Question Turn a single bladder rig into Dual Bladder

[jstotz]

I guess another option might be to wear the Katana 2 on your back and a Mae West/Horse Collar BCD like this one on the front, though that seems like it would be pretty bulky!

I would totally be that guy Haha. It makes sense in an emergency scenario, putting you in a head up position like a life jacket!

 

[ofg-1]

I say go for it. Converting one thing to another is always cost effective. I bought this Pinto out of a junk yard for only $200, and now look at it. Cost far less than a $80,000 new truck.

 

[jstotz]

I say go for it. Converting one thing to another is always cost effective. I bought this Pinto out of a junk yard for only $200, and now look at it. Cost far less than a $80,000 new truck.

I don't know about always cost effective, but often fun and rewarding. That is exactly the vehicular equivalent of what I'd like to dive with, assuming it's safe and reliable

 

[Jim Lapenta]

That was my idea. My instructor still made me buy and carry a 50lb lift bag.

Out of curiosity do you know what the buoyancy of a fully inflated 6-7ft DSMB would be? My guess is plenty

Depending on the diameter it is somewhere in the area of 20lbs or more for the larger ones. You also have the option to drop a cylinder in a true emergency. And on the surface to stay afloat you can drop both of them. I always carried 50lb lift bag for Great Lakes diving with a 36 inch DSMB. That was with LP85s and a stage or two. Only felt the need for 6 ft DSMB in the ocean.

 

[jstotz]

Depending on the diameter it is somewhere in the area of 20lbs or more for the larger ones. You also have the option to drop a cylinder in a true emergency. And on the surface to stay afloat you can drop both of them. I always carried 50lb lift bag for Great Lakes diving with a 36 inch DSMB. That was with LP85s and a stage or two. Only felt the need for 6 ft DSMB in t
of them. I always carried 50lb lift bag for Great Lakes diving with a 36 inch DSMB. That was with LP85s and a stage or two. Only felt the need for 6 ft DSMB in the ocean.

I suspect the vast majority of younger open circuit techies nowadays are using back-mounted steel hp100's. My tech instructor was my age, mid-30's. He used those AND a steel backplate. Even with his drysuit he must have been very negative, which might be why he didn't consider his drysuit to be adequate emergency buoyancy.

 

[inquis]

Even with his drysuit he must have been very negative

Define "very negative". A diver in a drysuit should be neutral with near empty tanks/wing just as a wetsuit diver should be at the safety stop. This leaves just the gas weight prior to that (or often less, see below).

As to your initial concern, a negative buoyancy of 12 lbs is not much at all. You can compensate for half (or more) by taking a larger breath, and swimming up the remaining 6 lbs is trivial. Even that assumes absolutely zero assistance from the damaged wing.

Since you bring up technical diving, I wonder if you're overlooking the fact that trimix is typically used, which cuts the weight substantially. (E.g., bottom gas on a modest 220 ft dive weighs about half that of nitrox.) Additionally, deco bottles and stages are typically AL, whose positive empty buoyancy partially compensates for the gas weight when full. No one adds lead when carrying multiple deco bottles to address the empty case (i.e., a positive bottle) because a) it's unlikely ALL bottles are empty and b) you can always send the empties up the DSMB line if necessary.

 

[lizardland]

There seems to be a lot of assuming happening.

I'm not sure ditchable weight is ever used in technical diving. As evidence for this claim, you'll notice that technical diving is done with Backplate+wings or sidemount rigs, while ditchable weight pockets are generally only found on jacket-style recreational BCD's.

You're confusing ditchable weight for weight that is instantly droppable. In the days of bigger canister lights these were considered "ditchable weight". Stage cylinders are ditchable weight. Lots of things are both "ditchable" and "weight". In the UK there is bizarrely a preference for Kent Tooling reels which are solid stainless and weigh a ton and divers have indeed been forced to ditch these in an emergency to make themselves more buoyant.

I was also trained with a lift bag in AN+DP for redundant buoyancy, though it seemed to me less practical to whip out, inflate, and control in an emergency.

Again, it comes down to how you define things. In my opinion, a recreational diver with half a dozen dives having a loss of buoyancy on a wall dive might be an emergency. A technical diver on a wreck having a loss of buoyancy is an inconvenience.

It takes time to deploy something like a liftbag and not **** it up but you really should not be at this level of diving and let time pressure be a huge issue. If seconds matter in solving a problem like this then chances are you didn't take enough gas or you need to practice the skill more. If deploying a bag is part of your planned contingencies then make sure you have the time to do it.

I suspect the vast majority of younger open circuit techies nowadays are using back-mounted steel hp100's. My tech instructor was my age, mid-30's. He used those AND a steel backplate. Even with his drysuit he must have been very negative, which might be why he didn't consider his drysuit to be adequate emergency buoyancy.

When I used to dive OC, I used to use Faber 12's which don't look wildly different from the specs of HP100's. Maybe a kg or 2 less negative when full. With a pair of 12's, canister light, the weight of regulators and tank valves, all the other shite you need to carry... I was absolutely not "very negative". In fact, I needed a little bit of lead to be comfortable at deco. I've used everything from twin 7 litre/300 bar to twin 20 litre/232 bar and never found any of them to be unmanageably heavy in the water. In fact, the 20's trimmed out beautifully. I'd much rather use them than the 12's.

I'm not really sure what age has to do with anything though. I was 32 when I swapped to CCR so I don't know how a mid-30's open-circuit diver would feel about it. They may be more negative, dragged down by the sadness of not swapping to a rebreather before a mortgage, meaningless relationship and kids killed their dreams and chances for a fulfilling life.

 

[halocline]

Ya know, I'm going to try that next time I get a chance. 12 lbs seems impossibly heavy to me but I admit I've never actually tried with a known weight.

Now there is also the issue of safely staying afloat on the surface of the water once you've made it there.

FWIW, I don’t believe you need to add 12-13 lbs for the gas in 2X AL80s. Realistically it’s more like 8 lbs. That’s usually enough to stay down at a 10ft stop with little gas in each cylinder. The tanks will not be completely empty or you would want to be on the surface anyways. And in a buoyancy emergency, you can abandon a tank, that’s one of the advantages of sidemount.

I dive SM with a 5mil wetsuit, two AL80s, and I can get by with no lead. I usually add 2 lbs because it’s a little better trim-wise, but between the two regulators, lights, assorted crap in the pouch there’s enough ballast to allow me to hold a stop with under 500PSI in each tank. That’s in fresh water, BTW.

Once you add a stage then you need more weight, but for two AL80s in a wetsuit, I don’t see the need for a redundant bladder.