Question about using a lift bag for redundant buoancy

[PfcAJ]

OK, so what do you consider a "balanced rig" in 23C-27C waters, when all that are available locally are AL80s [and maybe AL40s . . . or maybe not] for divers who use wetsuits?

Try swimming up 2x AL80 twins, plus 1x AL80 travel gas bottle, plus 1x AL80 bottle of EAN50, plus 1x AL40 bottle of O2, in a wetsuit, at the beginning of a dive when all cylinders are full -- I doubt you can do it without a lot of effort. I've tried it wearing a full-body 5mm wetsuit plus a 3mm hooded vest. That wasn't enough buoyancy for all 5 full bottles plus me, even though several DIR divers had done a lot of math to advise me about a "balanced rig."

AL bottles are quite buoyant when empty. They're really heavy when there are 5 of them and they're all full. Tech divers need to be adequately weighted, and that's hard to ensure when diving with a lot of AL cylinders while wearing a wetsuit.

If a diver uses a single-bladder wing, it can't hurt to know how to use a bag for redundant buoyancy.

---------- Post added March 25th, 2014 at 02:16 AM ----------

Sorry, let me clarify: I am not at all against a "balanced rig." In fact, I am trying to achieve a balanced rig. It isn't always easy in 3rd World places with limited equipment options.

What I meant to say is that achieving a balanced rig is not always possible . . . and in any case, isn't it a good idea to know some useful techiques one might use in an emergency?

If you're diving with a "travel gas", you're diving a hypoxic back gas. If that's the case, the double al80s are probably positive or at worst ~ neutral. So that's not an issue. The "travel gas" would be something like 35/25, and that too is right at neutral when full. So your negative tanks are 1 al80 of 50% and 1 al40 of oxygen (and that might be neutral unless you're boosting o2).

Ditch your weightbelt and move your flippers. thats how you swim it up.

 

[Makhno]

If you're diving with a "travel gas", you're diving a hypoxic back gas. If that's the case, the double al80s are probably positive or at worst ~ neutral. So that's not an issue. The "travel gas" would be something like 35/25, and that too is right at neutral when full. So your negative tanks are 1 al80 of 50% and 1 al40 of oxygen (and that might be neutral unless you're boosting o2).

Ditch your weightbelt and move your flippers. thats how you swim it up.

You're right, air and nitrox are heavier than trimix.

The only time I actually tried to swim up 5 bottles in a simulated wing failure was in a practice dive when the doubles and travel gas bottle were filled with air. So you're right, that wasn't entirely realistic.

However, it is not at all uncommon in tropical waters for a diver to dive 2x AL80 doubles filled with air or EAN28 or something similar, plus 1x AL80 filled with 50 plus 1x AL40 filled with O2. That's still hard to swim up when all 4 of those are full to 200 to 220 bar. Have you ever tried it? It isn't impossible, but it isn't a piece of cake, either. Would you like to try it with a foot cramp, or a broken regulator mouthpiece? I would rather not.

My point was not to argue against attempting to balance a rig. I think a balanced rig is a good idea, all else being equal. My point was that learning how to achieve redundant buoyancy with a lift bag or SMB is quite easy to do, and is something that divers should know how to do, and then I explained how.

I was also offering the OP an answer which was actually responsive to his or her question. boulderjohn's post was great and was responsive, and I wanted to add a little more detail about the how-to (plus offering the hold onto it method, rather than the hold it under the arm method).

Arguably, the "get a balanced rig and swim it up" answer to the OP's question is not only nonresponsive, but is also "an equipment solution to a skills problem."

I have never dived with twin 108s, but I will assume that as NWGrateful diver said, "Even with a balanced rig, double 108's are going to put you close to 15 lbs overweighted at the beginning of the dive when the tanks are full." 15 pounds is heavy. If what NWGrateful diver says is true, then I think that the OP, in asking how to use a bag for redundant buoyancy, was asking a very sensible question, and that "get a balanced rig" is not only nonresponsive, but also wrongly implies that a balanced rig, by itself, will take care of the OP's buoyancy situation in an emergency.

I am a bit perplexed: at a very basic level, this is an easy skill, and very useful in an emergency: what's wrong with knowing how to do it?

 

[PfcAJ]

You're right, air and nitrox are heavier than trimix.

The only time I actually tried to swim up 5 bottles in a simulated wing failure was in a practice dive when the doubles and travel gas bottle were filled with air. So you're right, that wasn't entirely realistic.

However, it is not at all uncommon in tropical waters for a diver to dive 2x AL80 doubles filled with air or EAN28 or something similar, plus 1x AL80 filled with 50 plus 1x AL40 filled with O2. That's still hard to swim up when all 4 of those are full to 200 to 220 bar. Have you ever tried it? It isn't impossible, but it isn't a piece of cake, either. Would you like to try it with a foot cramp, or a broken regulator mouthpiece? I would rather not.

My point was not to argue against attempting to balance a rig. I think a balanced rig is a good idea, all else being equal. My point was that learning how to achieve redundant buoyancy with a lift bag or SMB is quite easy to do, and is something that divers should know how to do, and then I explained how.

I was also offering the OP an answer which was actually responsive to his or her question. boulderjohn's post was great and was responsive, and I wanted to add a little more detail about the how-to (plus offering the hold onto it method, rather than the hold it under the arm method).

Arguably, the "get a balanced rig and swim it up" answer to the OP's question is not only nonresponsive, but is also "an equipment solution to a skills problem."

I have never dived with twin 108s, but I will assume that as NWGrateful diver said, "Even with a balanced rig, double 108's are going to put you close to 15 lbs overweighted at the beginning of the dive when the tanks are full." 15 pounds is heavy. If what NWGrateful diver says is true, then I think that the OP, in asking how to use a bag for redundant buoyancy, was asking a very sensible question, and that "get a balanced rig" is not only nonresponsive, but also wrongly implies that a balanced rig, by itself, will take care of the OP's buoyancy situation in an emergency.

I am a bit perplexed: at a very basic level, this is an easy skill, and very useful in an emergency: what's wrong with knowing how to do it?

Once again, your hypothetical dives are not something I would sign up for. The MOD of 28% is like 130ft. I wouldn't take 2 deco gases for a 130ft dive, nor would I use nitrox as back gas for that dive, and if I did take 2 gases, it would be two 40s. You can't get into enough deco at 130' on double al80s to warrant a 40 of o2 and an 80 of 50%.


And yes, a balanced rig WILL take care of the problems. That's the idea behind it. If you do lose your wing with those 108s, you can push the inflator button in your drysuit and you have instant positive buoyancy.

 

[Makhno]

Once again, your hypothetical dives are not something I would sign up for. The MOD of 28% is like 130ft. I wouldn't take 2 deco gases for a 130ft dive, nor would I use nitrox as back gas for that dive, and if I did take 2 gases, it would be two 40s. You can't get into enough deco at 130' on double al80s to warrant a 40 of o2 and an 80 of 50%.


And yes, a balanced rig WILL take care of the problems. That's the idea behind it. If you do lose your wing with those 108s, you can push the inflator button in your drysuit and you have instant positive buoyancy.

So if a drysuit is necessary to achieve a balanced rig with 108s, but the OP has said he or she simply cannot get a drysuit, then the OP simply can't dive those cylinders with a balanced rig. Advising him or her to do so is thus nonresponsive. It is good advice for others reading the thread, but it seems like a flippant reply to the OP, who has made it clear that a drysuit is out of the question for financial reasons.

AJ, if you can afford to always use trimix below 30 or 40 meters, that's great. I don't want to re-open a deep air debate here, but the reality is that a lot of tropical divers who use wetsuits dive air to 50 meters or so, sometimes in remote places where there aren't any AL40s, or there aren't enough AL40s to go around, so they use one or even two AL80s for deco bottles. Do they also need drysuits to achieve a balanced rig? If they do, I can guarantee you that there are a lot of wetsuit divers around the world who will never achieve a balanced rig. For those divers, knowing how to use a bag for redundant buoyancy is a good idea, isn't it?

 

[Reg Braithwaite]

So if a drysuit is necessary to achieve a balanced rig with 108s, but the OP has said he or she simply cannot get a drysuit, then the OP simply can't dive those cylinders with a balanced rig. Advising him or her to do so is thus nonresponsive.

It may be "nonresponsive," but why is that bad?

If I ask car enthusiasts "I can't afford to upgrade the brakes on my dragster yet, but I bought a bigger engine, how do I use a parachute to slow myself down?" I must be prepared to read a few responses from people saying "Don't go faster until you buy the brakes." That's not a bad thing, this is an Internet forum where your answers are to the OP, but also to everyone else using Google to search for advice.

 

[Makhno]

this is an Internet forum where your answers are to the OP, but also to everyone else using Google to search for advice.

I agree with you, as I said myself already.

It may be "nonresponsive," but why is that bad?

It's a matter of courtesy.

 

[PfcAJ]

So if a drysuit is necessary to achieve a balanced rig with 108s, but the OP has said he or she simply cannot get a drysuit, then the OP simply can't dive those cylinders with a balanced rig. Advising him or her to do so is thus nonresponsive. It is good advice for others reading the thread, but it seems like a flippant reply to the OP, who has made it clear that a drysuit is out of the question for financial reasons.

AJ, if you can afford to always use trimix below 30 or 40 meters, that's great. I don't want to re-open a deep air debate here, but the reality is that a lot of tropical divers who use wetsuits dive air to 50 meters or so, sometimes in remote places where there aren't any AL40s, or there aren't enough AL40s to go around, so they use one or even two AL80s for deco bottles. Do they also need drysuits to achieve a balanced rig? If they do, I can guarantee you that there are a lot of wetsuit divers around the world who will never achieve a balanced rig. For those divers, knowing how to use a bag for redundant buoyancy is a good idea, isn't it?

Yes. If you don't have the right gear to do the dive, don't do it. There are other options besides strapping on double 108s.

For our purposes today, I'll play along and go with 28% for your hypothetical scuba dive. You still don't need 2 deco gases. Even for a dive on air to 50m, you don't need 2 deco gases (when your backgas volume is double al80s). Its fantasy land stuff. Cooking up ridiculous dive plans to justify a poor choice doesn't cut it. And lets play make believe some more and say you DO a longer dive at 50m and need 2 gases. Fill each one to 2 grand and you have plenty of volume (enough for a 50m for 50min with an ample reserve) without the tanks being bricks. And guess what, 50min at 50m takes more gas than double al80s can hold. Hmm... Your argument just doesn't hold up when you look at specifics.

Past all that, the lift bag thing is beyond silly. Jumping in the water, weighted like a boat anchor, and thinking you're going to get out a lift bag and inflate it while plummeting to Davy Jones's Locker is ridiculous. Stop being a nickel rocket, get the right gear (either light tanks or a drysuit) and enjoy your scuba dive. Bandaid 'solutions' give nothing but false peace of mind and don't fix the real problem

And if people would stop giving out crappy advice, OP probably wouldn't have bought gargantuan cylinders (which cost like a thousand dollars new) in the first place. OP could have bought a proper set of doubles an used the rest for training or diving.

 

[Reg Braithwaite]

It's a matter of courtesy.

I suggest that the courtesy comes in being respectful and polite to each other, and focusing disagreement on the ideas rather than the people. It is the style of the Internet in the large and forums like this in the small that the important thing is to stay loosely on-topic. If the OP asks, "how do I use a lift bag given X, Y, Z," it is extremely restrictive to ban all discussion except the exact answer to that question on a discussion forum. There is a place for those specific Q&As, and that place is StackOverflow and its clones, they are designed for providing a very focused discussion and are ruthless in stamping out all tangents.

ScubaBoard is more like a bunch of enthusiasts having a conversation. If we were having dinner and someone asked this question, it would be perfectly normal for people to talk about swimming up balanced rigs, for people to suggest waiting on diving double 108s until the dry suit was in the budget, and for people to answer the specific question.

As long as we're all just getting along, it seems to me that the original question has been answered and the OP has onbtained something of value. The rest is just put on the table to take or to leave as the OP or anybody else sees fit.

 

[Makhno]

And if people would stop giving out crappy advice, OP probably wouldn't have bought gargantuan cylinders (which cost like a thousand dollars new) in the first place. OP could have bought a proper set of doubles an used the rest for training or diving.

As I said, I've never used 108s, nor did I have any idea how much they cost. For that kind of money, the OP could've bought a nice drysuit! :blinking:

Most of the diving I do is with a single cylinder, and on the rare occasion when I do technical diving I typically do shallowish stuff and only bring along one deco bottle.

However, a lot of divers like to use both EAN50 and O2 for air dives to 50m. Maybe they don't need to use them both, but they use them both because it considerably shortens the deco time compared to just using one deco gas. That isn't "fantasy land;" that's how many people are actually diving.

I don't have a deco planner with me now, but I vaguely recall that for a 30 minute dive to 50 m on air, using both EAN50 and O2 shortens the decompression obligation by almost 20 minutes compared to just using one deco gas or the other. Do you have a deco planning program handy? Can you run the numbers for a 30 minute dive to 50m on air, with one deco gas vs. two? I think I remember that using both EAN50 and O2 cuts about 18-20 minutes off the deco obligation compared to using just one deco gas. For a lot of divers, that makes enough of a difference to decide in favor of bringing along two deco bottles.

---------- Post added March 26th, 2014 at 11:26 PM ----------

I suggest that the courtesy comes in being respectful and polite to each other, and focusing disagreement on the ideas rather than the people. It is the style of the Internet in the large and forums like this in the small that the important thing is to stay loosely on-topic. If the OP asks, "how do I use a lift bag given X, Y, Z," it is extremely restrictive to ban all discussion except the exact answer to that question on a discussion forum. There is a place for those specific Q&As, and that place is StackOverflow and its clones, they are designed for providing a very focused discussion and are ruthless in stamping out all tangents.

ScubaBoard is more like a bunch of enthusiasts having a conversation. If we were having dinner and someone asked this question, it would be perfectly normal for people to talk about swimming up balanced rigs, for people to suggest waiting on diving double 108s until the dry suit was in the budget, and for people to answer the specific question.

As long as we're all just getting along, it seems to me that the original question has been answered and the OP has onbtained something of value. The rest is just put on the table to take or to leave as the OP or anybody else sees fit.

Right, and I didn't see any ad hominem attacks or anything especially nasty like that. I don't think anyone was being a real jerk. It's just a minor issue of tone. Sometimes things when written down seem flippant when that wasn't the writer's intention, and when it wouldn't seem that way at all if one heard the writer's tone of voice.

Agree that by now, the OP (and everyone else) has gotten what was requested from this thread, and more.

 

[PfcAJ]

I just put it into deco planner for you.

Buhlmann 20/85
150ft, 30mins, 21/00 (air) = 26mins deco time with o2 and 50%
150ft, 30min, 21/00 (air) = 36mins deco time with just 50%

10mins difference. 7mins difference if the back gas is 21/35. 10mins is not worth the effort (and even risk) of dragging a 2nd bottle, and its certainly not worth diving 2 al80s filled to 3000psi.