Extreme Dolfinism

[REVAN]

I agree with Trux that you need a major player to use the fin and with the high cost you will probably need a record to be set with it to prove its performance value over hyper type fins.

First, I need to get you competition freedivers fighting over who gets to set the record with it.

I do think there is actually huge potential to market monofins in the U.S. but no-body has done it yet... and you don't need to rely just on the current population of freedivers to sell to you can create new divers by creating a desire to use your fin.

That is all part of what I want to achieve. Creating an interest in the US market would grow the recreational base for freediving and create momentum for the entire sport. Imagine the difference it would make if just 10% of the recreational scuba divers in the US suddenly got interested in freediving. It would be like an economic tsunami sweeping the industry, bringing new energy and capitol the sport.

 

[trux]

First, I need to get you competition freedivers fighting over who gets to set the record with it.

Well, if the fin is really superior to a monofin, then I guess any of the top 10 or top 20 freedivers would be good enough to set at least a national record. Current ranking is available here: APNEA.cz - Ranking

 

[REVAN]

...a DOL-Fin scuba diver achieves about 3 times the fin amplitude per stroke. However, drop all of the drag producing scuba equipment and the fin produces enough thrust to propel the diver almost 5 times the fin amplitude per stroke.... An ideal freediving monofin would be closer to the sweet-spot near 3.

One option to get there would be to make the fin smaller to produce less thrust, but this would also reduce the swimming speed and the distance covered per stroke. The speed could be brought back up again by increasing the frequency of the flapping, but the distance per stroke would still be low and at some point the frequency becomes unreasonable without changing human biology to cycle really fast like the tail of a skipjack.

The other more reasonable option is to increase the amplitude of the fin stroke. This keeps the frequency to reasonable values and increases the distance covered per stroke while improving the Shrouhal number. Instead of just kicking the fin with larger amplitude which would increase the swimmer’s hydrodynamic drag, we can place the fin on an extension behind the swimmer such that it moves farther than the swimmer's feet when he/she is kicking it. This will increase the amplitude of the fin stroke without increasing the amplitude of the swimmer’s kick or the swimmer’s drag profile.

The first step toward evolving the DOL-Fin Classic into the ultimate freediving monofin was to build a test fin with adjustable length struts supporting the fin to investigate the relationship between strut-length and achieved Strouhal numbers. Other metrics which impact design choices were foot and ankle reaction loads and their impact on diver strain and comfort and also the distance covered per stroke of the fin.

After a thorough investigation of the design space I settled on a strut length and built a more durable test unit (with non adjustable struts) for prolonged evaluation and further development activities. This engineering test fin can be seen along with the DOL-Fin Classic in the following video.


I dove with this long strut configured DOL-Fin for a full season to get a good idea of the pros and cons of this arrangement for recreational freediving. The conclusion was that I definitely liked freediving with it better, but it introduced a new problem that I was going to need to deal with. I’ll cover that story in my next segment.

 

[Fondueset]

I like the look of the one with the long struts. I like the option to go with high amplitude (still no knees!) - low frequency - and still cover a lot of distance - this gets beyond your ideal ratio - but works very well in recreational diving where we do a lot of glide. The objective is to always maintain good form - knees straight - power coming through the core in a wave that goes from hips through arms and back down - (really right out through the toes). In terms of whats efficient - I'm on the fence. In pool dynamics I play with both a large amplitude (still within correct form) low freq and low amp hi freq. Last time I was in the blue hole Will T. was working with higher frequency/lower amp for constant weight dives.

What gets me excited though is seeing distance covered with minimal movement. - I realize thats a different priority.

 

[titan]

But the price you ask is to huge it's worth more to still buy the right hyperfin wich by the way are the new fashion

 

[REVAN]

But the price you ask is to huge it's worth more to still buy the right hyperfin wich by the way are the new fashion

I think you are jumping to a premature conclusion. This story is far from over and you don't know where it is going to end yet. I'll urge you to maintain an open mind. There may be good reasons why something may be worth the extra $$$.

 

[titan]

ok I will try to do it although I'm like a grumpy old stuck with bad habits myself
I'm not saying that you product isn't good otherwise I wouldn't be here tlking to you but the extra cash is simple to much unleass your fin really but really can make a diference

I would love to do see someone testing it with some max dynamics

 

[titan]

And consider yourself lucky because this is the forum with the greatest vibe and people arround the world

 

[cdavis]

Revan, there is another aspect to "barefoot" that you are missing. Many warm water divers don't want to wear anything on their feet except a fin. Boots, neoprene socks, even thin nylon socks are aggravating and we avoid them where possible. Its a comfort, gear-up time, gear simplicity sort of thing that has nothing to do with efficiency.

Good luck on your project. If Laminar still has a Dol-fin, I'll probably get to try it in October, hope so.

Connor

 

[wet]

'I have wondered whether there might be a soft "fabric" fin, unbreakable, that worked more like a tensional sail of a clipper ship rather than a compressive blade of a windmill.'

Me too, Wet. I cannot vision any way to do this without pulleys and guides.
Are you familiar with single side airfoils that are used in indoor and towline models (soaring birds, too)? Have you considered the elimination of the upstroke thrust?
I'd like to read your thinking along this line because fins seem to be opposite to propellers.

Actually I had been thinking of how the great white shark has no bones, just teeth and cartilage, and although whales and dugongs have bony pectoral fins (hands) their tail flukes aren't bone, just cartilage. Dugongs have very dense boned rib cages and dense skin, but not in their propulsive fluke components. Tadpoles have muscular non-bony cartilage tails. Most fish have thin bones but lots of muscle in their tails.

Point is that push-swimming (tail-fluke) and pull-swimming (forelimb fins) differ a bit in materials used, maybe a tensional fabric combined with flexibly rigid struts would be a good combo for some free diving. (Also considering manta ray 'flight'.)

So I was thinking that hard/dense monofins may give more powerful thrusting and speed but have higher relative energy needs over the longer period. It depends on the type of diving, the dive environment, the musculature used, preferred depth/ buoyancy/ballast, many variables. But I haven't come up with any prototype.

Great free diving video, like those sea lions. Sea lions propel with their forelimb fins, like penguins, unlike sea otters, dolphins & dugongs.

 

[Fondueset]

Titan - one edge the dol-fin has over any hyper-fin is durability. Performance remains to be seen - but comfort and durability are pretty much in the bag.

I am still running my oldest hyper fin - but after a couple of years of hard use you begin to see the fiberglass breaking down - and the rubber deteriorating.

Connor - the footplates on the one I tried looked to me like they could be made to accomodate just about anything. I'm thinking Revan could probably even set them up to take any standard layout bi-fin pockets without too much trouble - which would be a smart move

 

[titan]

How old is your oldest mono ? and by the way u llok like someone beats up and torture the poor hypers (frozen lake,lots of swimming,...)?

I didn't remenber exactly the price but correct if I'm wrong 1200$!!!you can go to dahab,playboy mansion or buy a car with this money even hyoerfins are to expensive
but the fact that some of them have anatomical footpockets and you chose your angle (more angle more glide less drag more efficient with less force) angle,ergomics,and transmission of force are the base cool blades com after lots of manufacters miss this

but again I think I can speak for all here we WANT to see a REAL max DYN performance of this baby and possibly we finally go back to the time were our fins don't have to extra for travel or be stucked in airport checks

Didn't ever to you guys any at an airport when you say the package is a fin, any girl at the check looked at you with that scared face saying ohhh should I call security or he is just a creppy guy?!?!?!

PS:it even asked once if carried a dead animal with me loooooooool

 

[Fondueset]

They always look at me coyly and say things like 'Wow! It sure is BIG!'

Maybe 2.5 years - My original Nemos are on their second and third owners - but the hypers take life a little harder.

Yup - lots of freezing, glue problems etc. Last glue job I used Gel type superglue and it's been really happy with that.

 

[laminar]

Thought I'd offer some thoughts here. Revan/Ron has asked me to help him with the needs, wants and desires of freedivers for his project. I have no financial stake in it, to be clear.

First, of all, I am excited to see the newest prototype from Ron in May/June. Having tried two versions of the Dolfin (the one you tried at Dean's, Fondue and an additional one last summer), I am happy that Ron hasn't given up on this yet. His approach has great potential and he is responsive to freediver feedback, as you can see here.

I echoed many of the challenges that you guys have raised on this thread so far:

Should feel good to swim with. Whether it is the feeling of stored energy or something new to replace it. Finswimming has a great kinesthetic reward that goes beyond maximum distance or efficiencies.

Kick and glide or continuous swimming should be possible.

Durable (check - what monofin have you ever used as a walking stick, self-defense weapon and igloo block cutter)

Low drag blade and footpocket (the blade just slides through the water beautifully. Awesome for FRC descents).

V.1.0 footpocket wasn't optimal from the freediver's point of view)

Simple to use and care for.

One size fits all: big drawback of hyperfins is how to get the right size. Unless you can try them on and return them easily, hyperfins and even traditional monofins will always have that disadvantage.

Easy to use. This is tougher to judge if you have lots of monofin experience. I think that learning to use the DOLfin (v1.0) has a few hurdles, but so does learning how to use a monofin with ease.

Performance

Now here is the tricky one. I also felt that for the DOLfin to have a chance at capturing attention among freedivers, it should at least match or preferably outperform the hyperfin. But because of the subjectivity of a freediving or swimming performance, it will rest on user impressions from influential people.

I think that if the DOLfin can match (allowing for subjectivity) the low effort kick and glide performance of a hyperfin, it will be a superior product. This will be a great challenge. Hope it can be done. It will only help develop better fins for us all. :friday

However, one important caveat. If the intended audience for Ron's fin is a new crowd of diver or snorkeler interested people with no previous exposure to freediving, what they will be looking for will likely be a whole lot different than what we want.

They may look for what they expect from other mainstream, mass produced products, as someone pointed out above:

ease of use (learning curve shouldn't be too steep)
durability
cool factor
comfort

For this crowd, I believe that the door is wide open for a fin that delivers more than traditional monofins, especially when it comes to comfort and durability.

Pete

 

[Fondueset]

Yo Pete,

Are you headed to Fla in October - or does Connor need to borrow my suit again?

for sure the Dol-fin has lower drag than anything else I've put on my feet underwater - forgot to mention that.

I also agree it'll be golden if it matches a hyperfin in performance - then we just need to whittle away at the price.

- FYI all - Pete is the most accomplished recreational monofinner i've ever seen.

 

[REVAN]

Hi Pete. Thanks so much for the in-depth perspective you provided above. I’m sure many people will appreciate it.

Now, it is time for the next chapter in the story.

Recall my comment from my second post regarding one of the advantages of the DOL-Fin Classic: “It is light weight and travels relatively easy (using a snow-board bag as a dive gear bag).” The new dimensions with the long struts kill that concept. The fin is now too long to fit cross-wise in a snowboard bag and too wide to fit in anything else. Since the DOL-Fins are modular systems, you can remove two screws and the fin detaches making it portable again, but you would still need something long like a show-board bag to put it in. Whereas a scuba diver has a lot of equipment and needs a dedicated gear-bag to travel it in, a freediver has much less equipment and a dedicated dive gear bag just creates additional travel complications and expense.

I had experimented with a shortened fin that was only 32 inches span verses the 48 inch fin I had been using. As would be expected from using a smaller fin the performance of the DOL-Fin dropped off, but the whole thing broke down in a minute and fit in a standard large suitcase along with the rest of my clothes and stuff. It was so easy to travel with. I was amazed at how big of a difference it made. It would be a minor revolution for recreational freediving to have a high performance monofin system that could travel so easy.

I thought there must be a way to have a high performance hydrofoil that also travels well and set out to determine how to make it work. Taking a hint from Navy aircraft, I decided the best way to proceed was to develop a fin with folding tips similar to the folding wing systems like the one shown in this attached photo of an F-18 Hornet. To be an effective solution, the system needed to be simple, robust and corrosion resistant. As it turned out, the DOL-Fin’s architecture was closer to supporting a solution than I thought, but the successful implementation would require incorporating some advanced aerodynamic (or in this case hydrodynamic) concepts to make it work.

 

[Fondueset]

I wondered about making the Dol-fin a little less wide - but deeper - how would that play out performance-wise? Might mess with angle of attack I suppose - across the broader surface area - unless you put in a sort of aileron!

What about a central rotating hing/lock - a bit like a pocket knife - but locks down into place? You'd have a flush button in the center of the blade to disengage the lock - then rotate the two halves in line with eachother.

The C4 monoflap travels nicely in a 29 inch bag - take the shoes off and partly roll the blade.

 

[REVAN]

What about a central rotating hing/lock - a bit like a pocket knife - but locks down into place?

The bending moment will be highest near the middle of the fin. While you could put a folding mechanism in there to fold the fin in half, it would have to be strong, probably machined from metal, and it would end up being expensive to manufacture.

I know that many of you are already having issues with the cost, but I have tried to be very attentive to not make design choices that I do not think will have a positive return value to the end user. It is going to be much less expensive to fold the fin tips over and leave the central portion of the fin a solid structure.

I wondered about making the Dol-fin a little less wide - but deeper - how would that play out performance-wise?

As for a less wide but deeper fin: The fin dimensions are a balance between performance and manufacturing cost. But, once again I have some tricks to unveil and you are getting a little ahead of the story; kudos to Fondueset, for forward thinking. :friday
...

 

[Fondueset]

I was just envisioning the carnage caused by swimming through a school of small fish with that wide blade

 

[Grant Smith]

All the fish I have seen are quite able to get out of the way! rofl