Stage bottle question.

[Jimmer]

I've got 2 deep dives on Saturday, and I've calculated that my double 72's (haven't got anything bigger right now), plus 80cf would be suitable gas volume for the 2 dives. So what is the best bet, sling an 80, breathe it down to 1/3 remaining, then switch to my backgas for the first dive, which would probably cover me on this dive anyway, then just dive backgas for dive #2, or bring 2 40's, dive the first to 1/3, then switch, finish the dive, then do the same on the second dive with a fresh 40?

 

[Reg Braithwaite]

I've got 2 deep dives on Saturday, and I've calculated that my double 72's (haven't got anything bigger right now), plus 80cf would be suitable gas volume for the 2 dives. So what is the best bet, sling an 80, breathe it down to 1/3 remaining, then switch to my backgas, which would probably cover me on this dive anyway, or bring 2 40's, dive the first to 1/3, then switch, finish the dive, then do the same on the second dive with a fresh 40?

I am not super-experienced, so what follows is pure speculation. But it's an interesting risk analysis.

Bringing your single 80 has some points in its favour: you have a greater margin of reserve on the first dive should things deviate from plan. There is no risk of accidentally getting into the water for the second dive with the half-empty 40 from the first dive.

Are there good points in favour of diving two forties?

 

[Jimmer]

Are there good points in favour of diving two forties?

Well the biggest point in favour of 2 forties for me, is that I have tons of dives slinging a 40, but only 1 or 2 slinging an 80.

 

[JeffG]

I've got 2 deep dives on Saturday, and I've calculated that my double 72's (haven't got anything bigger right now), plus 80cf would be suitable gas volume for the 2 dives. So what is the best bet, sling an 80, breathe it down to 1/3 remaining, then switch to my backgas for the first dive, which would probably cover me on this dive anyway, then just dive backgas for dive #2, or bring 2 40's, dive the first to 1/3, then switch, finish the dive, then do the same on the second dive with a fresh 40?

I would sling an 80 and concave it before using my backgas for dive 1. That would leave lots of gas in your doubles for dive 2.

 

[anytime]

Take the 80 and use all the gas in it on the first dive. Then just ue back gas on the second dive.

 

[wwunder]

I haven't any experience with stage bottles, but i'm interested since I also have double 72's...

How are working your gas planning? your total bottom gas is ~220 cuft so 1/3 essentially equals the usable portion of the 80, but that doesn't account for the second dive. If you only use the 80 for the first dive you will have 144*2/3 = 96cuft for the second. Or do you first subtract what you need for your second dive and then work out what is available for the first?

What are you carrying for deco and how will you deal with the extra bottle?

 

[battles2a5]

As others have stated, breathe the 80 dry and then switch to backgas. I don't know what "deep" mean to you or what kind of dive you are planning (NDL, wreck, shore, ???) but unless you are using the stage in a cave and dropping it, you won't really gain anything by breathing 1/3's on it. You have tons of gas in reserve on your back, so you can plan to breathe the stage down on the first dive and have the majority of you BG and one less bottle to carry for dive #2.

 

[Jimmer]

I haven't any experience with stage bottles, but i'm interested since I also have double 72's...

How are working your gas planning? your total bottom gas is ~220 cuft so 1/3 essentially equals the usable portion of the 80, but that doesn't account for the second dive. If you only use the 80 for the first dive you will have 144*2/3 = 96cuft for the second. Or do you first subtract what you need for your second dive and then work out what is available for the first?

What are you carrying for deco and how will you deal with the extra bottle?

There won't be any deco on this dive, I just need to "extend" my 72's for the 2 dives. Dive one is planned for a wreck that is about 135' to the mud, and dive 2 is 105' to the mud. After reading a few responses and thinking about it, I agree there is no point in leaving 1/3 left in the 80, since I'm not going to use it in dive #2, I might as well empty it out since I have my doubles for redundancy.

 

[NorthWoodsDiver]

I can dive that deep usually on a single 80 and barely escape going into deco. thats also before violating thirds. If its a current dive or bad viz or in a strange place maybe my gas consumption would require additional tanks but doubtful. I would just dive the 72's, of course if you only have 1 set of 72's than I would dive the 80 dry like everyone said just watch the buoyancy.

 

[Jimmer]

I can dive that deep usually on a single 80 and barely escape going into deco. thats also before violating thirds. If its a current dive or bad viz or in a strange place maybe my gas consumption would require additional tanks but doubtful. I would just dive the 72's, of course if you only have 1 set of 72's than I would dive the 80 dry like everyone said just watch the buoyancy.

Well that's the kicker, I only have the one set of doubles right now. When I had my double 108's with a slight overfill, I could easily do both these dives, but the 72's are cutting it way too close for my liking, especially when factoring in emergency gas for my buddy.