SMB as backup lift source.

[doctormike]

If you don’t need it, why take it?

Because the OP needs redundant buoyancy to pass his course, and he doesn't wear a dry suit. Are you saying that you shouldn't do tech diving without a dry suit? Or are you saying that the SMB is a better means of supplying redundant buoyancy?

 

[-JD-]

So, check me here for a dual bladder rig ...

Tilt head up, raise both hoses and dump. Once you get neutral, assuming a FAST or FULL RUNAWAY inflator leak (and only in that case would it be a crisis issue) one should be notably venting away. Release the dump on the good hose and unplug the bad inflator's hose.

Bad form maybe, quoting myself ...

Another thought, if it is a FAST or FULL inflator leak, it is likely to be very audible and even a small to moderate leak should be easily detectable if held up to an ear. I actually listen when I hit my inflator for confirmation I am getting the inflation that I'm seeking - and that is with it "stowed".

Revised procedure: Tilt up and dump both if ascending "rapidly", if not obvious from observation, listen to the left, listen to the right - vent and unplug the noisy one to get neutral.

 

[PfcAJ]

Because the OP needs redundant buoyancy to pass his course, and he doesn't wear a dry suit. Are you saying that you shouldn't do tech diving without a dry suit? Or are you saying that the SMB is a better means of supplying redundant buoyancy?

A lift bag might be ok. Probably not a smb because of the location of the dump valve.

Totally worthless though unless you can swim against the weight of the tanks and immediately arrest your descent.

 

[-JD-]

I suppose that would be a reasonable immediate action if you insist on diving an overweighted rig with a dual bladder wing with both hooked up.

It has nothing to do with being overweighted. You are conflating two different things.

Hypothetically, what if I am wall-diving in the Carribean with doubles wearing a rashguard, so maybe -12 early in the dive. Is unreasonable to use a hooked up dual-bladder wing to have redundancy and not become an instant lawn dart to -1000' if one bladder system fails?

Relying on swimming it up maybe 100' or more then ditching my rig seems foolish to me by comparison.

 

[doctormike]

A lift bag might be ok. Probably not a smb because of the location of the dump valve.

Totally worthless though unless you can swim against the weight of the tanks and immediately arrest your descent.

So you feel that a lift bag would be a better choice for satisfying the redundant buoyancy requirement of the OPs course than a double bladder wing, because you could deploy and inflate it faster in an emergency?

 

[Storker]

If you’re diving a balanced rig, you don’t even need redundant buoyancy because you can easily swim against the weight of the gas in the tanks.

Bear with me here, because I'm not tech certified. But I did a quick estimate of "the weight of the gas" for someone rigged for a rather deep (60-100m) dive. I'd guess that over here, that'd mean at least a twin 12x232 set (and maybe even a larger twinset than D12), at least one Al80 stage and at least one tank of deco gas. Just for the exercise, I'm assuming one Al40 with deco gas.

A twin 12x232, one Al80 and one Al40 is some 11+ kg (~25 lbs) of gas. If that diver is neutral with near-empty tanks, they'll be around 11kg/25lbs overweighted at the start of the dive. How is it possible to do a dive like that in a balanced rig as you're defining it here? I'm pretty certain I'd have some issues swimming up if I were 11kg/25lbs overweighted.

So I'd appreciate some help solving that riddle.

 

[PfcAJ]

So you feel that a lift bag would be a better choice for satisfying the redundant buoyancy requirement of the OPs course than a double bladder wing, because you could deploy and inflate it faster in an emergency?

No. I think both are baloney. If you have to futz with it to arrest your descent, it’s baloney.

IF you have a balanced rig and can flick your flippers to arrest your descent and then want futz with someonthing so you can stop kickin yer flippers, that’s cool.

I’m not interested in “class” and what goes on in a pool or the quarry at 25’. Im talking about real life stuff.

If your class doesn’t deal with real life stuff... reconsider the class.

 

[doctormike]

I don't use them myself for the reasons outlined above. But let me just point out that I'm not the only one who thinks that dual bladder wings might have a place in diving. Here is my tech instructor on the subject. I'm pretty sure that he has some experience with "real life stuff":

"When it comes to deeper diving, I don't need more lift, but I might need a Dual Bladder? A Dual Bladder Wing is not simply a good idea, it is essential for deep deco dives. Simply put, on deep dives we do not have the time to screw around with alternate ascent plans involving Lift Bags and SMB's, in the event of a torn corrugated hose or broken elbow, nut, whatever. So, a Dual Bladder Wing is good, but most Dual Bladder Wings are huge, and wide, and heavy, and 60#!!!! A corrugated hose over each shoulder is only like the cherry on top of the Crap Sundae.

So, for deeper diving I want to start out being weighted properly, and I want a Dual Bladder Wing that is no more than 45# of lift, but with as small a profile as possible, and because I am a wreck diver, I also need it to be rugged. The Dive Rite Rec XT, which offers the Dual Bladder option, works very well for me. It is a rugged, Dual Bladder Wing with 45# of lift, with a side mount Secondary Bladder corrugated hose that I hardly even notice is there."

 

[PfcAJ]

Bear with me here, because I'm not tech certified. But I did a quick estimate of "the weight of the gas" for someone rigged for a rather deep (60-100m) dive. I'd guess that over here, that'd mean at least a twin 12x232 set (and maybe even a larger twinset than D12), at least one Al80 stage and at least one tank of deco gas. Just for the exercise, I'm assuming one Al40 with deco gas.

A twin 12x232, one Al80 and one Al40 is some 11+ kg (~25 lbs) of gas. If that diver is neutral with near-empty tanks, they'll be around 11kg/25lbs overweighted at the start of the dive. How is it possible to do a dive like that in a balanced rig as you're defining it here? I'm pretty certain I'd have some issues swimming up if I were 11kg/25lbs overweighted.

So I'd appreciate some help solving that riddle.

A 100m Dive and a 60m dive are very different beats.

One helpful factor is the lightness of the helium.

But really, if you want to do deep dives, you need a drysuit. It’s the only way to be reasonable in the water unless you’re diving aluminum tanks and accept a shorter bottom time (which isn’t necessarily a bad thing in the ocean).

FWIW, double 80s with something like 18/45 are very light in the water. A 40 of oxygen with 2000 or so psi in it and an al80 of 50% is a pretty slick package.

 

[Storker]

A 100m Dive and a 60m dive are very different beats.

I kinda suspect that, I just chose that depth range to be sure the diver was carrying hypoxic backgas. Not being tech trained, I don't know where in that depth range it'd be smart to use a hypoxic backgas

One helpful factor is the lightness of the helium.

D'oh. I forgot to take that into my calculation. So, roughly how much would that affect the weight of the backgas if the twinset was filled with 18/45 or 15/55? A twin 12x232 holds some 5500 surface liters or nearly 200 cu.ft.

But really, if you want to do deep dives, you need a drysuit.

You won't see me argue against that