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    Re: Silicon Sea: Leg 81
    From: Dan Hogan
    Date: 2001 Oct 20, 7:46 PM

    On 19 Oct 2001, at 17:21, Noyce, Bill wrote:
    
    > > At 14:00:00UT {at} 08/07/2001, by log meter, we have traveled a distance
    > of
    > > 439.5 Nmi since our last DR position. True Course(TC) 289.9d.
    > >
    > > 1)  What is the current DR position?
    > > --  --------------------------------
    >
    > By Mercator sailing:  10d 19.8' N, 128d 34.8' W
    > (Mid-lat gives                     128d 38.1' W)
    
    OK
    
    > > 2)  What is the approximate distance and direction to the storm
    > >     (019d 45.0'W  120d 30.0'N) from our DR position at 14:00:00UT {at}
    > >     08/07/2001?
    > > --  ----------------------------------------------------------------
    >
    > How approximate is "approximate"?
    > dLat = 9d 25', dLon = 8d 5'
    > 9*9 + 8*8 = 145 ==> storm is about 60*12 = 720 miles away,
    > somewhat north of northeast.  I assume this is enough info
    > to estimate the storm's effect on us...
    >
    > More carefully,
    > Mercator:     760.0 nmi, 039.6d
    > Great Circle: 733.6 nmi, 038.7d
    
    If you are out there you need to plot the the storm direction its position at
    a given time. There is  a need to know where in the semi-circle of the storm
    you are and what wind and wave strenght can be expexted.
    >
    >
    > > 3)  What is the DR position at the end of this time?
    > > --  ------------------------------------------------
    >
    >   TC    Dist    Lat          Lon
    >               10d 19.8 N  128d 34.8 W
    > 289.9d  57.0  10d 39.2 N  129d 29.3 W
    > 278.0d  74.4  10d 49.6 N  130d 44.3 W
    > 275.0d  24.75 10d 51.7 N  131d  9.4 W
    > 270.0d  46.8  10d 51.7 N  131d 57.0 W
    >               =======================
    
    OK
    
    >
    > > 4)  What is the UT/GMT date and Time?
    > >     What is the Zone Time(ZT) and day?
    > > --  ----------------------------------
    >
    > Time adds up to 2 days 11.5 hours.
    > Time is 11 July 01:30 UT, zone is 9 hrs west,
    >         10 July 16:30 ZT
    
    OK
    
    > > 5)  What is the TC & Distance from the DR to our Hawaii landfall point
    > at (19d 30.0'N  154d 45.0'W)
    > > --  ---------------------------------------------------------------------
    >
    > by Mercator (Meridional Parts):
    > From- Lat= 10d 51.7 N  MP=  651.4  Lon= 131d 57 W
    > To:   Lat= 19d 30.0 N  MP= 1185.8  Lon= 154d 45 W
    >       dLat    518.3'   dMP  534.4  dLon 1368'
    >
    > TC = atan(1368/534) = N 68.7d W = 291.3d
    > Dist = 518.3/cos(68.7) =         1424.7 nmi
    >                                  ==========
    
    OK
    >
    >
    > > 6)  What is the unknown body?
    > > --  -------------------------
    >
    >   Vega.
    
    OK
    
    > > 7)  What is the FIX position at the time of the unknown body?
    > > --  ---------------------------------------------------------
    >
    > DR position at 03:40 was about 11d N, 132d 20' W.
    > The FIX draws out to about 11d 33' N, 132d 25' W.
    
    OK
    
    > I'm not very happy with my work on this fix.  I originally had
    > the wrong DR, and all my intercepts were over 60 miles long.
    > But at least Antares and Mars, with nearly the same azimuth,
    > also had nearly the same intercept.  (I remember showing the
    > Cub Scouts at camp last July how the Red Planet was right next
    > to the Red Star -- at least I thought it was cool!).  Found
    > the error in the DR, and recalculated the sights from there
    > -- but now my Antares and Mars lines are nearly 5 miles apart
    > and still nearly parallel.
    >
    >         Antares    Mars
    > GHA   98d 17.3     90d  1.2
    > dec   26d 26.2 S   26d 51.1 S
    > LHA   34d  2.7 E   42d 18.8 E
    > K     30d 57.8 S   34d 23.6 S
    > Hc    40d  2.7     34d  9.6
    > Ho    39d 33.3     33d 44.2
    > Int       29.4 A       25.3 A
    > Z        139.1d       133.5d
    
    Th problem was set up to have more than 30' intercepts on some bodies.
    
    Your Almanac data is within +/- 0.5'. The MARS Hc is less than my calculated.
    BUT that depends on the Sight Reduction method used. The accuracy is
    determined by plotting the results as a FIX.
    
    
    >
    > I've checked it by hand -- time to ask the computer where I
    > screwed up, I guess.
    >         -- Bill
    
    
    
    Dan Hogan WA6PBY
    C27 "Gacha"
    dhhogan{at}verimail.com
    Nav-L Page: http://www.wa6pby.com
    

       
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