You're motoring along when a faster vessel approaches from behind on your starboard quarter, seeing only your sternlight. As she draws level and her course now crosses ahead of yours with you on her starboard side, who must keep clear?

She does — once overtaking, she stays give-way until fully past and clear

You do — the geometry is now crossing and she's on your starboard side

She does — once overtaking, she stays give-way until fully past and clear

⛵ Crossing, Overtaking & Head-On: The Three Encounters

Almost every close-quarters situation between two power-driven vessels fits one of three geometries. Recognising which one you're in tells you instantly whether you must act. Recall the give-way / stand-on roles from earlier: in each geometry the rules assign those roles differently.

Head-on: two vessels approaching roughly bow-to-bow (you'd see the other's masthead lights in line and both sidelights). Neither is privileged — both alter course to starboard and pass port-to-port, like cars keeping right. Crossing: your courses intersect at an angle. The rule is simple — the vessel that has the other on its own starboard side is the give-way vessel and must keep clear (a handy mnemonic: if you see the other boat's red sidelight, you give way — 'red means stop'). The other vessel is stand-on and holds course and speed. Overtaking: you're coming up on another vessel from more than 22.5° abaft her beam (you see only her sternlight, no sidelight). The overtaking vessel is always give-way and must keep clear until fully past — and you stay the overtaking vessel even if the geometry later changes.

When in doubt about which geometry applies — especially between crossing and overtaking at dawn or dusk — the rules say to assume overtaking and keep clear, the more cautious choice. Whatever your role, the give-way vessel should act early and boldly (a large, obvious course change), and the stand-on vessel must be ready to manoeuvre if the other fails to.