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Extreme Dolfinism

Thread Status: Hello , There was no answer in this thread for more than 60 days.
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I don't think I knew about it! But it sure it a thought.

Just ordered me a new suit.
 
I think something less wide would be more appealing if you could get it to work, the very wide blade would make many of my favorite lava tubes off limits and I would probably stay further away from coral for fear of catching an edge damaging it.
 
I already had a fin tip in the original design that was really nothing more than a bumper strip set in the end of the foil of the fin. I thought I can extend that bumper strip into a hydrodynamic surface and then make that surface unplug and fold over for transporting it. The problem was the hydrofoil has a custom cross section for high performance thrust production and the extended bumper was going to be a flat plate. To make it work, I needed to find a way to keep the extended flat fin tips from stalling which would wreck performance and cause roll instability of the fin.

I found the answer in a relatively new aerodynamic device called a raked wingtip used on some modern aircraft including Boeing’s new 787 Dreamliner which can be seen in the photo below. A raked wingtip is characterized by a rapidly increasing sweepback of the wing near the tip, and in aircraft it is used, like other forms of wingtip devices, to improve the span efficiency of the wing and reduce its induced drag (drag produced from the production of dynamic lift).

The increasing sweep of the raked hydrofoil extension will flatten the lift curve slope for that part of the fin and will delay its stall beyond that of the rest of the hydrofoil. As with its implementation to aircraft wings, the raked tip affects the DOL-Fin’s induced drag and improves its span efficiency, so I was able to shave several inches off of the span. I think the raked fin tip looks really cool too, making the fin look more biological and graceful in the water. The new fin tips fold up in about 5 seconds without any tools other than your hands. The system worked so well, I decided I would offer it as an option on the original DOL-Fin architecture configured for scuba diving also.

At this point I had a fin that was adjustable and comfortable to wear, that felt great in the water and had very positive feedback and feel of what the fin was doing, and it all traveled with fantastic ease.
Though not quite meeting hyperfin level performance, I was thinking that I was now within striking distance of it. If I could implement effective streamlining to pick up another 10% cruising performance, I’d have it covered. This would not be a simple task, and for expediency, I will deliberately leave the dead-end failures out of this story.
 

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what is the energy expenditure like compared to doing the same distance with a hyper mono. On the sprint it seemed like twice the amount of kicks I would use for that distance, but i'm guessing that they are a bit easier with your fin since you are not pushing huge amounts of water like the traditional blade. The kick kick glide looked the most promising can the glide be held longer than that or is that just the pace you like swimming at
 
Video wouldn't work for me yesterday. I'd say the sprint pace is sort of arbitrary. I mean I can cover that distance in anywhere from 5 to 25 undulations just depending. He seems to do 12 but his form is not perfect and he's losing momentum on the backstroke from knee bending. My normal pace for 25 yards is probably 11 if I'm doing large amp and moving along pretty fast.

On balance it looks pretty promising to me.
 
monkeyhatfork said:
what is the energy expenditure like compared to doing the same distance with a hyper mono?
Click to expand...

I don’t have enough experience with hypers to give a specific answer to that question. I’m sure that any good answer would also have to be referenced to a particular monofin and blade stiffness. I’ll be relying on someone else (probably Laminar/Pete if I can get together with him in May) to observe and report on details like that.

In general, though, the DOL-Fin places significantly less load and stress on the swimmers feet than what I experienced with Pete’s Triton last summer. After about 20 minutes swimming with his hyperfin (my only hyperfin experience to date), I switched back to the DOL-Fin long-strut prototype. The load difference between how the two fins feel is huge. Work is (force x distance), so if the reaction loads are less but the distance of the strokes are the same, the energy expenditure should also be less.

Whereas the DOL-Fin force coefficients remain fairly constant as the swimming speed changes, I did not feel that was true when I used Pete’s hyperfin (a property I attributed to the hyper’s blade flexure). So, the accurate answer probably changes as a function of swimming speed. As an aerodynamicist by trade, my gut says the DOL-Fin has the largest advantage at the slower swimming speeds, but looses that advantage and approaches hyperfin efficiency at higher swimming speeds. Perhaps I should state that differently. The hyperfin improves in efficiency at higher speeds due to more effective blade flexure, and will tend to close the performance gap.
 
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In that it would be similar to the C4 monoflap - which seems very efficient at low speeds and for surface swimming.

I've notice with my softer Triton that the blade looses efficiency with too rapid an undulation - if it doesn't have time to fully return there is an increased dead space during transition. My stiffer fins tolerate a higher undulation rate but are not as nice a lower speeds.

For recreational diving I favor softer fins with one caveat - for u/w photography the sound of a monofin blade seems to be some kind of 'get the hell outta hear' signal for fish. A hard fin that does not generate flex noise is a real plus in those situations. Non-issue for the Dol-fin. (also the monoflap if you don't snap it)
 
Fondueset said:
I've notice with my softer Triton that the blade looses efficiency with too rapid an undulation...
Click to expand...
That sounds right to me. I would expect the optimum efficiency for a hyperfin to occur at a particular load and frequency kick stroke. Go either side of that optimum and the hydrodynamic efficiency will degrade. The DOL-Fin should be more consistent across the speed range.
 
And hyperfins and classic monofins blades are designed for continuous kicking, not kick and glide, for either fast sprints (stiffer fins) or long distance swimming (softer blades).

Even with the variations on the design made especially for freedivers, monofins are still not optimized for us.
 
A product with hyperfin level performance combined with the DOL-Fin’s other positive attributes could be a real breakthrough product for the sport of freediving. I thought that I was getting close and that the extra performance I needed would be gained if I could streamline the DOL-Fin’s support structure to reduce the diver’s drag. The question was how do I streamline this thing? Again, I would draw concepts from aircraft design principles to help guide me.

Feet are high drag. To an aerodynamicist, they qualify as a bluff body and are about as aerodynamic as is the engine of an airplane. To reduce aerodynamic drag of aircraft, the designers usually incorporate an engine cowl to streamline the engine package, essentially encapsulating all of the high drag stuff in a very low drag shape. To illustrate this concept, I have included two pictures below; it is not hard to visualize how adding the streamlined engine cowl would significantly reduce the aircraft’s drag, even though only a small part of the aircraft is being modified by adding the cowl.

It is not uncommon for drag of a bluff body to be reduced by 80% or more by using such techniques and I thought this concept should work here as well. The wake generated by the swimmer’s feet may account for less than a quarter of the swimmer’s total drag, but a significant change to that fraction may be enough to attain the extra performance I was looking for.
 

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This is much of the logic behind classic monofin form. In combination with the extension of the fin - which amplifies movement - minimal knee bending helps keep the feet and lower legs more in the hydrodynamic 'shadow' of the body.

Ted hypothesized that the feet were generating turbulence that jammed up the lunocet - hence our suggestion that the fin be moved down toward the toes. I think this is probably true - but only one part of a several faceted problem in that case.

I wonder if there would be any advantage to a curved design - modeled more on the tail of say - Tuna. Probably harder to produce I'm sure.
 
i agree fondueset, much of what Raven is going through is the same that more traditional monofin design has gone through from classic fins to hyper fins
- foot bed seperated more from the blade
- more hydrodynamic footpocket shape

will be interesting to see the sulotions Raven has come up with and how they relate to competitve freediving.

DD
 
My new goal was to make the support structure for the DOL-Fin as streamlined and low drag as I could. Streamlined shapes are pointy in the back and the long-strut prototype DOL-Fin support fixture outlined a rectangular shape. I was envisioning replacing the two squared off long struts with something more resembling the keel of a cetacean. Blend the swimmer’s feet together into a single streamline fairing. The feet will be close together rather than spaced several inches apart as in typical monofins and hyperfins. This will bring the swimmer’s legs and knees closer together for better streamlining of upper parts of the swimmer’s body. Overall, this arrangement seemed to have several advantages over the typical hyperfin layout.

A cetacean’s keel is tall and skinny. Mimicking this architecture allows for extra height in the foot pocket and, unlike hyperfin streamlining, allows room for the integration of a sturdy heel support for the feet without accepting a large drag penalty for doing so. This will maintain superior comfort, stability and support for the DOL-Fin while under dynamic loads. The narrowed fin supports will also soften the fin’s lateral rigidity providing the fin some give, which combined with the fin’s low area profile, reduce the chance of a swimmer twisting any joints if the fin gets torqued by any rogue hydrodynamic loads (as may be encountered in surf). It was all a lofty but enticing vision for a monofin, and in my imagination the system reminded me of a shortened version of the tail end of an orca (which would become the product’s name).

Fast forward through about 5 months of work, and this vision has finally become a reality. The rectangular structural support of the old DOL-Fin has now evolved into a tapered structure covered with streamline fairings resembling a cetacean’s keel and is designed to have low drag while both stroking the fin and while coasting. For safety, the structure is assembled with redundant fasteners and load-paths and the most critical hardware attaching the fin remains exposed for easy inspection. This also makes it very easy to swap out the fin’s trim plates to change the DOL-Fin’s version of what monofin users typically refer to as “blade stiffness”.

[ame="http://www.youtube.com/watch?v=yWceQyTNx-8"]YouTube- DOLFin Orca Freediving Monfin Prototype[/ame]
In its first swim across the 20 meter testing pool, the streamlined DOL-Fin Orca prototype doing a kick-kick-glide technique shaved 2 seconds off of the time of the non-streamlined long-strut prototype, and it achieved this performance while eliminating the initial push-and-coast off the side of the pool (I didn’t want to scratch anything because I had not taken pictures of it yet). I couldn’t be happier with these preliminary results and it would appear that the DOL-Fin Orca is on track to meet or exceed its performance goals.

I will be taking two DOL-Fin Orca prototypes to Kona Hawaii in April for the product's initial sea trials (thank goodness they will fit in my suitcase). After that I hope to have more pictures and video material available. In May, I will be in the Seattle/Tacoma area of Washington State, where I will debut the DOL-Fin Classic, HP, and Orca models at the Northwest Dive and Travel Expo. If you are interested in my work and would like to attend any of these events, details can be found on my website at http://www.smithaerospace.us/calendar/calendar.htm.

As I transition from proof-of-principle, to manufactured product development for the DOL-Fin Orca, I would like to hear diver’s questions and opinions regarding this design. If you are interested in becoming a future customer and user of the DOL-Fin Orca, please let me know. Initial production may be limited, and the best way to avoid a potentially long waiting list is to be near the front end of it.

Cheers,
Ron
 
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Great to see!

Looking forward to trying it out and also seeing what other fin swimmer types think of it.
 
As a skeptic let me be one of the first to say, that if the fin keeps evolving at this rate i will be VERY interesting in being a customer!

many of my biggest issues have been discussed and alot of what you ae changing is going a long way towards making this fin a practical option for both recreational/competitve swimming.

i have a couple of questions about the footpocket shroud. as there was no images of where the feet went in i am curious to see how you made this area streamlined enough to prebvent water from being captured in it a bit like a bucket i guess.
- how do the feet dit inside the new foot shroud?
- can the unit comfortabley be used with sox or barefeet?

couple ideas i have had in the past but never managed to really kick start but i think your footpocket shroud maybe the perfect carrier for is.

a mouldable foot "plug" a piece of rubber/silicone (like mouldable mouth guards) that fits inside the shroud. the diver would heat up the plug insert it in the shroud and place the feet inside until the plug sets,this would gie a near perfect fit for every user. not sure how you would do this in practise but i believe it would not only be more comfortable but also give excellent power transmission.

but keep up the evolution of the fin, its starting to come together very well.

its hard to believe the Ugly(sorry) original DOLfin and this fin are related.

DD
 
Revan,

now it looks just beautiful, thumbs up

Looking at the dates I just realized that You must be taking it to competition in Kona next month. What a great way to promote new product by bringing it to home of the best American freedivers.

I really hope You succeed and all Your work will pay off in this tough but growing market.

Good luck!
 
Looks very promising indeed, Ron. If you have some photos, please send them to me, so that I can add the new version into my Collection of Weird Fins too. And, of course, you can submit, another ad banner with a photo of the fin too. People do click on the one you have there, but I think the conversion rates (clicks-through/views) could be significantly better (seeing from the stats at other banners). Let me know if you want more details about the stats, or some help with it.
 
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