I just started drysuit diving myself and have 10 OW dives in a White's Fusion. I was taught, via PADI, to use only my suit for buoyancy during the dive and only my BC at the surface. To keep buoyant and trim at depth, I had to close my exhaust valve by several clicks and then remember to open it for the ascent. I was getting comfortable with this routine.
@
mintaka:
In essence, there's nothing really wrong with how you were doing things for those first 10 OW dives. Most exhaust valves will allow a diver to manually dump air from the suit even with the cap completely tightened down. This is definitely the case with your Si-Tech dump valve. Please refer to the owner's manual if you don't believe me.
Then last weekend I did a 100' wall dive (300' bottom) and during the descent I realized my inflator valve was not delivering air to the suit and I started descending very fast with a lot of squeeze. I quickly figured out that my hose wasnt really clicked in (i'll never again forget to check this pre-dive), so I fixed it and all was well (except for my racing heart). After the dive my tech-diver friends asked what happened and when I told them they said..."dont use your suit for buoyancy...use your BC.. only put enough air in your suit to compensate for the squeeze".
More importantly, what your tech diving friends should have emphasized is the importance of a pre-dive check ritual -- especially on a wall dive with no bottom within recreational limits. Yes, it was an oversight on your part...but if you are diving with a buddy/dive team, culpability should be shared by the
entire group. It's OK to take what more experienced divers say to heart, but let's not lose sight of what caused your problem in the first place -- an inadequate buddy check. I think that should have been the take-home message here.
Managing a large air bubble in the suit can be onerous if the air is being trapped in various areas. Quite frankly, the design of the Fusion, with its stretchy outer lycra layer, evenly distributes the bubble and makes it trivial to manage a larger-than-normal bubble. There are times when a diver may want to keep his undergarment more lofted (colder than usual water temps), so I think it's worthwhile to experiment with using the drysuit only for buoyancy. Since I like taking pictures while I ascend upslope on the way back to shore, by using my drysuit only for buoyancy during that phase of the dive, my hands are free to set up my shots. A simple right shoulder dip dumps a little air. For night dives, it's even more useful since one hand is operating a light while my opposite wrist has a computer strapped to it. By all means, though, choose how you want to dive. On dives to 100 fsw, my personal preference is to inflate my drysuit only down to about 25 fsw to offset squeeze...then I add a couple of shots to my BCD at about 50 fsw...and alternate inflation between the two to offset squeeze as I venture deeper. Many of my dives have a maximum depth of 60 fsw, so I end up putting very little air in my BCD. During ascent I typically dump all of the air in the BCD first and then ascend the rest of the way by exhausting air from my drysuit.
I really have to question why PADI teaches the suit-only buoyancy for recreational diving when it seems that in practice, most people dont do this.
The short answer to your question is that PADI thinks it's easier for a student to manage one buoyancy control device during ascent. IMHO, I think the other method should be taught as well.
Have fun and dive safe.
[Edited later: Oops! Just saw that
MaxBottomtime and others have already addressed your question. That's what I get for stepping away from the computer for a few minutes.]
