Yachtmaster Offshore Standard: Compass

Keep one direction record that another navigator can audit: source, reference, observation time, vessel heading and configuration, conversion, independent corroboration and the action trigger. A bare number such as 112° is incomplete. State whether it is compass, magnetic or true and whether it is heading, a bearing, water track or course over ground.

Heading is where the fore-and-aft line points; water track is the vessel's motion through the water; course over ground is motion over the ground. Tide, leeway, manoeuvring and sensor lag can separate all three. Converting a compass heading to true does not turn it into COG, and a stable COG does not prove the heading source.

Do not vote between the steering compass, a fluxgate display and a plotter. Two displays may share one sensor, power feed, calibration, alignment or data path. A portable speaker, tablet case, charging cable, steel tool or current-carrying conductor can disturb a magnetic compass. Heel can also change the residual deviation pattern. Identify dependencies before calling any agreement independent.

When the discrepancy is material and unexplained, protect sea room and reduce commitment. Hold, slow or move to safer water only as appropriate to the actual vessel and conditions; use known physical directions, depth, radar, position and other genuinely independent evidence. Restrict reliance on the suspect source, record the observation and arrange competent investigation rather than inventing one correction at sea.