COLREGs Explained: Maritime Collision Regulations Guide

The International Regulations for Preventing Collisions at Sea, universally known as COLREGs, are the rules of the road governing vessel navigation on the world's oceans and connected waterways. Adopted by the IMO on October 20, 1972, and effective since July 15, 1977, the COLREGs establish how vessels interact, who gives way, what lights and shapes must be displayed, and what sound signals are required. At least 155 nations representing approximately 99% of global shipping tonnage have ratified the convention.

For every mariner, from commercial ship officers to weekend boaters, knowing these rules is not just a legal obligation. Getting them wrong can cost lives.

How the COLREGs Are Structured

The COLREGs contain 41 rules organized into six parts, plus four technical annexes.

Part A (Rules 1-3): General. Establishes that the rules apply to all vessels on the high seas and connected navigable waters. Rule 2 is critical: no rule excuses a mariner from the obligation to exercise good seamanship and due caution, even when strict compliance with the rules might lead to danger.

Part B (Rules 4-19): Steering and Sailing Rules. The operational core of the COLREGs. Section I covers conduct in any visibility. Section II covers vessels in sight of one another. Section III covers conduct in restricted visibility.

Part C (Rules 20-31): Lights and Shapes. Specifies navigation lights and day shapes required for different vessel types and conditions.

Part D (Rules 32-37): Sound and Light Signals. Defines whistle signals for maneuvering, warning, and restricted visibility, plus distress signals.

Part E (Rule 38): Exemptions. Allows certain older vessels limited exemptions from specific light and sound requirements.

Part F (Rules 39-41): Verification of Compliance. Added in 2013 to support the IMO Member State Audit Scheme.

Key Rules Every Mariner Must Know

Rule 5: Lookout

Every vessel shall at all times maintain a proper lookout by sight and hearing as well as by all available means. A proper lookout uses eyes, ears, radar, AIS, and every other available technology to make a full appraisal of the situation and risk of collision.

Rule 6: Safe Speed

Every vessel must proceed at a safe speed at all times so that proper and effective action can be taken to avoid collision. "Safe" depends on visibility, traffic density, sea state, vessel maneuverability, radar effectiveness, and depth of water. Safe speed is a judgment, not a fixed number.

Rule 7: Risk of Collision

A vessel must use all available means to determine if a risk of collision exists. A consistent compass bearing on an approaching vessel with decreasing range is the primary indicator. If any doubt exists, the rule directs mariners to assume risk is present.

Rule 9: Narrow Channels

A vessel proceeding along a narrow channel or fairway shall keep as near to the outer limit on her starboard side as is safe and practicable. Vessels under 20 meters and sailing vessels shall not impede vessels that can safely navigate only within the channel. No vessel shall cross a narrow channel if doing so would impede such a vessel.

Rule 10: Traffic Separation Schemes

Rule 10 governs conduct in IMO-adopted traffic separation schemes, of which nearly 200 now operate worldwide. Vessels using a scheme must proceed in the appropriate traffic lane in the general direction of flow and avoid crossing lanes wherever practicable. When crossing is necessary, the vessel must do so at as near a right angle to the flow as possible. Fishing vessels and vessels under 20 meters shall not impede vessels following a traffic lane.

Rules 13-17: Right-of-Way Between Vessels in Sight

Rule 13 (Overtaking): An overtaking vessel must keep clear of the vessel being overtaken, regardless of vessel type.
Rule 14 (Head-on): Two power-driven vessels meeting head-on shall each alter course to starboard to pass port-to-port.
Rule 15 (Crossing): When two power-driven vessels are crossing, the vessel with the other on her starboard side is the give-way vessel.
Rule 16 (Give-way vessel): The give-way vessel must take early and substantial action to keep well clear.
Rule 17 (Stand-on vessel): The stand-on vessel shall maintain course and speed. If the give-way vessel fails to act, the stand-on vessel may, and eventually must, take action to avoid collision.

Rule 18: Responsibilities Between Vessels

A hierarchy determines right-of-way between vessel types (from most restricted to least restricted): vessel not under command, vessel restricted in ability to maneuver, vessel constrained by draft, vessel engaged in fishing, sailing vessel, power-driven vessel. A power-driven vessel gives way to all categories above it.

COLREGs vs. U.S. Inland Rules

The United States ratified the COLREGs and enacted the Inland Navigational Rules Act of 1980 for U.S. inland waters. COLREGs demarcation lines define where international rules end, and inland rules begin.

Key differences include whistle signal protocols in crossing and meeting situations, and special provisions for narrow channels on the Western Rivers. The USCG Navigation Rules and Regulations Handbook publishes both rule sets side by side for reference. Carrying the current edition of the COLREGs book on board satisfies the requirement to have navigation rules accessible to the officer of the watch.

Navigation Lights, Day Shapes, and Sound Signals

Part C specifies the lights every vessel must display between sunset and sunrise and during restricted visibility. A power-driven vessel underway displays masthead lights, sidelights (red to port, green to starboard), and a sternlight. Specialized vessels carry additional signals: two all-round red lights for a vessel not under command, white over red for a pilot vessel, green over white for a vessel engaged in trawling. The Poster: Light, Shape, and Sound Signals provides a visual quick-reference for bridge teams.

Rule 34 governs maneuvering signals: one short blast for altering course to starboard, two for port, three for operating astern propulsion, and five or more short blasts as a danger signal. In restricted visibility, Rule 35 requires fog signals at specified intervals. Vessels of 12 meters or more must carry a whistle and bell; vessels of 100 meters or more additionally require a gong.

Why COLREGs Knowledge Is Tested for Licensing

COLREGs proficiency appears on every USCG license examination, from OUPV through unlimited master. Questions cover rule interpretation, right-of-way scenarios, light recognition, and sound signal identification. Deck officer exam guides and the International Code of Signals support exam preparation.

FAQs

Q. Do COLREGs apply to kayaks and paddleboards?

Yes. Rule 1 applies to "all vessels," and Rule 3 defines a vessel as "every description of water craft." Kayaks, paddleboards, rowboats, and canoes are all considered vessels and must comply with applicable rules, particularly lookout, safe speed, and collision avoidance.

Q. What is the penalty for violating COLREGs?

Penalties vary by jurisdiction. In the U.S., violations can result in civil fines, license suspension or revocation, and criminal charges if a violation causes injury or death. Maritime courts worldwide reference COLREGs when determining fault in collision cases.

Q. Are autonomous vessels subject to COLREGs?

Yes. COLREGs currently apply to all vessels regardless of crewing arrangement. The IMO's non-mandatory MASS Code is expected to be adopted at MSC 111 in May 2026, followed by an experience-building phase. A mandatory code targeting January 1, 2032, will address amendments to SOLAS and potentially COLREGs. However, the IMO has agreed that COLREGs do not require amendment at this stage to accommodate MASS operations. Each autonomous vessel will have a designated human "master" responsible for operations from a remote operations center.