NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Murray Buckman
Date: 2025 Feb 7, 14:04 -0800
Hi DaveP,
It is an interesting question.
My assumption, and it is only that, is that the Kelvin balls would do their job with a ship's magnetic compass even if the ship was carrying a load of iron or steel, and that any master would swing the compass if a cargo with a potential impact on a magnectic compass is being carried for the first time, and intermitently thereafter.
"With a load of iron ore twenty-six thousand tons more, than the Edmund Fitzgerald weighed empty". (Gordon Lightfoot).
A quick search turned up IMO CIRCULAR 2014-002, which addressed iron ore:fines. Interestingly the multi-page circular includes a brief statement: "Iron ore cargoes may affect magnetic compasses."
Of course one of the great breakthoughs in pleasure boating was the introduction of the almuinium beer can. those old steel beer cans used to play havoc with the steering compass when placed in a can-stand on the binnacle. :-)
Murray B.
