What is COLREGS?

The Origin and Purpose of COLREGS

The International Regulations for Preventing Collisions at Sea — universally referred to as COLREGS — are the maritime equivalent of traffic law. They are the binding international rules that govern how vessels must behave to avoid collisions. Every vessel on navigable waters, from an ocean liner to a sailboat, operates under a version of these rules.

The current COLREGS stem from the 1972 Convention on the International Regulations for Preventing Collisions at Sea, adopted by the International Maritime Organization (IMO) and effective since July 1977. The convention replaced earlier, fragmented national and international rule sets that had been causing confusion — and collisions — since the age of steam. Before standardization, vessels from different nations were sometimes following contradictory rules when they met at sea.

The fundamental problem COLREGS solves: when two vessels approach each other on the water, both skippers need to make the same prediction about what the other will do. If one assumes right-of-way while the other does the same, a collision follows. COLREGS creates a shared language of expectation — a set of rules so widely understood that a US sailor and a Norwegian freighter captain can approach each other with confidence that they both know who yields.

Who Must Follow COLREGS

COLREGS applies to all vessels upon the high seas and waters connected therewith navigable by seagoing vessels. This broad language includes commercial ships, naval vessels, fishing boats, and recreational sailboats and powerboats. There is no exemption based on vessel size — a 20-foot sailboat is subject to the same fundamental rules as a 900-foot container ship.

In the United States, two parallel rule sets exist. The International COLREGS apply on the high seas and in waters seaward of the COLREGS demarcation lines — the lines drawn on US nautical charts that separate international from inland waters. The Inland Navigation Rules (sometimes called the Inland Rules) apply to the waters landward of those demarcation lines, which includes most US harbors, rivers, the Great Lakes, and many coastal waters. The Inland Rules are closely modeled on COLREGS but differ in specific ways — those differences are covered in detail in the Inland vs. International Rules page.

Naval vessels have a special status: they are bound by COLREGS but also operate under military rules that may take precedence in some circumstances (particularly in active military operations). As a recreational sailor, treat any military vessel as you would any other vessel under the rules — but give them wide clearance and expect that they may not always be free to maneuver conventionally.

No one is exempt from look-out obligations. Rule 5 of COLREGS requires that every vessel at all times maintain a proper look-out by sight and hearing. This rule is violated on recreational boats with remarkable frequency — a crew member below, loud music on deck, or an inattentive helmsperson can eliminate the look-out entirely. The consequences are legal as well as physical.

How COLREGS Are Organized

COLREGS consists of 38 rules organized into five parts, plus five annexes containing technical specifications. Understanding the organization helps you navigate the rules themselves.

Part A — General (Rules 1–3): Defines the scope of application (Rule 1), the requirement to follow the rules (Rule 2 — the 'General Prudential Rule' that allows deviation from the rules when necessary to avoid immediate danger), and key definitions (Rule 3 — what constitutes a vessel, power-driven vessel, sailing vessel, vessel not under command, and more).

Part B — Steering and Sailing Rules (Rules 4–19): The core of COLREGS. Divided into three sections: conduct of vessels in any condition of visibility (Rules 4–10, covering look-out, safe speed, risk of collision, and action to avoid collision), conduct in sight of one another (Rules 11–18, covering sailing vessels, head-on, crossing, and overtaking situations), and conduct in restricted visibility (Rule 19). This is where right-of-way, give-way, and stand-on obligations live.

Part C — Lights and Shapes (Rules 20–31): Specifies what lights and shapes vessels must display, when, and how. The arc of each light, its color, its range, and when it must be shown is all here.

Part D — Sound and Light Signals (Rules 32–37): Specifies the sound signals vessels use to indicate their maneuvers, warn of danger, and communicate status in restricted visibility.

Part E — Exemptions (Rule 38): Allows some older vessels built before the rules came into force to comply with modified requirements temporarily.

Annexes: Technical specifications for light positions, sound signal equipment, and additional signals — the engineering details that support the rules.