Bit of a moment with an uncontrolled ascent

[Littorally Diving]

I am a newly certified OW diver with only 2 certified dives under my belt. I had a bit of a scary experience on Sunday which I'll put out here to seek advice and in case that advice is useful for others. I am sorry if this is a bit long.

I was doing a nice easy beach dive on a wreck at 15' in decent visibility with a little current in 69 degree water. The wreck wasn't much more than a loose pile of old rust, being mostly buried by sand, so there were no issues with the environment. It really was more like a rock pile than a wreck. The leader was my former instructor and there was a certified divemaster and a wreck course trainee with us. This dive was very similar to my training dives, and there were no other stressors. I weigh 165lbs, was wearing a 7mm one piece, and was carrying 20lbs of weight with an LP85 tank.

About 30m into the dive I was at 15' and we rounded the stern of the wreck where the trainee was to tie off a reel. Being new I'm still having a little trouble controlling my movements and I came up behind them a bit fast. I didn't want to crash into them or the wreck, so I ascended about a foot to get over them. And kept ascending. I tried pointing down head first and finning down, but by the time I'd reached this orientation I was getting further away, probably at about 10' though I didn't check. Now I was feet up. I couldn't find the butt dump valve in time, but I was able to twist in the water and dump a _lot_ of air from the hose valve while still finning. I felt my fins break the surface which must have amused the fishermen on the beach. Then I descended rapidly. I managed to equalize on the way back down and got some air in the BCD before only just stopping short of crashing into the bottom. Computer log said I topped out at 4' depth. I was stressed after this; luckily the wreck trainee was taking a long time tying off so I was able to pause and recover for a minute before the group moved off. Nobody noticed, which I was happy about.

Things I did right (or got lucky on):
1. Didn't panic.
2. Re-oriented and vented from the hose as soon as I found I couldn't find the butt valve.
3. Kept breathing during the ascent (actually exhaling the entire way, in an attempt to get less positively buoyant).
4. Controlled (to a degree) the subsequent descent.

Things I think I did wrong:
1. Let it happen.
2. Try to fin first instead of dumping air.
3. Failed to find the butt valve instantly when I was pointing downwards.

Despite the OK outcome the entire thing shook me a bit. It seemed that my buoyancy was on a hair trigger. I was ascending and descending throughout the dive up to that point to clear rocks and the like, but without this kind of issue. Then I crossed some line and suddenly I was on the elevator. In general my buoyancy control is still bad, though I can get neutral at some points. I was having to do a lot with the BC earlier in the dive to try to keep neutral. Maybe I am overweighted? Over-using the BC? Is it partly because the pressure gradient at that shallow depth is so steep, every small change in depth has a big effect on the air in the bladder?

Thanks for reading.

 

[Barnaby'sDad]

I ran into something similar with an AL80 during my training dives (three of four).

Toward the end of the dive...I could feel (and observe on depth gauge) that I was gradually losing depth, despite operating the same as I had been earlier in the dive.

I thought (mistakenly) that I had dumped all of the air from my BC and I was still headed upwarded feet first...kicking downward, as you were.

Two things: 1. AL80 is a few pounds positively buoyant when it's headed towards empty. And 2. I did not orient my BC (straight uo or down) so that pulling on the dump would release the last of the air.

Going forward...I plan on doing two things: 1. Proactively orient myself around 1,200 psi to dump some air to offset the posive buoyancy that occurred around ~800-1,200 psi. And 2. If that doesn't address the issue...carry two pounds of additional weight (18 lbs vs. 16lbs) and see if that and dumping air from the BC fixes the issue.

 

[MaxBottomtime]

At fifteen feet you shouldn't have any air in your BC. The fact that you had to dump some means that you are overweighted. As a new diver you likely still move your arms unknowingly. Extra movement causes you to move up and down in the water. Try diving the same depth with an empty BC and if you continually sink to the sand take a couple of pounds of lead off. It takes many dives to get better buoyancy, but once you can get close to neutral at fifteen feet the rest will come easier.

 

[RyanT]

Having your buoyancy increase rapidly is a common thing when wearing a thick wetsuit and being in the 30 - 0' range. I took my buddy out to the springs recently and we practiced doing some horizontal ascents (just using breath control and BC venting) from 25'. For me, 17' was the switch point and I could feel myself rapidly getting light. When you hit that point (as you did) all it takes is a moment for that expanding gas bubble in your BC and your suit to make you dramatically lighter. You experienced it under the ideal conditions (super shallow dive with no safety stop needed). Now you have a better perspective on what to look for, when holding your depth becomes more critical on a deeper dive!

 

[Tokenwiz]

Couple of pieces of feedback.

First not being able to find your "butt valve" is a bit of a problem. Not sure if you are diving your own gear or rental gear but gear familiarity is key. Finning a little is OK, but what probably happened to make your situation worse is the effort of finning likely increased your respiratory rate and potentially your respitory volume resulting in you having more residual volume in your lungs compounding the problem, then you start working harder, kicking harder, breathing harder and you are in a vicious cycle. You did the right thing in giving up on this approach and turning head up to dump but at this point you're on the elevator up and it takes a bit of time for the reversal in buoyancy to happen. Glad to see you vented air from your lungs too on the way up, that also helped you.

Your subsequent descent also gives you the big clue that you were likely overweighted, crashing on the bottom on a relatively shallow dive shouldn't be a thing. Overweighted means you have to cary more air in your BC, meaning it's more prone to volume changes with slight depth changes (especially at the shallower depths), this was probably the biggest contributor in the event. If you are properly weighted at the surface you need to exhale to get down.

So the diagnosis from my perspective (1) overweighted (2) lack of familiarity/experience with gear (3) you just need to get more practice, get in shallow water or a pool and practice, practice, practice - it will come. Consider signing up for a buoyancy class if it doesn't. Oh and if you can, talk to your open water instructor - he or she might be willing to help you further.

 

[jlcnuke]

/snip

Things I did right (or got lucky on):
1. Didn't panic.
2. Re-oriented and vented from the hose as soon as I found I couldn't find the butt valve.
3. Kept breathing during the ascent (actually exhaling the entire way, in an attempt to get less positively buoyant).
4. Controlled (to a degree) the subsequent descent.

Things I think I did wrong:
1. Let it happen.
2. Try to fin first instead of dumping air.
3. Failed to find the butt valve instantly when I was pointing downwards.

Despite the OK outcome the entire thing shook me a bit. It seemed that my buoyancy was on a hair trigger. I was ascending and descending throughout the dive up to that point to clear rocks and the like, but without this kind of issue. Then I crossed some line and suddenly I was on the elevator. In general my buoyancy control is still bad, though I can get neutral at some points. I was having to do a lot with the BC earlier in the dive to try to keep neutral.
A. Maybe I am overweighted?
B. Over-using the BC?
C.Is it partly because the pressure gradient at that shallow depth is so steep, every small change in depth has a big effect on the air in the bladder?

Thanks for reading.

A. Almost definitely. You should be just starting to think about adding air in your BC as you go through 15' downward wearing a 7mm in my experience. You should NOT have enough air to dump a lot in, you should have hardly any, if any at all, air in the BCD at that point.
B. When you're over-weighted, that's the easiest way to compensate.
C. Yes, adjustments at shallower depths have a larger rate of change on air volume, so that will complicate the issue.

I'd recommend that you try doing a dive or two for the sole purpose of working on your buoyancy. On those, do proper weight checks so you can get your weight dialed in as that's a big part of establishing proper buoyancy. Your BCD should normally only need to be inflated/deflated to compensate for decrease/increase of buoyancy in your exposure suit as depth changes, your breathing should control your buoyancy however.

 

[Littorally Diving]

Thanks all. So I have some work to do here. Weighting seems the biggest problem. Luckily there is a salt pool near me with instructors for rent. I think a trip up there for a session getting properly weighted and just focusing on control is in order.

Tokenwiz - it's my gear. Second hand but it is mine. I have practiced a fair bit finding the various toggles and clips blindfolded at home, but once in the water, under stress, in gloves, I couldn't find it. So more practice here.

This is really helpful though guys, thanks.

 

[flyboy08]

weighting and buoyancy control is one thing, but you must spend time learning to control as well using your breath! Especially at your SS. its good you reached out here, there are so many awesome members drooling to share their expertise with all.

 

[Littorally Diving]

Thanks flyboy08 - "Especially at your SS" - what's SS?

 

[RyanT]

SS = safety stop