NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Gary LaPook
Date: 2011 Jun 3, 20:55 -0700
To add to the usefulness of the table I already uploaded I am attaching another table from H.O. 218 for determining the "conversion angle" which is the difference between the rhumb line and the initial great circle course, there is also one in Bowditch. The conversion angle was used commonly in the past for plotting long range radio bearings on Mercator charts. It was also used to figure out the initial great circle course after you measured the rhumb line course on the Mercator chart. But we can also use it in reverse, to determine the rhumb line course after we have computed the great circle course. You only have to remember that the great circle always aims closer to the pole than does the rhumb line. So, (in the northern hemisphere)if the great circle initial course is generally eastward then you add the conversion angle to the great circle initial course to find the rhumb line, if westerly then subtract.
gl
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