Rule 15 governs crossing situations between power-driven vessels.
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.
In this encounter, take early and substantial action under Rule 16. Passing astern may be appropriate, but Rule 15 does not prescribe one course alteration for every crossing: choose effective course and/or speed action under Rule 8 and check the whole traffic situation.
IMO COLREG 1972Official text
Full wording of the rule, reproduced from the official source below.
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.STCW Bridge Watch Lens
Rules 4–10 apply in any visibility.
Rules 11–18 apply to vessels in sight of one another; Rule 19 applies to vessels not in sight when navigating in or near an area of restricted visibility.
Build the traffic picture with sight, hearing, radar/ARPA and chart context.
Do not let AIS or one isolated bearing replace systematic observation.
After manoeuvring, keep monitoring bearing, range, CPA/TCPA and passing distance until the other vessel is finally past and clear.
Exam Focus
Identify the vessel types first, then the relative bearing, then whether one vessel is overtaking.
Misclassifying the encounter is the usual exam failure.
For vessels in sight, every overtaking vessel keeps clear until finally past and clear.
Rule 13 takes precedence over Part B Sections I and II; it does not override the other Parts of COLREG.
Key Takeaways
For two power-driven vessels in sight crossing with risk of collision, the vessel with the other to starboard gives way
If circumstances admit, avoid crossing ahead of the other vessel
Take early and substantial action to keep well clear; course and/or speed action depends on the circumstances
First check vessel types, collision risk and whether another rule such as overtaking applies
Common Mistakes
Crossing ahead of the stand-on vessel when it can be avoided
Confusing which vessel has the other on starboard side
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More rules in this Part
- Sailing VesselsWhen two sailing vessels approach, the one with wind on port side keeps clear. When both have wind on same side, the windward vessel keeps clear.
- OvertakingAny vessel overtaking another shall keep out of the way of the vessel being overtaken.
- Action by Stand-on VesselThe stand-on vessel shall keep her course and speed, but may take action when it becomes apparent the give-way vessel is not acting.
- Responsibilities Between VesselsRule 18 sets the basic responsibilities between vessel types. Constrained-by-draught vessels receive special consideration but are not simply another rung in a fixed hierarchy.
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