Does this BC product exist?

[ams511]

Wow, thanks for your time. That was very informative.

 

[ae3753]

Wow, thanks for sharing. Please let us know when you have a chance to digitize the thesis. I'm sure there are many who would be interested in reading it.

 

[Thalassamania]

Thanks Steve, I'll ask this before some of the BP/W fanatics jump all over you:

The modern wing designs that use a metal back plate permit very fine tuning about the pitch axis that is so critical to how the body presents to the water.

1. If we assume perfect "tuning" for a BP/W and for an ADV style BC, how do you think that they'd compare?
2. Now lets move to a situation where we're diving a large single and have say 4 kilos of gas in the tank which means about 4 liters of air on the vest, how do you think that they'd compare now (again assume good body position in the water).
3. And as a final item, how about the physical attachement of the cylinder to the body? With a single in the 50 to 100 range its no big deal, but when you start getting into doubles does not the ADV style become a bit problematic?

 

[MikeFerrara]

(cont...)


Wing type BCD's.

Deflated, many of these were not that great because the deflated wings would drag/flap. I know subsequent years and designs allowed for these wings to be pulled in with elastic. But if they aren't fully retracted, these wings still do more to hinder swiming than act as wings to fly.

Inflated. Ugh, this is where they started to flounder. Wings pulled the diver up, increased their angle in the water, and this drastically increased drag/effort. Now, if you are drift diving, who cares, but these units curl you up, and you have to kick against it.

On the surface, well, one of the biggest problems is floating safely on the surface without being tilted forward. And then swimming on the surface is an effort as it pushes you into the water. It takes getting used to, but you have the trade-off on floating on the surface, or being pushed into the water.

What kind of wiongs were these? That doesn't seem to be a good descrition of the wings I use.

First, I use a metal plat which helps place some balast closer to where the buoyancy making balancing for trim easier. When inflated the diver does NOT get lifted out of trim...which is common to see on a diver who has all his weight around his belly and all his buoyancy on his upper body. The potential for apposing forces is easy to see but a diver who knows how to put their equipment together and control body position can keep horizontal trim in about anything.

When my wing is deflated it wraps around the tanks and is, for all practical purposes virtually not there at all. Pump in a little air and that air is laying right along side the tanks. Isn't that one of the places you said was a good place to keep it?

On the surface...my small wing with a single tank lets me float as upright as can be. My large wing with steel doubles full of gas, actually allows the doubles to pull me on my back and I could go to sleep floating on my wing like a raft if I wanted. That's just because of the weight of the doubles and the fact that the tanks are behing me. Move some of the air in the BD forward and you'd be pushed back with even more force.


You can't leave out the rest of the configuration either. The harness including belt and crotch strap is key to storage and deployment of equipment as well as rigidity. That plate contributes to balance by virtue of it's weight and location and also contributes to rigidity. The whole package leaves the front and sides of my upper body clear for other things..stage/decompression bottles, can lights, HP hose ect. I don't want an air bladder under my arms.

 

[MikeFerrara]

Thanks Steve, I'll ask this before some of the BP/W fanatics jump all over you:

But I didn't really mean to jump.

The modern wing designs that use a metal back plate permit very fine tuning about the pitch axis that is so critical to how the body presents to the water.

Yes they do. having balast around the belly and buoyancy above helps creates the apposing forces that have most (many), especially cold water divers traveling at a 45 deg head up angle.

Trim pockets demonstrate a recognition of the mechanics but they often aren't in the right place. A plate and/or a steel tank rather than AL makes it easier to get there.

 

[StevenPaulet]

Well Thalassamania, I did test the ADV with twin cylinders if you recall. In fact, that was my rig of choice then. I'll have to dig up the data to see the percentages in differences, but you are right, configuration of the cylinders is critical in making sure the diver moves through the water as horizontal as possible.

I'll leave the wing questions for later (as that debate is long and lenghty, and I imagine heated, LOL. I made a few manufacturers mad when I tested their rigs, but the numbers, both mechanical and qualititative didn't lie.)(we'll come back to that when I have time to).

One of the other issues talked about was... ok, so we have a total "drag" number. What does this mean? ie... translate this into human performance. And hence the many subsequent discussions on using a solid set of trained divers (military) to use these "rigs" in timed distance drills, closed breathing systems to monitor intake, and start to relate the measured drag with the human response to see if the assumptions of empirical analysis are correct. There was some work on that, but nothing fully developed.

My feeling on it all is this, for the recreational diver, BCD's of today are trimmed well, and generally low in profile, hence drag. They are not as bad as the phenomena of large seajackets in vogue in the '80's. And, they tend to handle the tradeoffs (inflate, deflate, float) well enough. Recreational divers aren't encumbered by BCD's as much as they used to be. Sure, more can be done, but the fruits of further investment and investigation into finer tuning these recreational systems probably wouldn't be recouped well enough to make good sense. That wasn't the case in the 80's. But as you know, it was still far more about "marketing feature and benefits" than anything else. While low drag might have been an awesome discovery, it was still sold as "you can now access your drysuit valves, and float higher out of the water, and it just looks cooler". Can't argue with marketing genius. I know I tried.

So, now the discussion can go towards how to further "streamline" yourself underwater. Where as before, there was huge benefit to paying attention to the airbag surrounding you. Now, its a matter of common sense and tucking things in, hiding them behind, shadowing them behind your profile. Good. Done. Any problems here? Didn't think so.

Now, if the technical/commercial diving community is debating how to conserve as much energy as possible, then there are some noticeable differences in configuration, since the efforts of the diver are "more", as opposed to the recreational diver floating aimlessly around.

In the early '90's I had a commercial project where I was diving under the NYC Varrazano Narrows Bridge, and timing slack tide was laughable, and the current zipped through that channel at 5 knots, with only a slack of about 3 minutes. Nice place to dive... not. So, keeping a low profile was critical, let alone taping your mask onto your head.

If I'm going to comment on the variability of wings BP/W stuff, then understand that tuning is paramount first. And then, in watching those finely tuned beings zip traverse through the water horizontally still exposing a great frontal projection... where the BP/W is the minimal concern.

Like I said, we tested these, including the slim vest style with multiple tank set ups, including pony bottles. Much of this work was done when the test tank was freezing, and my test diver, Shannon, was wearing 2 different drysuits. So, that configuration was worked on as well.

But I believe, after all is said and done, the actual drag differences between the low profile vests (I had a proto-type single bag version as well), and the BP/W was minimal, where there were so many other configuration/tuning/trim factors that took a predominent role in the overall scheme of things.

So what you are talking about is splitting hairs, and the half hairs wouldn't be noticed under most human underwater performance (aerobic) confirmation.

But what do I know?

 

[Thalassamania]

Never mind. Thanks.

 

[MikeFerrara]

I'll leave the wing questions for later (as that debate is long and lenghty, and I imagine heated, LOL. I made a few manufacturers mad when I tested their rigs, but the numbers, both mechanical and qualititative didn't lie.)(we'll come back to that when I have time to).

Numbers don't lie but test conditions, the data collected and the inferences drawn can be misleading. In short, you have to ask the right questions, test and gather numbers that actually answer that question...my opinion after many years of designing test processes and test equipment.

So, now the discussion can go towards how to further "streamline" yourself underwater. Where as before, there was huge benefit to paying attention to the airbag surrounding you. Now, its a matter of common sense and tucking things in, hiding them behind, shadowing them behind your profile. Good. Done. Any problems here? Didn't think so.

Watching divers leads one to believe that the biggest source of drag is still head up trim.

But I believe, after all is said and done, the actual drag differences between the low profile vests (I had a proto-type single bag version as well), and the BP/W was minimal, where there were so many other configuration/tuning/trim factors that took a predominent role in the overall scheme of things.

So what you are talking about is splitting hairs, and the half hairs wouldn't be noticed under most human underwater performance (aerobic) confirmation.

But what do I know?

I can believe this, especially when we put it in the context of the rest of the equipment configuration over a range of conditions and equipment needs.

 

[StevenPaulet]

Oh... I know that "nevermind" from 2000 miles away. I had to run out, but give some more baseline to the thoughts. And I really don't want to go on how the main crux of this work was in the hydrodynamic testing procedures and systems, as opposed to the BCD's. Yeah, we were picky about getting real results, as opposed to numbers. Defensable, but not here. We can take that to an engineering board.

1. If we assume perfect "tuning" for a BP/W and for an ADV style BC, how do you think that they'd compare?

- if I assume perfect "tuning", then the difference is neglible. Hide all BCD flaps, and what do you have, a tank holder. That's tuning. But Dives don't traverse perfectly horizontal all the time. And if you are trimed up a bit, the wings are hidden behind the diver, but they do effect the drag in form/surface effects along the backside. So what you might think is "shadowed" behind the divers pose and attitude through the water, is still causing drag. And the ADV vests, the BCD is tightly wrapped around the body. If its a low profile system, it's not hangning out behind the tank. You know I've had this debate time and time again. One of those Harley vs Honda rants. So, I put them in a hydrodynamic testing facility, held all extraneous factors constant and controlled, and found that the ADV slipped through the water the order of 5% easier in drag force. But I say again that in a diving situation, you aren't going to feel a 5% difference in drag. Not at those low (less than 5 knots) stop and go speeds.

1. Now lets move to a situation where we're diving a large single and have say 4 kilos of gas in the tank which means about 4 liters of air on the vest, how do you think that they'd compare now (again assume good body position in the water).

- 4L of air in wings, versus 4 L of air around your body. Yeah, tested that too, but we forced the diver to go through the water at the same angle of attack for comarison. However, if wings are dragging 4L... they are bending the diver or tilting him. Air distributed around the torso keeps the attitude of the diver more consistent... and the numbers of actually testing the diver in true horizontal fashion is more correct. Hence, sure, the ADV type vests are less drag in this scenario, based on a few truisms/perceptions/observations/realities.

1. And as a final item, how about the physical attachement of the cylinder to the body? With a single in the 50 to 100 range its no big deal, but when you start getting into doubles does not the ADV style become a bit problematic?

Problamatic? Anything is problamatic if you are hanging cylinders for which it wasn't designed. Hang these on Stabjackets, and you have your own little submersible you have to swim within. Sure, the straps in the stabjacket can be modified, and therefore so can many of the other vest/adv/lowprofile vests. I did a good bit of modifying/tuning on my unit to make it so. But it's unfair as you won't get that product from a manufacturer. And as you know, the current slew of products offered today are so watered down with ballistic this and ballistic that and stainless steel D-Blings that they loose sight of form and function when opposed to fashion. But it looks good on them.

Now, don't tell me that people really care about the minutiae of diver drag anymore... no way.

Why on earth?

 

[Thalassamania]

Now, don't tell me that people really care about the minutiae of diver drag anymore... no way.

Why on earth?

Maybe just you, me and Shannon<G>.