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On a NDL dive, which computers' NDLs are not affected by GFLo?

Discussion in 'Computers, Gauges, Watches and Analyzers' started by Jay, Jan 15, 2019.

  1. Jay

    Jay Need to dive more!

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    Or in other words, GFHi is the sole relevant GF input to determine NDL.

    (Computer list/info from @scubadada post (Question about dive computers).

    From SB I only know of one computer's result. Do anyone have / know for the other computers?

    GFLo irrelevant:
    Shearwater runs Buhlmann ZH-L16C with preset or custom GFs, variable from conservative to liberal, HAI (PPS)

    GFLo relevant:
    ?

    [EDIT - lists amended as per ScubaDada's post #2]
    It should be easy to tell for those computers that have Custom GFs if GFLo affects NDL via the dive plan mode (and keeping GFHi unchanged). Computers that fall into this category:

    Divesoft runs Buhlmann ZH-L16C with custom GFs, variable from conservative to liberal
    Garmin runs Buhlmann ZH-L16C with preset and custom GFs, variable from conservative to liberal
    Ratio runs Buhlmann ZH-L16B with preset and/or custom GFs, variable from conservative to liberal, HAI
    Mares - Genius

    For the remaining (ZHL-16) GF computers that don't have a Custom GF function (and not allowing GFHi to remain fixed) I guess the answer would involve the manufacture's/coding insight:

    Divecomputer.eu/ Deep 6 Buhlmann ZH-L16C with GF, variable from conservative to liberal
    Heinrichs Weikamp (not available in US) Buhlmann ZH-L16C with GFs, variable from conservative to liberal, HAI
    Seac (made by Ratio) runs Buhlmann ZH-L16B with preset GFs, variable from conservative to liberal, HAI
    Suunto EON Steel - (unsure if custom or preset GFs)
    Technical Dive Computers TDC-3 (unsure if custom or preset GFs, and here's a link if you're like me and didn't know about this computer / google search turned up zip: Technical Dive Computers TDC-3)
     
  2. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
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    The list of computers running Buhlmann with GFs continues to expand:

    Divecomputer.eu/Deep 6
    Dive Soft
    Garmin
    Heinrichs Weikamp (not available in US)
    Mares
    Ratio/Seac
    Shearwater
    Suunto
    Technical Dive Computers

    All of these brands offer at least one model that runs custom GFs (I don't know about Suunto Eon Steel) and would allow one to answer the question of whether GFlow influences the NDL, or whether it is determined only by the GFhigh. We know that the NDL for Shearwater computers is determined by the GFhigh. My, now discontinued, Dive Rite Nitek Q's NDLs were also determined by the GFhigh. It would be interesting to know how Buhlmann is implemented in the other computers.

    MultiDeco planning software is not designed to calculate NDLs, but to plan decompression. In this application, GFlow is implemented before the GFhigh would otherwise be exceeded on a normal ascent. The Buhlmann implementation on the TDC-3 is of particular interest, as it may be linked to the MultiDeco planner.
     
    Jay likes this.
  3. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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  4. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
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    Just for fun, I ran through the NDLs for air to 80 ft on my Shearwater Teric, with changing GFs.
    The GF-low doesn't change anything, except that Shearwater disallows GF-low higher than GF-high.
    Here are the NDLs for various GFhighs, for 80 ft with air, For comparison, the RDP gives 30 mins for air at 80 ft, and Navy and NOAA give 39 minutes; Shearwater's Default recreational GFs are low conservatism 45/95, medium 40/85, and high 35/75.

    GFHi
    10 GF not allowed on Teric
    20 GF not allowed on Teric
    30 5 mins
    40 6 mins
    50 9 mins
    60 12 mins
    70 15 mins
    75 18 mins (high conservatism default)
    80 20 mins
    85 22 mins (med conservatism default)
    90 25 mins
    95 27 mins (low conservatism default)
    99 30 mins
    RDP 30 mins
    NOAA, NAVY 39 mins

    Note Added:
    I posted a version of this earlier (now deleted), worked out laboriously on my Perdix (the Teric is much easier), but in fact the computuer was set on 32% not air, so the NDLs were OK but the comparison with RDP/NOAA/NAVY was not, and the description was all wrong. I thank @scubadada for pointing out in a PM my error.
     
  5. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
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    If anyone dives a computer other than Shearwater or Dive Rite running Buhlmann, would you mind checking whether GFlo affects the NDL or not? Simply run 90/90 and 10/90, or something similar in the planner. They will either give the same NDL or not.

    Thanks and good diving
     
    Jay likes this.
  6. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

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    Jay, rjack321 and scubadada like this.
  7. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass ScubaBoard Sponsor

    # of Dives: 500 - 999
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    I think the way we are approaching this is a little misleading. Sure, if you decrease GF Hi, the NDL gets shorter and shorter.
    But when you run a given length dive through multi-deco, for the same GF Hi, lowering the GF Low will add in deco stops on a previously NDL dive.
    So in @tursiops example above, you can see the NDL's steadily decreasing with a lower GF Hi.
    What I'd like to see is a comparison of two dives with the same GF Hi and dive length, with decreasing GF Lo. I'll bet that, just like Multi Deco, the Perdix will add in a deco stop if you decrease GF flow.
    I'll try it on mine at home tonight if no one else does first.
     
  8. scubadada

    scubadada Diver Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: Philadelphia and Boynton Beach
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    @rsingler, see my comment re MultiDeco in post #2
     
  9. rsingler

    rsingler Scuba Instructor, Tinkerer in Brass ScubaBoard Sponsor

    # of Dives: 500 - 999
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    Yes, I did. And I ran Multi Deco with 1 sec stops, to find a GF Hi and duration that gave an "NDL dive", which I defined as one with only a single 1 second 10 ft stop. By decreasing GF Lo at that point, you could see Multi-Deco add in progressively longer stops for what was previously a no-stop dive, which doesn't make sense.
    But I'm betting the Perdix will do the same.
     
  10. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    It does not.It is just like the Teric.Tried it.
    MultiDeco has its own way of calculating and using GFlow.....and I'm skeptical of the kludge to work out "NDLs".
     

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