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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Digital Dead Reckoning Calcs
From: David Iwancio
Date: 2023 Nov 23, 20:52 -0800
From: David Iwancio
Date: 2023 Nov 23, 20:52 -0800
I made a mistake/misremembered parts of the math of "mid latitude." It's been at least a year since I looked at this stuff, but I was reminded by a problem I was having then but didn't seem to have now.
Going back to Bowditch 1906, the cosine of the "latitude of conversion" is the difference in latitude divided by the difference of meridional parts. It's this latitude you use to determine the difference in longitude along all points on the rhumb line.
The catch is that, using non-spherical merdional parts, you end up with cosines greater than 1 for sailings at low latitudes. But the ratio "DLat/m = DLo/dep" still holds.
David I
