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    Re: Silicon Sea: Leg 71 (belatedly)
    From: Bill Noyce
    Date: 2001 May 29, 10:45 EDT

    > 1)  At the log reading of 89.6Nmi, what is the DR position?
    > --  -------------------------------------------------------
    Mid-Latitude Sailing using L=13d 20'
    TC = 263.7  dLat = 9.8' S  dep = 89 nm W  DLon = 91.5' W
    DR position = 13d 15.8' N 63d 1.6' W
    > 2)  At the DR position what is the celestial phenomena that is
    starting
    >     at this DR Zone Time(ZT)?
    > --
    -------------------------------------------------------------------
    18:27:00 + 10.3 hrs = 04:45 ZT 30 May
    At this time and position, I find the sun's altitude is -13d 58'
    -- still 2 degrees short of the start of Nautical Twilight.
    But if we're actually 1.5 degrees east of here, that would
    explain most of the difference.
    > 3)  What is the FIX position?
    > --  -------------------------
    Using the above DR position,
    Body      Fomalhaut    Polaris       Deneb        Vega
    GHA       36d  3.0'   342d 53.1'    70d 20.8'   102d  8.4'
    Decl    S 29d 36.9'  N 89d 16.1'  N 45d 16.8'  N 38d 47.0'
    Hc        39d 50.8'    13d 23.4'    57d 23.5'    47d  5.2'
    Az        149.1d         0.7d       350.4d       313.9d
    Int        58.2' T      14.8' A      32.4 A       75.0' A
    Pretty long intercepts, and a poor cut.  I used Ageton's
    method, and for Polaris found why it's not recommended for
    LHA near 90 degrees with high declination -- you end up
    trying to find an angle whose sine is about 1.0, and since
    the function doesn't vary rapidly there, the angle isn't
    established with any precision.  So instead of using
          sin K = sin decl / cos R
    I tried
                                  cos T * sin R   cos T * cos d
          cos K = cot T * tan R = ------------- = -------------
                                  sin T * cos R       cos R
    Is this Sadler's modification to Ageton's method?
    Anyway, I tried again with an AP of 13d 0' N 61d 30' W
    and got intercepts of
      Fomalhaut: 0.3' A
      Deneb:     0.3' A
      Mars:      4.6' A
      Venus:     0.1' A
      Vega:      0.1' A
    and except for Mars, it looks like we're there.  I wonder if
    I made an obvious mistake here:
             Mars
    GHA    114d 23.9'
    decl  S 25d 47.5'
    K     S 38d 42.0'
    Hc      25d 33.1'
    Az      232.8d
    > 4)   What is the TC and Dist from our FIX to the Aruba Gap
    >      (13d 50.0'N  70d 00.0'W)
    > --  ------------------------------------------------------
    Mid-Latitude (using 13d 25')
    dLat = 50' N  Dlon = 510' W  log(dep) = 1.69897
    TC = 275.7d  Dist = 499 nm
    > 5)  What is the Compass Course(CC)/Course-to-Steer for Aruba Gap?
    > --  -------------------------------------------------------------
    TVMDC, West is Best, add 11d: 286.7d
    > 7)  What is the anticipated Speed Made Good(SMG) to Aruba Gap?
    > --  ----------------------------------------------------------
    Current essentially right on our tail, 9.3+0.8 = 10.1 kts
    > 6)  What is the time enroute to Aruba Gap?
    > --  --------------------------------------
    2 days + 1h 24m
    

       
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