A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2018 Jan 19, 07:08 -0800
Your 1975 vol. 2 Bowditch should have a table for converting radio bearings from GC to rhumb lines. Attached PDF at 1-7 shows a correction table from GC to Mercator (Rhumb line) that covers differences in longitude up to 7.5°.
This may be all you need. For larger longitude differences you will need to use a 1958 edition Bowditch radio direction conversion table. I don't have the 1958 Bowditch with me so can't tell you what page or table number but I seem to remember that it is the first table.
From: Bob Goethe
Date: 2018 Jan 18, 22:47 -0800