Your thoughts on dual bladder wing

[_Ralph]

Are you descending as fast as you can already?


Let's for amusements sake, say you're starting your dive 10lbs heavy (weight of gas in your tank). "Balanced" rig kinda deal.

Find a 10lb lead weight/rock. Drop that overboard. Are you descending that fast? Worst case, that's as fast as you'll descend.



_R

 

[RandomGuy1]

For me the 90ft/min was with a single steel and a wetsuit and arriving at 90 feet neutral. I could easily see double that if I jumped in with steel doubles in a wetsuit and didn't care about equalizing. With that said, I am pretty sure I could slow that descent by swimming up, but frantically swimming up would greatly slow the deployment of the lift bag and increase the risk of losing it. I think the only real world solution to this problem is a balanced rig.

 

[The Chairman]

I am an advocate for dual bladder wings.

That's what I dive most of the time if I have steel doubles. I only splash with a bathing suit and t-shirt. I've been diving them since 2000 with OMS's BWODs. I have a Dive Rite Dual bladder for my SF2 rebreather and all my side mount BCDs are also dual bladder. I do not attach an LP hose to the secondary inflator, but I can if I need to.

 

[DevonDiver]

I just looked through my log and the absolute fastest momentary descent rate I can find it 78 ft/min.

Based on what parameters? How many full cylinders of gas were you carrying at the time?

So, if it takes a full minute to deploy a lift bag, you shouldn't drop more than 60 feet, I think.

I think that's an unreasonably optimistic hypothesis.

There'd be a lot going on during descent. You'd have to be equalising...quickly and persistently. You'd be losing ever more buoyancy as you descended... accelerating. The gas put into your redundancy (lift bag) would be compressing quickly... and the flow with which you could fill it would also be diminishing.

If 1 min deployment was a best case, under optimal circumstances, then it shouldn't be used in conjunction with worst case scenarios.

I seem to remember an accident report of a tech instructor (?) who died having splashed without his gas on. The 'easy' rectification (reach back and turn valve on) wasn't achieved. Whilst the scenario is slightly different to a failed BCD, the issue nonetheless points firmly towards an extreme set of problems when faced with uncontrolled, rapid desent. These problems should not be underestimated.

And that's based on jumping in with an empty wing and immediately losing your elbow.

For what it's worth, I had a student experience EXACTLY this scenario for real. It was resolved easily because, with two (sidemount) tanks and a properly balanced rig there was a trivial amount of negative weight to deal with.

In fact, the diver wasn't even fully cognizant of the failure until reaching depth (~100ft), at which point wetsuit compression pushed them beyond where intuitively compensating concealed the issue.

Had the rig not been properly balanced, or if it was a multiple cylinder (4+) dive, then the resolution would have been much harder and more skill-critical.

The offending culprit:

I've also torn off an OPV when doing tight wreck restrictions. Towards the end of a dive, with (3) cylinders approaching neutral, it was pretty much a non-event. Trapping the 'bubble' was all that was needed to hold my deco stops.

 

[100days-a-year]

Glad to see you haven't died yet Pete,I didn't either when I've dove them.Despite their ferocious reputation for unplanned mayhem.I did have 2 LP hoses--primary long,secondary short on the same shoulder.

Now I mostly dive 18 to 23# wings wearing a 120 and carrying about 10 pounds of spearfishing gear,a SS STA and BP.I gave up the long hose as I prefer diving solo.

 

[stuartv]

Are you descending as fast as you can already?


Let's for amusements sake, say you're starting your dive 10lbs heavy (weight of gas in your tank). "Balanced" rig kinda deal.

Find a 10lb lead weight/rock. Drop that overboard. Are you descending that fast? Worst case, that's as fast as you'll descend.



_R

I said earlier, the fastest descent rate I found in my log was when I was descending as fast as I could, on purpose. And I was using double steel 120s, so closer to 20# negative.

For me the 90ft/min was with a single steel and a wetsuit and arriving at 90 feet neutral. I could easily see double that if I jumped in with steel doubles in a wetsuit and didn't care about equalizing. With that said, I am pretty sure I could slow that descent by swimming up, but frantically swimming up would greatly slow the deployment of the lift bag and increase the risk of losing it. I think the only real world solution to this problem is a balanced rig.

I also already mentioned that not panicking is always key, for any emergency situation.

If you don't panic, then even though you've just pulled your wing elbow off and are descending at an uncontrolled rate, you should be getting into normal horizontal trim and calmly pulling out your lift bag and clipping it to your scooter ring (or wherever you like). At that point, you should not at all be dropping like a weight thrown overboard, and you will have accomplished the only risky maneuver that is required (getting your bag clipped off without losing it). From there, you have all the time in the world to start getting some gas into that bag and arrest your descent. I choose to switch to my alternate, which is bungeed around my neck, and use my primary on the long hose to reach under the lift bag opening and purge some gas into it. If the water is really cold and the reg starts freeflowing, not a huge deal. You just jumped in, so your tanks are full. Once the lift bag has enough gas in it to keep you at least neutral, you won't need to put any more in and you can safely do a valve shutdown on the reg that is freeflowing. Then begin your ascent and use the dump valve on the lift bag to keep the ascent from becoming a runaway.

If you haven't ever tried it, you should, even if it's just one time and then you never do it again. For anyone at the level of diving doubles, taking out a lift bag, clipping it to your harness, and staying in good trim the whole time should not be that difficult or take very long.

 

[stuartv]

I seem to remember an accident report of a tech instructor (?) who died having splashed without his gas on. The 'easy' rectification (reach back and turn valve on) wasn't achieved. Whilst the scenario is slightly different to a failed BCD, the issue nonetheless points firmly towards an extreme set of problems when faced with uncontrolled, rapid desent. These problems should not be underestimated.

The idea of that scares me a lot more than the idea of jumping in and pulling my inflator elbow off. At the point I realize my gas is off, I could have just done a full exhale and might only have 30 seconds before I can't help gasping and inhaling water. Probably less given the possibility of it making me panic. Jumping in with my gas off scares me more than any other problem I ever think about.

But, as long as I can breathe, the lost elbow is something I can deal with. Even if I drop to 200', how big a deal is that? It's not like I'll incur a big deco obligation during the time I'm there. And my tanks are full, because it's the start of the dive. The only major problem I would foresee is if I were diving with a gas that gave me an MOD I was worried about busting. But, my MOD is normally going to be deeper than the bottom anywhere I'm diving, so it wouldn't be an issue.

 

[DevonDiver]

I also already mentioned that not panicking is always key, for any emergency situation...

If you haven't ever tried it, you should, even if it's just one time and then you never do it again. For anyone at the level of diving doubles, taking out a lift bag, clipping it to your harness, and staying in good trim the whole time should not be that difficult or take very long.

It should be noted that panic is unlikely in a pre-planned and anticipated 'scenario' practice. In no way does that reflect the physiological impact of an unanticipated failure.

Im not arguing that it can't be done. I'm merely suggesting that it's possible to see rose-tinted performance predictions having responded once to an anticipated and prepared for scenario.

One of the problems in technical diving is that it's easy to misconstrued performance capacity based on hypothetical or pre-anticipated scenarios - ignoring or downplaying the, very real, human factors that play a big role in problem resolution (or failure to resolve).

This goes beyond simplistic 'panic'...and simply accepts that problem diagnosis, problem solving and rectification steps take much longer when an unanticipated problem occurs... compared to a simulated and/or anticipated failure.

With rapid uncontrolled descents, you also have to add the possibility of hyperbaric trauma injury to the psychological impact. That shouldn't be underestimated, as pain is very capable of nullifying corrective actions.

 

[stuartv]

It should be noted that panic is unlikely in a pre-planned and anticipated 'scenario' practice. In no way does that reflect the physiological impact of an unanticipated failure.

Im not arguing that it can't be done. I'm merely suggesting that it's possible to see rose-tinted performance predictions having responded once to an anticipated and prepared for scenario.

One of the problems in technical diving is that it's easy to misconstrued performance capacity based on hypothetical or pre-anticipated scenarios - ignoring or downplaying the, very real, human factors that play a big role in problem resolution (or failure to resolve).

This goes beyond simplistic 'panic'...and simply accepts that problem diagnosis, problem solving and rectification steps take much longer when an unanticipated problem occurs... compared to a simulated and/or anticipated failure.

With rapid uncontrolled descents, you also have to add the possibility of hyperbaric trauma injury to the psychological impact. That shouldn't be underestimated, as pain is very capable of nullifying corrective actions.

Noted. I really appreciate the real world experience you bring to these discussions and the clear and well thought-out ways you communicate.

 

[Bennno]

But, as long as I can breathe, the lost elbow is something I can deal with. Even if I drop to 200', how big a deal is that?

It can be a pretty big deal, especially when you rip your ear drums half way down. There was a fatal accident on a wreck site close to my home town some years back.. the guy couldn't control his decent and hit the wreck pretty fast.

A lift bag as redundant BCD might sound fine but it is not practical.