How do I calculate my real SAC rate?

Ok so I am bored and stuck at home! I was scheduled to go for an ice-dive but the roads are blocked and I am sitting in my home with 3 filled tanks. Two HP 100s and one HP 80. I thought I should attach a reg and figure out my SAC rate. Any suggestions on how I can do that? I can time myself for 10 minutes breathing from a reg but if I am sitting down with an empty relaxed mind, that may not give a fairly accurate SAC. I can moderately exert and then try to breath the same reg after the same level of exertion but would that be considered accurate SAC rate?

Any and all tips and suggestions welcome.

Cheers -

CS

I don't think there's any legitimate way to do it without actually diving. In my AOW class I have my students take two measurements ... one before and after a 5-minute interval while swimming hard, and one before and after a 10-minute interval while swimming slowly. To use an automobile analogy, these will help you determine your "city" and "highway" MPG, respectively.

One must remember that like the MPG you get in your car, SAC isn't going to be a consistent number ... it's going to depend on the conditions and circumstances of the dive. If you calculate it for a number of dives, you'll discover it's slightly different each dive. Then spend some time figuring out what made it different ... that's when the fun really begins ...

... Bob (Grateful Diver)

Be sure and use a mask or nose clip...

Remember that "SAC" is actually the resting, at the surface, air consumption, not what you'll be using during most of a dive. The actual rate during a dive is the Respiratory Minute Volume (RMV), and most folks use these (incorrectly) interchangeably, so best not to get them confused.

No problem doing a sitting-down SAC....that is pretty much the minimum you'll ever have, like maybe on a really relaxed warm-water deco.
Then you can apply multipliers; x1.5 for an easy dive, x1.8 for a moderate dive, x2.0 for a tough dive, x2.5 for a stressful dive, x3.0 for serious stress (these are the numbers used in the SDI solo course).

For example, I'm pretty much in the 0.4 cuft/min range for my SAC, which I sometimes get pretty close to on a really relaxed reef dive. It can easily double if I'm working hard, and has tripled in high stress.

Note you can also easily calculate the RMV from a dive if your computer tells you average depth. Just take total gas used, work out the usage rate at the average depth, and then translate that to the surface.

I guess I'd rather base it on the analysis of the dives in my log book than one sterile incident on the couch.....

Snowed in? Get out your log book, and run the numbers. Why are they different? Gear? Temps? Stress? Start compiling all that, and build a foundation of knowledge you apply to the next diving scenario....

here's a nice short writeup on the subject: Determining SAC Rates

I download my computer and input the tank size and start/stop pressure and the program figures it out. It is always in the same area unless I'm filling lift bags or hovering in one spot all dive. It is a PITA to figure out by hand, unless you are on a square profile.

If I was to check in my living room it would turn out very low since I wouldn't be in a wetsuit fighting cold, low viz, and all the amusing distractions that make diving fun.


Bob
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The day I can't dive anymore, I will really need some other good reasons to stay alive. DarkAbyss

if you still go forward with it, just don't be watching the Playboy channel or other adult on-demand choices....

When I started looking at the numbers, it was interesting to see the swing of a new site, the swing of carrying a camera, different surface conditions, different visibility, different gear.... Some of the sites had quite varied results....

rhwestfall:

I guess I'd rather base it on the analysis of the dives in my log book than one sterile incident on the couch.....

Snowed in? Get out your log book, and run the numbers. Why are they different? Gear? Temps? Stress? Start compiling all that, and build a foundation of knowledge you apply to the next diving scenario....

Click to expand...

I do the same thing. I noticed that cold and exertion have the biggest impact on my sac.

I noticed toting that dam video rig (no, not a big one, but just adding something else) spiked mine (though a new site in cold water would do the same)..... It all seems to spike to the same "high", so I use that one for planning... The return to the same site, and just diving, usually had "normal" rates recorded. Sets a nice bar for planning.

101recon:

I noticed that cold and exertion have the biggest impact on my sac.

Click to expand...

... wear heavier undies ...

... Bob (Grateful Diver)