Part B · Steering and sailing rules · Rule 15
Crossing Situation
15 When two power-driven vessels are crossing so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel.
- “When two power-driven vessels are crossing so as to involve risk of collision”Rule 15 applies between two power-driven vessels whose courses cross, when risk of collision exists (Rule 7). It covers what is not overtaking (Rule 13) or head-on (Rule 14). If one of them is a sailing vessel, fishing, not under command or restricted in her ability to manoeuvre, Rule 18 decides instead.
- “the vessel which has the other on her own starboard side shall keep out of the way”If the other vessel is on your starboard side, you give way. If she is on your port side, she gives way and you are the stand-on vessel: keep your course and speed (Rule 17). At night, the give-way vessel sees the other’s red (port) sidelight.
- “and shall, if the circumstances of the case admit, avoid crossing ahead of the other vessel”Where possible, don’t cross her bow. The usual action is a clear alteration to starboard, or a reduction in speed, so that you pass astern of her. Make it large enough to be readily apparent (Rule 8(b)) and take it early (Rule 16).
Other vessel on your starboard side? You give way, and pass astern of her rather than ahead. Seeing her red sidelight means you are the give-way vessel.