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.

 

[tursiops]

Your stage tanks don't get emptied. You use maybe 2/3 of each.

 

[PEDiver]

Are you diving steel or aluminum doubles? With steel doubles + steel backplate I'm usually pretty negative to begin with. So even with 2x empty stages I'm not fighting positive buoyancy. I definitely don't need to add any additional weight.

Your stage tanks don't get emptied. You use maybe 2/3 of each.

This is only true if you're diving straight thirds on stages. Not if you're diving 1/2+200.

 

[inquis]

If you have to breath a deep deco bottle or bottom stage to the point you can't maintain neutral buoyancy (i.e., overcoming the remaining gas weight in other bottles, including backgas), just run it up the DSMB line or leave it on the cave line.

 

[tursiops]

Ei

Are you diving steel or aluminum doubles? With steel doubles + steel backplate I'm usually pretty negative to begin with. So even with 2x empty stages I'm not fighting positive buoyancy. I definitely don't need to add any additional weight.



This is only true if you're diving straight thirds on stages. Not if you're diving 1/2+200.

Either way, you don't empty the tanks....which is the point.

 

[Manatee Diver]

Your stage tanks don't get emptied. You use maybe 2/3 of each.

Either way, you don't empty the tanks....which is the point.

You are thinking deco bottles, and even they get drained sometimes. Stages are often to near empty, you typically have 500-700psi left at the end of the dive.

I am curious how others do it. Since I dive LP tanks which are positive when empty if I am weighted so that I can hold my stops with those near empty, I don't have an issue with two empty stages when my backgas are still at least a third full. In a cave I have the option of abandoning the stages on the line and easily going back later, or asking someone to grab them for me.

 

[PfcAJ]

Your stage tanks don't get emptied. You use maybe 2/3 of each.

Stage tanks do get emptied.

DIR forum. We do halves on stages.

So on a multi stage thing, a considerable amount (maybe even all) of your backgas is pure reserve. This weight offsets the positive buoyancy of the stages. If you need to dip into your backgas, ditch the empty stages.

You might run in to some weight issues if your backgas is a super high helium gas where it just isn’t heavy enough to offset the positive stages. If that’s the case, a few extra Lbs added is fine.

 

[PEDiver]

Either way, you don't empty the tanks....which is the point.

I don't think you understand 1/2+200.

 

[kierentec]

As mentioned, stages do get emptied, even on open water dives we breath the bottom stage empty first before switching to back gas.

By the time you’re diving with 2+ stages you’ll have a pretty solid idea on weighting and buoyancy swing. Managing the large shift in trim when going from 3 full stages to 3 empty ones is the tricky bit.

 

[steinbil]

So on a multi stage thing, a considerable amount (maybe even all) of your backgas is pure reserve. This weight offsets the positive buoyancy of the stages. If you need to dip into your backgas, ditch the empty stages.

That makes a lot of sense. I forgot about ditching empty stages in the worst case scenario.