Module 5 - COLREGs
Rule 18 — Responsibilities Between Vessels
What you will learn
Apply Rule 18 only after checking Rules 9, 10 and 13, and distinguish defined status from appearance, occupation or assumed right of way.
Rule 18 assigns keep-clear and avoid-impeding relationships, but it is not a universal ladder. Defined status, encounter context and earlier rules matter.
Except where Rules 9, 10 and 13 otherwise require, a power-driven vessel underway keeps out of the way of a vessel not under command, restricted in ability to manoeuvre, engaged in fishing, and a sailing vessel. A sailing vessel keeps out of the way of NUC, RAM and fishing vessels; a fishing vessel keeps out of the way of NUC and RAM so far as possible.
NUC means exceptional circumstance makes a vessel unable to manoeuvre as required. RAM means the nature of the vessel's work restricts ability to manoeuvre. A vessel is 'engaged in fishing' only when fishing gear restricts manoeuvrability. A yacht using propelling machinery is power-driven even if sails remain set.
A power-driven vessel constrained by her draught must navigate with particular caution. Other vessels, except NUC or RAM, should if circumstances admit avoid impeding her safe passage. The vessel may exhibit three all-round red lights or a cylinder under Rule 28; the signal is optional and does not create absolute right of way. Whatever the relationship, Rules 2, 5, 7, 8 and 17 continue.
Test a claimed status
AIS labels a vessel as fishing, but it shows ordinary power-driven lights and makes steady speed through a traffic lane while your yacht overtakes.
1. Use observed evidence
Do not convert an AIS label into a defined status without lights, shapes and operation supporting it.
2. Apply prior rules
Rule 13 makes the overtaking yacht keep clear; Rule 10 also remains relevant in the lane.
3. Monitor uncertainty
Allow generous clearance and reassess if gear, lights, shape or movement changes.
Sense check: If removing the AIS label changes the decision, the plan relied on reported identity rather than encounter evidence.
Common mistake or limitation
- Carrying fishing equipment does not itself mean 'engaged in fishing'; the gear must restrict manoeuvrability.
- Constrained-by-draught lights and the cylinder are optional signals, not compulsory proof of permanent priority.
Recap
- Check Rules 9, 10 and 13 before ordinary Rule 18 responsibilities.
- Use defined status and observed operation, not an AIS label or occupation alone.
- Constrained-by-draught signalling is optional and never removes collision-avoidance duties.
Optional quick check
Section 7 of 14
Which sequence is correct for an in-sight vessel-status encounter?
Sources and factual review
Reviewed 2 September 2026 - Compass Revision editorial review.
Practice the full encounter sequence
The complete module tests overtaking, crossing, restricted visibility, lights, shapes and responsibilities together.