Can you describe in more detail your free ascent practices. Do you just drop to 130' with a single Al80 and then immediately spit the reg out and start the ascent? How long does it take you to reach the surface from 130'? Do you hyperventilate yourself before spitting the reg out? Have you determined if there is a max ascent speed that you shouldn't go over?
There are two other threads on free ascents you might find useful:
http://www.scubaboard.com/forums/basic-scuba-discussions/384619-cesa-40ft-2.html#post5921024
That thread spawned:
http://www.scubaboard.com/forums/ad...ck-oxygen-during-free-ascent.html#post5921256
I progressively worked up to 130' and deeper years ago. I also do a lot of freediving now that I live on Californias north coast. As a result on most practice runs, I drop rapidly to 130' or more, usually on a single steel 72 or 80, rather than do a few workups from shallower. By rapidly, I mean maybe 100-120/minute, which is not swimming hard but a moderate kick it is the beginning of the dive so the tank is full and I am more negative. I take a short moment to orient, position myself upright and essentially simultaneously:
- inhale a moderate lung full of air, a little less than the top of a normal inhalation cycle.
- inflate BC to positive, but not nearly as much as if I dropped my 10KG/22 Lb. weight belt. Definitely a little more buoyant than when I normally start an ascend.
- pull the second stage out of my mouth and hold in my right hand poised to reinsert.
- thrust my lower jaw out, head up 45-60°, open airway, gently purse lips open.
- lift the BC hose overhead so I can vent on the way up with my left hand.
I usually dont kick much more than needed to steer around kelp. My computer starts whining that I am exceeding 30/minute. I probably exceed 60'/minute, but not by a lot.
There were a few times I wasnt comfortable and aborted/put my regulator back in before making it all the way to the surface. The discomfort wasnt so bad I was concerned over blacking out, just listening to my gut. I do this for fun these days so why get stupid over it?
I usually get a chance and try again within a few days. Each time so far I comfortably made it to the surface on the second attempt. I suspect that the aborted practice run made me more confident. You cant help but review it in your mind and conclude that I wasnt actually in trouble. The value of practiced free ascents is more about state of mind than physical prowess.
I want to emphasize this:
There is no reason to hyperventilate because you already have far more air than your lungs can hold and your blood is hyper oxygenated. You will be exhaling all the way up so a lot of CO2 goes with it. The only thing hyperventilation does is reduce your confidence in doing a free ascent in an actual emergency.
In response to this question on
http://www.scubaboard.com/forums/ad...ck-oxygen-during-free-ascent.html#post5921256:
What increments would you recommend I start with and build up to for practice?
I replied:
Start at 10' and add 10'. You will get to the point that where 10' increase seems like nothing. It is all builds skill and experience, which results in the self-reliant confidence you are ultimately seeking. Repetition at this point is as or more important than the depth. When you get to around 60', consider limiting them to two cycles at the beginning of a diving day. Maybe one cycle if/when you choose to try 100'+.
Keep your airway open and enjoy yourself.
See for yourself where your limits are. Like most things in life, practice will usually extend those limits. I like to think of free ascents for Scuba divers like parents that teach their infants to swim
often called infant drown proofing. Neither is truly drown proofing, but both stack the odds more in your favor.