NavList:

Hello everyone,

I recently purchased a Navy Mark V AN-5851-1 (A-14) sextant and was pleased to find it in remarkably good condition upon arrival. A bubble is easily formed and removed. The averaging mechanism runs precisely two minutes and is accurate to within 1’ or less. I have only a few minor complaints.

First, I took it out for a few sights and was disappointed to find it was reading significantly off. Aligning the bubble on the sea horizon and correcting for dip, I estimated an index error of -19’. After a day of sun sights at 30 minute intervals, I found the mean, median and standard deviation of my intercepts from a known location to be -17.3’, -17.6’ and 2.0’ respectively. Correcting my sights for an index error of -17’ placed my position within two miles of my known location.

This index error seems rather significant. Would it be worthwhile to make an adjustment to the sextant or just mathematically correct the sights with this index error? If I were to make this adjustment, how is this done? I’ve discovered some adjustment screws on the backside of the index prism. I’ve decided not to mess with these until I am sure I know what I’m doing.

Second, the shutter that should block the view as the timer runs down does not seem to be working. It is only slightly darker when the timer stops. It seems that maybe the shutter is sticking and only partially blocking the view. Is this worth a tear down to repair, or should I just live with it?

I have successfully restored a few A-10A’s and a British Mark IX. I just don’t have any teardown info for this sextant, so I am a little leery of opening this one up since it is in 95% working order.

Any advice from the experts of NavList would be greatly appreciated!

Dave Harwood

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