SAC Rate Poll What is normal? MALES ONLY

[pasley]

This poll is for males only. We will do females on a separate poll.
Take the average of your last 5 dives, what is your average Surface Air Consumption Rate as expresed in SCFM?

SUUNTO and other dive computers will automatically caculate this for you. For those who have to do it manually use this formula:

SCR = (1-P2/P1) x Vf/Aa/Tm

Where
P1 = pressure in psi at beginning of test dive
P2 = pressure in psi at end of test dive
Vf = actual volume of air in tank in cu. ft.
Aa = pressure in absolute atmospheres
Tm = time of dive in minutes

This is from Scuba Diving Mags site:
http://www.scubadiving.com/training...mption_rate)/

Why a SAC rate? To help with your gas management when planning a dive for yourself and your group.

 

[Diver0001]

13.4lpm or about 0.47cfpm. That's about normal for me using the gear I usually dive in. In the tropics it's quite a bit lower. The last time I dove in warm water my SAC averaged 9.7lpm or 0.34cfpm.

R..

 

[simbrooks]

SCR = (1-P2/P1) x Vf/Aa/Tm

Where
P1 = pressure in psi at beginning of test dive
P2 = pressure in psi at end of test dive
Vf = actual volume of air in tank in cu. ft.
Aa = pressure in absolute atmospheres
Tm = time of dive in minutes

This is from Scuba Diving Mags site:
http://www.scubadiving.com/training...mption_rate)/

A lot of people dont calc out exact numbers for Vf on every dive (or at least record them), so to find Vf = P1/Px*Vx
Where:
Px = rated tank pressure (likely 2400, 2640, 3000, 3442 or 3500) in psi
Vx = rated tank pressure at Px and of course SRT (standard room temp)

or you can rewrite that whole thing as:
(P1-P2)/Px*Vx/Aa/Tm

Aa of course is the average atmospheric pressure throughout the dive, not the deepest point.

Mine seems to be around 0.42 +/-, but that is in warm water Under stress, in caves or cold water it climbs to around 0.55-0.6 depending on flow.

 

[pipedope]

As my last 5 dives were working dives my SAC was somewhat higher at 1.0 to about 1.4.

For rec dives I am normally at about 0.5

 

[Uncle Pug]

Melvin.... it isn't easy to craft a poll that yields useful information (some would say that it cannot be done.)

Exactly what is the useful information you would like to pull from this poll?

 

[miketsp]

Melvin.... it isn't easy to craft a poll that yields useful information (some would say that it cannot be done.)

Exactly what is the useful information you would like to pull from this poll?

The big problem is that SAC is very sensitive to workload so fighting a current can be quite different from a drift dive.

 

[Gary D.]

With a mix of work and play it’s just impossible to get an average.

Depending on what I’m doing for play it can still be all over the board.

I just picked a middle of the road # on the poll.

Gary D.

 

[mccabejc]

I'm a new guy (25 dives), and I've been plotting my SAC since I started, and it seems to me that, given your type of diving is pretty consistent, the trend of the SAC should be pretty indicative of what you can expect.

Here's my most recent plot, including my dive today, and I think the trend is a pretty clear indication of what I can expect on my next dive (plus or minus a bit).

 

[pasley]

Melvin.... it isn't easy to craft a poll that yields useful information (some would say that it cannot be done.)
Exactly what is the useful information you would like to pull from this poll?

Uncle Pug,
Too true. Crafting a good poll is a challenge. This is a follow up poll to one I did previously. In that poll I have the largest numbers in a higher SAC rate than I anticipated so I have broken into finer numbers the range where the majority fell.
The intent of the poll? Well, to determine what "normal" is. Is is scientific? No. Just a rough estimate.

In short I know my SAC is 0.38-0.42 for most Southern Califrornia diving. Is that high or low? So the poll will give a rough yard stick to guage against. Now for lobster hunting it goes up.

 

[Charlie99]

I'm a new guy (25 dives), and I've been plotting my SAC since I started, and it seems to me that, given your type of diving is pretty consistent, the trend of the SAC should be pretty indicative of what you can expect.

Your graph shows that you are a much faster learner than I was

My SAC was 0.75cfm in the first dives. About 0.6cfm around dive #75. 0.5cfm after dive #130, gradually going down to a very repeatable 0.4 to 0.43cfm around dive #200.

Right now, my SAC is about 0.35cfm in a no motion drift, about 0.5cfm at a transit speed of 1kt (100'/minute), and 0.6 or 0.7cfm while swimming hard.