NavList:
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Re: Silicon Sea: Leg 81
From: Dan Hogan
Date: 2001 Oct 20, 7:46 PM
From: Dan Hogan
Date: 2001 Oct 20, 7:46 PM
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@verimail.com Nav-L Page: http://www.wa6pby.com