Buoyancy problem I can't solve

[on_two_wheels]

Dive buddy is using a steel 80 or 85. I'm guessing it's -7 full.

Steel plate and weighted STA. So we're at -19 lbs.

First dive she used I think another 16 lbs of lead so -35 lbs.

She's got a 30 lb Halcyon rental wing.

She's wearing a brand new 7mm suit with a used 3mm hooded vest.

These are the facts and they indisputable. ;-)

She descended (~ 50 fsw) and was quickly separated from 2 of the four divers she was with. She did have a buddy with her, though. She was immediately uncomfortable and needed assistance with ascent. Once on the surface, the comments made suggested with a full BCD, even finning, she couldn't surface.

I was shocked because while 16 lbs was way too much, with the suit/rig she still should have been able to surface. I'm thinking it was more of a mild panic. Any suggestions or is it likely she simply couldn't swim it up? She's in good shape so that's not a factor. No....I wouldn't have let her go with that much had I known.

Hopefully to keep this simple I'll clearly state the question:

1) Given the amount of weight (lead/plate/STA), the wing and the amount of neoprene, should she have been able to swim to the surface?

2) If so, what might have been stopping her? I thought about down current but given the location, not likely.

 

[redacted]

Was the wing working? Did she inflate it?

 

[Mr Carcharodon]

Yes given the buoyancy of the wet suit and the wing there should not have been an issue getting to the surface. For that matter even without the wing you need to be able to get to surface and stay there. That may mean ditchable weight.

No doubt you will get many recommendations to do a weight check. Pretty clearly if you are at the surface with a fully inflated BC and are sinking you are significantly overweighted. Of course if you change configurations (like getting a rental system) it is a good idea to do a checkout dive in shallow water. Everyone is different in buoyancy but your friend is diving with almost double the ballast I would use for a similar configuration which sounds like a lot. Did she change from a regular BC to a BP/W and leave her belt unchanged?

 

[on_two_wheels]

Keep in mind....this is NOT me but a buddy in our group. This diver has done this same configuration (same rental gear & weights) before with the only exception being the brand new wetsuit vs rentals up to this point. That should have made her MORE buoyant, though. I'm pretty sure she just stopped thinking because she was uncomfortable and on the verge of panic. I just want to rule out any other possible causes for her to need assistance surfacing other than lack of a cool head. No need for the comments that are posted EVERY time the word buoyancy is posted. I've read them, I know them, I do them.

 

[Saudi-Diver]

Hi have you talked to her, find out what happened? She should have been able to establish positive buoyancy with a 30lb lift wing and a 7mm suit even with a 16lb weight belt. Sounds like she had either an equipment Malfunction (wing not inflating) or a passive panic attack.

 

[Crush]

Last time I used my wetsuit I was using my minimalist BP with AL80. The rig was -3# in fresh water.

My 7 mm two-piece wetsuit with hood and gloves plus minimalist BP + AL80 require give-or-take 26-28# (depending on what else I am carrying) of weight to get me neutral at the surface. I am guessing that I am taller and wider than your female friend, so my 7 mm suit will likely displace more water than hers. I therefore find it very surprising (based upon these broad assumptions) that she was carrying -35# unless she is a very "well-rounded" individual. Even is her proportions are the same as mine, it would seem that she might be about 8# too heavy. This number is just a very approximate guess, but it factors in below.

I have found that, at depth, my suit compression leads me to be about -16 - -20#. If we assume that her suit compression was -16# and she was 8# too heavy, at depth she would have needed 24# lift to remain neutral. However, if her suit compression was -20# and she was over-weighted by 15#, she would have been -35# at depth (with a 30# lift bladder).

 

[on_two_wheels]

Thanks for the responses.

Hi have you talked to her, find out what happened? She should have been able to establish positive buoyancy with a 30lb lift wing and a 7mm suit even with a 16lb weight belt. Sounds like she had either an equipment Malfunction (wing not inflating) or a passive panic attack.

The latter is what I was thinking. The wing was fine and she did 3 dives after this incident with no problems, albeit with no weight.

Last time I used my wetsuit I was using my minimalist BP with AL80. The rig was -3# in fresh water.

My 7 mm two-piece wetsuit with hood and gloves plus minimalist BP + AL80 require give-or-take 26-28# (depending on what else I am carrying) of weight to get me neutral at the surface. I am guessing that I am taller and wider than your female friend, so my 7 mm suit will likely displace more water than hers. I therefore find it very surprising (based upon these broad assumptions) that she was carrying -35# unless she is a very "well-rounded" individual. Even is her proportions are the same as mine, it would seem that she might be about 8# too heavy. This number is just a very approximate guess, but it factors in below.

I have found that, at depth, my suit compression leads me to be about -16 - -20#. If we assume that her suit compression was -16# and she was 8# too heavy, at depth she would have needed 24# lift to remain neutral. However, if her suit compression was -20# and she was over-weighted by 15#, she would have been -35# at depth (with a 30# lift bladder).

Her plate, STA and lead totaled 35 lbs. Her wing had 30 lbs of lift. Therefore the rig alone was 5 lbs negative. Add in the full tank and she's about 41 lbs negative. However, she had a brand new 7mm wetsuit which is certainly a handful of pounds positive (as is the hooded vest), even after compression at ~50 fsw. So, the extra weight shouldn't have been enough to keep her down against her will. Over-weighted, yes....to the point of keeping her down when trying to fin to the surface? No. Hell, maybe I'm way off and some divers simply can't swim to the surface with an extra 10 lbs. I'm sure it's possible. ???

 

[UnderSeaBumbleBee]

Why is she diving with so much lead?

 

[TSandM]

The estimate they gave us in Fundies was that a 7 mil wetsuit could lose about 23 pounds of lift at depth. (IIRC, they had taken one down to 100 feet, and that's what they came up with.) Thus, if she was more than 7 lbs overweighted, she might be unable to establish neutral buoyancy. However, that should have improved as she ascended. Is it possible that she was using one of the extremely negative Faber tanks, and was more negative than you realized?

 

[on_two_wheels]

TSandM, always look forward to your info. She was using the same weight she used before with no problem (per log book), only difference was the suit. I already looked up the tank specs (hence the figure above). She didn't go THAT deep...I'm guessing about 50 fsw. I'm still leaning toward passive panic since she's used the weight before and didn't consider ditching any weight.