How are you computing your SAC?

[RIDIVER501]

FWIW, the deeper the average depth you use in your calculation, the 'better' the SAC number you'll get.

so that begs the question: " are we looking for the best SAC rate or are we looking for a more accurate SAC rate?"

If I spent the bulk of my dive at 40 feet and dipped to 60 to pick up a dropped item for a couple of minutes, do I use the 40 to get a more representative idea of my sac rate for the dive or do I use the 60 to BS myself into thinking I have a much better consumption rate then I really do?

This is just food for thought

 

[The Kraken]

RIDIVER501,

I think what were are looking for is a more accurate way by which to calculate the SAC . . . what we are striving for is to perfect our diving skills to give us a lower SAC without a conscious effort to obtain such.

The first is a compiled mathematical formula generated to deliver information.
The second is the culmination of good diving practices, physical and mental conditioning.

the K

 

[The Kraken]

FWIW, the deeper the average depth you use in your calculation, the 'better' the SAC number you'll get.

Depth, for the most part, has no effect upon the SAC rate. The SAC rate is a Surface Air Consumption index and, barring any outside effects, can be considered, to a certain extent, a constant.

Depth effects the SAC only as far as the volume of air that you use.

If your SAC rate is 0.4 then you use 0.4 cubic feet of air per minute at the surface.
At 66', all things being equal, your SAC rate is still 0.4, but you'll use 1.2 cubic feet of air because of the volume reduction due to increased pressure.

the K

 

[RIDIVER501]

Roger, understand that.

One can't track/see their improvement in SAC without the mathematics or a tool to show them the numbers.

but even with the mathematics, or the tools, if bogus info is put into the calculation, then you get a "garbage in - garbage out" situation. It may look good on paper but one is still sucking their tanks dry in no time flat.

perfecting one's dive skills goes with out saying, but divers shouldn't use math or tools to BS themselves into a false sense of improvement/proficiency. If bad data is being used in the calcs, then that is all they are doing.

 

[The Kraken]

Agreed . . .

the K

 

[Sideband]

Depth, for the most part, has no effect upon the SAC rate. The SAC rate is a Surface Air Consumption index and, barring any outside effects, can be considered, to a certain extent, a constant.

Depth effects the SAC only as far as the volume of air that you use.

If your SAC rate is 0.4 then you use 0.4 cubic feet of air per minute at the surface.
At 66', all things being equal, your SAC rate is still 0.4, but you'll use 1.2 cubic feet of air because of the volume reduction due to increased pressure.

the K

You are correct, but that isn't what he meant. I think what he was saying is, if you fudge and use a deeper average depth you can make the SAC look better than it is. That's basically what the OP was doing by using his max depth instead of his average depth.
Joe

 

[The Kraken]

Ah, my misunderstanding . . . apologies!

the K

 

[Charlie99]

You are correct, but that isn't what he meant. I think what he was saying is, if you fudge and use a deeper average depth you can make the SAC look better than it is. That's basically what the OP was doing by using his max depth instead of his average depth.
Joe

You mean I can't just use 130' as the average depth on that 130', 1 hour 18 minute dive on an AL80?

 

[The Kraken]

No, Charlie, you can't !!!!
You HAVE to use 132' because it equates to exactly 5 ATA.

the K

 

[Charlie99]

No, Charlie, you can't !!!!
You HAVE to use 132' because it equates to exactly 5 ATA.

the funny thing is that, as I was writing my earlier post I did the mental calculation of 80 minutes, 80 cu ft, 5ata = 0.2cfm SAC.