Rule 11 states that the rules in Section II (Rules 11–18) apply only to vessels in sight of one another. Two vessels are "in sight" when one can be observed visually from the other. Radar observation alone does not constitute being "in sight."
IMO COLREG 1972Official text
Full wording of the rule, reproduced from the official source below.
Rules in this section apply to vessels in sight of one another.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
Start every scenario by classifying the encounter: overtaking, head-on, crossing, narrow channel, traffic separation, or restricted visibility.
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
Section II only applies when vessels can see each other visually
Radar contact alone does not mean vessels are 'in sight'
Rule 19 applies instead when vessels are not in sight in or near restricted visibility
Common Mistakes
Applying crossing or overtaking rules when only detected on radar
Test Your Knowledge
Practise this topic and review the explanation for each answer.
More rules in this Part
- OvertakingAny vessel overtaking another shall keep out of the way of the vessel being overtaken.
- Head-on SituationWhen two power-driven vessels in sight meet on reciprocal or nearly reciprocal courses with risk of collision, each shall alter to starboard to pass port to port.
- Crossing SituationWhen two power-driven vessels are crossing, the vessel which has the other on her starboard side shall keep out of the way.
- Action by Give-way VesselEvery vessel directed to keep out of the way shall, so far as possible, take early and substantial action to keep well clear.
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