an anchor, especially if change in direction is part of starting to move. Seems like it takes a certain amount of time and effort to get the fin working right. The delay is annoying to a bifiner. That delay doesn't exist with the x18. You can start from any speed, any position, any kick style and instantly be developing reasonable thrust. You can accelerate very quickly from a wide range of positions, important for spearfishing with a sling.

A word about slow and smooth. For reef cruising and spearfishing, the ability to go slow, sometimes very slow, and do it smoothly with little effort, is critical. Bifins are good at that. The x18 for me is already very very good at that, better than bifins, and fast getting better.

Turning is still a bit of a mystery for me. I managed one smooth, fast 90 degree turn in the second session and did a lot of “snaking” across the bottom, but there is a long way to go. Mostly would have made a good entry in “Worlds funniest video”. Even so, the fin's small size makes it possible to move it in different directions easier and faster than other monos. Not quite like bifins, but close. My sense is this will come with time.

A little of the reported “side slippage” showed up at higher speed. During the first session, the fin wanted to twist to the right and lose power. Its caused by uneven foot pressure, and requires better technique. By the second session, this was almost entirely gone.

Something that did not occur to me until the evening after the first pool session (1.5 hours). I never felt any need to take the fin off. With all other monos, in 30 minutes to an hour(or less), I get a feeling of“Git this thing off me, RIGHT NOW. I can't stand having my feet stuck together another second!” The x18 is completely comfortable, all the time, no matter how long you wear it.
Another observation, I never felt “helpless” on the surface as other monos sometimes make me feel, resorting to maneuvering with my arms instead of the fin. Couple of times, I used my arms during the first session, before realizing that there was no need to. Surface performance of the x18 was far and away better than the other monos I've used. Laminar's “shark” swimming technique worked well, but is tiring for me, technique again. In the second session, it was better, but still tiring.

In summary, this is a very maneuverable, versatile fin, far more than any mono I've ever tried and I'm nowhere near being competent with it, yet. More practice and some open water experience will be required to see if it can replace my bifins, but it looks very possible.

Connor

 

[baiyoke]

I've just finished reading the entire thread... Lots of respect for this project, and the outcome in the X-20/Orca so far...

I really like the way all the technical development is explaned...

I also think it was a good plan to make this thread, and make the fin development be a narrative for the community to share... Thanks for that. I think you have partly achieved the excitement you hoped for.

I also think your openess derserves respect, because the danger in it becomes very real, when a beta-tester almost kills himself out of own ignorance and stupidity. Would have made something great turn terrible if it had happened... And bad enough with all the post that kind of mess up the technical thread with (more or less) useless negative info... I wonder why you didn't give a refund once you found out... but you kind of allready mentioned why earlier: To be open about the project. I still think things has gone too far with this beta-tester, but that's your call...

One good thing though: If keept more silent, I guess a developer also need less "knowledgeable" people to "mistreat" the product, to see more unexpected malfunctions. And also to know how a less insightfull customer, with exagerated expectations will respond... Because that's how the "big market" would probably look like.

I think that one thing that works against your project, is the long time it has/is taking before the product is good to go, and ready for orders. But not much you can do about that, and now it seems you are close...

Anyway, I'm most likely a future customer, because:
a) I like the scienceproject in it
b) It seems to be a good product at this phase; X-20 and ORCA.
c) I kind of want to support a project like that, in a very small sport/activity without the big bucks to support development.

With the price on it, it will be a matter of timing, before I purchase; at the rigtht moment, wich will be when having the right motivation, plenty/enough money, and a need to upgrade... Might be soon, might be a little later.


Many interesting technical aspects have been covered so far. One thing I still think about:

The angle of attack can be preset by you to a specifik angle.But this will also vary greatly when moving the feet, legs, hips and body. Especially on the downstroke. As I undetstand it, the upstroke is self stabalizing using some kind of rubberband.

I guess that it is one of the things you have to learn and get a feel for; when the thrust is ideal. But can you perhaps comment on your thoughts about the angle of attack in general, and how it may change during movements?

I like that it is possible to choose three diffent blade sizes. So you can customize the fin a little.

In future ideal products, I think it would be nice to be able to adjust the angle, and also perhaps the resitance in the rubberband (wich is kind of the same). Or would that mess up the "science" in your product?

I guess the extended ORCA will have a more stable angle of attack, since movements can be kept in a smaller range of angle.


One last thing:

It would make sense that bigger people get a bigger blade. But then again, it might not be that simple: I'm thinking that short people with the same musclemass/power will have more power at the feet/fin, because the fin will be attached closer to the lifting muscles (law of the lever...). I know this might not be the case, because muscle attachment will also change as a function of height/size. But in theory a smaller person might actually need a bigger blade, to compensate for smaller feet/fin movement, if the power is available I think.

What are your thought on choosing bladesize?

Oh, and the very last question: Do you know why Nathalia hasn't set a WR with your fin? Or any other person. Are there things like sponsor money claims involved (wich would make sense). Or what's going on. Anyone got any thoughts on why the fin is not WR setting allready ?

 

[REVAN]

Hi baiyoke,

Thanks for reading the thread... Its a looong one to read end-to-end.

Regarding fin blade sizing: The basic parameters that come into play involve the height and weight. These combined can be used to approximate the drag of the swimmer. The height can be used to approximate the amplitude of the fin stroke (i.e. - the lever arm as you put it). This is what was taken into account for blade sizing, and if you look at the sizing chart, you will see that the XL size trends with a bias toward shorter people relative to weight as you were suspecting.

Regarding changing blade angle: This is a bio-metric adjustment as much as anything. Not everyone's feet will extend to the same angle. To compensate for this, there are 3 trim plates with a 10 degree total spread in angles. With this, people will be able to get within 2.5 degrees of their ideal setting. Once you have that selected, there is not much reason to change it, unless you simply become more flexible with time. In any case, I felt it was important to have something that was consistent such that a diver will know how the fin will behave on any given dive. I have low priority to making a fin that is in-water adjustable, as I think that could potentially lead to mishaps under the wrong conditions.

From what I have heard, Natalia will not set a new WR unless and until someone else is challenging her existing one. When she does defend her title, I'm not sure if she will use the Orca or not. She has one of the original POP units. They were built to prove the principle behind the fin was viable and not built to last. Parts were held together with duct-tape and that fin might not be competition ready any more.

Ron

 

[trux]

Yesterday, a French guy posted a review of the DOL-fin HP on the forum Esprit Apnée. Perhpas it may interest some of you too. The Google translation (2nd link) is far to be perfect, but if you don't speak French, it gives you the idea:

Esprit Apne :: Voir le sujet - DOL-Fin Orca - une nouvelle palme exceptionelle
Google Translate

 

[baiyoke]

Regarding fin blade sizing: The basic parameters that come into play involve the height and weight. These combined can be used to approximate the drag of the swimmer. The height can be used to approximate the amplitude of the fin stroke (i.e. - the lever arm as you put it). This is what was taken into account for blade sizing, and if you look at the sizing chart, you will see that the XL size trends with a bias toward shorter people relative to weight as you were suspecting.
Ron

Hi REVAN.

Could you point me in direction of the sizing chart, all I can find is this binding size page

http://www.smithaerospace.us/Common_DOLFin/Common_SizeSheet.htm

Regarding changing blade angle: This is a bio-metric adjustment as much as anything. Not everyone's feet will extend to the same angle. To compensate for this, there are 3 trim plates with a 10 degree total spread in angles. With this, people will be able to get within 2.5 degrees of their ideal setting. Once you have that selected, there is not much reason to change it, unless you simply become more flexible with time. In any case, I felt it was important to have something that was consistent such that a diver will know how the fin will behave on any given dive. I have low priority to making a fin that is in-water adjustable, as I think that could potentially lead to mishaps under the wrong conditions.
Ron

Nice detail that you can adjust the angle allready...

I also don't think that in-water changing of angle is desired. I was thinking about something similar to what you allready made.

One thing I thought about after posting last time: With a finswimming monofin, the blade will bend more the stronger you kick. But it will to some extend also adjust itself according to speed. So it is partly selfregulating, but we are not much in control of how it behaves with different power and different speed, except that we can choose the stifness of blade. But the behaviour will change at different strokes and speed.

With your fixed angle blade, the swimmer can do slow, medium and fast stroke, with the same angle, except that it changes on the upstroke perhaps, bacause of the suspension.

So even if someone get a blade (DOL-fin) that is too big or too small to be ideal, a slower or faster stroke will actually make up for that, because the angle is roughly the same. Do you agree with that? If my blade is "too big", then I just stroke a little slower, the angle is the same, and I get the same thrust in the end.

And with a bigger blade, the stroke can be smaller, wich makes better streamlining.

And with a bigger blade, you will have acces to more "power-thrust" if needed when negative at depth.

So isn't it the-bigger-the-better, if the drag is still minimal?

Or do you think the 119cm blade will be to "high-geared" for some people?

 

[baiyoke]

Or is there a specific optimal stroke-speed for the blade, with that exact width (short side), that you have to try to hit... ?

 

[REVAN]

Or is there a specific optimal stroke-speed for the blade, with that exact width (short side), that you have to try to hit... ?

For ideal performance, the blade size should be matched to the swimmer's drag and stroke amplitude. The blade sizing chart should achieve near optimal Strouhal number performance of 0.3. To understand the Strouhal number and what it means to efficient thrust production, you can read here: style.org > The Strouhal Number in Cruising Flight and here http://www.smithaerospace.us/information_links/BioFoilPaper.pdf

The fin blade sizing is within the X-20 pre-manufacturing order forms located here: http://www.smithaerospace.us/images/X20_preOrder_Rev8.pdf

 

[cdavis]

Discovered something about the x18(and no doubt the x20) that is important to me, although I don't hear divers talking about it much. The fin is a rocket on acceleration, about 50 per cent better than my Cressi2000s, a good acceleration bifin. I used as a measure distance covered in 4 seconds starting from zero speed. Testing several other monos against the Cressi's in the same format, the monoflap was slightly slower and several others slightly faster, but not much difference either way. The x18 is in a completely different class.

If you spear free shaft, active play with spotted dolphins, want to take off fast after your turn in CW, etc, you would like this fin's performance. I want to try it subsurfing if we ever get some waves.

Connor

 

[REVAN]

...The fin is a rocket on acceleration, about 50 per cent better than my Cressi2000s, a good acceleration bifin....

Nice observation Connor. The hydrofoil provides a near direct transmission to generating thrust in the water. There is no flexing/loading of the fin blade(s) and minimal backlash slack to take up. The thrust feels instant from a human time-scale.

 

[cdavis]

I've been enjoying the "instant" thrust on this one.

Acceleration from a standing start encompases a lot more than that and was one of my big worries about how the fin would perform for me. Thrust should be instant, but mostly there needs to be a lot of it. I think of it as torque. Think big v8 engines that have hi torque at low rpms vs small high rpm engines that don't develop a lot of torque until they are turning pretty fast. That is why you don't see small hi rpm engines in drag racers. Another way to think about it is soft fins vs hard fins. The soft ones are much more efficient and just as fast, but don't have near the acceleration of hard ones. The x18 acts like an extremely good hard fin when I take off, then seems to transform into the equivalent of a softer fin as I get going.

Connor