A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2023 Sep 20, 09:49 -0700
As an air navigator and subsequent ‘lower-set’ maths teacher with little experience of the dark arts of marine navigation, I would say why bother. Just mark dLat and departure anywhere on your chart using the adjacent latitude scale; complete the parallelogram and measure the bearing and distance travelled with protractor and dividers. Alternatively, get out your scientific calculator and key in: departure, divide, dLat, =, shift, tan, = to get bearing.
Then without touching anything else key in: cos,=, ‘1/x’, X (i.e. times), dLat, = to get distance.
I tried it for 31 degrees and 8nm from your table I.e. dLat= 6.875, Dep= 4.120 and was surprised to find it worked first time.
However, it’s not good practice to feed back something you’ve just worked out into a subsequent calculation if you don't have to, so you might prefer to use distance sailed = root (dLat squared + departure squared). DaveP