Hydrodynamics - backmount vs sidemount

[ltowles]

We're making this way too complicated; all we need is a force gage (in this case a spring scale will work), two short bits of rope, and a set of divers to swap between sidemount and backmount. We anchor the force gage in some place with high flow with one piece of rope (right outside the ear at Ginnie, or the back of the cavern a JB would both work). Then we attach the other rope to the other side of the force gage. All a diver has to do is hang on for a moment. The value on the scale is the amount of hydrodynamic resistance. Measure the same divers in both rigs eliminates differences in the drag of our body shapes and our exposure protection. And doing this with a dozen different divers will deal with the differences in how we rig our gear. This way only takes a moment per measurement, and we get rid of all the complications of using air consumption as a measure.


For air consumption to work we would need each diver to do the entire run at exactly the same speed and follow exactly the same route for both runs. Even being on the outside vs. the inside of a passage makes a difference. I also suspect it would take many, many more divers before we could get a statistically valid result with the air consumption method.


Not only would this be useful research for divers everywhere it also sounds like a lot of fun.

Louis

[phillip1]

cool sounds good, I am really curious to see what the results will be.

[Sludge]

Louis, you have something there. You want to bring a spring scale down to JB sometime?

[Webmaster]

We're making this way too complicated; all we need is a force gage (in this case a spring scale will work), two short bits of rope, and a set of divers to swap between sidemount and backmount. We anchor the force gage in some place with high flow with one piece of rope (right outside the ear at Ginnie, or the back of the cavern a JB would both work). Then we attach the other rope to the other side of the force gage. All a diver has to do is hang on for a moment. The value on the scale is the amount of hydrodynamic resistance. Measure the same divers in both rigs eliminates differences in the drag of our body shapes and our exposure protection. And doing this with a dozen different divers will deal with the differences in how we rig our gear. This way only takes a moment per measurement, and we get rid of all the complications of using air consumption as a measure.

Exactly, that's what they do with the olympic swimmers. Of course they have a big fancy facility, but a cave with good flow would do it.

I think there could be a noticable improvement by going to a more streamlined kit altogether. Smooth, impermeable surfaces over fabric. Hoses and irregular surfaces better tucked or shrouded out of the slipstream. I've noticed a very marked reduction in drag just going from a drysuit to a wetsuit.

That would be a good way to test some changes and get immediate feedback on exactly what difference it did make, rather than opinon or anecdotal reports.

[DaveP]

Maybe clip the diver off to the scale instead of holding on to it (keep the divers hands/arms in the normal swimming position).

[RN]

I don't like the idea of losing a reg costing me 1/2 my gas volume, nor how sloppy stages carry in SM compared to BM.

You don't lose 1/2 your gas if you lose a reg. There are ways to salvage it. And you aren't carrying your stages properly if you think they're sloppier in SM than BM.


Russell, I'm up for this. However, I don't think I'll be scootering in BM. I have no issues on the scoot in SM, but I'd be afraid of wacking the manifold on the ceiling since I wouldn't have the clearance I'm used to. When I BM I just put the tanks on the back of my Nomad, so my configuration is identical except the tanks.

[cavemark]

It might be possible to make a simple strain guage with some bungee cord and some cord that would register the maximum stretch in the bungie. Then just use the guage when clipping to a scooter. You could even use it to refine your own position to present the least drag in any configuration.

[Webmaster]

It might be possible to make a simple strain guage with some bungee cord and some cord that would register the maximum stretch in the bungie. Then just use the guage when clipping to a scooter. You could even use it to refine your own position to present the least drag in any configuration.

Except that the flow would be too variable. The way to do it would be to measure the velocity of the flow from the cave, and be ready to test several things at once so you could do it under similar flow conditions. Then you could test again when the flow was back to where it was previously.

The idea being of course to get as close to just the one variable thing that you want to test as you can.

[SuPrBuGmAn]

Who cares? There's a hellovalot more cave to dive in SM.

[OFG-1]

You also have to consider the wet suit vs. dry suit issue. I propose having the same diver perform this experiment in sidemount, then backmount with first a wetsuit, then a drysuit, and as a control function, totally nude while breath holding. And then, the nude part, you have to repeat with a man and then a woman, just to account for various pieces parts that create drag. And then, a DD cup vs. A cup, nude naturally, to account for the additional bouyancy. And then, a bald nude guy vs a hairy nude guy . And beards, don't forget long flowing beards that reach out and grab the water molecules like a brillo pad on a greasy frying pan. And warts, find a guy thats hairy with a lot of warts.


BTW, the spring thing is not an indicator of anything other than leg strength. The term hydrodynamic implies a moving situation, a spring tests static loads. I propose time trials. Like the tour de france, we can call it a Tour de farce.