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    Re: Older Silicon Sea results
    From: Dan Hogan
    Date: 1999 Jul 06, 21:38 EDT

    Ed:
    Most of the error is my fault. I had a lot of distractions when I
    developed this Leg. I will correct Leg 49 archive and post a copy when
    I'm done.
    >Hi all; I've been going through the older Silicon Sea legs and
    >am having problems getting some of them to reconcile.
    >
    >For instance, leg 49 gives the following problem:
    >
    >    Our last position FIX was at (35d 00.2'S  156d 59.7'E) at 09:05:22 {at}
    >    18/02/1999GMT.Speed 8.7Kts, TC 86.8d Var 13dE, Dev 2.0dE. Current
    >    Drift 17 mi/day, set 185 according to the Pilot Chart. We continue on
    >    course through the night. The weather is deteriorating and it begins
    >    to rain. At 19:45:00GMT the wind heads us and we are forced to change
    >    our Compass Course(CC) 45d to port to stay close-hauled.
    >
    >As I read it, the last sentence means we turn 45 degrees to port,
    >to a new true heading of 86.8 - 45 = 41.8.  However, Answers.txt
    >says the new True Course Made Good is 72 degrees.  The current can't
    >be *that* strong.  Have I made a mistake somewhere?  Even assuming
    >that the puzzle meant to say that we turn port to a compass course of 45
    >degrees mag., that gives me a TC of 60 degrees, and after factoring in the
    >current, CMG = 64 degrees {at}XXX.XXX
    The change is from Compass Course(CC). Current effect, dev and var have to
    be accounted for. Try a velocity vector.
    >
    >The second part of the puzzle gives this table:
    >
    >    TC      Speed   Dist    Time/in/Hrs
    >
    >   072d     8.7     91.3    10:30:00
    >   027d     8.7     52.2    18:30:00
    >   122d     7.5    198.1    26:25:00
    >   095d     9.5    311.1    32:40:00
    >
    >I don't quite know how to read this.  Are the distances & times
    >cumulative?  I don't see how that can be, since the second distance
    >is a smaller number than the first.  However, I find it hard to
    >believe that it took 18:30 to travel 52 miles {at}XXX.XXX
    I should not have included the times. Work the problem using
    just the Speed and Distance. Ignore the times, You are only the second
    person that mentioned this error.
    >I had problems with the first part of the puzzle too, where it asks
    >for the DR position at the time of course change.  I did it with
    >plotter and paper and via computer and got roughly the same answer
    >(35?S, 158?'E), but Answers.txt gave 34?.7'S for the
    >lattitude.
    It is a problem solved by using one the Sailings. Speed and TC from
    the last FIX are given. Calculate the distance run from the FIX time
    and the time given for course change.
    >How do I determine Zone Time from lat,lon?  Is there a chart I'm
    >missing?
    The Zone Description(ZD) is calculated by the formula:
            ZD = Lon / 15
     Each zone is 15 degrees wide, one hour of time. The zones are
     7.5 degrees each side of the zone central meridian. Label the ZD
    (+) for West Lon and (-) for East Lon.
    >I'm convinced there are at least some errors in Answers.txt.  For
    >instance, in Leg 46, the answer to question 1 about total
    >distance is 114,112.8 mi which I'm pretty sure is wrong.  Even
    >*I* don't get that lost.
    Dan Hogan WA6PBY
    dhhogan{at}XXX.XXX
    Navigation-L: http://nav.cnchost.com
    

       
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