Do you use your SAC for anything? POLL

[rjack321]

There's no poll.

But yes, I use it for novel and/or new to me gas plans. Some planning I just "know" and don't need to calculate anymore.

 

[Rhone Man]

I use it for gas planning on planned deco dives.

For non-deco dives I just check it to measure my relative anaerobic fitness.

 

[Kevrumbo]

Your primary "gas gauge" during the dive is your SPG in pressure units --so I use the SAC rate converted to bar/min for the particular tank I'm using (my reference RMV is 22 litres/min).

For example, a single AL80 tank (11 litre/bar tank), my pressure SAC rate is 2bar/min. So in 10min breathing on the surface, I'll use 20bar of breathing gas.

But at 30m of depth (4 ATA), I'll consume instead 4-times-20bar equals 80bar in 10min nominal workload finning . . .I then check the SPG to confirm the delta change in pressure.

This is the way you should be actively utilizing your SAC rate, realtime as well as in pre-dive gas consumption planning . . .

See also http://www.scubaboard.com/forums/5714367-post15.html

 

[String]

What do you guys actually use your SAC rate for?

Planning dives.

Making sure ive got enough gas to get myself AND a buddy (if i choose to take one) out of the dive. Also for working out what size tank i need.

Its just how accurate do you really think it is since there is so much that can affect your SAC.

Its very accurate. My SAC in the same conditions never varies by more than 0.5SLM. Even adding in current, cold and other factors it doesn't change by THAT much and again its a reliable, repeatable amount. I know what my normal, what my working and what my cold SACs rate are and they're remarkably consistent between dives. Others i know are the same. It is more than accurate enough for dive planning.

Everything effects it temp/viz/current/surge/day/night. WTF!!!!

Not really. SAC is governed by fitness, comfort level and weight carried. Thats about it. None of those factors cause it to change massively.

As for why would anyone need it, in my view anyone going diving WITHOUT knowing their SAC is incapable of safely planning a dive. They have no idea if they've got enough gas to get them and a buddy out safely.

 

[FireInMyBones]

Yes.
I record my tank pressures for each dive so I can get a per dive gas usage for planning. Mostly, I've started to notice under what conditions I breath what rate.

I use it for gas planning regardless of a tech dive or a leisurely rec dive. I want to make sure that both my buddy and I have enough gas for ourselves and each other when it may be needed the most.

 

[GrumpyOldGuy]

I use it to refine my rock bottom gas plan and to give me confidence that the rock bottom reserve calculated will get me back to the surface safely. I can't conceive of diving without this basic knowledge.

 

[fisheater]

I use my SAC for planning and, because I record it for each dive, for monitoring my general dive fitness and approach.

 

[Peter Guy]

Hmmm, I use my SAC rate to figure out how narced I am. As I get closer to 100 feet, I make sure I calculate my current consumption rate by taking 5 minute PSI readings and the calculations generally go something like this:

a. Depth -- 100 feet

b. ATA -- 4

c. Pressure 2475 psi -- minute later 2200 psi -- that is 275 psi used

d. Uh, what was I doing? Oh, right -- depth 100 feet. Uh, How many psi was it? Uh, uh, uh...

If I can do the whole calculation, I know I am either on trimix or I am NOT at 100 feet!

 

[Charlie99]

I use SAC, but in kind of an indirect way.

When looking at dives (either square profile or multilevel) to see if the plan is reasonable for the amount of air, I total up the ata-minutes. By ata-minutes I mean time at each depth in minutes, multiplied by the ata for that depth.

For an AL80, I need to have ata-minutes less than 130, or 160 at the very most, and that only for multilevel dives where my rock-bottom reserve gas for ascent is very low for the shallower portions of the multilevel. (130 ata-minutes is the result of assuming I have 65 cubic feet available, and SAC of 0.5).

I most cases, I have already done the profile being considered, or one very similar, so I don't have to actually do the calculations.

If I am planning a dive with an instabuddy that I've never dove with before, I assume 80 ata-minutes available, or 100 ata-minutes at the most. Those numbers correspond to 65 cu feet with 0.8 cfm and 0.65 cfm SACs.

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Turn pressures, ascent pressures, and rock bottom take priority over any previous planning.

 

[aquaregia]

I calculate my SAC, but assume 1.0 for gas planning. Unfortunately, I know that my working SAC is above 1.0, so it's sort of like I calculate it only to ignore it. All my buddies have casual SACs of 2/3 or less of mine, so I assume that their working SACs are also 2/3 or less of mine (I know that's not a great assumption), but that comes pretty close to 2.0cf/min.atm for the pair of us.