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George Wrote:
>
> Yes, to fix by horizontal sextant angles you need to have three marks on
> shore, and in the right sort of geometrical alignment to give a good cut
> between the circles, as against only two marks for compass bearings. But in
> terms of the precision of the result, there's really no contest.

I'm in full agreement, assuming the objects are carefully chosen.

Regarding variation and deviation, I go online at the beginning of the
season and obtain mid-season variation and update the compass roses on my
charts as well as areas I frequently visit.

I have found my hockey-puck compass, in almost all circumstances to exhibit
no noticeable deviation if I pick a spot on a sailboat (usually coaming)
away from metal or electrical wiring).

With three objects onshore I take sextant angles between them, and a compass
bearing to the middle object.  If I draw a line from the center object with
that bearing corrected to true, and then the observed angles from that
center line through the objects, I have immediate feedback if my compass
bearing is off a bit--and in which direction--as the lines from the left and
right objects will not intersect the center line at the same point.

This method is of course limited by the precision and accuracy of the
plotting devices/protractor, but I am constantly amazed at the proximity of
the plot to the GPS position.

Bill





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