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    Re: Silicon Sea Leg 72
    From: Bill Noyce
    Date: 2001 May 29, 11:27 EDT

    > 1)  What is the DR position at the end of the Tack 4?
    > --  -------------------------------------------------
             Tack 1
    TC       322.0d       231.5d       252.5d       297.0d
    dist      30.0 nm      93.5 nm      40.0 nm      90.0 nm
    dLat    N 23.6'      S 58.2'      S 12.0'      N 40.2'
     Lat   N 13d 23.7'  N 12d 25.5'  N 12d 13.5'  N 12d 53.7'
    dep     W 18.5 nm    W 73.2 nm    W 38.1 nm    W 80.2 nm
    dLon    W 19.0'      W 75.1'      W 39.2'      W 82.3'
     Lon   W 61d 49.0'  W 63d  4.1'  W 63d 43.3'  W 65d  5.6'
    DR = 12d 53.7 N  65d 5.6' W
    > 2)  What is the DR position local Zone Time(ZT) and Date?
    >     What is the DR position GMT/UT time and Date?
    > --  -----------------------------------------------------
    33 hrs = 1 day 9 hrs:
        UT 31 May 17:50:10
        ZT 31 May 13:50:10
    > 3)  From the DR position, what is the TC to Aruba Gap
    >     (13d 50.0'N  70d 00.0'W)?
    > --  -------------------------------------------------
      TC = 283.4d  dist = 291.7 nm
    > 4)  What is the Compass Course(CC)/Course-to-Steer for Aruba Gap
    >     from the DR position?
    > --  ------------------------------------------------------------
    Is current set given in True, Magnetic, or Compass direction?
    Not that it makes much difference here.  I assumed True.
    Using Law of Sines, I find I need to adjust my course North
    about 1.5 degrees.
      CC = 283.4 + 1.5 + 9 = 293.9d
    > 5)  What is the FIX position?
    > --  -------------------------
    Roughly estimating progress westward for 16 hrs, I picked
      AP = 13d 20' N  67d 30' W
    It wasn't until checking my work that I noticed this puts
    us right on the border of a time zone, but if I get the
    conversion ZT->UT wrong the 15-degree error in position
    will be obvious.
    Body     Mars         Vega         Venus
    GHA    128d 45.8'   115d 58.2'    11d 32.5'
    Decl  S 25d 54.5'  N 38d 47.0'  N  7d 49.7'
    Hc      18d 41.3'    40d 19.9'    34d 47.7'
    Az      236.4d       310.0d        89.6d
    Int      35.3' A      16.3' A      31.2' T
    These give a position at about 13d 35' N  66d 57' W.
    This is about 30 miles east of my rough estimate.
    Perhaps we were running only about 12 hours instead
    of 16, due to UT/ZT confusion?
    > 6)  What are the names of the two unknown bodies?
    > --  ---------------------------------------------
    Running a signt reduction but exchanging Ho<->decl
    and LHA<->Bearing, I get
    Compass bearing     349.7d       327.3
    True bearing        340.7d       318.3
    computed decl     N 71d 17.2'  N 29d 51.2'
    computed LHA        87d 48.0'    33d 44.7'
    GHA                154d 45.0'   100d 41.7'
    SHA                119d 23.2'    65d 44.7'
    None of the planets are near the resulting position, and
    none of the 58 'standard' stars are very near.  I concluded
    that the northern one was in the bowl of the Little Dipper,
    but it's not Kochab; the second looked like it might be the
    head of the Swan, opposite Deneb in Cygnus.  Now that I see
    the second correction, perhaps I'll go back and redo them...
    > 7)  What is the TC and Distance to the Aruba Gap (13d 50.0'N  70d
    >     waypoint from our FIX?
    > --
    Mid-latitude using 13d 42'
    dLat = 15' N  dLon = 183d W  dep = 177.8 W
    TC = 274.6d  dist = 178.3 nm

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