I posted this in the Accidents and Incidents in reply to a story about a woman who was rescued in Edmonds WA after she somehow became inverted and needed help. I thought maybe I'd post it as a "Lesson Learned" too.
As an example of what could happen, and hopefully someone can learn from my ignorance......
My first dive in my new gear was also my first dive in an AOW class which for some unknown reason was also the Deep Dive in that class....apparently it isn't supposed to be the first dive in AOW.
That said, it was my first COLD water dive in Puget Sound with a back-inflate BC (with a 5mm shortie over a 7mm semi-dry wetsuit; lots of neoprene, which just adds to the buoyancy issues.) In my case a semi head-down attitude at some point during the dive caused air to get trapped in the lower part of the BC bladder and unbeknownst to me, I didn't have all of the air vented out. As I returned from depth with a lower-on-air tank, that air trapped in the lower portion of the bladder caused me to "stand on my head" and was causing an ascent. I tried to use the inflator hose to dump air, but it wouldn't vent, since I was feet-up. I didn't know enough to simply reorient myself to head-up and completely vertical: but I was trying to swim downward to stop the ascent, so I wouldn't have done that anyway. I remember thinking I was going to bounce to the surface feet first. Not a good plan after a deep dive. I had no idea what was going on. Not until after the dive was I told that the Instructor came behind me and vented some (or all) of the air using the bottom dump valve. I was so new (and, admittedly dumb - I should have become more familiar with the gear first) I didn't even know there was a bottom dump valve. But that air-dump still wasn't enough to keep my feet down. To stay down, I had to kick down for the rest of the ascent, which thankfully was a shore dive/gradual ascent.
An empty BC and more weight in general didn't cure the problem for subsequent dives. I started adding ankle weights and they keep my feet down, but I still haven't figured out how to solve the problem in any other way. I don't have this problem in warm water with this gear - so I keep coming back to the wetsuit, but I don't know any other possible causes or solutions.
As an example of what could happen, and hopefully someone can learn from my ignorance......
My first dive in my new gear was also my first dive in an AOW class which for some unknown reason was also the Deep Dive in that class....apparently it isn't supposed to be the first dive in AOW.
That said, it was my first COLD water dive in Puget Sound with a back-inflate BC (with a 5mm shortie over a 7mm semi-dry wetsuit; lots of neoprene, which just adds to the buoyancy issues.) In my case a semi head-down attitude at some point during the dive caused air to get trapped in the lower part of the BC bladder and unbeknownst to me, I didn't have all of the air vented out. As I returned from depth with a lower-on-air tank, that air trapped in the lower portion of the bladder caused me to "stand on my head" and was causing an ascent. I tried to use the inflator hose to dump air, but it wouldn't vent, since I was feet-up. I didn't know enough to simply reorient myself to head-up and completely vertical: but I was trying to swim downward to stop the ascent, so I wouldn't have done that anyway. I remember thinking I was going to bounce to the surface feet first. Not a good plan after a deep dive. I had no idea what was going on. Not until after the dive was I told that the Instructor came behind me and vented some (or all) of the air using the bottom dump valve. I was so new (and, admittedly dumb - I should have become more familiar with the gear first) I didn't even know there was a bottom dump valve. But that air-dump still wasn't enough to keep my feet down. To stay down, I had to kick down for the rest of the ascent, which thankfully was a shore dive/gradual ascent.
An empty BC and more weight in general didn't cure the problem for subsequent dives. I started adding ankle weights and they keep my feet down, but I still haven't figured out how to solve the problem in any other way. I don't have this problem in warm water with this gear - so I keep coming back to the wetsuit, but I don't know any other possible causes or solutions.