NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Accuracy of sextant observations at sea
From: Jeremy C
Date: 2010 Nov 27, 05:34 EST
From: Jeremy C
Date: 2010 Nov 27, 05:34 EST
Alan wrote:
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Having said that, and by the way, most of the discussions above
referenced, while academically interesting are quite far over my head, the
following questions remain.
1. What sort of boat or vesssel are the sextant shots made from?
2. Realistically speaking, standing on a smallish boat, a large ship is another story, what sort of accuracy can be reasonably expected?
3. How experienced is the "shooter?
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I can answer this and Antoine's question about equipment in one email
instead of two.
1) All of my Navlist examples are shot from the freighter I am currently
sailing on. The ship is 650 ft long with 105 ft beam. Height of eye
for my observations is 106 feet. The sextant is a Tamaya MS-733 aluminum
alloy frame with brass arc sextant built in 1984. It has a traditional
half-silvered/half-glass horizon mirror. The scope is a Celestaire 7x35
monocular (I believe the first one that Ken sold).
2) That is the question for the ages and one I am trying to experimentally
determine. Your fix accuracy varies with conditions (especially with
horizon quality) as well as observer. I am happy with <1.0 miles, okay
with 1-2 miles, and generally not happy with anything more than 2.0 miles.
This is from a ship and an experienced shooter. I don't think that
you will get as accurate a position from a small boat bouncing in the
waves.
3) I've been shooting stars since 1997.
Jeremy