SAC rate
- Thread starter PaulB
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Surface Air Consumption can be figured several ways but the easiest is to spend 10 minutes swimming at 33' noting the psi when you started and the psi when you finished. You can then figure your psi/min SAC rate by dividing the gas used by 20 (10 minutes at 2ATA.) You can figure your SAC rate in cubic feet by converting psi to cf specific to the tank size you were using.
Another way to do it would be to do a dive and take your average depth figured in ATA. Multiply that by your time in minutes and you have ATAminutes. Divide the amount of gas you used by the ATAminutes of the dive.
It is best to figure a working SAC and a resting SAC.
The reason figuring your SAC is important is so that you can use it for gas management purposes... planning your dive.
Another way to do it would be to do a dive and take your average depth figured in ATA. Multiply that by your time in minutes and you have ATAminutes. Divide the amount of gas you used by the ATAminutes of the dive.
It is best to figure a working SAC and a resting SAC.
The reason figuring your SAC is important is so that you can use it for gas management purposes... planning your dive.
the easiest way of all is to put your starting and ending pressure into the Suunto Dive manager after downloading your Stinger. 
Braunbehrens
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I think some of the air integrated computers like the cobra will calculate the sac for you!
Not that I would advocate using a such a device...heaven forfend!
When planning stuff count on your SAC rate doubling in a high stress situation. That's the rule of thumb I've always been told.
Not that I would advocate using a such a device...heaven forfend!
When planning stuff count on your SAC rate doubling in a high stress situation. That's the rule of thumb I've always been told.
but how do you account for factors like cold, excitment, and other variables?
Well, since I just learned all about this SAC rate thing... the advice I got was to track your SAC rate over multiple dives and just watch what happens on different dives to give you an idea what to expect. If you do 20 cold quarries dives, you can look at the average and make a good estimation of your air usage for the next cold quarry dive. If you then go to Bonaire and do a warm dive, you can look at how that compares to your "average" dive and be able to plan within a certain degree of error for the rest of your trip, calculating each dive and adjusting as needed. I was told that it's a process and you just need to start tracking to see how you, individually, react to different situations.
Rachel
Rachel
Braunbehrens
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Rachel, you got some excellent advice.
Another thing you can do, once you become more familiar with the calculation, is to estimate how much gas you are using. Check the spg once in a while to see how close you are. After a while you'll have a much better awareness of what's in the tank and how long it will last you.
All this stuff is 1000 times easier with the metric system...unfortunately I also use the imperial system.
Another thing you can do, once you become more familiar with the calculation, is to estimate how much gas you are using. Check the spg once in a while to see how close you are. After a while you'll have a much better awareness of what's in the tank and how long it will last you.
All this stuff is 1000 times easier with the metric system...unfortunately I also use the imperial system.
...what Rachel said... and when planning gas usage for a critical dive you should inflate the figures.
My SAC last Saturday working hard against a current in an unfamiliar area was .54 but later it was only .31 on a third dive loafing around at 33' with no current.
Most dives (cold water) I am .44~.46
However when I plan gas for a tech type dive I use:
1.0 for emergency/contingency
.7 for working portion of the dive
.5 for resting portion of the dive
My SAC last Saturday working hard against a current in an unfamiliar area was .54 but later it was only .31 on a third dive loafing around at 33' with no current.
Most dives (cold water) I am .44~.46
However when I plan gas for a tech type dive I use:
1.0 for emergency/contingency
.7 for working portion of the dive
.5 for resting portion of the dive
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