Understanding COLREGs: A Practical Guide for OOW Aspirants

If there's one subject that separates a confident Officer of the Watch from a nervous one, it's the COLREGs. The MCA examiners know this too — collision regulations questions appear throughout the Safety Critical assessment, often woven into scenario-based questions rather than simple rule recitation. You won't just be asked "what does Rule 15 say?" You'll be asked what you'd do at 0300 with a fishing vessel crossing your bow in restricted visibility.

This guide won't reproduce the rulebook verbatim — you have that already. Instead, think of this as the conversation a good Chief Officer would have with you on the bridge wing: what actually matters, where cadets trip up, and how to think your way through the exam and real life alike.

Rule 5 – Look-out

The rule in plain language: Every vessel must maintain a proper look-out by sight, hearing, and all available means, appropriate to the circumstances, to make a full appraisal of the situation and risk of collision.

Bridge scenario: You're alone on watch at 0200, autopilot engaged, radar on a 6nm range. A small wooden fishing boat with no AIS and a weak radar return is dead ahead. If you're heads-down on paperwork, you'll miss it until it's dangerously close.

Common misunderstanding: Candidates assume "all available means" means radar is sufficient. It isn't. Rule 5 explicitly includes visual and aural senses — a solo watchkeeper glued to the ARPA screen while ignoring the window is not complying, even with excellent electronics. Examiners love testing this: a vessel with working radar can still be in breach of Rule 5 if the OOW didn't look up.

Rule 6 & 7 – Safe Speed and Risk of Collision

Plain language: Rule 6 requires a speed that allows you to take proper and effective action to avoid collision, stopping within a distance appropriate to the circumstances. Rule 7 requires you to use all available means — especially radar — to determine if risk of collision exists, and to treat any doubt as risk existing.

Bridge scenario: Fog has rolled in, visibility 0.5nm. You're doing 18 knots because you're behind schedule. A target appears on radar with a steady bearing and decreasing range. Rule 7 says: if in doubt, assume risk exists. Rule 6 says: you should never have been doing 18 knots in that visibility in the first place.

Common misunderstanding: Many cadets think "safe speed" only applies in restricted visibility. It applies always — traffic density, manoeuvrability, draught, and background lighting all factor in, even in clear weather in a busy strait.

Rule 8 – Action to Avoid Collision

Plain language: Any action taken must be positive, made in ample time, and be large enough to be readily apparent to the other vessel. Small, hesitant alterations are dangerous because the other ship may not notice them.

Bridge scenario: You alter course 5 degrees to starboard hoping to open the CPA. The other vessel's OOW, watching your masthead lights, sees nothing meaningful change and continues to close. A 30-degree alteration would have been unmistakable.

Common misunderstanding: "Any alteration is better than none" — false. A token alteration that isn't obvious on the other vessel's radar or visually can create more danger, because it might be misread as a random course change rather than a collision-avoidance manoeuvre.

Rules 9 & 10 – Narrow Channels and Traffic Separation Schemes

Plain language: Rule 9: keep to the starboard side of a narrow channel; a vessel of less than 20m or a sailing vessel should not impede a vessel that can only navigate safely within the channel. Overtaking in a narrow channel requires the overtaken vessel's agreement if a two-blast/one-blast signal exchange under Rule 34 is needed. Rule 10 governs Traffic Separation Schemes (TSS): use the lane matching your direction, avoid crossing lanes at a shallow angle (cross at as near right angles as practicable), and don't anchor in a scheme without good reason.

Bridge scenario: You're transiting the Dover Strait TSS. A vessel wants to cross your lane. Under Rule 10, they should cross at as near to right angles as practicable — if they're crawling across at 20 degrees, they're not complying, and you need to be alert because they're increasing their time in your lane.

Common misunderstanding: Many candidates think TSS rules override the steering and sailing rules (13–17). They don't — Rules 13 to 17 still apply within a TSS. A crossing situation in a TSS is still resolved by Rule 15, not by TSS etiquette alone.

Rules 13, 14 & 15 – Overtaking, Head-On, and Crossing Situations

This trio forms the backbone of situational awareness questions.

• Rule 13 (Overtaking): Any vessel coming up on another from more than 22.5° behind her beam (i.e., in the overtaking vessel's sternlight sector) is the overtaking vessel and must keep clear until fully past and clear — regardless of what type of vessel is overtaken.
• Rule 14 (Head-on): When two power-driven vessels meet on reciprocal or nearly reciprocal courses, both must alter course to starboard, passing port-to-port.
• Rule 15 (Crossing): When two power-driven vessels are crossing so as to involve risk of collision, the vessel with the other on her own starboard side is the give-way vessel and must avoid crossing ahead.

Bridge scenario: You spot a vessel fine on your starboard bow, tracks converging. If she's showing you her port sidelight (red), you may be head-on or crossing — check the bearing. If she's crossing from your starboard side, you give way. Turn early, turn boldly, and turn to starboard where possible so she can see your action and you pass behind her stern.

Common misunderstanding: Cadets often confuse "overtaking" with "crossing." The 22.5° aft-of-beam sternlight sector is the legal test — not just "is she faster and coming up." Also commonly missed: once you are the overtaking vessel under Rule 13, you remain the give-way vessel throughout the manoeuvre, even if the geometry later starts to resemble a crossing situation.

Rules 16 & 17 – Action by Give-Way and Stand-On Vessels

Plain language: Rule 16: the give-way vessel must take early and substantial action to keep well clear. Rule 17: the stand-on vessel should initially maintain course and speed, but may take action if it becomes apparent the give-way vessel isn't acting appropriately — and must take avoiding action (any action, including slowing or stopping) if collision cannot be avoided by the give-way vessel's action alone.

Bridge scenario: You are stand-on in a crossing situation. The other vessel isn't altering course as she should. Rule 17 doesn't mean sit there hoping — once it's clear she isn't giving way, you're permitted (and eventually obligated) to act. Rule 17(c) even specifies: if you must act, avoid altering course to port for a vessel on your own port side in a crossing situation where that would be the wrong response — think it through, don't panic-turn.

Common misunderstanding: The biggest exam trap: candidates believe the stand-on vessel can never act until collision is imminent. In fact, Rule 17(a)(ii) permits action as soon as it's apparent the give-way vessel isn't complying — you don't have to wait until the last minute, though last-minute action, if needed, should avoid turning to port for a vessel on your port bow, and should not be a turn towards a vessel on your own beam or abaft it if that worsens the situation.

Rule 18 – Responsibilities Between Vessels

Plain language: This establishes the hierarchy: power-driven vessels give way to sailing vessels, vessels engaged in fishing, vessels not under command (NUC), restricted in ability to manoeuvre (RAM), and generally to vessels constrained by draught, in roughly that pecking order — with some nuance depending on the exact combination.

Bridge scenario: A dredger displaying RAM shapes is working mid-channel. Even though you're on a "clearer" course, you must give her way — she cannot manoeuvre to avoid you as easily as you can avoid her.

Common misunderstanding: Cadets sometimes think a sailing vessel always has right of way over everyone. Not true — a sailing vessel must still keep clear of a vessel NUC, RAM, or engaged in fishing, and Rule 9/10 provisions about narrow channels and TSS impedance still apply to her too.

Rule 19 – Restricted Visibility

Plain language: In restricted visibility, none of Rules 13–17 apply in their normal visual sense (you likely can't see the other vessel), and action must be based on radar detection alone where visual contact isn't possible. Critically: avoid altering course toward a vessel forward of the beam (unless overtaking), and avoid altering course toward a vessel abeam or behind the beam being overtaken.

Bridge scenario: Thick fog, a radar contact fine on your port bow, closing. Rule 19 tells you: don't turn to port toward her. A turn to starboard, or a reduction in speed, is the safer response.

Common misunderstanding: Many candidates try to apply Rule 15's give-way/stand-on logic in fog. That's wrong — in restricted visibility there's no "stand-on vessel" concept the same way; both vessels must act prudently based on radar plot, and course alterations toward a forward contact are specifically discouraged.

Lights, Shapes, and Sound Signals

• Lights (Rules 20–31): Know your sidelights (112.5° arcs), sternlight (135° arc), masthead lights, and the all-round lights for NUC (two red), RAM (red-white-red), fishing (red over white), and anchored (single all-round white, or two if over 100m).
• Shapes (day signals): Ball, diamond, cone combinations mirror the light patterns for day use — a vessel at anchor shows one ball; NUC shows two balls.
• Sound signals (Rule 34/35): One short blast = altering to starboard; two short = altering to port; three short = operating astern propulsion; five short = doubt/danger signal. In restricted visibility, one prolonged blast every two minutes for a power vessel underway.

Common misunderstanding: Confusing manoeuvring signals (Rule 34, used in sight of one another) with fog signals (Rule 35, used regardless of visibility on a timed basis). They serve entirely different purposes.

Bringing It Together

The COLREGs aren't a memory test — they're a decision-making framework. On the exam and on the bridge, the process is always the same: assess the situation, identify who's who under the hierarchy, act early and obviously, and never stop looking and listening. Learn the rules cold, but more importantly, learn to think in COLREGs — because one day the fog won't lift on cue, and the exam questions become real ships.