Boat Sailing in Fair Weather and Foul, 6th ed.

by A. J. Kenealy

North, North-W.

North by West

North

These points are sub-divided into quarter points, and again into degrees. The table given on pages 142-143 shows the angles which every point and quarter point of the compass makes with the meridian:

POINTS, ANGLES AND BACK BEARINGS OF THE COMPASS.

The mariner's compass does not, however, give the true direction of the various points of the horizon. The needle points to the magnetic North and not to the true North, the difference between them being called the variation of the compass, which differs widely in various parts of the world, being sometimes easterly and sometimes westerly, and constantly changing. The amount is generally marked on the charts. In New York the variation for 1894 was 8° 26´ West, or three-quarters of a point to the West of the true North. Thus, to make good a true North course, the vessel would have to steer North three-quarters West. A rule easy to remember is that westerly variation is allowed to the left of the compass course, or bearing, and that easterly variation is allowed to the right of the compass course or bearing.

To convert true courses and bearings into compass courses and bearings with variation westerly, allow it to the right of the true course or bearing, and with variation easterly allow it to the left of the true course or bearing.

Deviation is another error of the compass caused by local attraction, such as the ironwork and iron ballast in a boat, or the proximity of a marlinespike to the binnacle. In a wooden boat, if proper care is taken, there should be no appreciable deviation of the compass. Deviation can be discovered by swinging the boat as she lies at her moorings, having first obtained the true magnetic bearing of some distant object, such as a lighthouse or a church steeple. As the vessel's head comes to each point of the compass, a compass bearing is taken of the object, and the difference between that bearing and the true magnetic bearing is observed and noted, and afterward tabulated. It will often be found that the deviation differs not only in amount, but in name, for different directions of the ship's head, being easterly at certain points and westerly at others.