Common for SAC to just drop?

mikemill · Apr 22, 2009

On Sunday I did three dives off a boat and on the third dive I was able to dive with my brother (he was doing his AOW so the first two dives were with his class).

The last time we dove (a few months back) we had nearly identical SAC rates but on this dive I outlasted him. When we got back onboard I had well over 400 PSI more and he started at a few hundred PSI more than I did.

When I got home I downloaded my computer and did the SAC calculations. My previous rate was in the 0.85-0.90 range. That day my first dive was 0.91 (not surprising as I ended up bobbing around on the surface for 10 minutes while the boat dealt with diver issues and it was a 110' dive so slightly excited), the second was 0.7, and the third was 0.66.

Gear wise the differences were a drop of 2lbs and using steel 80s (over filled to about 90 ft³) instead of LP 95s or HP 100s.

tc · Apr 22, 2009

You're learning to relax- that's the difference.

It happens at different points for different divers, once you get comfortable with your gear and in the water your air consumption goes down.

Congrats!

mikemill · Apr 22, 2009

I was expecting it to go down but I thought it'd be a gradual decline not a sudden drop

More good news: I can drop more wait

Sas · Apr 22, 2009

Well I had the same thing happen. My SAC rate was around .8 when I started and remained that for a fair few months and over a short period of time after this dropped to 0.4ish. I attribute mine to switching to a drysuit when its cold, dropping a tonne of weight, getting a camera and learning better kicking techniques. It all happened around the same time really and my SAC really dropped off. If you've switched your gear around it is quite possible that you've changed how much weight you wear and how you trim out. Fixing those can cause a huge drop in SAC.

That being said, my SAC can jump up to 0.5-0.6 in really bad conditions such as strong current where I have to work very hard. My buddy's air consumption triples when very overworked too. So, your base line can be much lower than your stressed SAC rate so try to work out what your base line is, then different situations where it might change (strong current, getting stressed, etc).

pittyyofool · Apr 22, 2009

yes it is common. My buddy when he learned to dive, sucked threw a steel 95 in 1/2 the time it took me to empty an old steel 72. Now 3 months later he learned to relax and a he finishes an 80 in the time it takes me to go threw a 72. I could work out the sac's for you but whatever...

Riger · Apr 22, 2009

Without actually doing the math and making the calculations, I had previously sucked when it came to using air when compared to my wife.

I used to dive with a 0.5mm wetsuit and even though I "felt" the cold, it never bothered me. On a recent trip to the Red Sea, I decided to get a 3mm suit (for the first time) and will you believe it? the difference in consumption between my wife and I has drastically narrowed.

I guess there are many factors that improve efficiency of consumption, the one I just tried has had a significant "jump" for me and this of course allows me to relax even more and the consumption improves again.

It seems like a self feeding spiral.

Best Regards

Richard

The Kraken · Apr 22, 2009

Yep, what TC said.

One thing that may have factored in your reduced SAC rate was that you were concentrating on your brother's actions and not on other things.

the K

jvilalta · Apr 22, 2009

Aside from being more relaxed and comfortable like everybody else suggested, it probably also has to do with the fact that you dropped 2lbs. Assuming you are compensating with your lungs for these extra 2 pounds (some people do) if your dive was to 99 feet we're talking about a change in your sac rate of about 0.125. (2/64)(99/33+1)

TSandM · Apr 22, 2009

It's very common for people to have fairly high gas consumption as newer divers, and as they get the whole thing figured out, it will drop. By the same token, doing a dive that raises your anxiety quotient can make it go right back up again -- One of the first practice dives I did running a reel, my SAC almost DOUBLED!

My gas consumption plateaued out pretty early and stayed steady for two years. For some weird reason, this winter, it took a nosedive that I can't explain at all (dropped about 25%). Maybe it's because my buoyancy control is better, or I'm more comfortable in the Fusion. I don't know. It was really unexpected.

Gombessa · Apr 22, 2009

I think there's a direct correlation with how quickly you gain comfort in the water. If you slowly get acclimated with diving, you'll likely see a gradual reduction of SAC rate. If you dive a few times and just one day find yourself significantly calmer and more "in tune" with your dive, chances are you'll notice your SAC is suddenly significantly better.

Another thing that helps a lot of warmth - jumping from wetsuit to drysuit made a pretty big difference for me in the space of maybe 3 dives.

Common for SAC to just drop?

Please register or login

mikemill

Contributor

tc

Miscreant Moderator

mikemill

Contributor

Sas

Contributor

pittyyofool

Contributor

Riger

Contributor

The Kraken

He Who Glows in the Dark Waters (ADVISOR)

jvilalta

Guest

TSandM

Missed and loved by many.

Gombessa

Contributor

Similar threads