Is it the BCD or some screwy buoyancy issue?

[ScubaJE]

I've been diving a long time, but when I stopped for a long break, BCDs barely invented yet (except for the orange horse shoe style!) and this is a question that has been puzzling me lately. My wife has been diving with the same gear, same weights for the last two years. She hasn't gained or lost body weight lately (she's been the same weight since I met her 45 years ago). About a month ago, she suddenly had difficulty with positive buoyancy. We were diving in Puerto Galera in the Philippines on our last dive of 3 days of daily diving and at the safety stop she suddenly began to surface. Our DM and I had to pull her down and we both tried her BCD dump valves and no air was released. We attributed it to a long dive that left her with just about 50 bar in her tank which was unusual for her. We generally surface when she has around 80-100 bar since I use up air faster than she does. About two weeks later, we were diving in Anilao also in the Philippines where she was getting advanced certifications (no flights that might have expanded her wetsuit), and she didn't have any issues with buoyancy. Two weeks later, we were again in Anilao and suddenly her buoyancy issues came back during two dives. On two occasions, I had to grab her fin and pull her down and so did the DM. She was trying to dump air and none was being released and I was also helping by checking her dump valves and no air was released.

• Her gear has been the same for every dive she has done in about 80+ dives.
• Her body weight has been the same for at least 45 years (125 lbs... who wouldn't kill for that!)
• She wears a ScubaPro 3mm full wetsuit and booties, no gloves, no hood, two years old
• Her BCD is an Aqua Lung ProHD jacket style.
• She carries 10 lbs of weight distributed among the waist pockets and trim pockets.
• Her buoyancy control is usually pretty good. She is certified PADI AOW and did the Peak Performance Buoyancy specialty, so she is aware of buoyancy control. She is able to control buoyancy with breathing.
• Our gear is pretty meticulously maintained; her regs just had their annual servicing which we do every 6 months since we dive a lot. BCDs are thoroughly rinsed and flushed with fresh water after a day of diving and also drained of any water. No repairs or o-ring maintenance have been done to the BCD.
• The tanks she has used over the last month when this issue began came from different dive shops/resorts. Always air, not Nitrox.
• We have our own lead weights which we take with us on resort dives where no flying is involved. So weight discrepancies can be eliminated. The only thing supplied by the resorts are the tanks and air.
• Normally, she is slightly negatively buoyant below about 12 meters (40 feet), and pretty much neutrally buoyant at the safety stop with 60 to 100 bar of air remaining. This is by design as it's her preference.
• As expected, her BCD would release some air as she ascended. But even after releasing that air, we still had to hang on to her at the safety stops. No more air was releasing, no matter what her attitude was (upright for the top dump valves and the fill hose and rear-end up for the bladder dump valve at the bottom of the BCD. She also tried to press down on the waist area of the bladder to force any trapped air out.
• She had 90 and 100 bar (1300 to 1450 psi) respectively remaining in the cylinders after the two dives in Anilao and about 50 bar in Puerto Galera. On the dives in between that had no issues, her remaining air was about 90-100 bar also.
• Over the years, I only had a couple of occasions where I had self inflating BCDs, both were rentals and easily resolved by disconnecting the air hose from the BCD until I surfaced. So, later on the boat, we left her regulator attached to the tank and BCD, and with the tank valve open, waited about 15 minutes and checked for BCD self inflation. The tank pressure stayed the same, so self inflation does not seem to be the culprit.
• We normally dive with a group of instructors, a technical diver and DMs and except for adding weight for a solution, none of us can come up with a reasonable cause. My wife and one other female diver are the only ones that wear jacket style BCDs.

The most obvious solution is to add a pound or two of lead, but I still can't figure out why. What have I missed here? Is it possible that her BCD has pockets of air that do not release no matter what depth? I'm not too familiar with wing style BCDs as I wear a backplate and wing. Her BCD is only a couple of years old with a little over 80 dives; can we expect deterioration in that short length of time?

I would be grateful for any ideas! Thanks in advance.

 

[johndiver999]

I think old people loose density, possibly a loss of bone density that makes them more buoyant. In any regard, I have seen some skinny old people who need more lead than you might expect. I'm sure loss of muscle mass is also contributory as well.

 

[Marie13]

Add a bit more weight - say two lbs and see what happens. That’s the easiest solution and will probably help.

 

[Lorenzoid]

Rather than racking your brain trying to diagnose a cause, why not just add two pounds of lead and go back to enjoying the diving. She’s neutral at the safety stop, which is the ideal, but a little negative buoyancy might improve her comfort.

 

[Gone for diving]

If it happens again try to feel the top of the bcd and see if there is air in the bladder,
That she is having a hard time getting out,. Be sure to lift the shoulder with the dump,
But adding a pound or 2 will not hurt, it's just a matter of elimination,
Not sure but is it always the same tanks? There can be slight differences, especially if you are weighted on the edge of minimum lead,

 

[jadairiii]

Same weight but it does not mean same percentage of muscle vs fat. And as others have said, bone density.

As you age, you will lose muscle. Add a few pounds and fix the problem.

 

[chillyinCanada]

Wait, she was doing a series of dives but this only happened 3 times, did I understand that correctly?

Was she particularly tired for those specific dives?

 

[Couv]

Take a closer look at the tanks she is using. Some AL 80s are 4#s positive when empty (Luxfer 80), some are slightly negative (Catalina C80)

See this post for the lowdown.

Updated SCUBA tank specifications list -- in PDF and spreadsheet

Hello! I have wasted my entire day re-working a SCUBA tank specifications list. I've been working with the Huron Scuba list for *years*, but I'm suspicious of the information: where did it come from? Also, it includes a lot of junk I've never seen in real life, as well as tanks that no one...

scubaboard.com

 

[ScubaJE]

Wait, she was doing a series of dives but this only happened 3 times, did I understand that correctly?

Was she particularly tired for those specific dives?

Yes, that's correct, and why it's kinda puzzling. No more tired than normal. She's in pretty good shape in general, runs half marathons and works out regularly

 

[ScubaJE]

Thanks all for the replies... I will check into the tank possibility; but for the moment, adding weight and forgetting about analyzing is what we will do (actually already doing anyway). Maybe a good excuse to pretend it's her BCD and get her a new one for Christmas! Happy holidays to all!