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    Re: Lindy Line
    From: Aubrey O?Callaghan
    Date: 2002 Dec 5, 08:38 -0400

    When I studied Ocean Sailing by correspondence course with the National
    Marine Institute (a very good course) I came across this method as not to
    go too far North/South on a Great Circle course. An amount of the course
    was taken from Admiralty Manual for Navigation.
    On opening my Admiralty Manual of Navigation,  volume III 1938 ed., under
    Great Circle Sailing chapter, subsection Composite sailing there is a sentence:
    "When danger is likely to be encountered in high latitudes, the
    great-circle track must be modified to avoid it and yet remain on the
    shortest track open to the navigator. The resulting track is known as a
    composite track because it is formed by two great-circle arcs and an arc of
    the limiting or safe parallel beyond which the navigator will meet danger"
    
    I have not done the mathematics, but we all know that sometimes when going
    from A to B along a GC track we will head North/South of the rhumb line.
    Perhaps in George's method of 2 composite great circles at point X we could
    still have to head further North to make the second great circle.
    
    In fact the graphics in the Admiralty Manual (fig. 31) illustrates this
    nicely. I don't have a scanner but I'll  see if I can get hold of one if
    the thread continues.
    
    Aubrey.
    
    
    At 23:02 04-12-02, you wrote:
    >On Wednesday, December 4, 2002, at 05:01 PM, George Huxtable wrote:
    >
    >>I have come across this recommendation before, and it puzzles me
    >>somewhat.
    >>Take the middle leg, where Dan would be sailing due West at his
    >>furthest
    >>North latitude, and put an X at its mid-point. Now, if you are going to
    >>travel from Seattle to X, why not do it directly by the shortest path,
    >>on a
    >>great circle between Seattle and X? Similarly, when reaching X why not
    >>then
    >>turn through an angle onto a new great circle between X and Yokohama?
    >>Each
    >>of these two legs must be shorter than its "composite" equivalent which
    >>uses part of the great circle Seattle to Yokohama, and what's more
    >>spends
    >>less time at extreme Northerly latitude. Am I missing something?
    >
    >No, you are not missing anything.  I should have noted that the example
    >came from a website somewhere on the net.  I did not write it.
    >
    >I am not advocating this method; I'm with you George!
    >
    >Dan
    
    
    

       
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