NavList:

Francis,

The lunar and bubble intercept numbers are for obsevations taken from land. Lunars and bubble observations are not at all accurate while underway on a sailboat. I find both types of observations very difficult even when at anchor.

Greg Rudzinski

From: Francis Upchurch
Date: 2015 Jul 18, 21:25 -0700

Lu,

I've done hundreds of cel nav sights on my 35ft yacht over the last 10 years or so and agree with Greg. 1-2' sextant accuracy in the back yard ok but on the boat in a seaway, that is another matter! (3-5' often, but sometimes 10'). Lunars very difficult in rough weather. (Greg, I'm  interested to hear you can do lunars with a 7x scope. I find even my 4x scope difficult in any swell. )

So I still think the sextant reading is often the main source of error at sea. (see my previous posts on that).

Obviously, you want to limit any addtional sources of error, like the LOP sight reduction calculation which has been the main discussion point here.If it is in the opposite direction to the sextant error, great, but that would be pure luck, may be same direction  and compound the sextant error.

Practice nearly makes perfect. My sextant performance seems to improve by the end of the cruise.Likewise my LOP reductions (I generally use the Bygrave)

Best wishes

Francis