What Is a Bearing?
A measure of which compass direction an object lies from you in — even in the GPS age, still the most reliable eye for spotting collision risk.
A bearing is the compass degree showing which direction a target — a lighthouse, headland or boat — lies from the observer. Plotting the bearings of two or three fixed marks on the chart and taking their intersection is the classic way to fix your position, but in the GPS age its real value lies elsewhere.
A bearing does something GPS cannot: collision analysis. The rule is vital.
Constant-bearing rule
If it is not changing, pay attention: if the bearing of an approaching vessel is not changing over time, you are on a collision course with her.
Constant bearing, closing distance: one of the most vital rules of seamanship, applied in seconds with just the eye and a compass.
Watch out for visual error: lining up against the guardrail stanchion is a handy bearing check, but as the boat swings on her heading it can mislead; if in doubt, use the compass. A hand-bearing compass will also lie next to metal and speakers, so an open deck gives the cleanest reading.
At night, build the habit of checking the bearing of every approaching light every two or three minutes. If it changes, you will pass clear; if it does not, the decision is yours — and that decision is made by eye, not on a screen.