Anyone not measure their SAC?

[soggybadger]

Hi folks. Just wondering if anyone on here doesn't record their air consumption. I don't log dives at the moment and haven't bothered to record my gas use per dive. This is not a problem as I always seem to have plenty for my dives and redundancy. If and when I get a bit more technical I will log but at the rec level I just don't see the point. Thanks.

 

[MargaritaMike]

While I don't "log" my SAC, it is recorded on my computer. I watch it sometimes when I'm diving as a reminder to slow down and smell the roses. I will say that when I returned to diving this year after several years off, my SAC was 20ish. After about 20 dives my SAC is now 10 or less. IF I can get it to zero, I would have unlimited bottom time. It's a goal - probably won't get there, but I can try.
Cheers - M²

 

[Compressor]

I did not record my SAC all the time until I got my Perdix AI; now it does it for me when I log my dive electronically.

 

[MaxBottomtime]

I still log my dives after 28 years but not my SAC. It changes too much. Some dives require more work, while some are nothing more than resting underwater.

 

[soggybadger]

Thanks for the replies fellas. I took that as no's.

 

[HantsDiver]

Not really anymore.

When I was doing more technical diving - and thought I was something special I did it a lot more.

However - reality hit me hard. Firstly I can judge it now without doing calculations to some degree. And what's more it changes so easily that it's not actually relevant in reality. Now... I'm going to upset people with that. But it changes depending on so many things I just use a conservative number for my calculations.

In the event of a suit flood at this time of year - your SAC is going to be ridiculously high. If you get stressed it will go up silly high. If you get lost in a wreck it will go up ridiculously.

Some of those things "should" never happen - but I'm not perfect. And those who claim they don't suffer from such maladies either don't do challenging dives or they are trying to sell something. Your instinct is important. You know when to call it a day - you know when you are using a lot of gas.

 

[Chilly_Diver]

I log my RMV for each dive as SAC is not particularly useful if you use more than one tank size at any point in your diving life. It also makes it easier when discussing gas consumption with others.

 

[Kevrumbo]

I log my RMV for each dive as SAC is not particularly useful if you use more than one tank size at any point in your diving life. It also makes it easier when discussing gas consumption with others.

Your SPG reads in Bar pressure units for the particular cylinder that you're actually using and breathing at depth, so RMV in Liters is not very useful in that respect.

For example, a RMV of 22 liters/min per ATA with an Aluminium 11 liters/bar (AL80) cylinder yields a SAC of 2 bar/min per ATA: that is RMV divided-by Cylinder Rating equals SAC -or 22 liters/min per ATA divided-by 11 liters/bar equals 2 bar/min per ATA.

Therefore at 20 meters depth (3 ATA), you will consume three times as much of your SAC: or 3 ATA times 2 bar/min per ATA equals 6 bar/min.

Hence you know in ten minutes at 20m depth, you should nominally consume 60 bar in that 10 minute time interval; so if you started with 200 bar reading on your SPG, you would expect it to read 140 bar remaining at the end of ten minutes elapsed time (and 80 bar after another ten minutes; and finally 50 bar remaining after five minutes in which you should be already ascending to your safety stop).

 

[Chilly_Diver]

Your SPG reads in Bar pressure units for the particular cylinder that you're actually using and breathing at depth, so RMV in Liters is not very useful in that respect.

For example, a RMV of 22 liters/min per ATA with an Aluminium 11 liters/bar (AL80) cylinder yields a SAC of 2 bar/min per ATA: that is RMV divided-by Cylinder Rating equals SAC -or 22 liters/min per ATA divided-by 11 liters/bar equals 2 bar/min per ATA.

Therefore at 20 meters depth (3 ATA), you will consume three times as much of your SAC: or 3 ATA times 2 bar/min per ATA equals 6 bar/min.

Hence you know in ten minutes at 20m depth, you should nominally consume 60 bar in that 10 minute time interval; so if you started with 200 bar reading on your SPG, you would expect it to read 140 bar remaining at the end of ten minutes elapsed time (and 80 bar after another ten minutes; and finally 50 bar remaining after five minutes in which you should be already ascending to your safety stop).

Bar and liters? What is this sorcery?

 

[RayfromTX]

Knowing your sac rate and how it varies by condition and planned work effort makes accurately planning your gas consumption possible. I find it really quite accurate but I have a knack for remembering numbers and patterns of behaviors. My planning is usually based on my wife's air as she has a higher sac rate and a smaller tank but our turn times and pressures usually align pretty well. We usually turn on time with pressure not far behind. I find my sac starts a bit high and falls throughout the dive, all else equal. Cold water lake dives with skills work and finning practice will be planned at .6 and we will end up around .58 or so. Drifting in Coz will be around .45 by the second or third day.