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What is your average Air Consumption?

Discussion in 'Basic Scuba Discussions' started by Diver0001, Sep 21, 2003.

Choose range for avg air consumption

Poll closed Oct 5, 2003.
  1. 6-10 lpm (0.2-0.35 cf/min)

    7 vote(s)
    8.4%
  2. >10-12 lpm (0.36 - 0.42 cf/m)

    11 vote(s)
    13.3%
  3. >12-14 lpm (0.43 - 0.49 cf/m)

    15 vote(s)
    18.1%
  4. >14-16 lpm (0.50 - 0.57 cf/m)

    22 vote(s)
    26.5%
  5. >16-18 lpm (0.58 - 0.64 cf/m)

    11 vote(s)
    13.3%
  6. >18-20 lpm (0.65 - 0.71 cf/m)

    10 vote(s)
    12.0%
  7. > 20lpm (0.72 or higher)

    7 vote(s)
    8.4%
  1. coliseum

    coliseum Instructor, Scuba

    # of Dives: I'm a Fish!
    Location: UAE
    206
    0
    0
    I have an air integrated computer.. it graciously tells me how many minutes of air I have emaining at the current depth and amount of breathing...

    I still dunno how to measure SAC??!?!
     
  2. paulwlee

    paulwlee Divemaster

    # of Dives: 200 - 499
    Location: San Francisco Bay area
    741
    1
    0
    Which computer do you have? If you have a Suunto computer, you can get the dive manager and it will calculate SAC for you. It's really nice to know how your SAC varies for each dive you do.
     
  3. paulwlee

    paulwlee Divemaster

    # of Dives: 200 - 499
    Location: San Francisco Bay area
    741
    1
    0
    I get maybe .50~.55 while on slow leisurely dives, and .6~.7 on dives with some serious swimming.

    I've been in around the same range since I started measuring, but it doesn't look to me that there is any room for improvement. On the slow dives, I'm not constrained by the need to breath. I can certainly breath slower and be fine, but doing so will adversely affect my buoyancy and make me go up and down. Breathing shallower seems like a bad idea.

    Any thoughts on this?
     
  4. scubasean

    scubasean Loggerhead Turtle

    1,742
    0
    0
    Measuring your consumption in PSI is only useful when you also know the volume of the tank.

    For example, using 2500 PSI out of a lp100 means you used the entire 100 cubic feet...(actually, you used more than the 100, technically), but using 2500 PSI out of a neutral buoyant 80 means you used
    (2500/3300) * 80 = roughly 60 cu ft.

    That is only part of the calculation of surface air consumption, but you get the idea.
     
  5. Genesis

    Genesis Great White

    4,427
    12
    0
    you'll risk building up CO2, which is bad news.

    As you dive more, you'll find that while you still breathe deeply (if you're breathing as you should!) your RATE of breathing goes down.
     
  6. Charlie99

    Charlie99 Solo Diver

    # of Dives: 500 - 999
    Location: Silicon Valley, CA / New Bedford, MA / Kihei, Maui
    7,966
    160
    63
    Ultra-calm, yes, but I'm 6' 185#. Normal finning mode is modified frog kick which just uses my ankles, with my legs fully extended so that I'm streamlined (no energy wasting bending of the knees so my legs are up in the slipstream). Those are real numbers, calculated from about 25 different dives. I don't have an air integrated computer, but I'll occasionally download my computer, eyeball average different segments, then calculate.

    Not believing the 0.36 of one calculation, I downloaded it an Excel spreadsheet and got the same results. That was a drift dive off of Boynton Beach where I was diving with a local that uses HP100's and I didn't want him to go up early because of my AL80. 40 minutes at 85' average before going up to the reef top at 45' for 10 minutes, then slow ascent for total dive time of 60 minutes. Nitrox is very useful!

    When down in the Florida Keys, about every other day I'll use the same tank for both 1st and 2nd dives -- except on my trip earlier this month. When I boarded Silent World for my 2nd trip, the Capt pointed to a pair of compact 60's and said "those are your tanks, Charlie"

    I do NOT skip breathe, but rather have a very, very long breathing cycle with really full inhales and exhales.

    I have found that being in good physical condition doesn't affect the resting/drifting SAC very much, but makes a big difference in how much your SAC will increase while working hard, such as finning against a current.

    Much like Genesis noted, I started out around 0.8, then did a lot of dives around 0.65 cu ft/min, then somewhere around dive 100-150 something happened ---- it wasn't the result of any conscious action, but my SAC dropped dramatically.

    p.s. DeepScuba -- while sub 0.5 SAC isn't common on resort boats, you will find a lot of divers in that range in places like West Palm Beach and Boynton Beach where the locals are out drifting the reef almost every Saturday. I had been on the boat Splashdown 3 or 4 times before I noticed that one local, Peter, was doing 2 dives of 1 hour each at 60' on the same 95 cubic tank (I didn't ask what it really held). The downside of relaxed, drifts is cold --- Peter wears a drysuit for 78F.
     
  7. Atticus

    Atticus Instructor, Scuba

    # of Dives: 500 - 999
    Location: Lake Tahoe
    609
    2
    18
    I think I'm comparing apples to oranges - I'm diving a cold mountain lake in doubles.
     
  8. Genesis

    Genesis Great White

    4,427
    12
    0
    Cold increases your breathing rate if you are ACTUALLY cold. If so, wear more exposure protection :)

    As for doubles, they don't "cost" you SAC provided you're not trying to move them rapidly. If you are, SLOW DOWN! They aren't "heavy" in the water, but they do have mass, and you have inertia to deal with.

    Where it becomes an issue is when you HAVE to work against something (e.g. current.)

    I burn more air in my drysuit, but that's usually due to what I'm doing more than the suit - most of the time in the winter I'm spearfishing here, as the grouper come inshore - and they are WAY too tasty for their own health :)
     
  9. Atticus

    Atticus Instructor, Scuba

    # of Dives: 500 - 999
    Location: Lake Tahoe
    609
    2
    18
    Ok, good points. I sugget that the doubles will increase the effort to move through the water however, no matter what speed your traveling at. Also, the heavier exposure suit increases drag a little bit...

    Ok, we're picking nits. My RMV blows :)
     
  10. DeepScuba

    DeepScuba Manta Ray

    724
    1
    0
    OK Charlie, lets flesh this pony out somemore.

    This is exactly the type of exagerations people do (I'm not talking about you Charlie, I'n stating this in general, and in this case, as it pertains to SAC rates)

    I personally only know of 95cf bottle that are steel, rated 2640 PSI. So if there's ALU 95 3000PSI tanks the numbers are slightly different.

    Lets assume his steel 95cf/2640PSI bottel were pumped to 3300 PSI, and he left 300PSI in the tank when he got on the boat.

    At 60' for 120 minutes, his SAC rate would have to be 0.32

    I'm assuming wet suit or zero fudge for drysuit, but even still, it's basically irrelevant unless we're going to 6 decimal places!!!

    For an ALU, pumped to 3300PSI (Rated 95cf/3000PSI) the SAC rate is 0.28

    So we can see we're not talking a huge difference, and 300PSI still in the tank is about as low as most would ever get.

    Why do I think this is complete hog-wash???

    Lets compare Aquaman (Peter) to myself.

    With the above assumptions, I would be back on the boat with 800PSI while he still had 2250 given an ALU80 to 3000PSI . (We are comparing SAC rates, so here I'm using the "standard" tank so everyone can get a feel for what we're saying here).

    2250PSI vs 800PSI..........hog-wash.

    Lets look at it another way. Lets use the 120 minutes at 60' scenario. I'd HAVE to be back on the boat at around 40 minutes, and would be waiting for him for a further 80 minutes!!!!

    Hogwash.

    I may not be the lightest breather in the world, but I am not anywhere's NEAR that bad! Or put more correctly, he isn't anywheres CLOSE to that good.

    Now, if Aquaman was really doing 80-90 minutes at 50', I'd say we have a ballpark decent SAC rate to discuss.
     

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