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>> 1) When adding air to a lift bag, I add enough air so that it's only a
>> couple of pounds/kilos positive. Assuming that I send it up from, say,
>> 132 feet, with 1 kilo positive, it will hit the surface at 5 kilos
>> positive (12 pounds positive). I CAN hold position against 5 kilos
>> positive (although I'll be working like a banshee).
>
>I'm sure I won't be the only one to jump on this one. The 1 kilo positive
>bag will
>be MUCH more positive than 5 kilos unless it is only displacing 1 kilo of
>water to
>start with (at 132 feet).
>
eeeyaahhhh! When I was writing that particular comment, I was thinking
about lift bags deployed for decompression hang purposes, not for lifting
artifacts. Kind of tunnel-visioned there for a while.
Dave is quite right about the lift bag being far more than 5 kilos
positive - it will be 5 times the starting buoyancy. Since I was only
considering a bag sent up for deco hanging, it would only start at 1 kilo
positive. If you hang something something off it (say a 50 pound
artifact), then it will end up (assuming no air escaping) at 205 pounds
positive at the surface (assuming no air venting) - a bit more difficult
to hang onto than I originally wrote...
::sigh:: that sort of tunnel-visioned thinking (on my part) can REALLY
ruin a diver's day.
On the other hand, though, why are you releasing bags from very deep?
You SHOULD be maintaining near-neutral buoyancy on the bag by swimming it
up and venting the air as you ascend. Of course, releasing it from 20
feet so that you can do a hang gives you a buoynacy value of 3/2 the 20
foot buoyancy of the bag - generally more than I want to restrain.
-- Kevin --
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