DIR- GUE Adjust weighing for stage bottles?

[steinbil]

Since stage tanks are usually (always?) aluminum tanks, they will be positive when empty. This affects the balanced weighting of the entire rig. I have heard that stage tanks are not calculated as part of your weighting, since you need to be balanced in the event that you drop/stage/leave tanks. But does that also hold true for the positive buoyancy of empty stage bottles?

Having let's say two more or less empty AL80s (bottom stage + deco stage) when you arrive at your final deco stop would provide quite a bit of positive buoyancy, that you need to deal with. Or is there something I'm missing? I realize there will usually be gas reserves in play, but in the worst case scenario with gas sharing, I assume you wouldn't want to struggle with being too light on top off an already sticky situation.

TLDR:
Do you adjust your weighting to account for positive buoyancy of empty stages. If so, how? Do you just add the weights you estimate for the buoyancy characteristics of the stage bottle? Or do you do a weight check with each configuration?

PS.
I assume this will be covered in a tech class, but I like to get a head start on the topics covered before I take a class.

 

[rjack321]

Interesting. I didn't consider the salt/freshwater difference. I also assumed there would be some reserve of backgas in an ocean deco dive, to account for possible loss of deco gas etc, but since I've never actually done this kind of gas planning or diving I don't have a feeling for how much or how it would be different than in a cave.

If you're diving a stage in the ocean you aren't going to be decoing out on backgas ever - even if you lost a deco gas. You'd either have reserve deco gas spread amongst your team or you'd have a safety diver or both.

 

[rjack321]

Also consider the possibility of sending a floaty bottle up the SMB line if you find yourself miserably light.

Either up an SMB line or pass them off to a safety diver. My preference is to not have that be a *requirement* to stay down. If I'm weighted for an empty stage then I can put a little extra gas in my suit if I manage to get rid of the stage. If the ascent is busy and maybe I can't get rid of the stage at all then it's not a big stress just to move it back on the leash and leave it floating on my butt.

 

[Wibble]

If you're diving a stage in the ocean you aren't going to be decoing out on backgas ever - even if you lost a deco gas. You'd either have reserve deco gas spread amongst your team or you'd have a safety diver or both.

Or diving to ANDP levels; one deco stage with sufficient backgas to run your decompression in the event of a failure.

 

[rjack321]

Or diving to ANDP levels; one deco stage with sufficient backgas to run your decompression in the event of a failure.

The OP was asking about 2+ AL80s. The typical way that happens since we don't use 80s of O2 is either: 1) a bottle gas and a 50% deco gas in the ocean, draining the bottom gas 80 and some of the backgas then doing ~25mins of deco on the deco gas 80. Then you have enough left in your doubles to do a 2nd dive along with another ~20-25mins of deco on the deco 80. OR 2) its a double stage cave dive, in which case both 80s end up empty but you have an extra 80cf of gas in the doubles.

I suppose it's possible on the ocean for you to end up with a used 80 of bottom gas and something about the 50% bottle drains that too. But you still wouldn't to 2x the ascent and deco out on backgas, the rest of that team has full 80s of 50% still. Unless you're alone too, but that's like 2+ major failures which isnt really something you plan for.

 

[Wibble]

Scenario: deco stage failure in a team of two (or more).

Arrive at deco stop. Diver 1 continues on backgas. Diver 2 switches to their deco stage and completes their deco obligation at that stop then switches to backgas and hands over the regulator to diver 1 to complete their stop. Then they all ascend to the next stop and repeat until they surface.

Whilst the deco stage wouldn’t be emptied (because diver 1 has partially decompressed on backgas), the whole safety process depends upon the principle of only half the deco stage contents are consumed by one diver for a normal ascent and that sufficient backgas remains.

If a deeper dive with multiple decompression gasses, the same principle would apply until diver 1 can switch to the working rich(er) mix.

Obviously you’d use a dive computer to calculate the "disabled" diver’s decompression obligation when switching gas out of plan.

 

[RedSix]

Scenario: deco stage failure in a team of two (or more).

Arrive at deco stop. Diver 1 continues on backgas. Diver 2 switches to their deco stage and completes their deco obligation at that stop then switches to backgas and hands over the regulator to diver 1 to complete their stop. Then they all ascend to the next stop and repeat until they surface.

Whilst the deco stage wouldn’t be emptied (because diver 1 has partially decompressed on backgas), the whole safety process depends upon the principle of only half the deco stage contents are consumed by one diver for a normal ascent and that sufficient backgas remains.

If a deeper dive with multiple decompression gasses, the same principle would apply until diver 1 can switch to the working rich(er) mix.

Obviously you’d use a dive computer to calculate the "disabled" diver’s decompression obligation when switching gas out of plan.

Just to make it clear, since we are in the DIR forum:
this is not a DIR or GUE strategy.

 

[rjack321]

Scenario: deco stage failure in a team of two (or more).

Arrive at deco stop. Diver 1 continues on backgas. Diver 2 switches to their deco stage and completes their deco obligation at that stop then switches to backgas and hands over the regulator to diver 1 to complete their stop. Then they all ascend to the next stop and repeat until they surface.

Whilst the deco stage wouldn’t be emptied (because diver 1 has partially decompressed on backgas), the whole safety process depends upon the principle of only half the deco stage contents are consumed by one diver for a normal ascent and that sufficient backgas remains.

If a deeper dive with multiple decompression gasses, the same principle would apply until diver 1 can switch to the working rich(er) mix.

Obviously you’d use a dive computer to calculate the "disabled" diver’s decompression obligation when switching gas out of plan.

you're both doing about 1.5x the required deco time for each stop and using 2x the deco gas. I'm not sure how this relates to the question of weighting - other than ensuring that you'll have empty 80s on you

 

[Wibble]

Just to make it clear, since we are in the DIR forum:
this is not a DIR or GUE strategy.

How would a DIR-compliant team resolve a “lost” deco stage?

you're both doing about 1.5x the required deco time for each stop and using 2x the deco gas. I'm not sure how this relates to the question of weighting - other than ensuring that you'll have empty 80s on you

That’s the point, you can end up with empty stages as you would with a bottom stage.

 

[steinbil]

How would a DIR-compliant team resolve a “lost” deco stage?

Pure guessing here: What about passing the deco bottle more than once to finish each stop more or less at the same time?

I'll step back now and let the people who know answer...

 

[jeffmg]

How would a DIR-compliant team resolve a “lost” deco stage?



That’s the point, you can end up with empty stages as you would with a bottom stage.

On a tech 1 dive you donate to the lost deco gas diver on one stop, then keep it for yourself on the next stop, alternating, in a 3 diver team one donates on one stop, then the next donates on the next stop, then both use their own gas on the next stop

then double your 20' stop time

or make the switches at each stop on your computer and ride it up

I'm only tech 1, I don't know if that changes at a tech 2 level