Ships do not have lanes, traffic lights or brakes in the same way as cars. They operate in changing weather, at different speeds and with radically different manoeuvring capabilities. The International Regulations for Preventing Collisions at Sea, 1972—usually called the COLREGs—provide the shared rules that help vessels predict one another’s actions and avoid collision. They are essential knowledge for officers and useful awareness for recreational sailors, passengers and anyone interested in marine safety.
What the COLREGs are—and what they are not
The COLREGs apply to vessels on the high seas and waters connected to them that are navigable by seagoing vessels. They contain 41 rules in six parts, together with technical annexes covering lights, shapes, sound-signalling appliances and distress signals. They are international rules, but local port regulations, traffic services and pilotage requirements may add further obligations. A safe navigator must know both the international framework and the local information for the voyage.
The rules do not operate like a right-of-way certificate. Their central purpose is to avoid collision. A vessel that technically has a “stand-on” role must still monitor the situation and act if the other vessel is not taking appropriate action. Rule 2 makes clear that responsibility is not removed by relying mechanically on a rule or by ignoring the ordinary practice of seamen and the special circumstances of a case.
The foundation: lookout, safe speed and risk of collision
Rules 5, 6 and 7 are the heart of collision avoidance. Rule 5 requires a proper lookout by sight, hearing and all available means appropriate to the conditions, so that the bridge team can make a full appraisal of the situation and collision risk. This means looking outside as well as at screens. It also means using radar, AIS, VHF information and charts intelligently without assuming any single source is perfect.
Rule 6 requires every vessel to proceed at a safe speed. Safe speed is not a single number in knots. It depends on visibility, traffic density, manoeuvrability, background lights, wind and sea state, proximity of hazards, draught in relation to available water and, for radar-equipped ships, radar limitations and the ability to detect small targets. A speed that is safe in open water on a clear night can be unsafe in a crowded approach in rain or fog.
Rule 7 says every vessel must use all available means to determine if collision risk exists. A constant bearing combined with decreasing range is a classic warning sign, but the rule cautions against assumptions based on scanty information—particularly scanty radar information. The officer of the watch should acquire targets early, use visual and electronic evidence together, check CPA and TCPA trends and call the master in accordance with standing orders whenever doubt exists.
Rule 8: make the avoiding action early and obvious
When action is necessary, Rule 8 requires it to be positive, made in ample time and with due regard to good seamanship. Small, hesitant alterations can confuse other vessels and may be ineffective. A bold alteration of course is often easier for another ship to recognise than a tiny change. Reducing speed, stopping or reversing can also be decisive where space, traffic and propulsion response permit. The right action depends on the whole picture; a manoeuvre that solves one close-quarters situation must not create another one.
Bridge teams should communicate intentions when necessary, but VHF conversation never replaces compliance with the Rules. Informal phrases such as “you go first” can be ambiguous across language and radio-quality differences. The safest practice is to make a clear, Rule-consistent manoeuvre, observe the other vessel’s response and continue monitoring until the danger has passed.
Any visibility: narrow channels and traffic separation schemes
Rules 9 and 10 are particularly important in confined waters. In a narrow channel or fairway, a vessel should keep as near as safe and practicable to the outer limit on her starboard side. Small vessels and sailing vessels must not impede a vessel that can safely navigate only within that channel. Crossing a channel is prohibited if it would impede such a vessel. The practical lesson is simple: a deep-draught ship in a channel may have very little freedom to turn or leave the dredged track.
Traffic separation schemes organise traffic flows in busy areas. Vessels using a lane should proceed in the appropriate traffic direction; ships joining or leaving should do so at a small angle to the flow; vessels crossing should do so, as far as practicable, at right angles. A scheme does not remove the duty to keep a lookout, assess risk or avoid collision. Fishing vessels, sailing vessels, pilot vessels and other craft all have specific considerations, but no one should assume that another ship will have unlimited room.
When vessels are in sight: overtaking, head-on and crossing
Rules 11 to 18 apply when vessels are in sight of one another. The first question is always: which situation actually exists? Misidentifying the situation is a common route to error.
Overtaking: A vessel coming up from more than 22.5 degrees abaft another vessel’s beam is an overtaking vessel and must keep out of the way. If there is doubt, treat the situation as overtaking. The overtaking responsibility continues until the vessel is finally past and clear; a change of relative bearing during the manoeuvre does not automatically convert it into a crossing case.
Head-on: When two power-driven vessels meet on reciprocal or nearly reciprocal courses with risk of collision, each should alter course to starboard so they pass port-to-port. Recognition depends on lights at night and the apparent heading by day. If a situation is uncertain, prudent navigation demands early assessment rather than waiting for perfect certainty.
Crossing: When two power-driven vessels cross so as to involve risk of collision, the vessel that has the other on her own starboard side should keep out of the way and, if circumstances allow, avoid crossing ahead. The other vessel is generally the stand-on vessel. “Stand-on” does not mean “do nothing”: maintain course and speed while the situation is normal, but be prepared to act when it becomes apparent that the give-way vessel is not taking appropriate action.
Responsibilities between vessel types
Rule 18 sets out a hierarchy of responsibilities in particular situations. A power-driven vessel underway should keep out of the way of a vessel not under command, a vessel restricted in her ability to manoeuvre, a vessel engaged in fishing and a sailing vessel. A sailing vessel should keep out of the way of vessels not under command, restricted in ability to manoeuvre and fishing. However, the hierarchy is not a licence to create danger. A vessel constrained by her draught, for example, may display relevant signals, but still has duties under the rules and must navigate with due care.
Navigation students should learn the definitions, lights and shapes associated with each category. “Not under command” means a vessel cannot manoeuvre as required by the rules because of exceptional circumstances. “Restricted in her ability to manoeuvre” refers to the nature of the work being performed, such as certain dredging, cable-laying or replenishment operations. These are operational conditions with real limits, not labels that can be used for convenience.
Restricted visibility: Rule 19
Restricted visibility is a special case: vessels may not be in sight of one another, so the visual crossing and head-on rules do not apply in the same way. Every vessel must proceed at a safe speed adapted to the conditions; power-driven vessels should have engines ready for immediate manoeuvre. A vessel that detects another by radar alone must determine whether a close-quarters situation or collision risk exists and take avoiding action in ample time. Certain alterations, especially turning to port for a vessel forward of the beam or turning toward a vessel abeam or abaft the beam, should be avoided so far as possible.
Hearing a fog signal apparently forward of the beam is another critical trigger. A vessel should reduce speed to the minimum at which it can be kept on course and, if necessary, take all way off. The bridge team must integrate radar plotting, sound signals, engine readiness, lookouts and conservative speed. In fog, time and distance disappear much faster than they seem to from the chart table.
Lights, shapes and sound signals
Lights and shapes allow vessels to communicate status and aspect without radio. Masthead lights, sidelights, sternlights, towing lights, all-round lights, day shapes and special combinations identify whether a vessel is underway, at anchor, fishing, towing, aground, restricted, not under command or engaged in pilotage. Learning them is a visual language exercise. Students should practise both directions: identify a vessel from the lights seen and select the correct lights for a stated operation.
Sound signals are equally important. Manoeuvring signals indicate alterations of course or astern propulsion in sight of another vessel, while fog signals communicate vessel type and condition in restricted visibility. Sound signals must be produced by correctly maintained equipment and interpreted in context. A whistle signal is a warning, not a magic shield against collision.
COLREGs and modern bridge technology
ECDIS, radar, AIS, ARPA, GNSS and route-exchange tools improve situational awareness, but none makes the rules obsolete. AIS information can be inaccurate, target tracking can be lost and electronic displays can become cluttered. The most resilient bridge team cross-checks the planned route, visual scene, radar picture and navigational sensors. It avoids overconfidence and manages workload so that someone remains alert to the developing situation outside.
Practical habits that prevent close-quarters situations
- Look out early and continuously; do not allow screen work to replace the visual scan.
- Acquire and assess targets before CPA becomes small.
- Use a speed that leaves time and sea room to act.
- Make avoiding action positive, early and easy for others to understand.
- Check the result of every manoeuvre until vessels are past and clear.
- Call the master early whenever visibility, traffic, equipment status or doubt requires it.
- Use VHF carefully and never negotiate yourself out of the Rules.
Final perspective
COLREG competence is not memorising a list of give-way vessels. It is a disciplined way of thinking: maintain a full lookout, create time and distance, recognise the actual encounter, act decisively and never surrender responsibility for safety. That is why the Rules remain central even as shipping becomes more automated.