“Fairly” Uncontrolled Ascent - Please help me understand what went wrong

[gordonscuba]

Regardless of the wetsuit, we know that on the second dive, OP started out very negative, felt overweighted and sank like a stone. An AL80 going from full to 1000psi translates to about 4 lbs of total buoyancy change, which would be happening gradually. I don't see that causing the reported effect.

 

[Angelo Farina]

Cressi BCD. They have a rare but known fault causing free flow in their inflator.
My wife has one and when this happens she simply disconnect the LP hose.
After years of this occurring randomly (and always towards end of the dive), while apparently working well out of the water, I finally decided to gift her with a new "generic" inflator. Problem solved. 30 euros well spent...
So I would not waste time and money debugging the fault: just buy a new power inflator. The LP hose does not need to be changed..

 

[rongoodman]

I stay negative during my safety stop, and my whole climb back to the boat. If I stop finning, I sink.

That sounds like a really bad idea. If you can't stay neutral at a stop I'd suggest there's a problem(s) that you need to address. Among other things, it implies that you're vertical in the water and probably overweighted. If you do start to rise, you can't use your fins to move back down in the water column or use the rear dump on your wing/BC to dump air quickly. What happens when you get distracted and stop finning? Being flat in the water presents more surface area and slows everything down, rising or sinking. As for the OP, I'd begin by replacing the inflator. It's a cheap and easy first step to troubleshooting the problem. Checking the IP would be worthwhile too.

 

[MidOH]

To me this sounds like a bad habit. No every dive site will have something to hold for a safety stop. On top of that swimming to the boat like that could end bad if you get a bad cramp or a fin comes off. I would recommend learning to control your buoyancy at any depth and at any point in the dive.

Not that negative.

 

[crofrog]

Hello everyone, I’m on a dive trip in Turks and had two upsetting dives this morning. I am a good diver, although only 120 dives, and can’t figure out what happened. I think it was equipment related. I have an Aqualung Micron and a Cressi BCD. I’ve been diving with both for 5 years without any problems.

Dive started fine. At about 45 mins the first dive and 35 mins second dive I started ascending. I dumped all my air, using dump valves and the shoulder dump. I squeezed the bcd the best I could to get air out. Nothing worked. I grabbed the safety stop bar and even that wouldn’t keep me down.

Was air coming out the entire time?

My weights are fine. I even added 2lbs the second dive. Sank like a rock and knew I was overweighted.

How fast you sink at the start of the dive is only loosely correlated to how much weight you need.

 

[FreqFlier]

@KristenK said everything was working fine during both dives (for 45 and 35 mins) until she started the ascent (two separate instances? Or coincidence?).

I'd bet on a malfunctioning dump valve? Or maybe internal BCD bladder (5 yrs old...) got stuck together inside creating an air pocket at the moment she got vertical? Meaning only two factors were in play - getting vertical and inability to dump air. Would it make sense to try to dump air head down using bottom dump valve?

If it was LPI issue or any kind of inflator issue - even at a very slow fill rate she would've noticed freefilling BCD a while before the ascent.

AL Mikron has a flow adjustment knob (mini/maxi) - my guess is @KristenK you already knew that?

 

[johndiver999]

@KristenK said everything was working fine during both dives (for 45 and 35 mins) until she started the ascent (two separate instances? Or coincidence?).

I'd bet on a malfunctioning dump valve? Or maybe internal BCD bladder (5 yrs old...) got stuck together inside creating an air pocket at the moment she got vertical? Meaning only two factors were in play - getting vertical and inability to dump air. Would it make sense to try to dump air head down using bottom dump valve?

If it was LPI issue or any kind of inflator issue - even at a very slow fill rate she would've noticed freefilling BCD a while before the ascent.

AL Mikron has a flow adjustment knob (mini/maxi) - my guess is @KristenK you already knew that?

I've had a slowly filling inflator. It is surprisingly easy to fail to notice if it is slow. I just felt like I was messing up and having to dump air from the BC more frequently, until I finally told myself.. something is messed up, I am not THIS uncoordinated. Didn't hear anything or see bubbles coming out.

Obviously, a slowly inflating BC should be a minor inconvenience, but if the diver does not notice and really starts floating up (and especially if they are wearing extra lead) it can spiral into a buoyant ascent with a tiny bit of inattentiveness, particularly in shallow water.

My guess is slightly overweighted and a sticky inflator.

 

[Boarderguy]

Replace your power inflator. They're less than $20 for a generic K-style inflator. Also check to see if your shoulder dump valve is actually working. In your panic you may have broken one of the connecting points or the cable.

 

[rongoodman]

I've had a slowly filling inflator. It is surprisingly easy to fail to notice if it is slow. I just felt like I was messing up and having to dump air from the BC more frequently, until I finally told myself.. something is messed up, I am not THIS uncoordinated. Didn't hear anything or see bubbles coming out.

Same thing happened to me a few years back. I could barely hear it and it took a little while to figure out what was going on. I swapped out the inflator with a spare during the surface interval and went on with the trip.

 

[FreqFlier]

But she said she tried to dump air before ascending - unsuccessfully. This has absolutely nothing to do with inflator imho.