COLREG - Encounter Classification (Head-on / Crossing / Overtaking)
Classify a two-ship encounter as head-on (Rule 14), crossing (Rule 15) or overtaking (Rule 13) from relative bearings and aspects.
Formula, assumptions, limits
Rule 13 (overtaking): own ship approaching another vessel from a direction more than 22.5 degrees abaft the target’s beam. Rule 14 (head-on): two power-driven vessels meeting on reciprocal or near-reciprocal courses. Rule 15 (crossing): two power-driven vessels crossing so as to involve risk of collision, neither overtaking nor head-on. The encounter classification depends on the relative bearing of own ship as seen from the target (aspect) and the target’s course relative to own course.
Classification thresholds
ConditionEncounterOwn role
Aspect of own from target >157.5degOvertaking (Rule 13)Give-way (overtaker) Reciprocal courses, target aheadHead-on (Rule 14)Both alter course to starboard Crossing, target on own starboardCrossing (Rule 15)Give-way Crossing, target on own portCrossing (Rule 15)Stand-on (Rule 17)
In short
Head-on, crossing, or overtaking classification under COLREG Rules 13, 14, 15.