True Bearings and Courses for Chartwork

Navigational bearings are measured clockwise from north: 000° or 360° is north, 090° east, 180° south and 270° west. IHO chart specifications require charted bearings to be true and normally written with three figures, such as 005°, 045° or 230°.

A bearing is the direction of an object or line from the stated north reference. A course is the direction selected for the vessel to travel or steer. Heading is where the vessel's fore-and-aft line points at an instant; track is the path actually followed through the water or over the ground. Wind, current and steering can make those quantities differ.

Write T, M or C whenever the context could be ambiguous: true is referenced to True North, magnetic to Magnetic North and compass to the vessel's compass after its local deviation. Do not combine a compass observation with a true chart line until the required corrections have been applied and checked.

The reciprocal of a direction points along the same line but the opposite way. Add 180° to bearings below 180° and subtract 180° from bearings of 180° or more. A bearing of 045°T from the vessel to a lighthouse therefore defines a position line plotted from the lighthouse on 225°T.