Extreme Dolfinism G2

[karl bellamy]

Great, very informative thanks, I have something thing to consider.

 

[derelictp]

New config report from Maldives:
1kg at neck
0,5kg at waist
NO SUIT

Near perfect - neutral at approx 8m, I prefer little more boyant but with some packing it's spot on.

With this comfig I'm even more stable at the freefall phase, even in strong current like today.

Significantly negative at 30m offcourse but not affecting the ascent at all.

I could not keep up with the eagleray I tried to swim with though.

Very satisfied with this fin.

 

[derelictp]

Today I had a camera -woman at the reef and caught me on my first dive of the day. You can see how relaxed the Orca allow me to be but still taking me at a steady pace to the bottom of approx 28m.

 

[REVAN]

I finally have a little monofin news to update (I've been working on several different projects lately, plus it is tax season here):

This is the mold model for the small frame Orca Mk-2, top half of the fairing (soon to be followed by the bottom half). This monofin should fit divers with foot sizes in the range of 35 to 40 when it is done. Also in the works is a large frame Orca Mk-2 for foot sizes 45 and above. So, one down and three to go on the fabrication of new mold models. It is an awful lot of work to build this stuff. But, then I think back on how much work it was building molds for the original Orca back when I was doing everything by hand, and then I think, this isn't nearly as much work as that was. Thank you 3-D CAD and CNC mill!

This marks a fairly significant milestone in the process to getting the new sizes of Orca Mk-2 monofins to production status.

Though not monofin related, this mini-series coming out on DB over the next few days will show some of the other project work I've been involved with recently: https://www.deeperblue.com/diving-performance-beyond-drag-part-1/

 

[REVAN]

FYI: I thought I'd make my original draft available from my "Diving Performance - Beyond Drag" series. This contains all 4 parts of the article, with Part 4 having quite a few differences with what was published (the published article had missing pictures).

 

[Kray]

Can somebody explain how come the skinny g2 monofin can be as efficient (or better) as the regular full sized monofins?

 

[REVAN]

Can somebody explain how come the skinny g2 monofin can be as efficient (or better) as the regular full sized monofins?

The short answer is that it is hydrodynamically a bigger fin than the "full sized monofins". It may be physically small, but it is wider and affects a larger volume of water as it sweeps through the fin stroke.

 

[cdavis]

Remember that, at any given time, most of that big blade on a traditional mono is not producing thrust, just drag. The aluminum foil has far less drag and pivots as the fin is being stroked, so that it is producing thrust almost all the time.

 

[REVAN]

The short answer is that it is hydrodynamically a bigger fin than the "full sized monofins". It may be physically small, but it is wider and affects a larger volume of water as it sweeps through the fin stroke.

This image is relevant to understanding why the small looking DOL-Fin foil can be better than the large looking hyperfin blade. The hyperfin is a deep delta wing shape, it has a long chord length, but a shorter span. The DOL-Fin has a short chord length, but it has a long span that grabs a larger stream tube of water.

The induced drag of the fin is a function of span loading and span efficiency. The chord length is not a factor of the induced drag, but a long chord will increase surface area does add to parasitic and form drag.

If you want the full report and more information, this image came from Barnaby Wainfan's Wing Design Lecture:
http://www.wainfan.com/wingdes.pdf

 

[Julian Chapman]

Interesting stuff but there is are important differences between a fin and an aerofoil: (1) Diving fins are designed to produce thrust, rather than simple lift. Admittedly, they do so by a similar mechanism- they produce a pressure differential across the blade and this is directed astern as thrust ((i.e. the lift is redirected into the direction of travel). Any drag reduction or efficiency can only help: The hydrodynamic profile of our fins reduces form drag as far as possible. A smooth surface reduces frictional drag. You have correctly noted that chord length does not affect induced drag- this will depend on the flow profile and pressure differential. (2) Wings do not flex significantly compared to diving fins. The large flexion of delta fins allows the centre of thrust to "roll" down the fin as the stroke and flexion progress. With a less flexible fin, the centre of thrust (hydrodynamic centre) is restricted to a small area which might be less forgiving of variances in stroke, perhaps leading to more frequent stalls. I am willing to be corrected/educated on this subject- these are simply my first thoughts on the matter. Incidentally, is there a different finning technique required for using the Dolfin design?

 

[REVAN]

The large flexion of delta fins allows the centre of thrust to "roll" down the fin as the stroke and flexion progress. With a less flexible fin, the centre of thrust (hydrodynamic centre) is restricted to a small area which might be less forgiving of variances in stroke, perhaps leading to more frequent stalls.

A deep delta will be very forgiving of a stall. It can be said that a deep delta will not stall, but will instead experience a steady buildup of drag until at some point the drag is larger than the lift. This condition is characteristic of a stall, but there is no hard break in the performance, just a steady increase of performance degradation.

A high-aspect ratio fin like the DOL-Fin can have higher lift with less drag, up to a point and then it goes bad really fast if the foil stalls. The reason the DOL-Fin works has to do with the mechanism that controls the fin's angle of attack to prevent the foil from being able to stall. It takes more technology to make it work than a something as simple as flexible foot pockets like on a hyperfin, but with the issue of stall averted, the DOL-Fin feels and works very well.

Incidentally, is there a different finning technique required for using the Dolfin design?

The DOL-Fins will work well with a traditional monofin technique. The fin likes to supply more thrust on the return (up) stroke than a classic monofin. To get the best performance from it, the stroke should be slightly modified from the perspective of ankle motions to accentuate the up stroke motion of the fin. With or without this nuance, the fin works very well.

 

[cdavis]

Never experienced stalling with my Dol-fin.

If you want to go fast, the traditonal mono technique is best. Going slow, like a reef crawling diver, other things may work better, such as just using your ankles or ankles with the slightest bit of hip thrust. It probably depends on how comfortable you are with traditional technique. My experiance, coming out of a bifin background, is the fin produces pretty good thrust with almost any technique(very unlike a traditional mono), but I'm personally much more efficient when going slow with ankles plus a bit of hip.

The pivot of the Dol-fin produces the same effect as the flex of the delta shaped fin, without all the attendant drag. Also, the aluminum blade is wider than the traditional mono, so it grabs more water. It has the strange characteristic of feeling like a very soft fin when you are not putting a lot of effort in, but morphs into a very stiff fin when you really put the hammer down.

 

[karl bellamy]

Totally agree with cdavis, I have the same experience and have come to the same conclusions regards technique.
On the wish list of mine (Revan) is there any thing being looked at to reduce drag that can fit over the head and flare out
across shoulders, this allowing to fin with arms along side rather than outstretched? Ref cycling time trial helmet, something to narrow the frontal mass.

 

[Julian Chapman]

Thank you for the replies. I will take a look at the Dolfin and perhaps buy one to experience it myself. I am very interested in all new technology. KArl´s suggestion of a fairing to improve streamlining is a good idea and worth some examination.

 

[Julian Chapman]

Where can I buy one?

 

[REVAN]

@Julian Chapman , I sent you a PM.

 

[REVAN]

I finally finished the molds for the small size Orca2. My fingers are raw from all the sanding. The next step is to have the molds mounted to the jigs for the molding machine. It'll take a little while to get the first parts from these molds to build the first units, but it is a step closer now.

 

[Azrael3000]

What's the status of the SR1?

 

[REVAN]

From what I've been able to observe, the public response to the SR-1 has appeared spotty, a few people really excited by it, but overall pretty flat. Economically, I'm not sure if I should continue to develop it. The bi-fin market is big, but there are also a lot of options in the market. My impression is that most people don't have a good handle on the difference between a good fin blade design and an adequate fin blade design and simply migrate toward the cheapest product that looks like what they are expecting (long blade, fiberglass or carbon fiber, etc...).

The Orca2 is a really great fin that has slowly but surely been earning a solid reputation. For now, I've decided to focus efforts on working toward completing that product line. That is proving to be enough work to keep my busy for now.

I'm going to let the idea of the Pilot SR-1 percolate in the background for a little while and see if it feels right to invest more in the project after I complete my Orca2 work.

 

[Azrael3000]

Thanks for the response Ron. I fully understand your reasoning. Still a shame though. For me as a recreational diver the SR1 would fill a nice niche that is a durable, high-performance fin, with which you can swim also in dolphin style efficiently and at the same time be flexible as safety without needing a fin swap. But I can see that most serious (competition) divers move towards a monofin and the rest do not care enough about performance to spend a signficiant amount on fins. Which is quite unlike scuba divers imho.