When do you start to calculate your SAC rate

[ScubaSteve1962]

I've seen many post about knowing your SAC rate, when do you start to calculate it for dive planning. Mine changed drastically from my dive in Oct to my dive in March, I went from 25 Min's with less than 500 psi remaining to 50 Min's with over 500 psi remaining. Should I just keep my eye on my computer until it settles down then start using it for my dive plans??

[Insta-Gator]

SAC can be calculated for every dive (after the dive is completed.) Track it over time to see if you are improving or not. SAC can be affected by your physical fitness and your diving skills. Early in your diving career it will be affected most by how relaxed and comfortable you are in the water. Getting a lock on your buoyancy control is key.

http://www.ndc.noaa.gov/pdfs/AirRqmtFormulas.pdf

[ScubaSteve1962]

SAC can be calculated for every dive (after the dive is completed.) Track it over time to see if you are improving or not. SAC can be affected by your physical fitness and your diving skills. Early in your diving career it will be affected most by how relaxed and comfortable you are in the water. Getting a lock on your buoyancy control is key.

http://www.ndc.noaa.gov/pdfs/AirRqmtFormulas.pdf

Thanks, I always download to my computer and compare my dives. And been working on getting my buoyancy under control

[RonFrank]

Tracking SAC Its definitely important for new divers or if doing deco diving and planning. SAC is impacted by Depth, Water temp, Current and Visibility.

Depth - You suck down more gas the deeper you go. In addition deep dives can be more stressful which can result in added air use. Keep a close eye on the SPG when going deep. Below 100', pay attention as narcosis kicks in. If you realize your sucking down air and you are deep get shallower. This is not always possible, but even 10' will make a difference.

Cold - There are so many things that make cold water diving more difficult, cumbersome exposure suits, more weight, hoods, and thick gloves all make the diving more challenging. Its normal to use more air in cold water even for an experienced diver.

Current - current is not an issue unless you have to exit at the same spot you entered. I always swim into the current at the start of the dive when possible. If your planning a dive in current swim into the current for 75% of your planned time or more. Its amazing how much ground you cover swimming with the current. Do not swim past your exit point.

Visibility - Low vis makes things harder especially if you don't dive in low vis much. Harder = higher SAC. We were in the FL keys, the weather was awesome, but the vis was less than 10' after a storm. Eight people on the boat, four never made it to the reef. Two sat out the dive, and two guys spend time in water were 10' vis is considered good! Unfortunately poor vis takes practice and means more stress.

Realize any event that is stressful UW will general result in a higher SAC rate. This is compounded by depth.

[TSandM]

Hmm . . . may I respectfully offer that SAC is not affected by depth, unless being at depth unnerves the diver? SAC is normalized to the surface, so it is corrected for depth. Gas consumption definitely increases with depth, though.

I think it's quite useful to keep track of one's SAC rate until it plateaus . . . and then check it occasionally anyway, because it may change. I plateaued out very early, and then several years later, had another substantial drop (not sure at all why).

[scubadada]

Tracking SAC Its definitely important for new divers or if doing deco diving and planning. SAC is impacted by Depth, Water temp, Current and Visibility.

Depth - You suck down more gas the deeper you go. In addition deep dives can be more stressful which can result in added air use. Keep a close eye on the SPG when going deep. Below 100', pay attention as narcosis kicks in. If you realize your sucking down air and you are deep get shallower. This is not always possible, but even 10' will make a difference.

Cold - There are so many things that make cold water diving more difficult, cumbersome exposure suits, more weight, hoods, and thick gloves all make the diving more challenging. Its normal to use more air in cold water even for an experienced diver.

Current - current is not an issue unless you have to exit at the same spot you entered. I always swim into the current at the start of the dive when possible. If your planning a dive in current swim into the current for 75% of your planned time or more. Its amazing how much ground you cover swimming with the current. Do not swim past your exit point.

Visibility - Low vis makes things harder especially if you don't dive in low vis much. Harder = higher SAC. We were in the FL keys, the weather was awesome, but the vis was less than 10' after a storm. Eight people on the boat, four never made it to the reef. Two sat out the dive, and two guys spend time in water were 10' vis is considered good! Unfortunately poor vis takes practice and means more stress.

Realize any event that is stressful UW will general result in a higher SAC rate. This is compounded by depth.

Depth is taken into consideraton of SAC but the anxiety of depth may not be. Other factors such as current and visibility are often not taken into acccout. I find it useful to calculate all my SACs using Oceanlog software. It's very interesting and informative to see the factors affecting SAC. Cold water and exertion are two obvious factors affecting SAC.

[Bob DBF]

Depth is taken into consideraton of SAC but the anxiety of depth may not be. Other factors such as current and visibility are often not taken into acccout. I find it useful to calculate all my SACs using Oceanlog software. It's very interesting and informative to see the factors affecting SAC. Cold water and exertion are two obvious factors affecting SAC.

I also use oceanlog and today my second dive sucked but I was filling a few lift bags @ 100'. I always note what I was doing so I get an idea why my SAC is way out of line.


Bob
-------------------------------
I may be old, but I’m not dead yet.

[Tigerman]

I also use oceanlog and today my second dive sucked but I was filling a few lift bags @ 100'. I always note what I was doing so I get an idea why my SAC is way out of line.


Bob
-------------------------------
I may be old, but I’m not dead yet.
Personally I always note anything "not regular", even if my air consumption is not obviously hurting my SAC. Maybe my SAC has just increased and the "activity" does infact affect it, but isnt obvious because of the general improvement?
I also have had a couple of incidents where one would suspect the sac to increase much more than it actually did.

[RonFrank]

I forgot, depth is built in....DOH....Nice catch Lynne! So anxiety may increase with depth.

[Doomnova]

I forgot, depth is built in....DOH....Nice catch! So anxiety may increase with depth.
Honestly my best dive with a .60 sac was actually my deepest average dive. Something like 65ft average for 36 min for a sac of .62. I've been watching my SAC since i started to dive (26 dives ago today) just a personal interest to see my consumption change. I was around 1.1 when I did my Ow dives. then dropped to around .8 by the time I was in the 10-15 dive range. Now it seems to be sitting around .62-.64. I noticed the biggest change after my PPB which is where the final drop from about .8 down to my current .62-.64. Also after getting all my own gear put me down around the .8 mark. Now its just enjoying the scenes. Had a good 51 min dive today on the breakwater. Which is not my longest dive. :D

I think a lot of it has to do with comfort more than anything. How comfortable are you with the dive for the day. How well are you acquainted with the gear you are using. How good your physiological condition is. Buoyancy control is nother are you adding and then dumping a lot of air.

[dumpsterDiver]

We really don't need SAC to two decimal places... You previous SAC is used to predict your future SAC, that along with an estimate of your buddy's future SAC which then can be combined into a new estimate which is used to estimate when you should probably start going up....Lotsa estimating... 2nd decimal place isn't all that useful in my estimation....

[spectrum]

Honestly my best dive with a .60 sac was actually my deepest average dive.

I think I know what you mean. On a nice deep dive with the right buddy I can be very relaxed and do especially well with air. Maybe I'm borderline happy narced, I duno.

As to the Op, Yes SAC is a journey track it as you go and keep an eye on how the dive/gear effects your performance. Use the most recent relevant numbers to plan your dives.

Pete

[DivemasterDennis]

To answer the original question, I have actually never factored SAC rate in to my dive planning, not on dive 3 nor on dive 803, or after. The same is true for my wife/divebuddy Debbie (200 dives.) It isn't even something I actively computed until fairly recently. I log all dives, not depth, time, and consumption or air (or other breathing gas. I will also say that most divers I know, and the dive pros at my LDS, are like me in this. Just wanted to answer the original post truthfully.
DivemasterDennis

[Tigerman]

If you answer that you dont consider your SAC in your dive planning and indirectly advocate not doing so, it would be very helpful to let people know WHY you dont instead of having people guess, especially as your name and post indicate that you work at an LDS and is a dm yourself..

[TSandM]

Honestly, for a lot of recreational diving, knowing your SAC rate is pretty optional. If you are doing shallow shore dives off Maui, it's really enough to say "back on shore with 500 psi" and just figure you'd better turn back before you get quite to a half tank.

Where knowing your SAC rate becomes important is when you are doing deeper dives. It goes along with understanding the concept of minimum gas reserve -- once you have figured that out of your supply, you can use your SAC rate to decide whether the remaining gas gives you enough time at the depth you propose to make the dive even worth your while. If you KNOW you only have ten minutes of gas at depth, it won't come as quite a horrible shock when you have to end the dive at that point. And you won't start a dive that obligates you to be at depth for a certain period, if you're aware that the small tank you have simply won't permit that dive (a situation that killed a woman in Seattle the year I learned to dive).

The diver who is going to mosey along at 40 feet and check his gauges every five minutes is going to do fine without a lot of calculations. The one who's doing the 80 foot reefs off West Palm with a single Al80, not so much.

[Tigerman]

That was kinda my point TS&M.
Also you might "just know" how your gas is going to be used without actual numbers other than those on the pressure gauge and constantly do gas planning without "actually" doing gas planning..

[FinnMom]

I find it useful to know what my SAC normally is and over what range it normally wanders. You need this information for calculating whether you have enough gas and you need to keep in mind (1) enough gas means enough to get both you and your buddy to the surface on just your gas (2) if you two have problems your SAC rates will both probably go to the high end of ya'lls SAC ranges => calculate the "enough gas"-question with that in mind.
SAC is not a competive stat, it's an individual stat. But it is very useful information, esp. for deeper or more demanding dives.