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Hi, Patrick, and Welcome Aboard -

I used a plastic EBBCO (East Berks Boat Company; England; no longer in
business) for years - 1972 to 1975 - at sea with good results. I.e.,
we always found our destination and quite often on the expected day.
:-)

A month ago, I had the experience of sharing a Davis Mark 15 on a
5-day passage in the Caribbean with three other guys. Two of them
consistently got positions within 2' (2 nautical miles) of what the
GPS said.

The Mark 15 is a modern micrometer-drum sextant. Looks just like a
metal one except it's black plastic.

As noted by the other guys it's necessary to check index error after
each sight. In the hot sun we found swings of 3' off- to 3' on- the
arc. I also had  the experience with a group of seven last weekend
where it stabilized at zero after half an hour's exposure.

The other shortcoming of the Mark 15 was for star sights - we found it
best to remove the scope and just sight through the mounting brackets
naked-eye at the horizon mirror. Again, quite acceptable results,
though not as good as with the sun - 3' to 5' against the GPS.

Last time I looked, Celestaire.com (there you go, Ken) was selling the
Mark 15 for $125, a lot less than Davis is charging on their web site.

I recently bought a Davis Mark 3 from Celestaire ($39 for the sextant,
$23 for the case which is foam-lined and really nice) and am going to
see what sort of results I can get with it down here under the hot
Caribbean sun.

The Mark 3 is a vernier sextant, so it's more akin to a 19th century instrument.

Hewitt

On 2/22/10, Patrick Goold  wrote:
> There are many people of remarkable erudition on this list.  It is with some
> trepidation that I post the jejune request of a neophyte to celestial
> navigation for help concerning sextants.  I have been teaching myself the
> theory and mathematics of CN and now feel I need to start taking sights.
> What is the best buy for a beginner who wants one that is useable for actual
> navigation but who will probably never depend on it for that?  Are the Davis
> plastic sextants acceptable?  What are the chances that one bought used
> (ebay has many) is still accurate?   What actually do I need?
>
> Thanks in advance for any help you give!
>
> Patrick
> --
> Dr. Patrick Goold
> Department of Philosophy
> Virginia Wesleyan College
> Norfolk, VA 23502
> 757 455 3357
>

   

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