Do you avoid people with bad sac rates?

[b1draper]

My SAC rate on a AL80 ranges between .45-.65 depending on the dive if it's a deep dive (100 + feet) then the SAC is going to be higher than a dive around 60-70 feet. If you're doing a dive where it's cold or your fighting a current than the SAC rate is going to be higher.
I've never not dove with a person because of their SAC rate; because we've all been there with the high SAC rate and the only way a newer diver is going to get their SAC rate down is to dive. As time goes on and a diver gets more comfortable and streamlined things are going to get easier.

On trips to the bahamas or some other place like that my dive will average around 40-45 minutes and that's usually when the DM is trying to get us up on the boat then I'll drain my tank down to 300psi doing an extended saftey stop. I'm usually the first in and last out.

 

[RikRaeder]

My SAC rate on a AL80 ranges between .45-.65 depending on the dive if it's a deep dive (100 + feet) then the SAC is going to be higher than a dive around 60-70 feet.

Forgive my ignorant question, but would't one's SAC rate be the same at 10m or 20m or 100m?

 

[Randy43068]

what a dumbass thread ...



OK, OK, this has some pretty good discussions going on. I should have read through it before commenting. But the OPs question seems a little offbeat to me.

 

[b1draper]

Forgive my ignorant question, but would't one's SAC rate be the same at 10m or 20m or 100m?

Not really, here's a good site that explains what a SAC is and how to calculate it.

Surface Air Consumption Rate

 

[vondo]

Forgive my ignorant question, but would't one's SAC rate be the same at 10m or 20m or 100m?

It depends on the diver's anxiety level. Mine isn't the same from what I can tell.

 

[Chernish]

Hello RikRaeder,

The SAC rate increases with depth. At first only slightly, then significantly. I saw figures stating that the SAC rate at 100m was around 15% more than at 40m. Not that I ever went there. We're a little bit out of the scope of "recreationary" diving In any case don't let this worry you for recreationary dives: the way you fin and the general conditions will have more effect on your SAC rate than the depth.

I have never cared about the SAC rate of the people I dove with, and never will. The only "bad" experience I had was with a guy straight out of the OW, entusiastic but not very gifted. Of course we don't dive with 80cuft tanks, that might help too

Cheers!

 

[steve2281]

One of my all-time favorite dive buddies is my practice partner. He's about 6 feet tall and very strong and fit, and he is an absolutely beautiful diver, and imperturbable in the water. He also has a SAC rate of about .8. It isn't inefficiency or improper weighting or bad breathing technique or a lack of comfort in the water. It's just who he is. So he dives doubled 130s to my 85s. Works out fine.

I assume you're not talking about a cave dive. If you matched gases, your buddy would still only have 1/3 the volume of your 85's to use.

When possible, I would rather dive with equal size cylinders reguardless of air consumption. Then forget all the math, and the first one to 1/3's turns the dive.

 

[Rick Inman]

The SAC rate increases with depth. At first only slightly, then significantly.

Well, just to clarify, the SAC (SURFACE Air Consumption) doesn't increase with depth, but the amount of gas consumed does. You multiply your SAC (calculated as CFM)times depth (ATA's) times minutes to get cubic feet of gas consumption. For example, your SAC is .5, you'll be at 99 feet for 10 minutes.

.5*(99/33)*10=15 cubic feet of gas consumed.

Your rate stays the same, but the amount of gas consumed increases with depth.

 

[ClayJar]

Forgive my ignorant question, but wouldn't one's SAC rate be the same at 10m or 20m or 100m?

More or less for "recreational" diving, but probably not at *100m*, since other factors would have come into play (helium is special :biggrin.

Someone might be more stressed on a deep dive, or it might be colder, both of which would increase a diver's air consumption. If they didn't have a good grasp of buoyancy, constantly adding and dumping BC air volume at the higher pressure might add up to something noticeable, although considering the volume of each breath, I find that unlikely (people who have not developed good buoyancy usually haven't developed the calmness and normal breathing that you'd need to be able to tease the buoyancy air consumption out of the total). For me, there's really no discernible difference between an 85 foot dive and a 25 foot dive.


Oooh! Oooh! I've got to tell one tiny story!

Early last year on one of our checkouts, a father was diving with his young college-age daughter on her checkout trip. She was well toward the stick end of the spectrum, with probably less body fat than your average asparagus -- one of those almost sickeningly healthy people. Anyway, we're down on the dive, and I'm stealing glances at all the students' SPGs as I hovered around as an extra pair of eyes for the instructor.

I look at the first guy. About 1800. I pirouette on my head to check the next guy. 2100. A quick somersault maneuver above the really big guy's left shoulder. 2000? Not bad. Then I get to the young daughter. 1100. I move to-- waitaminute!... I check again. 1-1-0-0?!?

I did a quick assessment of her apparent state of mind (no fear or discomfort evident in her eyes, and she's not acting stressed). I glanced across all her gear (no slowly free-flowing octo... no leaking BC... all seems fine). So, having eliminated the impossible, the only thing I had left (however improbable it may have seemed), was that she was breathing the *wazoo* out of her air. I signaled her air state to the instructor, and he handed her (and her dad/buddy) off to the other instructor from the first group in, who was starting an ascent.

She had an *astonishingly* high SAC for someone so small, and it was like that all weekend. She was enjoying herself and said that she wasn't the least bit stressed, and she was certainly in quite reasonable physical shape. We couldn't come up with any reason why she sucked the life out of the tanks, but hey, she was having a great time diving. We just adjusted the dive plan (by putting her in the water last), and had a great weekend of diving.​

Anyway, coming back to the original topic, although my normal SAC may be better than all but the lightest-breathing students on the boat on one of our checkout trips, I'm an air hog compared to my compressor-buddy. I dive a 100cf to her 80cf, and still, I end the dive every time. It would be highly hypocritical for me to refuse to dive with someone else because their air consumption was markedly greater than mine while my best buddy dives with me in spite of *my* markedly greater SAC.

 

[TSandM]

I assume you're not talking about a cave dive. If you matched gases, your buddy would still only have 1/3 the volume of your 85's to use.

No, we're talking purely recreational diving here. When he and I cave dive together, we'll both be on Al80's, and the dive will be limited by his gas consumption, which is something he worries about. But, shoot, I'd rather do a short great dive with a great buddy, than a long dive with somebody I'd rather not be there with!