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Subject: Re: Silicon Sea: Leg 81
From: Dan Hogan (dhhogan@XXX.XXX)
Date: Sat Oct 20 2001 - 21:45:48 EDT
On 19 Oct 2001, at 17:21, Noyce, Bill wrote:
> > At 14:00:00UT @ 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 @
> > 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@XXX.XXX
Nav-L Page: http://www.wa6pby.com
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