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Good rmv and sac rate

Discussion in 'Basic Scuba' started by Kevin W. Blaylock, Mar 6, 2020.

  1. Kevin W. Blaylock

    Kevin W. Blaylock Registered

    # of Dives: 50 - 99
    Location: North Carolina
    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.
    markmud likes this.
  2. saxman242

    saxman242 Contributor

    Work on getting your buoyancy and trim dialed in and your sac rate will mostly take care of itself
  3. Lorenzoid

    Lorenzoid ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: I just don't log dives
    Location: Atlanta, USA
    This is probably the most recent thread on what are considered good or average SAC/RMV rates: What's a good SAC

    As far as tips for improving, in addition to proper weighting, and getting more precise with your buoyancy and trim, the tip that worked best for me was: stop thinking about SAC/RMV. As soon as I stopped caring about what is "good" or "average," my SAC/RMV improved.
  4. Marie13

    Marie13 Great Lakes Mermaid ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Great Lakes
    There’s going to be a whole lot of variables. Water temp, exposure protection, body size/style, how in shape you are, etc.

    If you’re not in shape, start working out. It can make a huge difference.
    Lorenzoid likes this.
  5. GreggS

    GreggS Contributor

    # of Dives: 200 - 499
    Location: Thomasville, NC
    I would say that these are the most important 2 elements to achieving good air consumption. But there is one more element that is very important but rarely mentioned. And that is...patience. Most relatively new divers, especially men, are gas hogs. I had almost resigned myself to being a perpetual gas hog even after more than 50 dives. But then I eventually got my weighting right (I always had pretty good trim) and just got more and more accustomed to breathing under water, and suddenly, my air consumption started dropping.

    So work on your weighting, and trim, and the air consumption should improve dramatically.
    NothingClever likes this.
  6. saxman242

    saxman242 Contributor

    Agreed. Slowing way down helps things out a lot
    NothingClever and Lorenzoid like this.
  7. jstrang

    jstrang Instructor, Scuba

    # of Dives: 500 - 999
    Location: burlington, ON, CANADA
    A lot of new divers waste gas filling their bcd - if you are properly weighted it should hardly need any air in it. If you are forever adding air to the bcd drop a couple of pounds.

    to be a better diver you really need to dive regularly- try to get in with a group who are doing training dives and go at least once a week. That is where you should be working on buoyancy trim and propulsion.

    have fun and good luck.
  8. Cap335

    Cap335 Dive Shop

    # of Dives: I'm a Fish!
    Location: Houston
    Slow down and look around, you will see more and use less air. Also don't worry about how much air you use it will go down over time. If it just won't go down use larger tanks.
  9. TMHeimer

    TMHeimer Divemaster

    # of Dives: 500 - 999
    Location: Dartmouth,NS,Canada(Eastern Passage-Atlantic)
    What's an rmv? I suppose I should know.
  10. markmud

    markmud Self Reliant Diver--On All Dives.

    # of Dives: 200 - 499
    Location: South Lebanon, Ohio
    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.

    Bob DBF likes this.

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