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.
Encounter type
Crossing
Rule applies
Rule 15
Own role
Give-way (target on starboard, Rule 15+16)
Formula, assumptions, and 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
| Condition | Encounter | Own role |
|---|---|---|
| Aspect of own from target >157.5deg | Overtaking (Rule 13) | Give-way (overtaker) |
| Reciprocal courses, target ahead | Head-on (Rule 14) | Both alter course to starboard |
| Crossing, target on own starboard | Crossing (Rule 15) | Give-way |
| Crossing, target on own port | Crossing (Rule 15) | Stand-on (Rule 17) |