Compass bearings

The angle between the direction of a place or object and compass north is called the compass bearing.  As previously stated it is distinguished by the suffix (C) after the bearing.  Like true and magnetic bearings it is written in three figure notation.  In order to change a compass bearing to a true bearing, the navigator must correct it for deviation and variation.  It is important to remember that the heading of a vessel determines the amount of deviation.  All bearings taken whilst on a particular course must be corrected according to the amount of deviation determined by the ship’s heading.  Only when the ship alters course will the amount of deviation change.

Procedure for converting compass bearings

When converting a compass bearing to a true bearing one must first remove the deviation.  This will provide one with a magnetic bearing.  By next applying the variation correction one will finally arrive at the true bearing.  If the deviation is easterly, it must be added to the compass bearing.  If the variation is also easterly it must be added to the magnetic bearing.  In both cases, if the deviation and variation is westerly, they will be subtracted from the compass and magnetic bearings respectively.  If one needs to convert a true bearing to a magnetic and compass bearing, the reverse of the above is applicable, ie you subtract the easterly deviation and variation and add westerly deviation/variation.  The following is a good aide memoir.