Inexperience resulted in OOA at 66 feet (long)

[lamont]

I'm curious to know how much air you actually used vs. your predicted use. In my deep class, we discussed and worked out problems for turn pressure. It was more of an empircal approach using the diver's SAC and other factors like expected currents. For me, Lamont's rock bottom turn pressures (computed by Ayisha) are extremely conservative. 1900 psi is a lot of air at 30 feet. I could dive for an hour with 1900 psi. You can make a CESA at 30 feet.

You can also get bent doing a CESA, even from 30 feet, particularly if you're doing repetetive diving where you might already have a lot of free-phase gas.

Rock bottom gas management rules assume that the diver, even a recreational diver, does not consider a CESA to be an acceptable way to plan to get out of any situation. If you're still relying on a CESA as a crutch then of course you'll find rock bottom rules overly conservative. You also may not have enough gas to cut yourself out of an entaglement and depth and may wind up dead because you ran your dive time margins way too close.

On a typical Florida Keys dive at 30 feet, you go out against a current and return with a current.
Your gas consumption going out is greater than coming back. With such a rigid formula you are either going to make extremely conservative dives or carry enough gas to herniate a disc.

The 'turn pressure' calculation is a simplification for an idealized out and back trip where it is desired to return to the same point. If you've got a more complicated dive you should break the dive up into its components and calculated the planned gas consumption on all the phases of the dive and add them together. If you've got favorable currents on the way back, your gas requirements on the way back will be lower. If you've got unfavorable currents on the way back ('siphoning' if it were a cave) then you'll need more conservative gas requirements.

You guys in the Northwest dive in more extreme conditions and I'm sure it that there is a psychological effect from deep, dark and cold as opposed to deep, warm and I can see the surface at 130 feet. I'm not a reckless diver, yet I'm more inclined to plan my profiles based on my diving experience rather than a rigid formula which is over conservative for my air consumption and the conditions in which I dive.

You are making up most of the rigidity.

I had a 2nd stage freeflow at 50 feet which could have resulted in an OOA. I just swtiched to my octo and made a 30 ft per minute ascent to the surface with my buddy. It was no big deal. This happened right after I had my reg serviced and I've read that it is not uncommon.

And it was early enough in the dive and you had enough gas in order to do that. You'd probably have a different experience if both you and your buddy were down to 300 psi when that happened, which is where rock bottom becomes useful...

The stuff they teach in rec diving courses works for most recreational dives.

I disagree and see lots of room for improvement.

It's when you push the limits you need more conservative rules.

Disagree. I think on every dive you do you should always be able to find an exit, and it needs to be conservative enough that you can find it with certainty, and it needs to leave you unbent and unhurt with certainty. Anything else is just putting yourself at unnecessary risk.

I find it ironic that Shek Exley, the originator of the Rule of Thirds, died on an extreme solo dive to 900 feet.

I don't find it very ironic. Exley nearly died on multiple occasions because they didn't know any better back then and he pushed the limits.

 

[TheRedHead]

You are making up most of the rigidity.

And it was early enough in the dive and you had enough gas in order to do that. You'd probably have a different experience if both you and your buddy were down to 300 psi when that happened, which is where rock bottom becomes useful...

I disagree and see lots of room for improvement.

Disagree. I think on every dive you do you should always be able to find an exit, and it needs to be conservative enough that you can find it with certainty, and it needs to leave you unbent and unhurt with certainty. Anything else is just putting yourself at unnecessary risk.

Lamont,

I never come close to running out of gas and I do calculate a turn pressure that is less conservative than yours because I have a much better rmv than is assumed in that formula. It's the female advantage. My rec Deep Diver class did teach gas planning, and the first step was to calculate your SAC from your log data.

I'm a very conservative diver and I dive with 2 computers and a copy of my combined air/nitrox tables. I'm usually back with over 1000 psi on most of my dives. I carry shears, safety sausage, signal mirror, whistle and I dive with the same trustworthy buddy. I don't feel I put myself at undue risk. I don't penetrate wrecks or dive in caves. I look at statistics and see that most recreational dives are made safely and that common sense dictates that if standard NDL diving procedures were truly inadequate, we would see many more accidents and deaths. The problem is panic and failure to follow procedures learned in training.

 

[Scuba_Steve]

On second thought.....forget it.

I'm just gonna go practice my CESA's for when I really it up. LOL



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[JeffG]

On second thought.....forget it.

I'm just gonna go practice my CESA's for when I really phuk it up. LOL



_

Spare Air dude...its the only way

 

[Scuba_Steve]

LOL.

The Avatar keeps getting better too

 

[TheRedHead]

On second thought.....forget it.

I'm just gonna go practice my CESA's for when I really it up. LOL



_

Seeing that you're an instructor, dontcha get to do a whole bunch on them on a regular basis? I have no objection to rock bottom - as long as it's my rock bottom. I know that if I turn my 30 ft dive on Molasses Reef at 1900 psi, I'm going to turn up on the boat with 1400. I do so like to get my 59 minutes in. If some wretched soul managed to tangle himself on the upline (anchor line) surely one of the 4 or so DMs hanging out on the boat are going to notice him. Perhaps one of the other 20 or so divers might see him before they tried to haul him up.

 

[Scuba_Steve]

Seeing that you're an instructor, dontcha get to do a whole bunch on them on a regular basis?

Yeah 2-3 per student, but long before then I tell them if they ever really come to that point in their dive, they've done so much wrong that they are now reaping their just rewards........then I may throw in a RB idea or two or three as a way of keeping the reaper at bay. Then I lay on the couch the rest of the day with a splitting headache. LOL OUCH

 

[JeffG]

then I may throw in a RB idea or two or three as a way of keeping the reaper at bay.

You are a bad man. Dive Tech must love you.

 

[Scuba_Steve]

Oh sorry, RB in this case was Rock Bottom, not a Breather.........but I think they at least like me anyway Enough to accept Mr AMEX a few times a season.

hijack off/

 

[MXGratefulDiver]

Seeing that you're an instructor, dontcha get to do a whole bunch on them on a regular basis? I have no objection to rock bottom - as long as it's my rock bottom. I know that if I turn my 30 ft dive on Molasses Reef at 1900 psi, I'm going to turn up on the boat with 1400. I do so like to get my 59 minutes in. If some wretched soul managed to tangle himself on the upline (anchor line) surely one of the 4 or so DMs hanging out on the boat are going to notice him. Perhaps one of the other 20 or so divers might see him before they tried to haul him up.

Therein may lie the difference in perspective ...

Around here we don't dive with DM's ... if a diver was tangled up in something more than 10 or 15 feet away, you wouldn't see them ... and if the boat has more than 10 or 12 divers, we won't go on it ...

... Bob (Grateful Diver)