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Peter Hakel asked-

"Nevertheless, I would like to know just how accurately one can measure
azimuth in the field/ocean and what portable devices (besides compasses),
are available for this (if any)."

Even under benign conditions, I wouldn't trust any compass on a small
vessel, carefully corrected as necessary for variation and deviation, to
indicate true North as a reference to any better than one degree either way.
I can't say whether the gyro-compass on a big ship would do much better than
that (but rather doubt it...).

I doubt if Peter Hakel's suggestion of navigating by altitude and azimuth of
a body has much potential. Geoffrey Kolbe has pointed out some pitfalls
already. For each degree, measured down from the zenith, of a body, an
uncertainty of 1 degree in azimuth would give rise to an error in deduced
position of about a mile, roughly speaking. From that point of view, high
altitudes would be better. However, it's only possible to assess the azimuth
of bodies near the horizon with any accuracy. Higher altitudes would call
for a sighting device on a stabilised mounting, which was kept accurately
horizontal. Such a platform might exist on a big ship, however.

George.



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