Weighting for Stages/Deco Bottles

[PfcAJ]

LP120s are kinda silly for ocean tanks. Even for most cave diving, 104s are in order. I think you'll tire of the 120s.

lp85s are pretty sweet ocean tanks. Add a stage and you're golden for stuff in the 250' range and you're not a big huge bus trying to get back on the boat.

 

[Michael Guerrero]

Yeah, the 120s would strictly be for caves. Roubidoux in southeastern Missouri is deep. 120s should only be about 5lbs more per tank than a 108. That's what I do all those squats at the gym for.

 

[tbone1004]

do you drive to cave country?

The Deco Stop

That's a pretty sweet deal for 104's, and they are by far the best tanks for doubles diving for tall people, especially if you need lead already. 3.3lbs negative per tank.

 

[Michael Guerrero]

I saw those, but I only dive locally and no one wants to ship tanks.

 

[Doppler]

Does anyone add weight to compensate for potentially empty stages or deco bottles, or do you just figure you'll unclip them and let them float if you breathe them down?

Does this change if you're in a cave?

I factor buoyancy shift into weight calculations... rarely do much about it though... since the majority of technical dives begin with the diver carrying far more weight (gas) than he/she will have at the end, the "balanced rig" is in essence, the results of the gravity vs buoyancy equation at the end of the dive... and not the beginning.

 

[PfcAJ]

Yeah, the 120s would strictly be for caves. Roubidoux in southeastern Missouri is deep. 120s should only be about 5lbs more per tank than a 108. That's what I do all those squats at the gym for.

That sounds legit.

 

[Michael Guerrero]

I factor buoyancy shift into weight calculations... rarely do much about it though... since the majority of technical dives begin with the diver carrying far more weight (gas) than he/she will have at the end, the "balanced rig" is in essence, the results of the gravity vs buoyancy equation at the end of the dive... and not the beginning.

I guess the dilemma I'm running into is that if I plan for what I consider to be the worst case scenario (outside of getting lost in a cave), it would be that I've breathed down my tanks and stages to near empty. If I don't account for the inherent buoyancy in the tanks, then I will be positive, unable to hold any stop without a lot of effort swimming down, and possibly pinned to the ceiling of the cave.

So, if I plan for that not to happen, it means adding lead on top of my heavy doubles. That serves to further overweight me during the start of the dive, and means I will be overweighted throughout the duration of all my dives, except for the one where the poop hits the fan and I use all my gas trying to getting myself and a buddy out alive.

Intuitively, I feel like the proper thing to do is to weight myself for that occasion. But that means I'll be pushing 60lbs negative at the start of the dive if I'm using a couple stages/deco bottles. I've read some accounts of cave divers who haven't had to turn their valves off to unscrew their regs because they were that close to empty after a bad problem that they barely survived.

 

[PfcAJ]

Breath stages to half plus 200. If you're backgas is low or empty then drop the stages when they're empty. Boom no extra positive buoyancy.

 

[Michael Guerrero]

Yeah, dropping the stages is a good recommendation and what I think I'll plan to do. It's the tanks on my back that cause the bigger issue. But like we've been talking about, I'll just plan to add lead to account for their buoyancy, and will just dive heavy. If that restricts penetration then so be it. I think it's safer. And I think I'll go for some Worthingtons or PSTs rather than the Fabers as they have better buoyancy characteristics.

 

[eelnoraa]

But that means I'll be pushing 60lbs negative at the start of the dive if I'm using a couple stages/deco bottles. I've read some accounts of cave divers who haven't had to turn their valves off to unscrew their regs because they were that close to empty after a bad problem that they barely survived.

How did you get there? How many stages? Maybe it is time for rebreather if you need that many stages.