Anyone not measure their SAC?

[lowviz]

As the video pointed out:

Nominal Working SAC: 0.75 cf/min or 20 l/min;
Relaxed (Safety Stop/Deco): 0.5 cf/min or 15 l/min;
Emergency/Stressed: 1.0 cf/min or 30 l/min. ...//...

So we are all the same and none of us have to determine individual values? That does make things easy, ignore the finer points and go with an average over all divers. You ever paired with a petite diver who knew what she was doing?

Those are all completely reasonable numbers for guesstimating what a generic diver will consume. But isn't that information being presented by one of the guys who doesn't even bother to adjust for altitude? Aren't you the guy who bent yourself into a pretzel doing ratio deco? I don't dive that way, I need a bit more pertinent information about how I behave underwater. After all, I'm the only one I ever see down there.

 

[scbaNE2179]

As a recreational diver I never had an interest in calculating my SAC rate. I see it as if I return to my entry point/boat with 500 psi, it really doesn't matter to me. I once had an overzealous and arrogant DM who was hell bent on promoting the importance of SAC rates. I pretty much ignored him but a small part of me wished the gods above would grant him a leaky mask just to silence his arrogance. I'm one of those divers who cannot care less about the numbers, I just want to dive and see stuff.

 

[kelemvor]

Out of curiosity, what is your RMV and what tanks do you use? And what is your typical dive depth?

I've never calculated RMV. I guess I could pull up some old dive logs and take a whack at it. I use subsurface to log my dives, and it automatically calculates SAC for me. When diving in Florida I use steel lp108's. The dives I do at home vary quite a bit, if I had to choose a number as typical I might say 40' but that's totally a guess. I dive different sites a lot, with the ballroom at Ginnie springs being the site I've repeated the most (about 50' deep).

 

[stuartv]

I've never calculated RMV. I guess I could pull up some old dive logs and take a whack at it. I use subsurface to log my dives, and it automatically calculates SAC for me. When diving in Florida I use steel lp108's. The dives I do at home vary quite a bit, if I had to choose a number as typical I might say 40' but that's totally a guess. I dive different sites a lot, with the ballroom at Ginnie springs being the site I've repeated the most (about 50' deep).

I had a feeling that would be the case - that your typical dive depths are on the shallow side. And it makes TOTAL sense that dives like that would normally be gas limited. Even with Nitrox and a big tank.

My "normal" dives are Nitrox and big tanks, but generally between 80 and 120 feet. I am always limited by NDL, not gas, on those dives.

One of these days I should do the math and figure out where the consumption and NDL curves cross for different sized tanks, to find the sweet spot of tank size for different depths. I.e. for any given depth, the optimum tank size so that you hit Turn Pressure and NDL at the same time.

 

[Steve_C]

I mean, how do you KNOW that, if your buddy goes out of air on you right when you were about to turn the dive anyway (so you're already getting low on gas), you have enough gas for both of you to breathe (at what would probably be an elevated rate) all the way through an ascent at a safe speed, with a safety stop? Do you even know, at ALL, what your buddy's consumption rate is, in order to figure out if you have enough reserve for the both of you? If you dive with an insta-buddy, do you ask? Obviously, if your buddy asks you the same question, you don't have an answer, so your buddy can't really plan his/her reserves with any confidence.

Those are good considerations. However, I dive in a solo configuration when I am diving in the ocean. Last Sunday I had an instabuddy with 20 or so dives stretched over a period of time. He made the comment that he was not good on air yet and was diving an AL80. Plan was he would follow me around and let me know when he was at 1000. We would be back at 60ft on the top deck at that point. After a nice swim around and swim through he indicated 1000 psi. I pointed up. We were back at the anchor line. Took him to anchor line and a group going up. At that point I was at 2000 psi on an HP100 not counting my AL19 pony. He went up with them. I dove for another 20 minutes or so. Point is that if you do have a buddy that sucks air, you have plenty of reserve for them because you have most of yours left. (PS: Swim through, assent with another group, etc., were all cleared with him prior to the dive).

 

[lowviz]

As a recreational diver I never had an interest in calculating my SAC rate. I see it as if I return to my entry point/boat with 500 psi, it really doesn't matter to me. ...//....

I have no problem with that. Why calculate something that is useless to you. No sarcasm, either. I get it.

 

[stuartv]

I have no problem with that. Why calculate something that is useless to you. No sarcasm, either. I get it.

I get it, too. I just don't feel the same way for myself.

I prefer to dive solo. But, when I dive with a buddy, I take the buddy obligation very seriously. Where I most often go for fun dives, they commonly rent HP100s, so my buddy and I could easily both be diving 100s. If my buddy turns out to be the type that huffs through a whole 100 right quick, I figure that buddy could also be the same type that fails to notice until he or she is totally out of gas. As such, I want to know that if they go OOA right when I'm down to my turn pressure, I will have enough gas to get us both to the surface while still doing at least a 3 minute safety stop.

If my plan is to start my ascent in time to arrive at the surface with 500 psi left, will that be enough? How do I know?

Even as a recreational diver, it is worthwhile to me to know my own RMV and, ideally, get some idea of what to expect from my buddy as well. If I'm diving with an insta-buddy and I'm lucky, they will feel the same way - and we probably will not have to worry about it at all. Unless one of us blows a tank valve O-ring or 1st stage HP seat or 1st stage diaphragm or....

 

[Kevrumbo]

So we are all the same and none of us have to determine individual values? That does make things easy, ignore the finer points and go with an average over all divers. You ever paired with a petite diver who knew what she was doing?

Those are all completely reasonable numbers for guesstimating what a generic diver will consume. But isn't that information being presented by one of the guys who doesn't even bother to adjust for altitude? Aren't you the guy who bent yourself into a pretzel doing ratio deco? I don't dive that way, I need a bit more pertinent information about how I behave underwater. After all, I'm the only one I ever see down there.

Nominal Working SAC: 0.75 cf/min or 20 l/min;
Relaxed (Safety Stop/Deco): 0.5 cf/min or 15 l/min;
Emergency/Stress: 1.0 cf/min or 30 l/min.

0.75 cf/min or 20 l/min RMV/volume SAC rate is a reasonable value for any beginning to novice Diver to achieve, and a fair conservative reference baseline value to start and compare individual rates with:

Average Gas Consumption

 

[lowviz]

...//... Average Gas Consumption

You make my point better than I was able to.

Look at the RANGE of that average. We are all alike?

 

[Kevrumbo]

. . .Emergency/Stress: 1.0 cf/min or 30 l/min.

0.75 cf/min or 20 l/min RMV/volume SAC rate is a reasonable value for any beginning to novice Diver to achieve, and a fair conservative reference baseline value to start and compare individual rates with:

Average Gas Consumption

You make my point better than I was able to.

Look at the RANGE of that average. We are all alike?

Of course not.

The point you're missing (along with the useless rhetoric you're posting @lowviz ) is again that 0.75 cf/min or 20 l/min is a reasonable working conservative RMV value at the upper range to start for beginning gas planning with the novice diver. And 1.0 cf/min or 30 l/min each for two divers is the max stressed value for a gas plan to cover an emergency air share contingency.

As a diver-buddy pair gains experience (and "logs their progress in air consumption"), they're entirely free to use any improved working RMV value they achieve. . .