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Your Gradient Factors?

Discussion in 'Technical Diving Specialties' started by CAPTAIN SINBAD, Nov 20, 2020.

  1. elmo

    elmo DIR Practitioner

    # of Dives: 200 - 499
    Location: Melbourne
    188
    125
    43
    I do genuinely appreciate it you going to the effort to try this.
    You just won yourself one whole hour of extra bottom time because you used an average depth, and you didn't exceed the NDL permitted by the eRDPML.

    That is the point I was making. No more. No less. I won't pretend planning based on average depth gives you the optimal answer, but it can give a useful answer. As I said in my earlier post, averaging a shallow-to-deep profile (especially one as extreme as 40ft to 100ft) and planning using "square tables" would not be safe - but we both know the eRDPML won't permit it either.

    If I were on a boat with my PADI tables, and my eRDPML (let's pretend I own one) got splashed with seawater and wasn't working, I would happily plan that dive using the tables and average depth.
     
  2. PfcAJ

    PfcAJ Orca

    # of Dives: 5,000 - ∞
    Location: St Petersburg, Fl
    7,880
    7,158
    113
    You guys really aren’t going to like what happens if you put 70ft for 45mins into Bühlmann 50/85.
     
  3. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    I thought for a long time in this discussion that people were simply moving goal posts. Now I see that they have not even agreed on what the dame is.

    I thought the statement that you can use average depth with tables and get effectively the same answer was what was being said, and that such a practice was widespread.
    Now you are saying that your point is you get a safe answer, but not the same answer. OK.
    But then the other players are not even using average depth of the dive, but rather average depth of the bottom (or the deep segment of the dive) as far as I can tell. Totally different game. Then others are arguing about 4h dives or trimix or saturation or something. Different game, not even the same playing field. And some say well that's what we do locally, which is hardly "widespread."

    It certainly appears that the DIR/GUE/UTD guys doing heavy deco have figured out a way to do some sort of (to me arbitrary) averaging that allows them to mostly stay away from DCS. Great.

    But folks using the usual tables, from the mainstream agencies, really ought to avoid this "average depth" nonsense. It demonstrably does not work to give the same answer as their max depth and the tables. yes, it may provide a safe answer, although that has not really been shown...just some example where it does work. It would be even safer on a multilevel dive to just use the max depth -- as the tables intended -- and accept that the dive will be shorter than desirable. Or use a multi-level diving tool. Or use a damn computer.
     
  4. NothingClever

    NothingClever ScubaBoard Sponsor ScubaBoard Sponsor

    # of Dives: 200 - 499
    Location: Red Sea and Atlantic Ocean
    934
    1,105
    93
    I get a 1:40 stop at 6m that will probably evaporate before I get there and the 7:00 snooze at 3m is probably just enough time to get into a Rubik’s Cube before I gotta wrap things up.

    And I only burn 2700 liters out of 4400 total.

    What am I missing?
     
  5. PfcAJ

    PfcAJ Orca

    # of Dives: 5,000 - ∞
    Location: St Petersburg, Fl
    7,880
    7,158
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    8mins of mandatory deco but the NAUI table says 0.
     
    RyanT likes this.
  6. Storker

    Storker ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: close to a Hell which occasionally freezes over
    16,767
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    Try 30/60.

    You can always find an algorithm which is more conservative. The recent discussion was about tables (which generally are rather liberal) and the use of average depth. Quit moving the goalposts, it doesn't become you.
     
  7. elmo

    elmo DIR Practitioner

    # of Dives: 200 - 499
    Location: Melbourne
    188
    125
    43
    Your earlier post complained that all the examples of using average depth were beyond the scope of recreational diving performed by the majority of divers. I gave you an example that was within "recreational limits", and independent of any agency.

     
  8. PfcAJ

    PfcAJ Orca

    # of Dives: 5,000 - ∞
    Location: St Petersburg, Fl
    7,880
    7,158
    113
    None of this is precise enough to be concerned with goalposts.

    certainly not precise enough to be overly concerned over 6ft.
     
  9. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
    13,898
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    Hi @PfcAJ

    What was your example of 70 ft for 45 min used to illustrate? You did happen to choose a depth where the NAUI table appears to have an outlier long NDL, nearly as long as USN and considerably longer than PADI. It would correspond to a Buhlmann GF high well in excess of 99. You could just as easily chosen 60 ft. Here the NDL is in line with the PADI NDL and would correspond to a Buhlmann GF high of somewhere just above 99. Why did you compare to a GF high of 85?

    upload_2020-11-24_15-32-8.png
     
  10. PfcAJ

    PfcAJ Orca

    # of Dives: 5,000 - ∞
    Location: St Petersburg, Fl
    7,880
    7,158
    113
    Simply highlighting that none of this stuff is exact.

    And as such, avg depth works pretty darn well.
     
    rjack321, kensuf, jale and 1 other person like this.

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