Posted by Kendall Raine on August 20, 2002 at 17:26:02:
In Reply to: Re: One last try. posted by Steve on August 20, 2002 at 13:49:57:
Negative buoyancy of accessories in salt water(estimated):
Reels: 1/2 lbs max total
Lights: 2 lbs for canister. 1/4 lb per back up
Deco bottles: 2.5 lbs per 40 full w/reg. Neutral empty.
Argon bottle: 1.5 lbs full w/reg. Neutral empty.
Other stuff: N/M
Total: 8.5 lbs full give or take. 3 lbs empty
BTW, trimix weighs less than air, so assume the gas weighs around 12 lbs at 3000 psi.
Double 104's at 200 psi, regs and SS plate is about negative 17 in salt water. Take off 6 for an aluminum plate.
You are most definitely negative at the start of the dive. This is one reason you really don't want a bungie on your wing. For my set up, I'm net negative about 20 lbs full and about net 2 empty. I typically finish a dive with between 1/3 to 1/2 my backgas and about 1/4 to 1/3 of my deco gas so I'm still overweighted on the hang by about 7 to 12 lbs. The extra negative buoyancy is useful in that I can blow up my suit and stay warmer on the hang.
In your nightmare scenario where there was no available lift from either suit or wing, and you had a full gear package, you'd need about 40 lbs of lift to get back up. This can be done with an SMB or lift bag. This is less if I ditch the canister light and weight belt (8 lbs combined), but I'd still need the SMB. As I said, this scenario is hypothetical since a typical drysuit "flood" results from a blown seal which would still allow for partial inflation.
The simple fact is that 80's don't cut it if you're going to any serious depth for any length of time. Your gas planning must include getting you and your buddy back without skipping any deco and despite having to overstay your planned bottom time. Because of the use of deep stops, about 1/3 of the deco time can be spent on backgas.
As I said, 80's are fine for the Moody. They're lighter and easier to swim. Below about 200, they don't afford enough margin for error if you're going to do any penetration or swimming around. Gas planning in OE isn't limited to what you think you'll need, it has to include what you and your buddy will need if everything goes wrong. Because 104's are really 140's, they're optimal for many extended range situations and will suffice for all but the most serious cave penetrations at which point an rb starts to become a reasonable compromise.
You see, if you ask a straight forward question or make a coherent argument, you get a straight forward response. No invective and no ridicule. You don't even need to agree, either. I don't care one way or the other. The smartass stuff doesn't work, however.