How are you computing your SAC?

[MXGratefulDiver]

I use SAC to determine the capacity of the tank required for a dive based upon a general SAC rate developed for that particular type of dive. I use the SAC for planning.

The PSI/min rate is a great tool to use to determine one's activity at depth or to determine an inordinate usage of breathing gas. I use the PSI/min for monitoring.

the K

Bing, bing, bing, bing, bing ... give that man a cheroot !!!



... Bob (Grateful Diver)

 

[jpedwards]

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

I just use the 'average' depth reported by my computer (Suunto Gekko) to calculate SAC. Don't know what algorithm it uses - sample every 30 seconds maybe?

 

[fmw625]

If you don't have a computer and dive the tables (square profile), how do you figure your average depth?

 

[Sideband]

If it is a "square profile" then your max depth IS your average depth.

Joe

 

[The Kraken]

If it is a "square profile" then your max depth IS your average depth.

Joe

Well, not quite.
Suppose you did a 100' dive for 3 minutes . . .

Say 2 minute descent, 3 minutes on the bottom and then another 1 minute to ascend to 30', then another 1/2 minute to ascend to 15' and then 3 minutes at a 15' safety stop.

That comes out to about a 46' average dive depth.

Hummmmmm . . . .

 

[Sideband]

Right, but I wouldn't use such a dive to figure my SAC. I don't think 9.5 minutes actually constitutes a dive does it?
Joe

 

[RIDIVER501]

Right, but I wouldn't use such a dive to figure my SAC. I don't think 9.5 minutes actually constitutes a dive does it?
Joe

the 2 rules of thumb I was taught and always use are:

1. meeting any two of the following constitutes a dive.
depth of 15 feet or deeper.
burned 1500 or more psi.
down for 15 or more minutes.

2. any dive where a safety stop is recommended.

 

[The Kraken]

It's not "what" constitutes a dive, it's just an example that illustrates that the max depth of a square profile dive can't be used as the average depth of a dive with which to compute an SAC.

the K

 

[fmw625]

This is a great discussion, but I need guidance in how to figure average depth for SAC calc. Max depth won't work, You will wind up short on air. I know because I was using max depth. When I figured the time I could be down using my Average SAC over the last 10 dives I had to surface sooner than expected. Monitoring my air regularly I never got into any trouble. I was disapointed that I had to cut the dive short.

 

[Charlie99]

This is a great discussion, but I need guidance in how to figure average depth for SAC calc.

If you have a computer or electronic depth gauge/timer that you can download a profile from, then just average that.

Otherwise, do as an earlier poster suggested and swim at a constant depth for a while and note how many psi you use over some period such as 10 minutes. Then just calulate SAC using that 10 minutes, the depth, and the PSI used.