NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Metal versus plastic or better telescope?
From: Lu Abel
Date: 2012 Mar 27, 12:05 -0700
From: Lu Abel
Date: 2012 Mar 27, 12:05 -0700
I want to echo both posts from Alan.
A Davis Mk 15 is certainly far, far from an Astra. But it is pretty darn good for what it costs (about 1/3 of an Astra's price). We haven't discussed it, but I believe the Davis Mk 25 is made from a better quality (ie, more stable) plastic.
Beyond that, we should be asking what is an acceptable accuracy for a celestial sight. As Alan points out, the United States Power Squadrons requires an accuracy of 5NM in its basic celestial course (sun sights only) and 3NM in its advanced celestial course.
While a metal sextant can make achieving these goals easier, I've just taught a class where 3/4 of the class used Davis sextants and all met the required accuracy.
Something never discussed is the accuracy achievable -- even with the best of sextants -- on the heaving deck of a small craft at sea. On land or on the Titanic we might possibly see the effect of index error inaccuracy. But I wonder if it matters all that much when one experiences minutes of error in sights simply due to the inability to hold the sextant level on a swaying, heaving boat.
From: Alan S <alan202@verizon.net>
To: NavList@fer3.com
Sent: Tuesday, March 27, 2012 10:49 AM
Subject: [NavList] Re: Metal versus plastic or better telescope?
Randall:Enjoy the Astra. You likely bought yourself a very nice gift, aassuming that the 111B hasn't been abused.Strangely, I too have an Astra and a Davis Mk. 15, with which, at times, I have gotten good sights, and fixes shooting from the beach at Emerald Isle, North Carolina.While the Davis sextant will work, it's a useable instrument, mechanically, re materials of construction, it leaves something to be desired. Its' optics do not compare with the standard telescope furnished with the Astra, a 3.5 power x 40mm telescope.Of course, there is a significant price difference, one getting what they pay for. If it is possible for you to get to the sea coast, I believe that you will notice significant differences between results obtained with the two instruments.Enjoy.Alan----------------------------------------------------------------
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