COLREG Navigation Rules Complete Guide 2026

COLREGs — the International Regulations for Preventing Collisions at Sea, 1972 — are the closest thing the sea has to traffic law, and unlike most regulation a seafarer deals with, these are rules applied in real time, under pressure, with a closing speed measured in minutes rather than days to think it over. They apply to every vessel on the high seas and connected waters navigable by seagoing vessels, and while the full set runs from Part A through several annexes, a fairly small subset of rules does almost all the work in keeping ships apart — and the same small subset shows up again and again in collision inquiries.

Steering and Sailing: Who Gives Way and Who Holds Course

Rules 4 through 19 govern conduct of vessels in sight of one another. In a head-on situation (Rule 14), both power-driven vessels alter course to starboard so each passes port-to-port — and if there’s any doubt whether the situation is truly head-on, the rule says to assume it is and act accordingly rather than wait for certainty. In a crossing situation (Rule 15), the vessel that has the other on her own starboard side is the give-way vessel and must act early and substantially; the vessel being kept on the other’s starboard side is the stand-on vessel under Rule 17 and must hold course and speed — but not blindly: if collision becomes otherwise unavoidable, the stand-on vessel is required to take her own avoiding action. Overtaking (Rule 13) is different again: whichever vessel is coming up from more than 22.5 degrees abaft the other’s beam remains the give-way vessel for the entire manoeuvre, regardless of what the two vessels’ types or usual rule status would otherwise suggest.

Rule 2 and Rule 5: The Two Rules That Actually Decide Inquiries

Ask any experienced Master which two rules get cited most often in real collision investigations, and the answer is usually Rule 5 and Rule 2, not the crossing or overtaking rules everyone studies for exams. Rule 5 requires every vessel to maintain a proper lookout by sight and hearing, and by all available means appropriate to the circumstances — meaning radar and AIS supplement a lookout, they don’t replace one, and a watch kept purely on a screen has repeatedly been found inadequate in inquiry findings. Rule 2 is the rule that acknowledges the others aren’t a mechanical formula: it requires compliance with the ordinary practice of seamen and the special circumstances of the case, and it explicitly allows departure from the other rules when necessary to avoid immediate danger — the in-extremis principle that recognises a rulebook cannot anticipate every situation a bridge team will actually face.

Reading Lights and Shapes to Know What You’re Looking At

Rules 20 through 31 and Annex I define what a vessel must show so others can identify her type and status without asking. A power-driven vessel underway shows sidelights — green to starboard, red to port, each visible across an arc of 112.5 degrees — a masthead light forward, a second higher masthead light aft for vessels over 50 metres, and a stern light. Vessels not under command, restricted in their ability to manoeuvre, engaged in fishing, or constrained by draught each carry distinct light and shape combinations precisely because their ability to keep clear differs, and the give-way vessel needs to know that before deciding how to act. Getting this wrong — showing incorrect lights, or misreading another vessel’s — is a frequent and serious PSC deficiency precisely because it undermines every other rule in the collision-avoidance framework.

Sound Signals for When Sight Isn’t Enough

Rules 34 and 35 cover manoeuvring and warning signals in sight of one another, and fog signals in restricted visibility — one short blast meaning “I am altering course to starboard,” two short blasts for port, and five or more short blasts as the doubt-or-danger signal used when a vessel’s intentions aren’t understood or agreed. In restricted visibility, a power-driven vessel making way through the water sounds one prolonged blast at intervals not exceeding two minutes, a signal that exists precisely because COLREGs assumes there will be situations where sight-based rules alone cannot keep vessels apart.

Chat with SailorGPT