How much negative bouyancy is too much?

H2Andy · Jun 14, 2005

ok... this came up in another post, but not to hijack

-- assuming your BC or wing fails at depth and you can't fix it (huge hole)

-- assuming you ditch your weights

how much negative bouyancy left over can you overcome to get to the surface?

five pounds?

ten pounds?

fifteen pounds?

Diver0001 · Jun 14, 2005

H2Andy:
ok... this came up in another post, but not to hijack

-- assuming your BC or wing fails at depth and you can't fix it (huge hole)

-- assuming you ditch your weights

how much negative bouyancy left over can you overcome to get to the surface?

five pounds?

ten pounds?

fifteen pounds?

Do you hvae a source of redundant buoyancy in this scenario?

R..

Walter · Jun 14, 2005

That will vary from diver to diver. You should never have much to overcome, if you do, you're over weighted. If the failure takes place at the beginning of the dive, you'll need to overcome wetsuit compression and the weight of the air in the tanks. Dropping your weight belt should compensate for wet suit compression.

Charlie99 · Jun 14, 2005

I did a real world test a few months ago when my dump valve stuck open. 5mm suit, 16# of lead, full AL80, 130' depth. I was overweighted by the 6 pounds of air and whatever buoyancy my 5mm suit lost at 130' --- probably another 6#.

While it was bothersome enough that I spent most of the dive up at 60', it was relatively easy to swim on up at 130'.

I had signalled my insta-buddy that there was a problem and pointed to the bubbles streaming out, just so he'd know something was going on, but he thought my dump just wasn't dumping. I guess he was used to divers swimming around at a 45 degree angle

IMO, dropping weights is really an action of last resort. If you drop the whole weightbelt you will have an uncontrolled ascent towards the end.

H2Andy · Jun 14, 2005

Diver0001:
Do you hvae a source of redundant buoyancy in this scenario?

ok... let's say wetsuit, AL backplate, and a combination of steel tank(s) to
be determined

how much negative bouyancy (unditachable weight-gear-tank-air) can you
overcome from 130 feet (rec. limit) do you think?

Charlie99:
IMO, dropping weights is really an action of last resort. If you drop the whole weightbelt you will have an uncontrolled ascent towards the end.

that's true... so basically you have to get yourself up for about 60 feet or so
(from 130), and then your suit's bouyancy will come back into play?

maybe a partial weight ditch would be better, if you absolutely can not swim up

jonnythan · Jun 14, 2005

Probably between 10 and 15 pounds.. which means that full double steels at 130' in a wetsuit will usually mean you're either dead or ditching your entire gear at depth... or dumping gas I suppose.

Diver0001 · Jun 14, 2005

H2Andy:
ok... let's say wetsuit, AL backplate, and a combination of steel tank(s) to
be determined

how much negative bouyancy (unditachable weight-gear-tank-air) can you
overcome from 130 feet (rec. limit) do you think?

Quite a bit in terms of just swimming against it. Any number I say will be abitrary, though, because I've never done it. A buddy of mine had a BCD malfunction with 5kg of negative buoyancy (beginning of a dive) and I think he would have have trouble surfacing with it.

The real trick is staying buoyant on the surface. In a mid-water situation you'd need to dump your entire kit once you made the surface. The wetsuit will keep you afloat after that.

R..

mrobinson · Jun 14, 2005

I thought eveyone dove with a drysuit in Florida...

Charlie99 · Jun 14, 2005

H2Andy:
that's true... so basically you have to get yourself up for about 60 feet or so
(from 130), and then your suit's bouyancy will come back into play?

maybe a partial weight ditch would be better, if you absolutely can not swim up

Even at 60' I was negative, but it was very manageable by adding a few pounds of buoyancy by changing my breathing pattern to "extra full lungs most of the time".

To expand on what Walter said, what you have to swim up is

1. weight of gas you are carrying
2. wetsuit compression, plus
3. any excess weighting

The only people that should have trouble swimming it all up are divers with large doubles, and divers with tons of neoprene (7mm full + 7mm FJ, for example).

Charlie99 · Jun 14, 2005

jonnythan:
Probably between 10 and 15 pounds.. which means that full double steels at 130' in a wetsuit will usually mean you're either dead or ditching your entire gear at depth... or dumping gas I suppose.

Or using some alternative form of lift ..... drysuit, liftbag, surface signalling sausage, the crumpled up plastic bag I used to collect trash, etc.

How much negative bouyancy is too much?

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