A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Bob Goethe
Date: 2018 Mar 14, 11:15 -0700
I live inland, and so when I take sextant sights over water, it is usually over a lake surface. This leaves me keenly interested in knowing if the lake is wide enough, in the direction I am shooting, that I am seeing a "true horizon". Most often when I take sights on salt water, I am surrounded by islands, and have exactly the same question I want to answer.
Bowditch 2017, of course, has table 12 that relates the height of eye to the distance of the horizon...but I never seem to have that table ready at hand.
As I was reviewing a piece of Bowditch, howeveer, I had an "Aha!" moment as I looked at these two sections that were right next to each other (screen capture attached to this post). It had never occurred to me until this week that I could relate dip to the distance-to-horizon. But if you have your Nautical Almanac in hand, you can get an approximation of the distance to the horizon with this, which one can do in his head:
Dip x 1.2 = distance-to-horizon-in-nautical-miles