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    Re: Silicon Sea: Leg 71 (belatedly)
    From: Dan Hogan
    Date: 2001 May 29, 13:38 EDT

    On 29 May 2001, at 9:45, Noyce, Bill wrote:
    > > 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
    OK
    > > 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.
    Ok--it's MNT
    > > 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
    Hmmm...something very wrong with the Polaris Dec. CAN'T be that high.
    Polaris gives your latitude with its LOP.
    > 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
    ??? FIX
    > > 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
    Hmm, TC is off. Check the FIX.
    > > 5)  What is the Compass Course(CC)/Course-to-Steer for Aruba Gap?
    > > --  -------------------------------------------------------------
    >
    > TVMDC, West is Best, add 11d: 286.7d
    OK
    > > 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
    OK
    > > 6)  What is the time enroute to Aruba Gap?
    > > --  --------------------------------------
    OK
    > 2 days + 1h 24m
    Dan Hogan WA6PBY
    dhhogan{at}XXX.XXX
    Nav-L Web Page: http://www.wa6pby.com
    Catalina 27 "GACHA"
    

       
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