Conversion angle (CA) is the angle between the great circle track WP 1 to WP 2 and the rhumb line track, which is the 60ºS parallel of latitude.


CA = ½ x chlong x sin mean lat = ½ x 10º x sin60º = 4½º

Departure distance 60ºS 030ºW – 60ºS 025ºW = chlong(‘) x coslat = 5º x 60 cos60º = 150 nm

CA is the angle between the GC and RL at 030ºW. At 025ºW the GC and RL tracks are parallel. A straight line from 60ºN 030ºW to 60ºN 025ºW will bisect CA at 030ºW.

Using 1 in 60 rule we can estimate distance from RL at 025ºW
Track error = ½ x CA = 2.2º and distance along track = 150 nm.

Calculator: (track error/60) x distance along track = (2.2º/60) x 150 = 5.5 nm

CRP5: Put 60 on inner scale next to 2.2º on outer scale, go to 150 nm on inner scale and read 5.5 nm on outer.

At 25ºW the great circle track
is 5.5 nm South of 60ºS at 60º05.5’S.