Old as Dirt!
Join Date: Nov 2008
Location: Tampa Bay Area
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Declination is the horizontal angle between true north and magnetic north at a given location. Whereas declination changes as one's location changes, and at a given location changes over time ("variation"), how could one resonably "set" it for a voyaging yacht? (Although one might for a yacht confined to a given area). Some of the old compasses, particularly those of the Grid type, did have an azimuth ring or bezel that one could rotate but that's rather a lot of mechanization for a rather simple matter, no? I recall that the rotating bezel on the standard US Army field (lensatic?) compass merely rotated a reference line in the covering lens but not the underlying arc.
For our part I find having to shift from True to Magnetic and back rather tedious and so use a plotting board that allows one to adjust the north referance lines so that one is always reading magnetic rather than true bearings off the chart. This does not, however, take into account deviation which is the local error between magnetic bearings and indicated magnetic bearings for a given yacht for which one must make up a deviation card to have handy at the helm.
"It is not so much for its beauty that the sea makes a claim upon men's hearts, as for that subtle something, that quality of air, that emanation from the waves, that so wonderfully renews a weary spirit."