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Lake Pleasant, AZ, adjust for altitude?

Discussion in 'Southwestern Region' started by PBcatfish, Nov 17, 2019.

  1. PBcatfish

    PBcatfish Regular of the Pub

    # of Dives: 500 - 999
    Location: Florida
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    Several people here seem intent on bashing me as if I am speaking heresy for calling Lake Pleasant an altitude dive. I think that I have qualified my comments sufficiently & I’ll even go so far as to say that I think my comments have been pretty much correct.

    I’m not going to single out individuals who made specific comments because I don’t want to be argumentative. I will, however, try one last time to state my position more clearly.

    When I dove in that area, I was diving under the instruction of the US Navy Dive Manual. I no longer have access to the hard-copy of the older version of that manual that I used at the time, but I was able to find public unclassified access to the current version - Naval Sea Systems Command > Home > SUPSALV > 00C3 Diving > Diving Publications

    If you look at table 9-4, you may notice that SLED corrections are to be made at altitudes of 2,000 feet or more, even for very shallow dives and for dives to 150' or more, altitudes as low as 1,000 feet require a correction. As I remember Lake Pleasant, the roads leading in & out of there went up from the water. If the water was at 1,700’, then I think there was a pretty good chance that I hit 2,000' feet before I left the park. Regardless if I then went to Prescott or Mesa afterwards, the fact that I hit 2,000' one time, means that if I am following the book correctly, an altitude correction was indicated, even for a dive to as little as 10'. As was already stated by another, if I then went way up the hill to some place like Flagstaff, the altitude would be considerably more. In that case, a more substantial correction would be needed.

    It may be common practice to dive that spot without taking altitude into consideration. The current tables & algorithms may have enough safety fluff built into them to allow you to ignore that detail without penalty if you leave the park & go to Phoenix, rather than Flag or the Snow Bowl. Altitude may not have been a factor in this incident. That does not mean that the dive is not correctly identified as being an altitude dive. ...at least if you believe the US Navy definition of the term.
     
    markmud likes this.
  2. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    PADI uses 1000 feet and above as Altitude.
     
    markmud and PBcatfish like this.
  3. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    6,721
    7,159
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    My computer uses 2000 feet and above as altitude.


    Bob
     
    markmud likes this.
  4. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
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    Best I can tell, my Shearwater uses whatever altitude I'm at.....no special level at which it become an "altitude" dive.
    Does anyone have info to the contrary?
    NOAA Dive Manual follows US Navy rules, and says:
    4.5.1.4 Need for Correction
    No correction is required for dives conducted at altitudes between sea level and 300 ft. The additional
    risk a
    ssociated with these dives is minimal. At altitudes between 300 and 1,000 ft., correction is required for
    dives deeper than 145 fsw (actual depth). At altitudes above 1,000 ft., correction is required for all dives.
     
    markmud and FreeFlyFreak like this.
  5. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    6,721
    7,159
    113
    How would it know when to start applying a correction, does it start applying a correction at 0 feet? Or does it even apply a correction, is an altitude correction done as a user input?


    Bob
     
    markmud likes this.
  6. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
    8,318
    6,051
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    This is what the manual says.
    I assume this means that the appropriate corrections for diving at altitude are applied no matter what altitude you are at.
    So, in effect, every dive that starts above sea level is an altitude dive....it is just that the corrections are insignificant unless you start at...300 ft? 1000 ft? Unclear...but by 1000 ft they must be significant enough for USN/NOAA to worry about them.
    ---------------------------------
    upload_2019-11-21_22-43-28.png
     
    markmud likes this.
  7. tursiops

    tursiops Marine Scientist and Master Instructor ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: U.S. East Coast
    8,318
    6,051
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    Are you the coroner and medical examiner? Are you quoting from some official report I've missed?
     
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  8. Bob DBF

    Bob DBF Solo Diver

    # of Dives: I just don't log dives
    Location: NorCal
    6,721
    7,159
    113
    965 mbar is approximately 1350' of elevation. Thanks for the info.


    Bob
     
  9. kelemvor

    kelemvor Big Fleshy Monster ScubaBoard Supporter

    # of Dives: 100 - 199
    Location: Largo, FL USA
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    Glad you're here to keep us riffraff in line.
     
    FreeFlyFreak, Bob DBF and markmud like this.
  10. BFRedrocks

    BFRedrocks ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Phoenix, AZ
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    FWIW. I dove Lake Pleasant last Sunday with my Shearwater Teric and it reported surface "altitudes" of 947 and 952 mbar.

    Those of us that dive Lake Pleasant recognize the small differences in how computers deal with approximately 1,700 feet amsl as our water surface (e.g., a Suunto Vyper Air has a correction for >1000 feet amsl but a Mares Puck Pro doesn't for that elevation), but as was mentioned above, that does not appear to have impacted what ultimately happened on this particular tragic dive.
     

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