Persistent Buoyancy Issues - Advice Please

[Locus]

My buddy is continually having problems getting too buoyant at safety stop depth. She often needs help staying down and by the time the stop is over she floats up without even having to kick. She insists that her bcd and drysuit are completely vented at these times.

She dives AL80's with a mares kaila jacket bcd and a sea-tux neoprene drysuit with low-loft thinsulate undergarments.

We know the AL's get positive by the end of a dive, but she's been wearing 42.5lbs of lead and it seems like that should be more than enough to compensate (she's about 5' 5" and 120lbs).

We're a bit stumped. Any ideas what might be causing this?

 

[OkByMe]

That is a bunch of weight for someone that size, there has to be a bubble somewhere. How does the BC look at depth when neutral... is it well inflated, suggesting being over weighted? I'll bet there is a bubble trapped in the back of the dry suit under the jacket. When she says the suit is squeezed and the BC is dumped, have her pull open the neck seal while vertical and curl up into a ball with the elbows pulled into the stomach. That should pull the back of the suit tight and force air out of the neck seal. I dive a Sherwood Avid and it is built just like that. I have to be slightly forward of vertical to completely dump it because some air stays in the wrap around portion.

 

[Dr. Lecter]

42.5lbs on a 120lb girl? I don't care if she's diving in a 7mm neoprene drysuit with a huge undergarment and empty double AL80s -- something's not "completely vented" and I suspect it's the suit. That is an insane amount of weight.

How tight does she wear the suit, and how far open does she leave the exhaust?

 

[WhiteSands]

My buddy is continually having problems getting too buoyant at safety stop depth. She often needs help staying down and by the time the stop is over she floats up without even having to kick. She insists that her bcd and drysuit are completely vented at these times.

She dives AL80's with a mares kaila jacket bcd and a sea-tux neoprene drysuit with low-loft thinsulate undergarments.

We know the AL's get positive by the end of a dive, but she's been wearing 42.5lbs of lead and it seems like that should be more than enough to compensate (she's about 5' 5" and 120lbs).

We're a bit stumped. Any ideas what might be causing this?

You could try troubleshooting it in a pool. First with equipment only (BCD + tank full/empty) then with diver (fins, mask, wetsuit) and check how much weight is needed to make each component neutrally buoyant? It'll give you an idea of how much weights you need with an empty tank at the surface. If you need much more than that, something must be trapping air.

Just an idea.

 

[DougieIL]

42.5 POUNDS? Is she a 2 litre bottle? I agree with the pool idea. Troubleshooting isn't perfect in a pool but a controlled environment is helpful. Has she talked to anyone about breathing? She could be airing her BC too much. It's hard to imagine that she not struggling against that amount of weight. It would be great if your dive shop had someone who was good at bouyancy issues.

 

[flots am]

We're a bit stumped. Any ideas what might be causing this?

My best guess is it's the air required to float the 42 pounds of lead.

For a person her size, with thin underwear, I'd expect somewhere between 20 and 32 pounds (max), but possibly even less than 20.

I'm 6' tall and weigh 215 pounds, and use 16 pounds of lead with my thin Weezle underwear and a steel tank in fresh water. In salt, it might get up to 20, but I'm a lot bigger than she is.

The first thing I'd recommend is at the end of her next dive, with an almost empty tank, take off all her weight, vent all the air from everything, and see what she actually needs.

Somewhere there's trapped air. You need to find it.

Just a "head's up" some drysuit underwear would become air-tight and actually obstruct the exhaust valve when it gets damp, so that's something to check if she's having suit-venting problems.

flots.

 

[supergaijin]

+1 Get a near empty tank, make her descend in a pool or very controlled environment where she can properly exhale (without stress). Make sure she 'properly' exhales.

You're essentially making a buoyancy check. With an empty tank it is more realistic.

I'd suggest breathing and no-relaxation may be to blame. I've seen small people able to hold up a lot of negative weight just through this.

How's her trim underwater?

 

[daniel f aleman]

The fact that you/she don't consider carrying 42lbs. of weight a problem bothers me. You/her need to take a buoyancy class AND get with a really good drysuit retailer that can judge your/her needs.

 

[Frosty]

I'd suggest going back to basics.Roll in-go straight to the safety stop with full tanks and see what happens.
Im betting neutral boyancy or a bit negative. Go down to 40 feet stop a minute to establish neutral boyancy then back up to safety stop again slowly of course.then see what happens. Figure out where that air is sitting IMO its an important enough matter to sort out to be worth "blowing " a dive. I bet as others have said that theres roughly a 15lb lift sized air bubble somewhere.
Another thought if she isn't able to be convinced . Loan her a 7.0mm wetsuit and roll in for a quick dive see what happens. If she's suddenly hugely overweighted then she will know definitely the issue is air in the drysuit.If she's still a bit boyant. then you guys only need to find the air pocket in the bc

 

[steveharriss]

How long has she been diving? What level is she at? It sounds like they have overweighted her for an OW course and that it's become the norm. With that amount of weight she should be walking along the bottom! As other members have identified there must be air somewhere. Does she use an auto dump or cuff dump? Auto dumps need to be a couple of clicks back from fully open; left is loose. In either case she has to ensure that the dump is the highest point when she goes to remove excess air. I'm reasonably sure you'd be able to see that amount of air in the BCD.

Back to basics to resolve this. Even worth going through the pain of wearing a drysuit in a pool to ensure she only has the right amount of lead to sink when completely exhaling.