Diving Performance - Beyond Drag (article Series And Discussion)
- Thread starter REVAN
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I am not sure you can say that previous faired systems did not reduce drag. I have dove the UDS-1 system and it most definitely reduces drag and flat plate equivalent area. The fins remind me of the Farallon Fara-Fins
How do you know that dolphin kicking is lower energy, what equipment determined that?
Aside from putting a hydrodynamic faring on the cylinder you are essentially diving with minimal equipment and free diving fins. Looks exactly what I dive with from my kayak.
I like what you are doing. I would rather see timed swims, in lieu of an instrumented diver in a flow, over some distance, say about .25 miles, using your various configurations. Distance vs. time, measured/monitored heart rate to keep the effort the same, air consumption vs distance. Seriously though, aside from the tank fairings, you are diving vintage or minimalist, essentially a free diver with a tank and a single regulator added.
Good effort. Nice work.
N
How do you know that dolphin kicking is lower energy, what equipment determined that?
Aside from putting a hydrodynamic faring on the cylinder you are essentially diving with minimal equipment and free diving fins. Looks exactly what I dive with from my kayak.
I like what you are doing. I would rather see timed swims, in lieu of an instrumented diver in a flow, over some distance, say about .25 miles, using your various configurations. Distance vs. time, measured/monitored heart rate to keep the effort the same, air consumption vs distance. Seriously though, aside from the tank fairings, you are diving vintage or minimalist, essentially a free diver with a tank and a single regulator added.
Good effort. Nice work.
N
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Eric Sedletzky
Contributor
I applaud the effort to bring back minimalist diving with a modernized approach. I've been trying to do this now for many years.
To me "Vintage" almost has a stigma; like those that partake in it are somehow stuck in the past or refuse to change, or are weirdos like those medieval re-enacters or something. I don't think that with all of them (but maybe some). I think that most people in it realize the simplicity of the gear really works well, and second to that there is a "coolness" factor.
I don't really care about being vintage. For me it's all about reducing drag and optimizing slipstream. I'm a modernist with gear because I feel brand new or at least more current gear will always be available with parts and service without needing to go to some obscure website. Any dive shop can obtain parts and work on modern regs sets, etc. for those that aren't concerned about DIY service.
As soon as there is a max year placed on an activity then it stops the progress of that activity and prevents it from growing and morphing along with new technologies. This also means that anybody willing to get into modern minimalism can do so without being ostracized that they aren't "vintage" enough.
Modern gear will always be able to supply a movement and keep it growing and relevant.
I think Revans work is outstanding and it continues to grow and develop without any "rules".
Vintage can't do that, or it's no longer "vintage".
To me "Vintage" almost has a stigma; like those that partake in it are somehow stuck in the past or refuse to change, or are weirdos like those medieval re-enacters or something. I don't think that with all of them (but maybe some). I think that most people in it realize the simplicity of the gear really works well, and second to that there is a "coolness" factor.
I don't really care about being vintage. For me it's all about reducing drag and optimizing slipstream. I'm a modernist with gear because I feel brand new or at least more current gear will always be available with parts and service without needing to go to some obscure website. Any dive shop can obtain parts and work on modern regs sets, etc. for those that aren't concerned about DIY service.
As soon as there is a max year placed on an activity then it stops the progress of that activity and prevents it from growing and morphing along with new technologies. This also means that anybody willing to get into modern minimalism can do so without being ostracized that they aren't "vintage" enough.
Modern gear will always be able to supply a movement and keep it growing and relevant.
I think Revans work is outstanding and it continues to grow and develop without any "rules".
Vintage can't do that, or it's no longer "vintage".
The UDS-1 reduced drag by reducing the frontal area with the 3 small tanks. The fairing is still a bluff body though. It will not recover the pressure drag from the flow, which is what I have done here. I think I may have been the first one to effectively do this, but I haven't put any effort into researching the history of it to really know.
Another issue, and probably why it was not more successful, is that the 3 tank arrangement is expensive. It is much more economical to use a single tank. And by using a standard AL80, I can just take the nose cap and tail cone on a dive trip (it's not even a full fairing), and I can rent the tank from a dive shop at the destination. Traveling with something like a UDS-1 would not be even remotely practical.
Reducing the drag of the scuba equipment by 85% is a pretty significant improvement. I'm sure it has to be much better than the UDS-1.
Correct. It is all very simple and effective. I want to make something much more efficient still, but this kit is done and works pretty well as it is.
I've started working on a new design that is intended to be much better still, but it has a long way to go before it will be ready for primetime and may prove to be a flop. Hopefully, it will be revolutionary instead and worth all the effort. All I can say at this point is that a lot more work is going into it than went into the other kit. Efficient cruising at 3 knots is not easily accomplished by divers. The best DPVs can hardly do that, and I'm trying to accomplish it without a motor for assistance.
Interesting question. Dolphin kick in streamline is the fastest way to swim underwater. I have no cite for it, it's just something all competitve swimmers are told early on and we corroborate it by personal experience. It probably is the most energy-efficient if you want to get someplace fast.
On the dolphin kick:
Take a look at the illustration "Vortex generation by a pair of dive fins", about 1/2 way down on this page: DOL-Fin Technology - Smith Aerospace
Note how the vortices between the two fins are both rotating in the same direction, adding to each other and intensifying the wasted energy. If they were dolphin kicked instead of scissor kicked, those vortices would be opposite in rotation, tending to cancel eachother out. It acts like one large fin with twice the aspect ratio, instead of 2 small fins.
Take a look at the illustration "Vortex generation by a pair of dive fins", about 1/2 way down on this page: DOL-Fin Technology - Smith Aerospace
Note how the vortices between the two fins are both rotating in the same direction, adding to each other and intensifying the wasted energy. If they were dolphin kicked instead of scissor kicked, those vortices would be opposite in rotation, tending to cancel eachother out. It acts like one large fin with twice the aspect ratio, instead of 2 small fins.
REVAN,
Maybe restricting to an Al 80 is hamstringing your efforts. When diving minimal gear, I personally can absolutely feel the additional hydrodynamic drag from an Al 80 (7.25" O.D.) over that of an old-school steel 72 (6.9" O.D.). And summer before last I dove my OMS/Faber LP 46 (5.5" O.D.) strapped to a plastic backpack which I had configured for my then-preteen daughters to play with. The reduced drag compared to my steel 72 was significant, indeed! (An OMS LP 50 has the same 5.5" O.D.)
You might consider using a skinny, long tank for your testing. I think this will pay huge dividends. (FWIW, Faber makes ~6" O.D. 3AA tanks one model of which has the approximate capacity of an Al 80, IIRC.)
Maybe I missed the point of your testing, but won't simply using minimal gear that includes a tall, skinny tank, a free diver's mask, and free diving fins (the kinds that Dan Volker raves about) readily deliver what you're attempting to achieve?
Safe Diving,
rx7diver
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There are a lot of things that could be smaller and, therefore, intrinsically have less drag than an AL80. However, the AL80 is the standard that I can count on having available just about anywhere I may travel. In that regard, basing a system on something else would hamstring my efforts in that I might not be able to use it when I need it. In theory, I could make a small O2 rebreather and reduce the drag that way, but an O2 rebreather also has restrictions I don't want to accept. It's about finding the right system compromises for what I want to be able to do. Economical traveling without taking my own custom tanks along in my luggage is one of those requirements.
In my case, I decided that I wanted to make my performance goals with an AL80 at the foundation, whether or not that may have a slight handicap due to its thick walls and reduced volumetric efficiency. I'll just need to work a little harder at it, with the payoff of being able to use it just about anywhere. Another benefit to designing for the AL80 is that I should be able to substitute a HP120 steel tank when it is available and get the same swimming efficiency with 50% more air available. It would be nice to accommodate this with little or possibly no modifications. The AL80 and the HP steel tanks have the same diameter, so there are a lot of choices available when the AL80 is the baseline design requirement. HP steel tanks are a secondary goal I have that's not an absolute requirement, but I favor design choices that will provide the ability to accommodate that upgrade at some point in the future.
In my case, I decided that I wanted to make my performance goals with an AL80 at the foundation, whether or not that may have a slight handicap due to its thick walls and reduced volumetric efficiency. I'll just need to work a little harder at it, with the payoff of being able to use it just about anywhere. Another benefit to designing for the AL80 is that I should be able to substitute a HP120 steel tank when it is available and get the same swimming efficiency with 50% more air available. It would be nice to accommodate this with little or possibly no modifications. The AL80 and the HP steel tanks have the same diameter, so there are a lot of choices available when the AL80 is the baseline design requirement. HP steel tanks are a secondary goal I have that's not an absolute requirement, but I favor design choices that will provide the ability to accommodate that upgrade at some point in the future.
I never really answered this question.
In my testing, I have showed that, even as a freediver in long blade fins and swimming with arms overhead in streamlined form, the fastest long term sustainable cruising speed I've measured was only 2.3 knots. That's without any tank at all. I'm attempting to achieve an efficient cruise of 3 knots with a level of effort not to exceed that of walking down the street.
So, no matter how small and skinny the tank, this approach is destined to fall short of my goal. The streamlined kit I made earlier was also destined to fall short, but I made it anyway because I thought it was an important stepping stone for gaining the experience needed to eventually be able to achieve my goal.
The solution must take a more radical 'whole diver' system level approach to streamlining and propulsion.
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