What water sees.

[MrSig]

rx7diver

Maybe I'm just a big nerd, but I thought it was really cool comparison. But then again as an engineer I see that you're sketches do have some potential to produce some really good data. If one was interested in finding out how to become more aerodynamic in the water, which would allow them to move through the water with less effort using less air and increasing your overall dive times. Being that drag is a function of cross-sectional area you could use this type of sketch to accurately calculate out your area using different types of equipment. This could be beneficial if you had to dive in high current conditions and were trying to select what type of gear you are going to purchase.

Assuming the models were to scale it would appear that the jacket style BC would be more aerodynamic in the horizontal position than the BP/W would be. This is assuming all other things are equal. I've never used a BP/W before but based off of what I have seen in pictures of them I would have to assume that they would have the smaller cross-sectional area and thus be more aerodynamic, not only in the horizontal position, but the vertical (perpendicular to the current) position as well.

Mark

 

[undrwater]

Please add in the "danglies" of the equipment.

 

[rx7diver]

Please add in the "danglies" of the equipment.

undrwater,

Must danglies can be eliminated/reduced/restrained, I think.

However, I did revise my graphic to show a slung bailout/pony bottle (Luxfer Al 19, OD = 3.47"). I actually had superimposed an old Al 30 (OD = 4.87"), an Al 40 (OD = 5.25"), and an Al 80 (OD = 7.25"), too. Extremely revealing. However, the graphic became much too cluttered. So, I removed them all except for the Al 19.

My profile shows that I dive a Scubapro SSJ, a Freedom Plate, and, recently, a VDH double hose regulator backplate, depending. Love them all. Every single one. Use them for different purposes.

I eschew a conventional doubles backplate used with a single tank. Several years ago I wrote on here about my extreme displeasure with this configuration. The middle diver in my graphic suggests why: The cylinder was too far away from my back--whether or not I was using a STA. Made me extremely unstable. Whether diving wet or diving dry. The Freedom Plate and the VDH plate do NOT suffer this problem, since they locate the cylinder very near my back--as near, in fact, as does my SSJ. No ~2" standoff. In addition, they simply are much more comfortable. Even if I am wearing only a tee shirt.

What's interesting is, I never noticed the additional drag that a conventional plate introduces from having the water "see" so much more of the tank, as suggested by my graphic: I never wore that configuration long enough to sample this additional drag. I couldn't get out of that configuration fast enough!

About the bailout bottle. I actually have never worn an Al 19. However, I wore an Al 40 (or two Al 40's; OD = 5.25") when I was tech diving in the 1990's; they replaced my OMS LP 46's as my deco bottles used with my PST HP 100 doubles and PST HP 120 doubles), and, so, I tried an Al 40 as a bailout bottle for single tank recreational diving. Hated it! Much too wide/heavy/big/cumbersome/unwieldy for the single tank recreational diving I do.

Last year or the year before I tried an old Al 30 (OD = 4.87"). Not bad at all. Much narrower and "friendlier." In fact, I special-ordered one from my LDS (whose bottle I had tried). When it arrived, it was the new style Al 30, which has the same OD as an Al 40! I didn't even take it home. Not about to dive it; my experience with the Al 40 was enough!

So, the Al 19 would seem to fit my type of single tank recreational diving. It has sufficient capacity. And, on paper, it would seem to be sufficiently small (for me). Which is why it is pictured in my graphic.

More about the bailout bottle: 1. I have actually never worn a slung bailout bottle with my SSJ--although I understand some have, which is why it is included with the left diver.

2. I have read that some divers, configured like the middle diver, are wearing their small bailout bottle more like a side mount diver wears a side mount tank (i.e., under his/her arm, adjacent his torso). Wearing the Al 19 that way would keep the water from "seeing" the Al 19. I will probably try this some day--when I eventually purchase an Al 19.

3. The third diver presents an interesting option for not having the water "see" the bailout bottle: eliminate it altogether. If a diver wears baby doubles, he/she might wear them as independent doubles, or use an isolator valve with them. Either of these approaches eliminates the need for a separate bailout bottle! (However, if the diver wears his baby doubles as a single-reg rig, perhaps with a single center valve to accommodate his double hose regulator, then he is back to carrying an Al 19 bailout!)

Anyway, the newest revision of my graphic is attached.

Safe Diving,

rx7diver

 

[undrwater]

I can't comment on the traditional backplate. I went from a back inflate BCD to a freedom plate with wing. The single biggest impact on stability I have felt was the addition of a crotch strap. That was like finding religion.

In all those configurations, I would imagine the hydrodynamics would be measurable by some kind of instrumentation. I doubt a "blinded" diver would be able to tell much difference. All of your divers are in good trim, so their respective gas use is minimized.

I'd bet there are other factors in play that impact how smoothly one moves through the water. I remember doing some research on "drag coefficient", and what I discovered was completely counterintuitive.

Have fun!

 

[undrwater]

And I'm dreaming of baby doubles. I wish Santa still existed.

 

[MrSig]

undrwater

What did you find counterintuitive about the drag coefficient? Just curious because when I try ok fluid dynamics in school I found it to be fairly straight forward.

Mark

 

[w3dge]

Do you have the numbers for the extra area presented by the inflated wing compared to the jacket? Whilst the wing looks a larger area at first glance, I wouldn't mind betting that although the jacket looks narrow, its area is also quite long, and so the areas may be quite similar. Or at least not so vastly different as appears at first glance.

 

[undrwater]

@MrSig , i was looking into drag coefficient as it relates to cars. As a layman (No engineering background), I had certain expectations what a low drag coefficient car would look like. I was surprised. I don't know if that can be generalized to fluid dynamics or not.

 

[rx7diver]

undrwater and MrSig,

My graphic is intended to help people think some more about their own rec diving configurations.

I am more a pragmatist than a modeler, more a proof-of-the-pudding-is-in-the-eating type. I would urge a diver to actually try out different configurations and see if any makes a difference with respect to the type of diving he/she does. I would advise a diver to do this rather than to wholeheartedly drink anyone's Kool-Aid.

Models are useful (fluid dynamics or otherwise), I suppose, but perhaps only to predict a direction to pursue. Ultimately, the configuration that actually works better for you, um, works better. Agree?

Safe Diving,

rx7diver

 

[undrwater]

This thread is similar to @REVAN 's related to minimalism. I'm curious if he's looked in here.