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.

 

[Guille G]

Using 1/2 (or 1/2+200) and leaving more in your bg also leaves you with more to recalculate and visit other lines on your way back without carrying the stage each time, so it is more comfortable even if nothing goes wrong.

 

[inquis]

How is divide by 2 and add 200 more complicated than divide by 3?

That part is easy, of course. However, this approach must also reserve that same amount of gas in the BG tanks, which are usually a different size. Thus, gas matching math (or you do it once and make a table in your wetnotes).

In a cave, you can remember the bottom line impact on turn pressure. For example, the 1300 psi used from an AL80 stage effectively adds 200 psi to the turn pressure of double LP85s.

Diving thirds on the stage WILL leave you short in some situations (e.g., dead/missing stage after an air share). Done correctly, half+200 handles those situations.

 

[tursiops]

then don't join in

Got it. No more posting on this forum.
It is an echo-chamber, not a discussion forum.

 

[rddvet]

Got it. No more posting on this forum.
It is an echo-chamber, not a discussion forum.

Come on dude. You really have to be such a baby all the time. I truly was asking a question about why 1/2s is more difficult to deal with than 1/3s. I’m open to other peoples’ thoughts if there is merit behind them and even if I disagree.

 

[rjack321]

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.

Short form...
In the ocean yes, an extra kilo or so per stage
In a cave generally no

Why yes in the ocean? If I bring an 80 stage, I plan on using that gas in the ocean (plus backgas). I don't want to ditch it just to stay down. Plus 80s are significantly positive in salt water. 40s with a reg on them are more or less neutral.

Why no in a cave? Because I am not planning on using all of my backgas if I am diving stages in a cave, yes the stage gets positive but I have reserved that gas in my backgas. If I burn into that backgas in an emergency I can and will ditch the stage. Also 80s with a reg aren't that positive in freshwater so I have to significantly breath down my backgas to get to the point of needing to ditch stages.

 

[steinbil]

Short form...
In the ocean yes, an extra kilo or so per stage
In a cave generally no

Why yes in the ocean? If I bring an 80 stage, I plan on using that gas in the ocean (plus backgas). I don't want to ditch it just to stay down. Plus 80s are significantly positive in salt water. 40s with a reg on them are more or less neutral.

Why no in a cave? Because I am not planning on using all of my backgas if I am diving stages in a cave, yes the stage gets positive but I have reserved that gas in my backgas. If I burn into that backgas in an emergency I can and will ditch the stage. Also 80s with a reg aren't that positive in freshwater so I have to significantly breath down my backgas to get to the point of needing to ditch stages.

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.

 

[PfcAJ]

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.

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

 

[Imla]

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.

Short answer... You only ever have this issue if something went wrong. In those cases, you ditch the stages if they are an issue.

(Although... I do remember a dive to Hobby where my buddy had forgotten half his required lead, and had just the required amount on his bail-out tanks.) The combo light diver, light tanks was a bit more than was fun. We fixed it with an extra stop under a barge where we could trade stages. His light ones for me (which incidentally had a bit much lead) and my heavy (just home from cave-trip) cave filled bail outs.
Fun dive...

But normally, I just weigh for Appendix1, and leave stages/bailouts as separate entities.
Oh.. and usually, the reason for having not perfect dives is the "foregoing" of GUEEDGE. (Or whatever pnemonic floats your boat).

 

[Wibble]

Why yes in the ocean? If I bring an 80 stage, I plan on using that gas in the ocean (plus backgas). I don't want to ditch it just to stay down. Plus 80s are significantly positive in salt water. 40s with a reg on them are more or less neutral.

This is a Bottom Stage for open circuit. Breathed until near empty and switch to backgas.

When used, you'll have (several) other full decompression stage(s) which will counteract the loss of the (helium rich?) gas in the bottom stage making the cylinder positively buoyant.

When at deco and half of your deco gas has been consumed, there should still be sufficient weight in your rig to hold the empty bottom stage down. However, in extremis, such as the loss of a decompression stage, the positive buoyancy of the empty bottom stage may become significant.

Aside from positively buoyant stages being a real pain during the bottom phase, especially if penetrating, it may be useful to attach some additional weight to a bottom stage to help control it when it's empty.



Bit of a moot argument though as deep dives on OC with a bottom stage are rare nowadays as most people would use CCR due to helium shortages and extortionate costs (not to mention the myriad other benefits of CCR)

Of course a "normal" CCR would have to have sufficient weight to counteract an empty bottom bailout (and deep travel bailout). Less of an issue if using backmounted dual bottom bailout+diluent as is used on the GUE JJ and Fathom, although these configurations will also need travel gas bailouts if v.deep.

As this is DIR, any empty bailouts would be distributed across the team to ease the load on the bailed out diver.

 

[Imla]

As this is DIR, any empty bailouts would be distributed across the team to ease the load on the bailed out diver.

Very good point.
Sharing of load in team. Relieve the diver with problems of taskloading.
Examples could be like this, taking empty bottles, camera, lights, being just a little better referance for depth/time and so on.