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> I should think that they have in mind distance off by
> vertical angles (height of a lighthouse etc) and
> horizontal angles.

I tend to do distance off, as well as two-object fixes with a hockey-puck
compass. The sextant is especially useful in finding your position with
three objects on a chart and a three-arm protractor.    The *really* nice
three-arm-protractors like Alex's Soviet unit can be dialed in to 0.1' if I
recall, so would demand input of equal precision and accuracy for optimal
results.  For a plastic three arm (or metal three arm for civilian use), it
would follow a plastic sextant will probably be better than is needed if
they are similar to my plastic two-arm protractor. (Before I fuel another
running gun battle in a corner, I have not personally handled a plastic
three-arm-protractor--they may be accurate and precise to the nearest 0.1'
or so).  I would personally prefer my metal unit for height-of-object
distance-off sights, but believe a plastic unit more than adequate for
horizontal measurements unless navigating a large military or commercial
vessel. Also less stressful and more durable to have bouncing around the
cockpit for frequent use in coastal piloting.

In any case, a practical concern might be how close can you come to the
*center and/or published position* of a water tower, smokestack, lighthouse
etc. with any instrument? Plus parallax error if nearer than a couple of
miles from the objects.

The parallax-conundrum posts should be in the archives.  Some of the more
learned members had some interesting (valid IMHO) views on parallax error
etc vs real-world use. My simplified summary (if I recall their arguments)
were that (parallax ignored) there are other practical limitations even with
the best equipment and operator.  I would add the footnote that if you are
so close that parallax is a problem, you should probably be paying attention
to more important matters ;-)

Bill

> --- Herbert Prinz wrote:
>
>> I am wondering about Starpath's recommendation of
>> the Mark 3 as
>>
>> "... the sextant of choice for coastal piloting."
> ...
>>
>> What applications do they have in mind?
>
> I should think that they have in mind distance off by
> vertical angles (height of a lighthouse etc) and
> horizontal angles.  For those applications I would
> agree that a Davis Mark 3 would be quite adequate.
>
> Chuck Taylor
> North of Seattle

   

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