How much negative bouyancy is too much?

[ScubaDadMiami]

Swimming up the rig is only part of the issue. You would also have to hold stops along the way. See how well you can hold at 20 feet for five minutes on the way up. This is not something that gets to be much fun if you are negative. Five minutes can seem like a really long time.

If you are going to dive wet, you should stay away from steels that are very negative. Resort to a lift bag, etc. if you need to.

Of course, you can always dive dry, and then you won't have these problems. :11ztongue

 

[TeddyDiver]

Swimming up the rig is only part of the issue. You would also have to hold stops along the way. See how well you can hold at 20 feet for five minutes on the way up. This is not something that gets to be much fun if you are negative. Five minutes can seem like a really long time.

It's not the issue having safety stops when having failure like this.
Swimming up if you were not already overweighted before the dive isn,t a problem when having less than 4mm neoprene. With thicker ones it depends on your fitness and the depth you are. With 7+5mm neoprene below 20m (60') don't even try. It's at least 20kg (40lbs) negative.
The hole or broken valve in your BC is anyway in some place in your BC. Taking a different solution to this serious problem is to take an advantage of the usefull volume of the broken BC. Flipping over to fins up your left side down would do the thing when mainvalve malfunctions. Not very comfy way to get to surface but working one. Remember there should not be anything sqeezin the air out from your BC in case something like this happens. If there is, wrip them of! It's not very likely to have multiple holes or totally ripped BC, but if thats the case consider this: If close to shore, the anchor line or the ascending line just swim, along the bottom and climb up (line is easier than shore).
And of course there's allways buddy of yours

 

[TeddyDiver]

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..

Real trick is not to be overweighted. When not you don't have to dump anything when made the surface (unless you have a serious doublefailure both in BC and DS)

 

[mania]

We did such excersice during the Adv. Nitrox. The idea was there is a failure of all buoyancy devices. We had doubles 2x12 liters (steel ones) plus v-wieght (in my case 4,5 kilo and I was way overweighted) plus 7l stage (alu one). The aim was to dump air from all devices and see whether we are capable of swimming up from 30 meters. It was difficult but can be done....
Mania

 

[simbrooks]

When i first bought my Genesis HP-120's i was diving wet. I tried out the rig in a local 30ft deep lake, at one point i tried swimming the rig up full and couldnt, but when the tanks were down to half (~1700psi +/-) full i could just about swim it up from 30ft. I was wearing a fairly old wetsuit as well, so chances are its compressed anyway. The bouyancy of those tanks full, half and empty is around -12#, -8# and -4# per tank, respectively. So the total might have been >16# for the tanks, and 6# for the SSBP less a bit of buoyancy for my body and wetsuit, which probably accounts for the SSBP. I do know that trying to swim that rig up was not easy, i cant see doing stops being easy and of course the constant kicking gets your heart rate up which probably isnt good for your deco'ing either. Now i dive the doubles dry.

As for normal AL80, SSBP wetsuit diving, usually i carry no additional weight if in a thin suit or only 4-6# for salt water in my thicker suit - i find this easy to swim up when the tank is full. I estimate the total would be 6# plate, 2# tank, 6# weight plus a little for the wetsuit compression = at least 14# there. Subtract a little for whatever wetsuit buoyancy there still remains (couple of pounds?) and my personal buoyancy (which might be 4-6# as i float around eye level in my swimsuit and half full lungs), so more realistically the excess weight might only be 6-8#, which isnt hard to swim up.

 

[Sideband]

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?

If I was negative after I ditched my weight belt, then why was I wearing a weight belt?

You can test this easily enough. Get some extra lead and jump into the pool. How much lead can you swim to the surface with?

Joe

 

[jonnythan]

If I was negative after I ditched my weight belt, then why was I wearing a weight belt?

You can test this easily enough. Get some extra lead and jump into the pool. How much lead can you swim to the surface with?

Joe

Maybe because you were wearing 6 lbs on a weight belt, but you were also wearing a two piece 7mm suit at 130 feet.

 

[Don Burke]

If I was negative after I ditched my weight belt, then why was I wearing a weight belt?

Maybe because you were wearing 6 lbs on a weight belt, but you were also wearing a two piece 7mm suit at 130 feet.

This has interesting implications if you need to make a stop.

 

[jonnythan]

This has interesting implications if you need to make a stop.

I was not recommending the practice of weight ditching, I was detailing a scenario where you can still be negative after ditching your belt. Just for clarity.

 

[H2Andy]

If I was negative after I ditched my weight belt, then why was I wearing a weight belt?

most likely to help overcome the bouyancy of the wetsuit at the surface

at depth, the wetsuit compresses, loses bouyancy, and voila...

you ditch your belt, and are *still* negative