Electronic Dive Log & SAC Rates

Does anyone know how the SAC rate works on an e log book - using single 12.2 litre steel tank verses twin 12.2 lt tanks (ie 24.4 lt total) my SAC rate goes from around 13 or 14 to 23 or 24 it doesn't make any sense to me. I know another diver who also has same issue - any ideas welcomed.

Well, when you use a single tank, as opposed to doubles, you're going to use twice the psi. If the computer doesn't know the total tank VOLUME, it's going to think you are using twice as much gas.

On my Tusa IQ750 and Oceanic NX180 Dive logs you can add tanks so you would just add an entry for a set of twins like you have 2 al80's (valume 77ft3 x2 = 154ft3 .air pressure 3000spi x 2=6000 starting pressure.

I dive an Oceanic VT3 AI computer as my primary and use the Oceanlog to download my dives. Any cylinder configuration can easliy be configured and is then used to calculate your SRMV (SAC). There is a dropdown list with one cylinder designated as the default and then all of the other cylinders you dive. One only needs to enter cylinder size and working pressure.

For twin Al 80s this would be 154.8 cu ft @ 3000 psi. The software then takes your dive time, pressure drop, avg depth and cylinder characteristics and calculates your SRMV. For a non-AI computer, it would work identically, but you would have to enter your pressure drop manually.

Thanks for the feedback. I have entered twin 12.2 lt tanks so 24.4 lt and 230 bar which is what the pressure is when both tanks full and SAC is 23 or 24. But SAC for single 12.2 lt tank at 230 bar is 13 or 14 so something still seems wrong.