Why do the big OMS wings have 2 inflators?

[JeffG]

There are plenty of dives where there's just no way to jump in without being grossly over weighted. Tech people need the air they need, period. Big tanks weigh what they weigh. I non neoprene drysuit on a non fat guy ain't gonna float twin 120s and a set of slung 40s.

Well...jumping in with my dual 130's and two 40's for deco being a non-fat guy in a non-neoprene drysuit I don't have a problem with being overweighted.

But then again, I don't use air and I use luxfer 40's for deco bottles.

 

[cool_hardware52]

There are plenty of dives where there's just no way to jump in without being grossly over weighted. Tech people need the air they need, period. Big tanks weigh what they weigh. I non neoprene drysuit on a non fat guy ain't gonna float twin 120s and a set of slung 40s.

It appears you have dived planned that requires 2 deco gases.

I'll assume that if you need 2 deco gases you have at least some He in your mix. Tx21/35 is about 70% the density of air, or about .055 lbs / cu ft.

240 cuft X .055lbs / cu ft = 13.2 lbs of back gas.

(Even with air 240 cu ft of gas is only ~19 lbs)

If the diver starts the dive negative by the weight of his back gas + 2 lbs he would be about 15~16 lbs. negative

16 lbs buoyancy is trivial for a drysuit.

The deco bottles are a red herring. If the diver needs to breathe down 100% of his back gas and 100% of his deco gas he has either done a very poor job of dive planning, or experienced an emergency.

If the deco bottles are a problem they can be handed off or dropped. Full bottles might be lost and empties are near neutral.

If the diver selects components carefully and or adjusts their ballast so they are about 2 lbs negative with empty tanks and a shrink wrapped drysuit they will always start the dive negative by the weight of their back gas + 2 lbs.

This is not difficult to achieve. It does not require obese divers or neoprene drysuits.

For example: 2 x E-8 130, + bands, manifold, dual regs, can light, light weight back plate and harness is only about -14 lbs. Very few drysuits of any type will be less than 14 - 2 = 12 lbs buoyant.

Tobin

 

[Lucy's Diver]

Or the failure of the primary bladder could be a non event requiring no ditching of expensive gear, just a shift to a redundant system designed for its intended purpose to safely abort the dive without relying on a system of bouyancy not designed for bouyancy.

Look I get it. I'm on DIR heavy scubaboard. They way I dive recreationally ain't DIR, and DIR people would shudder at the thought of some of the ways I dive for work. I dive gear heavy fairly non simple, but I'm just used to working underwater where the diving is secondary and I need to figure out tools, lines, umbilicals, and work in low to zero viz without having to put my mind on the diving part, even when the diving part is in different configurations all the time (dry, wet, hat, aga, bite reg, SSA, non SSA, bailouts of different sizes and mounting depending on all kinds of issues, etc. etc.). I dive in a low math environment. It is a jump in the water figure your crap out even if its not ideal get the job done environment. I dive with way heavy double tanks and way more air than I need on recreational dives because (among other things) its how I need to dive for certain fairly rare types of work dives, so I might was well keep in practice and the gear is free.

We're not going to agree. All the math is meant to prove that you don't really need the second bladder. Let's pretend all that is true: there is no downside to the second bladder. Give me something with no downside that has a pretty decent chance of being useful and I'll jump in with it. When a liveaboard I was on gave me a EPRIB for the week I didn't reject it with formulae proving how their chase boat really should be there. I strapped it on and figured I'd deal with the really minimal downside and use it if I needed it.

The OP asked why the second bladder was there. Its there in case the first one fails. Want to argue its not really necessary? Rock on.

 

[JeffG]

Look I get it. I'm on DIR heavy scubaboard. They way I dive recreationally ain't DIR,

So? Still doesn't change physics.

DIR people would shudder at the thought of some of the ways I dive for work.

No we don't shudder.

We understand that your diving has absolutely nothing to do with recreational diving, except the fact that some water is involved.

I dive with way heavy double tanks and way more air than I need on recreational dives because (among other things) its how I need to dive for certain fairly rare types of work dives, so I might was well keep in practice and the gear is free.

We're not going to agree. All the math is meant to prove that you don't really need the second bladder.

Sorry. again...that pesky physics thing

Let's pretend all that is true: there is no downside to the second bladder.

That is were we disagree.

The OP asked why the second bladder was there. Its there in case the first one fails. Want to argue its not really necessary? Rock on.

That's what forums are for.

 

[cool_hardware52]

Look I get it. I'm on DIR heavy scubaboard. They way I dive recreationally ain't DIR,

No kidding?

and DIR people would shudder at the thought of some of the ways I dive for work.

Maybe, maybe not. I would expect most "DIR folks" can recognize the difference between commercial diving and non commercial diving.

I dive gear heavy fairly non simple, but I'm just used to working underwater where the diving is secondary and I need to figure out tools, lines, umbilicals, and work in low to zero viz without having to put my mind on the diving part, even when the diving part is in different configurations all the time (dry, wet, hat, aga, bite reg, SSA, non SSA, bailouts of different sizes and mounting depending on all kinds of issues, etc. etc.). I dive in a low math environment. It is a jump in the water figure your crap out even if its not ideal get the job done environment. I dive with way heavy double tanks and way more air than I need on recreational dives because (among other things) its how I need to dive for certain fairly rare types of work dives, so I might was well keep in practice and the gear is free.

I have great respect for those who dive commercially, however ScubaBoard is not a commercial diving school. For most gear is not free, and simplicity has many benefits.

All the math is meant to prove that you don't really need the second bladder.

You have made claims that are simply not true. A drysuit can easily provide the amount to buoyancy that a rationally equipped tech diver might need if their wing failed.

The OP asked why the second bladder was there.

Right. Now the OP has learned that commercial divers, or those who choose to dive grossly over weighted, or those who choose to "tech" dive in wetsuits all need redundant bladder wings.........

Tobin

 

[Lucy's Diver]

Well, a couple things.

My point about diving free gear is this: I know I could dive a lot of things that would make me less negative overall and still give me reasonable air for my recreational dives. I don't want to buy those things. The things I have for free are double steel 120s so I dive them when I dive anywhere I don't fly. I get that ideally I'd be more balanced and probably more comfortable with less tank but my economics just don't allow it. Additionally, I find that diving the doubles on wrecks in the northeast, even on no D dives, fulfills the redundancy requirement that most captains want to see. That's just the way most people dive up here: for most part I see 1/3 RBs with ponies, 1/3 guys in doubles, and 1/3 guys in singles with ponies, and from what I've seen pretty much every double set is bolted to a redundant wing.

I keep hearing there are downsides to the second bladder just sitting there waiting to be used. Tell me what they are. I'm open to hearing it. I figure it takes up no room and is there if I need it. I carry a can light connected (via heavy, strong surg tubing) to the right side of my backplate (I know, the horror), and the shorter inflator is bungeed along that with much lighter bungee. Its tucked away tight and always there and I can get it easy, I've practiced. The Jersey upline (pretty much a requirement here) is bungeed along the left side of the plate and kind of balances out the rig. Both these items (light and jersey reel) are pretty negative. If this is a deathtrap tell me why.

I also don't agree that its "factually" inaccurate that a drysuit can float a rational tech rig. Some tech people just need a lot of air for really long dives, that stuff weighs (which as I understand it is physics). Apparently the argument is just don't do those dives, or at least configure so you can ditch all kinds of air (which to me begs the question: why ditch when you can float?).

I have also been involved in a body recovery in which the drysuit was the bouyancy, it failed, and the victim had no gear on at all. Maybe that makes me unusually leery of the drysuit as bouyancy at all. I won't leave the cabin of a boat with a drysuit zipper open. I'll admit I have used the suit as bouyancy plenty of times - but I'm only willing to do so when hardlined to the surface on coms so I can be pulled up immediately if the suit fails. To me that's a recognition of the real limitations of the suit as bouyancy.

So tell me what's the real downside of the second bladder? No drag, just a little power infaltor tucked away tight - is a a deployment/use issue?

 

[cool_hardware52]

My point about diving free gear is this: I know I could dive a lot of things that would make me less negative overall and still give me reasonable air for my recreational dives. I don't want to buy those things. The things I have for free are double steel 120s so I dive them when I dive anywhere I don't fly. I get that ideally I'd be more balanced and probably more comfortable with less tank but my economics just don't allow it.

First you say your gear is free and now your choices are driven by economics.

Cost should never trump function, but I'll point out again that Redundant bladder wings are more expensive, often much more expensive than conventional wings.

I keep hearing there are downsides to the second bladder just sitting there waiting to be used. Tell me what they are. I'm open to hearing it.

No piece of gear is all benefit and without drawbacks. The relative "pros" and "cons" can be debated, but no gear is without drawbacks.

The obvious benefit of a redundant bladder wing is the redundant buoyancy if provides.

The potential negatives include:

Added "clutter"

Added cost

Consider the scenario under which a 2nd bladder would be employed. Our hero diver, who is grossly over weighted, (up to 50 lbs negative according to some "authorities") suffers a total failure of their primary wing. They are plummeting into the abyss.

Now they need to find, and orally inflate their redundant bladder, if they leave the LP hose disconnected. Can a diver who is grossly over weighted and dropping fast orally inflate quickly enough to solve the problem?

Ok, run the second inflator connected to the 2nd LP hose so our "hero" who is grossly over weighted and dropping fast can power inflate. One problem solved, but the risks of unrecognized "auto" inflation returns to the mix.

Contrast that with the diver who is Properly weighted, and is never more than slightly more negative than the weight of his backgas. If this diver should suffer a wing failure they simply add a little gas to their suit, problem solved.

Pony bottles and redundant wings lead to the same flawed logic. For ponies it boils down to "I can take risks because I have a pony"

For redundant bladder wings it becomes "I can dive 50 lbs over weighted 'cuss I have an extra wing"

Look at it this way, if the diver is not grossly over weighted, a redundant bladder wing with a stowed, disconnected 2nd inflator presents little risk, OTOH it is not required either, because the properly weighted diver can easily handle a wing failure with their drysuit. If you don't need it don't take it (or buy it)

I have also been involved in a body recovery in which the drysuit was the bouyancy, it failed, and the victim had no gear on at all. Maybe that makes me unusually leery of the drysuit as bouyancy at all. I won't leave the cabin of a boat with a drysuit zipper open. I'll admit I have used the suit as bouyancy plenty of times - but I'm only willing to do so when hardlined to the surface on coms so I can be pulled up immediately if the suit fails. To me that's a recognition of the real limitations of the suit as bouyancy.

Drysuits are not without risk. I've said this before in this thread. The difference is the drysuit is necessary equipment, and the redundant bladder wing is not.

The fact that a drysuit can loose all of it's initial buoyancy in the event of a total failure does not mean that it cannot be used for redundant buoyancy. It does mean that the loss of this buoyancy needs to be considered when sizing the diver's wing.

Tobin

 

[Lucy's Diver]

OK, I hear ya.

Let me make clear: my choices are driven by economics inasmuch as I can dive for free any gear we have in our inventory. All our BP/W for doubles are redundant, and all tanks are either ponies of various sizes 40 and under, single AL80s, or twin steel 120s. Thus I dive this stuff for free, anything else I buy myself. So I dive the drysuit I have for work and the twin steel 120s when I dive locally with the backplate and redundant wing, all from inventory.

I can live with the clutter, its really very little. I've trained and practiced deploying the thing pretty quick, and I do recognize that in the emergency you posit a drysuit will at least buy me some time, as will swimming the rig up. I just do not think drysuit alone is an adequate solution. I base this on my own experience in my own drysuit.