How much negative bouyancy is too much?

[Rick Inman]

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 buoyancy left over can you overcome to get to the surface?


five pounds?

ten pounds?

fifteen pounds?

I usually have my dry suit as a redundant buoyancy system, but assuming the BC failed and the drysuit failed, then I could always blow some gas into my sausage, but assuming that failed too, and I was too tired or lazy or unable to swim myself up, I could always pull an Uncle Pug and hitch a ride on my buddies back.

Recently when I was in Coz, I tested this out a bit. I'd brought my steel BP, and even with no weight I was negative (not sure by how much). So on a shallow solo dive (25') I dumped my air to see if I could swim the rig up. I wasn't negative by much, so it was pretty easy. But if you were more than a few pounds heavy, the challenge might be, I would think, staying up on the surface for any length of time.

 

[Walter]

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

Not exactly. That's the max you will ever swim up. You don't have to swim any of it up. If your butt is stuck to the bottom, you can ditch as much as you need to get to the surface. Hopefully, that'll just be lead, but if you are diving twin 130s and don't have a dry suit or lift bag, you can ditch your tanks. It's better to plan so you'll never need to do so, but it is an option. That is, of course, assuming you aren't in an overhead.

 

[H2Andy]

Hopefully, that'll just be lead, but if you are diving twin 130s and
don't have a dry suit or lift bag, you can ditch your tanks

this has little appeal to me


so my question was, what should you plan for, negative bouyancy wise,
that you would be able to "swim" with to the surface assuming no other
source of bouyancy and no ditchable weights.


does jonnythan's 10-15 lbs sound about right?

 

[jonnythan]

Why don't you take the rig in question, find somewhere with a hard bottom at 30 feet, slap on a 10 lb weight belt, and see how it goes?

 

[H2Andy]

....because... that would not make for a good ScubaBoard thread, would it?




actually, 30 feet wouldn't be deep enough... i'm thinking about 100 feet minimum

 

[jonnythan]

....because... that would not make for a good ScubaBoard thread, would it?

Oh yes, it would involve actual experience with the matter at hand

FWIW, I can fairly easily swim up a bit less than 10 pounds.

 

[jonnythan]

actually, 30 feet wouldn't be deep enough... i'm thinking about 100 feet minimum

Sure it would. That's what the extra weight belt is for

 

[mossym]

But if you were more than a few pounds heavy, the challenge might be, I would think, staying up on the surface for any length of time.

very true, but once at the surface you could dump your weights, if you're carrying them...if not..well you buddy better be close with some extra lift....

 

[H2Andy]

Oh yes, it would involve actual experience with the matter at hand

well, nobody's ever accused me of that

 

[ScubaDadMiami]

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

We do.