Hello everyone. Im fairly new to diving (about 23 dives under my belt now) and have been tracking my rmv and sac rates since my open water course. What are considered good rmv and sac rates? I am an airhog and would like to work on both sac and rmv to make my dives last longer. Any help would be appreciated.
Hi Kevin,
You are on the right track. You recognize a problem and are trying to improve skills verses getting a bigger tank. Some of us are big people, who have large lung capacities and need a bigger tank.
The terms SAC and RMV create problems for some of us because there is no industry standard for these. They are used interchangeable by many. There are whole threads on this controversy.
I was taught that Respiratory Minute Volume is a medical term. A doctor gauges your lung capacity while you are at rest in an exam room.
Furthermore, I was taught that Surface Air Consumption is a real-world gauge of your gas usage while performing moderate work u/w. The data is collected and converted to 1ATA. You then use that number for planning dives by converting it to the depth you are diving at.
Others use different definitions which is OK. I will stick to PADI's definition as taught in Tech 40 and Self-Reliant.
My SAC is about ½ cubic foot a minute as converted to 1 ATA derived from historical evidence and the PADI prescribed u/w test. Some use less and some use more. This is probably a close approximation for experienced divers, or an average number. Some small ladies don't use hardly any gas. Some large men with large lung capacities use more.
My Shearwater gives me SAC in PSI per minute. That is dependent on tank size and depth (ATA). When I convert the Shearwater number to PADI SAC, I get .47 SAC. ½ cubic foot per minute PADI SAC and .47 are pretty darn close.
Shed the lead, get fit, and get trim. Your SAC will improve.
cheers,
m