Looking for a bcd without high side''chaps''?

[Snoweman]

Over inflating the wing is only going to try to pitch you forward, so you don’t do it.

OK..., maybe this is the confusion. I was referring to being on the surface where I usually have my BCD fully inflated.

 

[rek_diver]

I'm just wondering if the people at my diving club won't look at me like I'm some crazy person if I tell them I've bought a backplate + wing...

There's a bigger issue here.

 

[MichaelMc]

OK..., maybe this is the confusion. I was referring to being on the surface where I usually have my BCD fully inflated.

The BP/W gives up the ability to float chair like high out of the water for a more streamlined uncluttered front in the water plus modularity of components across many vendors, including your local hardware store.

Yes, if your jacket BC has big air tubes wrapping around your waist, and you use them to float with your upper chest out of the water, you will not be able to replicate that with a BP/W. It is a trade off.

 

[leadduck]

I don't have the feeling of sitting in a chair with a BCD as there's no crotch strap. Most of the bladder volume is on the lower back and creates lift there if fully inflated. When not fully inflated, there's no air in the lower part of the bladder and the tubes on the side don't matter.
The worst I have is sidemount gear; these bladders are only on the lower back. They try to lift my butt out of the water when fully inflated, and I really feel being pushed forward with face in the water unless leaning back and trying to lie on the bladder.
Note that life jackets should keep your face out of the water when unconscious. A good part of their bladder has to be on the front, like the Scubapro Masterjacket's.

 

[Snoweman]

You are asking a very good question. And, approaching the issue from the perspective of physics is 'spot on'. I really wish more divers would approach their buoyancy and weighting in that manner. I am not sure that you are 'missing' something, as much as possibly needing to give a bit more consideration to the effect of weighting, both total amount AND distribution, and the positioning of the external buoyancy and weight relative to the diver's physiologic center of lift (the thorax). I am working on some pictures, because this topic is not in frequently the subject of SB discussion, but that is taking time. So, some 'textual' thoughts in the interim:

1) I might suggest an alternate view to the statement that weighting which leaves the diver upright on the surface 'won't work well when diving'. I think it can work. I have several jacket BCDs. I use them in the pool for teaching, as much because they are inexpensive yet functional, as because of any buoyancy characteristics. I can dive in good horizontal trim using those jackets, BUT that is primarily because I am properly weighted, I need to use VERY little air, if any, in the bladder underwater, and I have very little weight on my waist, pulling my legs down (see additional comment on that, below). But, the more over-weighted I am, and the more air I have to use in that jacket BCD, the less stable I become. So, the problem is primarily weighting - total amount and distribution - not the configuration of the badder.

2) To the extent possible, I prefer (and recommend to others) that both external buoyancy AND added weight be placed as closely adjacent to the physiologic center of lift as possible - the lungs, i.e. adjacent to the thorax. That has not always been the case with weight belts and BCDs, be they jacket or back-inflate, although that situation has fortunately changed to some extent over the years. Traditionally, divers have used weight belts, which place the weight well below the diver's physiologic center of lift ( which should be the primary lift during diving if the diver is properly weighted) and below the external center of lift (BCD), when horizontal. That alignment - weight below (i.e. more toward the feet) the center of lift when horizontal underwater - has a tendency to pull the legs of most divers down, because the lift in the BCD and lungs is seeking to align itself vertically with the weight. So, divers end up in a foot-low configuration, that I refer to as being a '45'er'. That produces a host of problems, which are the subject of another discussion. And, over time, since many divers were using jacket BCDs, and many divers were also over-weighted, jackets BCDs developed a bad rap, even though the problem was primarily one of weighting and weight distribution as much as bladder configuration. One other factor to keep in mind:- many divers using jacket BCDs also developed the habit of floating at the surface with much of their upper body above the water, even though it was unnecessary, simply because that where the bladder of their jacket BCD positioned them when it was (over)inflated. That bladder, when fully inflated, wanted to be on the surface, and that bladder was positioned closer to the diver's waist than their neck, so divers got used to sitting high in the water, when on the surface. In contrast, look at some episodes of the classic TV series, Sea Hunt, where you see Mike Nelson (who didn't use a buoyancy compensation device) floating at the surface. His head is above water, and that's about all. And, that's all that is needed. You really DO NOT want to 'bob like a cork' at the surface.

3) So, along come back-inflate BCDs, which move the center of external lift into closer alignment with the diver's physiologic center of lift. That's good, and divers like it, and it does facilitate horizontal trim to an extent, although probably not quite as much as is often asserted. But, it is also more streamlined, and there is less of a tendency to roll, which jackets may create simply because of of the design and placement of the air bladder. Notably, at the same time that manufacturers were moving in the direction of back-inflate BCDs, they ALSO were moving toward weight integration. And, the majority of back-inflate, weight-integrated BCDs put those weights a) below the center of lift, but NOT as much below as weight belts did (so there really was some improvement in horizontal trim), and b) forward of the diver's vertical midline, when viewed from the side. Now you have a configuration which works reasonably well underwater, but has the potential for problems on the surface. The external center of lift is behind the diver (it is, after all, a 'back-inflate' BCD), the center of weight / gravity is in front of the diver (forward of the vertical midline), and those two entities seek vertical alignment - lift directly over weight. That is obviously not a problem underwater. In fact it is ideal. But, at the surface, it may be an issue. If there is little / no weight (which should be the case), and the diver doesn't (need to) use much air in the BCD to float comfortably (head only above water) on the surface, there isn't a problem. If the diver is a bit overweighted, that weight is in front of their vertical midline and it pulls their front down just a bit toward the water. The diver - who wants to float too high on the surface anyway - doesn't like that, and adds air to the BCD. All that does is make the problem worse, as the weight, and now added lift behind the diver, seek vertical alignment. So, back-inflate BCDs CAN create a sensation of the diver's face being pushed toward the water, WHEN the diver is over-weighted, and that weight is positioned forward of the diver's vertical midline, viewed from the side. Fortunately, over time, equipment manufacturers realized that there was a problem and they started equipping BCDs with trim pockets which moved weight to a) the back side of the diver's vertical midline, and b) a position more closely adjacent to the diver's center of lift (thorax, and wing)

4) Finally, let's add in another element - the metal (negatively buoyant) backplate. What a wonderful addition to the diver's options for weighting! The plate sits adjacent to the diver's physiologic center of lift AND to the the external center of lift - the wing on the back. In fact, it is sandwiched between the two, so the surface flotation characteristics are better balanced. The plate also allows the diver to take weight off of the waist (weight belt) and/or away from the weight-integration pockets (forward of the vertical midline so a)horizontal trim is facilitated, b) the 'face down' tendency of fabric back-inflate BCDs is nicely offset.

This is an admittedly simplistic description - it doesn't consider the effect of cylinders (e.g. steel vs AL), buoyancy of fins, etc. But, it gets at the heart of the issue in many ways. And, not everyone's buoyancy characteristics are the same. Some people are 'leg heavy' (negatively buoyant lower body), some are 'leg floaty', etc. Each diver really needs to work out their optimal weighting, and their optimal weight distribution. One of the reasons that I like, and recommend, metal backplates is that they address one important component of weighting - distribution of weight toward alignment with the diver's physiologic center of lift, and external center of lift. I know what works for me, and am happy to outline why (all of the 'stuff', above). But, each diver should figure out what's best for them. I do like to see accurate information disseminated whenever possible.

With regards to #4: What happens when you change the steel to aluminum? Or, better yet, carbon fiber? How does this affect your buoyancy calculations?

 

[divad]

With regards to #4: What happens when you change the steel to aluminum? Or, better yet, carbon fiber? How does this affect your buoyancy calculations?

When I switched from SS to AL, I was able to but 4 lbs of weight on my hips which is part of why I don't get "pitched forward" @ the surface.

 

[Aloha Joe]

I just got certified. I didn't want 'stuff' at my sides either so I bought myself a BP/W to learn in. I had similar concerns about feeling weird showing up as a newbie with a 'tech rig'. Some dive shop people made some comments, but my instructor and class were really accommodating.

I have nothing to compare it to, but I never felt uncomfortable at the surface. I just kind of lay back on the wing and it feels like I'm in a lounge chair. It feels like I could float like that forever! If I was over inflated I'd end up more vertical, but it didn't take long to understand that and appropriately adjust the wing. I think I ended up swimming backwards at the surface more than the rest of my class - which isn't a big deal at all.

Donning/doffing in the water is easy. The crotch strap basically just falls away when you doff the rig. It takes an extra step to don, but I imagine it's not that different than buckling a chest strap.

I'm really happy with my decision. I looked at the travel BCs too, but since it would be a primary rig diving with a 7mm wetsuit, it seemed like there was always a compromise of durability or weight capacity.

 

[msinc]

When I got certified the dive shop instructors wouldn't let us use our own equipment. I learned in a "poodle" jacket and I have to say that I have no trouble swimming with that type underwater {at least i don't think I do} and no trouble floating on the surface. Admittedly, divers spend most of the time underwater, so it seems like that should be the biggest consideration regarding which type BC. I have no problem trying new things and will no doubt give a whack at a BP/W BC and I might even fall in love with one like everyone else has.
I cant see myself swimming when I dive, so maybe if I was video'ed doing it I might be looking for a BP/W the next day, but I just do not feel like I either need help getting horizontal or like I am not able to get horizontal "enough". Many divers comment on how "uncluttered" it is, or feeling much more "free" with a BP/W, but again, odd man out here...I am comfortable in my "poodle" jacket and I just don't have any issues to drive me towards a BP/W at this time. It seems like being horizontal all the time would lead to a neck ache always trying to hold your head up to look at things straight ahead.
Best I can tell these days, if someone was going to be looked at funny by a dive club it would probably be me!!! I have a Atomic BC1 for local dives and a Scuba-Pro Go vest for travel. Somebody straighten me out quick!!!

 

[stuartv]

I am comfortable in my "poodle" jacket and I just don't have any issues to drive me towards a BP/W at this time.

And that's all that matters. Well, that and being safe, but there is nothing inherently unsafe about a poodle jacket. So, you're good.

The thing about being perfectly horizontal and having minimal "stuff" on your front (or anywhere else) is just "gravy". The real benefit is, to put it simply, improved air consumption. When you are totally horizontal and have minimal stuff, you are the most streamlined and "aerodynamic" (really, hydrodynamic) every fin kick pushes your further through the water for the same amount of air you consume.

Plus, if you are not perfectly horizontal, when you do kick there is a tendency to have your BCD a little underinflated, so that you are a little bit negative in your buoyancy. If you are slightly head up when you kick, then the kick would tend to have you go a lot forward and a little bit up on every kick. Having your BCD a little negative results in you actually swimming forward and not up. The problem is that when you stop, you will then start to sink. IF you are one of the people who does that (and I'm not saying you are!), then the net result of that is you will tend to be fiddling with your BCD more. Frequently adding a little puff of air here and letting out a little puff of air there. Which, in the end just means that much more air used out of your tank.

Put all that together and the difference in your SAC between totally horizontal and very streamlined, versus a little head up and with "stuff" all over you, can be noticeable and have some impact on your dive. If you're good on air and have a big tank, it probably doesn't matter. If you're not great on air and you're diving an AL80, it could (just COULD, not necessarily would) be the difference between staying down until your NDL versus having to turn the dive because you got low on air before you got to your NDL.

But, none of that says you can't do just about as well in a poodle jacket as in a BP/W. I said "just about" because I think a BP/W (that is configured in a somewhat minimalist fashion) will always have a bit of advantage in streamlining over any poodle jacket on the market. But, if you get your weighting dialed in to be just right and you get your trim to be naturally totally horizontal, you will get the vast majority of the benefit that you would get from a BP/W.

@The Chairman posted a great thread on this subject a while back.

Master Neutral Buoyancy: The Importance of Horizontal Trim (Simple Vector Physics)

 

[stuartv]

I cant see myself swimming when I dive, so maybe if I was video'ed doing it I might be looking for a BP/W the next day

About this: Something I do sometimes to check myself is get in a pool. I will descend to the bottom and hover. When I think I am in proper horizontal trim, I will exhale to let myself slowly drop to the very bottom. If the first thing that touches the bottom is my belly, then I know I'm in good trim. If my knees touch first, then I'm not.

Once you can hover at the bottom in good trim, you should be able to frog kick forward and stay just barely above the bottom with no effort. And if you stop finning, still be hovering right above the bottom.

No video camera really required.