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Thread: Fitness and SAC

  1. #1
    Grouper
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    Fitness and SAC

    I've been on a fitness routine for about a year that includes a three mile run three times a week plus some PT with situps, pushups, lunges, pullups and chinups two days a week. Got in the water for the first time this season and my SAC rate was between 23 and 25 over a few dives. Looked at my log book for last season and my SAC rate was between 28 and 30. I guess there is something to be said for excersize.

  2. #2
    Grouper
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    The SAC rates I'm using are from a NAUI calculator wheel which is giving me what the PSI used per minute would be at the surface. I've seen most SAC rates given in cfm; is there an easy conversion?

  3. #3
    Grouper
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    what is SAC
    We just completed our first week at the gym, so this is timely

  4. #4
    Grouper
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    SAC = surface air consumption. The deeper you dive, the greater the amount of air you take in with each breath so the tank empties quicker. SAC is a way to reference your air consumption to a standard to help calculate how much time you can spend at different depths.

  5. #5
    Grouper
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    How is it measured
    The term is familiar now, used for charts correct?

  6. #6
    Megalodon
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    What type of comupter are you using? One way is to note the average depth of a dive that you have an accurate reading on your PSI before and after the dive and then use a very complex formula to figure it out:

    Starting PSI - ending PSI = psi used. psi used / by tank psi * full tank cuft = total cu ft used on the dive.

    add 33 to your average depth and divide by 33 = ATA of the dive. divide total cu ft by ATA for your SAC rate.

    Or depending on your computer, you might be able to down load your dives and most computer download software will automatically calculate your SAC. I know Oceanic, Aeris, Mares and Suunto do

    I once saved a man in Wichita just to watch him dive...(inventor)

  7. #7
    Grouper
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    The formulae I use are:

    Tank Rated Vol / Working Pressure = cf/psi

    cf/psi x psi used = cf used

    cf used / dive length = Raw SRMV

    raw SRMV / deep or ave atm = deep or ave SRMV (note: atm = depth/33 +1)

    SRMV is Surface Respiratory Minute Volume
    My personal SAC = 0.31

    (Target Depth / 33) + 1 = Depth Factor
    SAC x Depth Factor x Dive Factor = RMV

    RMV x Dive Length = Air Required
    Useable Air / RMV = Allowable Dive Length

    RMV is Respiratory Minute Volume

    It is important to note the difference between SAC (which is an actual measured, at rest rate of air consumption on the surface, usually a couch) and RMV or SRMV (which are calculated, extrapolated rates). The difference is that SRMV and RMV include a number of dive variables (grouped under "Dive Factor") which always vary dive to dive. Things like temp, work rate, physiology, vis, current, etc. The only consistant comparable measure is SAC.

    The dive log software that comes with the Mares Icon HD does the calculation for you if you have the CF used. THe Mares Icon air integrated gets that directly.

  8. #8
    Barracuda
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    I have IPhone and there is a APP that calc sac rates and I'm sure other phones have app also. A quick google search show several online ones and here is a example DiveNerd - SAC Rate / RMV Calculator, Imperial Units of one.
    - Dennis ><()))">

  9. #9
    Grouper
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    Quote Originally Posted by navyhmc View Post
    What type of comupter are you using? One way is to note the average depth of a dive that you have an accurate reading on your PSI before and after the dive and then use a very complex formula to figure it out:

    Starting PSI - ending PSI = psi used. psi used / by tank psi * full tank cuft = total cu ft used on the dive.

    add 33 to your average depth and divide by 33 = ATA of the dive. divide total cu ft by ATA for your SAC rate.

    Or depending on your computer, you might be able to down load your dives and most computer download software will automatically calculate your SAC. I know Oceanic, Aeris, Mares and Suunto do
    Using an older Aeris XR1 (air only) computer to get my average depth, then using the NAUI wiz wheel calculator to get the SAC in PSI. Using the SAC in PSI has been good enough for me to measure my improvement over time and to estimate are usage but I was just wondering about comparing it to all those who figure it in cu/ft.

  10. #10
    Megalodon
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    Quote Originally Posted by russp View Post
    Using an older Aeris XR1 (air only) computer to get my average depth, then using the NAUI wiz wheel calculator to get the SAC in PSI. Using the SAC in PSI has been good enough for me to measure my improvement over time and to estimate are usage but I was just wondering about comparing it to all those who figure it in cu/ft.
    The biggest difference in using psi vs. cu ft for your SAC is whether or not you have the possibility of using multiple size tanks. If all you use are AL80s, then psi will do fine and is indeed easier to figure. I have a couple of AL80s, hp119x8s, lp85s and AL40s so knowing the cuft/min as a sac is beneficial. In the case of AL80s; 1 cuft = 38.76 psi so an AL80 would last you 77 minutes at the surface if your SAC is 1 cuft/min. Remember, an AL80 is actually 77.4 cuft.

    My SAC is .6 cuft/min so that would be 23.25 psi/min.

    I once saved a man in Wichita just to watch him dive...(inventor)

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