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Dan Allen said-

>Composite lines are a bit more legit: they are a combination of great
>circles and parallels.  Here is an example:
>
>If you were to sail a great-circle course from Seattle Washington to
>Yokohama the course would cross the Aleutian islands, so the procedure
>would be to sail the great-circle to a maximum safe latitude, sail
>directly West until you meet the great-circle again, and then continue
>following the great-circle to the great-circle destination point off
>the coast of Japan. This procedure is known as composite sailing.

Comment by George Huxtable.

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?

George.


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george@huxtable.u-net.com
George Huxtable, 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
Tel. 01865 820222 or (int.) +44 1865 820222.
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