NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: US Navy and celestial...
From: Stan K
Date: 2017 Sep 15, 15:47 -0400
From: Stan K
Date: 2017 Sep 15, 15:47 -0400
An interesting spec on the Navy Mark II was that it has the largest usable arc of any sextant I know of. The arc is graduated to 145 degrees, and the index arm can actually reach this point. Sure, there wasn't much index mirror left to see at this angle, but it was there. The Mark III, on the other hand, was graduated to a more typical 125 degrees, which it could reach. Admittedly the extra range of the Mark II was only an advantage for artificial horizon sights, back sights, lunars (and that would be pushing it), and horizontal angles, all of which I suspect were not often (perhaps never) done by the Navy, especially since the time of the introduction of the Mark III.
Stan
-----Original Message-----
From: Paul Hirose <NoReply_Hirose@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Fri, 15 Sep 2017 14:50
Subject: [NavList] Re: US Navy and celestial...
From: Paul Hirose <NoReply_Hirose@fer3.com>
To: slk1000 <slk1000@aol.com>
Sent: Fri, 15 Sep 2017 14:50
Subject: [NavList] Re: US Navy and celestial...
Back in the 1990s, when I was still on active duty (USAF, not USN), I looked up mil spec for the Navy Mark III sextant. The spec appeared to be a clone of a C. Plath. There was a name (maybe a trademark?) for the metal of their frame, and the mil spec required that same metal. I think it also called for their ergonomic handle. To me it looked like a case of "specmanship." Such manipulation of the military procurement system was an occasional tactic. You couldn't say "I want this model from that manufacturer." The correct procedure was to state the what properties the device had to possess. Then the supply people would search for the product that met your requirements at lowest cost. By carefully crafting the parameters of your request, you could guarantee the only match would be device you wanted. The mil spec for the Mark III included the test procedure. The sextant was clamped to a precision rotary table, with the index mirror at the center. A collimator, also attached to the table, was aimed into the horizon glass to simulate the horizon. A fixed collimator aimed at the index mirror simulated a star. By rotating the table you could control the altitude of the "star." Tests were made with and without shades. I forget the maximum permissible error.
