Interpreting Astro-position Lines at Sea

Extract

‘The mark of a good navigator is not so much his ability to obtain accurate information as his ability to evaluate and interpret correctly the information available to him.’ So writes Captain Alton B. Moody, U.S.N.R. in the course of an interesting correspondence in the February number of the U.S. Naval Institute Proceedings. In the August 1961 number (page 132) Captain Robert Lee Rhoads, Jr., a shipmaster, suggests that the ‘cartwheel’ set of astro-sights, where four position-lines intersect each other at angles of about 45°, is inferior to the square where the position-lines intersect at approximately 90°, which gives a more reliable fix. One of Captain Rhoads's illustrations shows a case of a 4-minute systematic error in a ‘cartwheel’ fix giving a position 6 miles in error, where the same error would have had no effect on the position interpolated from four sights taken at 90° to each other.