Underwater Streamline

[elmer fudd]

This might be interesting as a stand-alone experiment but from a whole diver perspective, it's like treating split ends when you have a hatchet wound.

I definitely see your point, but it also seems to me that every little bit improvement will add up. No one really argues that it's not a good idea to maintain proper trim or minimize the danglies, and that's being done for the exact same reason. If you cut or minimize enough sources or drag eventually it will become apparent in both speed and air consumption.

Now of course having a cone attached to the bottom of your tank is a bit ridiculous and impractical, but I'm guessing it might make a significant difference to streamlining.

I'm planning on trying it out sometime this summer during a boat dive. I'm thinking that attaching traffic cones to the bottom of my tanks during shore dives with my buddies is probably a good way to end up solo-diving.

 

[Jorgy]

Streamlining is good.....

Unfortunately, I have this ungainly camera rig that messes it up.......

Just having fun......

M

 

[Blackwood]

The front of the tank already has a fairly aerodynamic profile. The regulators sure don't, but the tank and valve form a nice cone shape. The butt end of the tank however is about the worst aerodynamic profile you could get, especially an aluminum tank or a steel tank with a boot.



The reason I ask about the boot is because on a steel tank it takes what would be a hemisphere and gives it straight 90 degree edges. Now obviously a hemisphere is a pretty poor trailing edge, but it still beats the hell out of a flat surface running perpendicular to the direction of travel.

What I'm actually thinking of doing is taking a traffic cone, cutting off the bottom, cutting a series of slits in the sides and then wrapping some duct tape around it to make it slide up over the bottom of my tank like a tank boot. No, this isn't going to become part of my regular kit. It's going to be more of an experimental thing. I'm curious what affect it will have on my speed and SAC rate.

If you can show experimentally that putting a cone on the back end of your tank creates a measurable and repeatable decrease in your SAC rate, I'll pay pal you ten bucks.

Would it slightly decrease the drag of a cylinder alone? Possibly (depends on geometry, Reynolds number, etc.).

Within the context of a diver, it's going to be in the noise. The back end of your cylinder is probably within the wake of your body anyway.

 

[elmer fudd]

If you can show experimentally that putting a cone on the back end of your tank creates a measurable and repeatable decrease in your SAC rate, I'll pay pal you ten bucks.

Your $10 are probably safe. While I suspect that a fairing of some sort will indeed improve streamlining, any measurement of my SAC rate or speed will be purely subjective. It will be the kind of thing where if the amount of air I use relative to my buddy goes down or it seems like I'm going faster with less effort, then I'll say I saw an improvement. Trying to quantify the difference isn't going to be something I'm going to attempt. I'll readily admit however that many of the things I come up with don't work at all, so I'll have no problem acknowledging failure if it does occur.

Within the context of a diver, it's going to be in the noise. The back end of your cylinder is probably within the wake of your body anyway.

I've also thought that instead of a cone a better shape might be a taper leading back towards the legs.

 

[thomjinx]

FWIW, I switched from a jacket style BCD to a DSS BP/W with a small 17 lb lift travel wing and noticed a significant decrease in drag.

I think tapering the trailing edge of a tank would only make a significant difference in drag at speeds that are faster than you could swim anyway.

-Thomjinx

 

[tomboyy]

wheres the race at ?

 

[UaVaj]

wheres the race at ?

never about race. always about efficiency.

 

[kanonfodr]

never about race. always about efficiency.

Efficiency is great, but I think changing your tank diameter to accommodate that wish will not earn you much. Case in point: AL80s versus LP95s. AL80s are 7.25" in diameter and 28" long, approximately. LP95s are 8" in diameter and 24" long, and they have a dreaded boot on them. With a good fill on both I hit the water with almost 20 cu ft of extra air in the 95s. Guess which one I stay down longer and explore further with?

Yup, there's no replacement for displacement. My 95s will get me a bit further than my AL80s, because they give me more gas. Period. I also carry less lead, the tanks trim better (for me, but trim and tanks are very personal subjects); I'm now more efficient with a larger diameter tank because I perform better as a diver in the water, not because of my tank.

Once again, your tank has very little to do with overall efficiency of your rig since the diver makes the rig and not vice versa. Hell, if nothing else you can get a bigger tank that carries more gas and your efficiency you've strove so hard for got shot to pieces because you may be Mr. Super-Duper Efficiency with your steel 50 cu ft tank, but I'm diving double HP130s and I've got a helluva lot more gas than you could dream about having in your tank. And that includes the fact that I suck as a diver and hoover my air, but I've got 5 times the breathing gas you do.

Efficiency is nice, but realism and consideration of the total diver is far more likely to get you somewhere.

Peace,
Greg

 

[charlesml3]

This topic always tickles me. A diver is about as streamlined as a cinder block. If you're going to great (or any) lengths to try to "steamline" yourself in a effort to reduce drag and therefore air consumption then You're Trying to Move Too Fast.

Slow down. The slower you go, the more you see. Let the reef life come to you.

-Charles

 

[UaVaj]

Efficiency is great, but I think changing your tank diameter to accommodate that wish will not earn you much.

You (and some of you) need to read everything and stop reading whatever you want to read. This has nothing to do with selling a tank and buying a new tank just for that 0.00001 improvement.

It is about someone who wants to buy a new gear (obviously they have a choice) and they can decide if they want long and thin OR short and thick. (sorry ladies if that did not come out right)