NavList:

Thanks David,

I am just learning celestial but as soon as I read this it confused me. We are all aware waves and swells are never uniform in height but to attempt to consider this factor while working out a sight must be unrealistic. In my considered opinion we must consider the waves & swells are in fact uniform and the view of the horizon is made up only of crests. Therefore we need to take our sight when our yacht is as close to the crest as possible. I understand the horizon we need to use will be parallel to the celestial horizon and a line drawn from crest to crest achieves this. As does a line from trough to trough but the visible horizon is not made up of troughs and our view in a trough is of the face of a wave. A line drawn from half way up a wave to the crests of the waves on the visible horizon is not parallel to the celestial horizon. It is also clear that in unfavourable conditions as with all position fixing we should not be over confident about the accuracy of any fix obtained.

Very happy to have any of the above corrected.

Mike