Is it the BCD or some screwy buoyancy issue?

[ScubaJE]

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

I will check this, thanks! The issue occurred mostly with tanks from two dive shops, so that could be interesting...

 

[Angelo Farina]

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

This is the only sensible explanation.
Tanks seems all equal, but they are not...
I and my wife own two "identical" twin sets, called Aralu, made of a pair of Luxfer tanks, 9 liters each.
My ones weight 10.7 kg each, my wife's are 10.3 and 9.8, so in total her tanks are 1.3 kg lighter than mine...
Same brand, same year (1973), same capacity, different weight.
Here the law mandates to engrave both capacity AND weight on each tank, so when you rent them you can adjust your weights.

 

[scoobert]

Her body weight has been the same for at least 45 years (125 lbs... who wouldn't kill for that!)

That is obese in the Philippines

My fiancée is 95 pounds soaking wet.

 

[Eric Sedletzky]

Did you guys eat any gassy foods like beans or other fiber rich gas producing foods? Sometimes upon ascent after the deep part of the dive your stomach/ intestines will activate from gas producing foods and you have another instant gas pocket that increases in size as you come up. 15’ is the most critical depth when it comes to pressure changes, right smack in the middle of the first full atmosphere of change, that’s why it’s the safety stop depth. It’s also to touchiest depth with gas pressure changes, just a few feet up or down makes a big difference. If she’s right at the minimum with her lead maybe this is just enough to throw it off? Just a thought.
Sounds funny but theoretically possible.

 

[Bob DBF]

Service the inflator, a small and/or intermittent leak by the Schrader valve will cause this also.

 

[jeepkaren1]

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.

I joined this forum because I am having similar issues and can't seem to find a solution. I have been diving for almost 20 years and am in great physical shape. I am very conservative with my air and have always had perfect buoyancy. In the last few years I have had an impossible time controlling my buoyancy, adding more weight, trying to adjust my breathing and constantly fiddling with my bc didn't help, the DM had to hold me down multiple times. I appear to be negatively buoyant and have no trouble descending, but 10-15 minutes into a dive I am literally fighting to stay underwater. My last two dives I had to hold hands with the DM. It guarantees I wont miss the boat, but if anyone has some suggestions I will be diving later in July.

 

[Marie13]

Do you have your own gear or do you always rent?

 

[lowwall]

What kind of dives? If you are using too much weight and thus have to add a bunch of air when you get to the bottom, you'll get noticeable buoyancy changes with fairly small changes in depth. Especially if it's a shallow dive.

And seconding Marie13's question. It could be an equipment issue. Perhaps you aren't always fully emptying the air from the BCD. Maybe some gets trapped somewhere. Another possibility is a slow leak from the inflator. Is it your gear?

 

[scoobert]

I joined this forum because I am having similar issues and can't seem to find a solution. I have been diving for almost 20 years and am in great physical shape. I am very conservative with my air and have always had perfect buoyancy. In the last few years I have had an impossible time controlling my buoyancy, adding more weight, trying to adjust my breathing and constantly fiddling with my bc didn't help, the DM had to hold me down multiple times. I appear to be negatively buoyant and have no trouble descending, but 10-15 minutes into a dive I am literally fighting to stay underwater. My last two dives I had to hold hands with the DM. It guarantees I wont miss the boat, but if anyone has some suggestions I will be diving later in July.

Uhhhhh.... Steel tanks....

 

[crofrog]

I joined this forum because I am having similar issues and can't seem to find a solution. I have been diving for almost 20 years and am in great physical shape. I am very conservative with my air and have always had perfect buoyancy. In the last few years I have had an impossible time controlling my buoyancy, adding more weight, trying to adjust my breathing and constantly fiddling with my bc didn't help, the DM had to hold me down multiple times. I appear to be negatively buoyant and have no trouble descending, but 10-15 minutes into a dive I am literally fighting to stay underwater. My last two dives I had to hold hands with the DM. It guarantees I wont miss the boat, but if anyone has some suggestions I will be diving later in July.

Has your first stage been serviced recently? What’s it’s IP? When was the last time you replaced the power inflator