A bearing measured by a ship's compass, requiring correction for both variation and deviation to obtain a true bearing.
In practice
The OOW takes compass bearings by aligning the azimuth mirror or pelorus with charted objects and reading the compass card. On older vessels without a gyrocompass, all navigation is conducted in compass bearings, requiring the officer to maintain and apply an up-to-date deviation card for every heading. Even on modern vessels with gyrocompass output, the ability to take and correctly convert compass bearings is a mandatory STCW competency, assessed in oral examination. In scenarios where the gyrocompass is unserviceable, the OOW must be fully proficient in using magnetic compass bearings to navigate safely.
Regulatory detail & full definition
A compass bearing is the direction to an object as read directly from a ship's magnetic compass, before any corrections have been applied. It is the raw instrument reading and must be corrected for deviation (which varies with the ship's heading) and then for variation (which depends on position) to arrive at a true bearing suitable for chart plotting. Bowditch (American Practical Navigator) provides worked examples of the full correction sequence, and the Admiralty Manual of Navigation emphasises that compass bearings must always be clearly labelled as such when recorded, to prevent confusion with magnetic or true bearings.
The OOW takes compass bearings by aligning the azimuth mirror or pelorus with charted objects and reading the compass card. On older vessels without a gyrocompass, all navigation is conducted in compass bearings, requiring the officer to maintain and apply an up-to-date deviation card for every heading. Even on modern vessels with gyrocompass output, the ability to take and correctly convert compass bearings is a mandatory STCW competency, assessed in oral examination. In scenarios where the gyrocompass is unserviceable, the OOW must be fully proficient in using magnetic compass bearings to navigate safely.