NavList:

My experience in doing lunars is limited on land and zero at sea. But my
impression is that the main difficulty is holding the sextant at a
more-or-less horizontal angle which, because it was not designed to be so
held, leads quickly to a rapid 'tremor' due to muscle fatigue. At sea, on a
vessel whose weight is four figures of tons rather than yachts, which bob
about with only single figures in tons, I would have thought the slow
movement of the vessel (in reasonable seas) would have been much less of a
problem and so contribute much less to the errors of the measurement than
the fatigue of holding a heavy, unwieldy instrument.

Comments, anyone...?

Geoffrey Kolbe

 

Lunars are the most difficult shot I have ever shot for the very reasons you mention.  My ship's rolling period is 13 seconds, and we roll from less than a degree up to 20 degrees.  The lunars I have shot recently have been with the ship rolling about a degree or so.  In addition to the roll, there is engine vibration to deal with, so I have recently found that sitting on the bridge wing helped a bit with getting a more steady platform to shoot.  I cannot lean against anything however as the vibration affects the sextant.

 

I am using a 4 x 40 scope on this sextant.  The sextant itself seems to be free of any real errors, but IE is always a challenge.

 

I will be posting some more raw lunar data here soon from my recent trip to sea.

 

Jeremy

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