What Is COLREGS? The 72 COLREGS and IRPCS Explained

If you've started studying for a Coast Guard license or just bought your first boat, you've probably seen the word COLREGS everywhere. Here's the short answer, and then a friendly walk through everything around it.

COLREGS stands for the International Regulations for Preventing Collisions at Sea, 1972. They're the international "rules of the road" for vessels, covering who gives way, what lights and shapes vessels show, and what sound signals mean. People also call them the 72 COLREGS, the COLREGs, the International Rules, or IRPCS.

What the letters stand for

• COLREGS comes from "Collision Regulations," the short name for the International Regulations for Preventing Collisions at Sea. You'll see it written COLREGS, COLREGs, or COLREG.
• 72 COLREGS adds the year of the Convention, 1972, to separate it from earlier versions. The U.S. Navigation Rules use this name throughout.
• IRPCS is simply the initials of International Regulations for Preventing Collisions at Sea. You'll see it more often in British and Commonwealth materials, but it means the same rules.

Where the 72 COLREGS came from

The official U.S. Navigation Rules from the Coast Guard Navigation Center (NAVCEN) give the history in their introduction:

• The International Rules "were formalized in the Convention on the International Regulations for Preventing Collisions at Sea, 1972, and became effective on July 15, 1977."
• The 72 COLREGS were developed by the Inter-Governmental Maritime Consultative Organization (IMCO), which in May 1982 was renamed the International Maritime Organization (IMO).
• Vessels flying the flags of states that ratified the treaty are bound by the rules. The United States ratified it, and Congress adopted the rules as the International Navigational Rules Act of 1977.
• The rules have been amended several times since. The NAVCEN introduction lists amendment rounds that took effect in 1983, 1989, 1991, 1995, 2003, and 2009, the last one updating the distress signals.

The rules even look back before 1972. Rule 38 gives certain exemptions to vessels that comply with the 1960 International Regulations and whose keels were laid, or that were at a corresponding stage of construction, before the 1972 rules entered into force.

How the COLREGS are organized

The 72 COLREGS have 41 rules in six parts, plus Annexes:

The Annexes cover the technical details: Annex I for positioning and technical details of lights and shapes, Annex II for additional signals for fishing vessels fishing in close proximity, Annex III for sound signal appliances, and Annex IV for distress signals.

For most mariners and every Rules of the Road exam, Parts A to E are the heart of it. Part F is about how countries are audited, not how vessels behave. You can read every one of Rules 1 to 38 in plain English on our rules index.

The ideas at the core of the rules

You don't need to memorize all 38 rules to understand how they think. A handful of ideas carry most of the weight:

• Good seamanship always applies. Rule 2 says nothing in the rules excuses neglecting any precaution required by the ordinary practice of seamen, and it allows departing from the rules when that's needed to avoid immediate danger.
• Always keep a look-out. Rule 5 requires a proper look-out by sight and hearing, and by all available means, at all times.
• Always go a safe speed. Rule 6 requires a safe speed at all times, not just in fog.
• If in doubt, assume risk of collision. Rule 7 says so directly, and treats a steady compass bearing of an approaching vessel as a sign that risk of collision exists.
• Act early and obviously. Rule 8 calls for action that's positive, made in ample time, and large enough to be readily apparent to the other vessel.
• Know your place in the pecking order. Rule 18 sets out who keeps out of whose way, with vessels not under command and vessels restricted in their ability to maneuver near the top.

Practice this on your phone. COLREGS: Rules of the Road puts all 1,272 questions, with diagrams and spaced repetition, on your iPhone and iPad. Get the iOS app

COLREGS vs the U.S. Inland Rules

In the United States, the 72 COLREGS aren't the whole story. The U.S. also has the Inland Navigation Rules, now in 33 CFR Part 83. NAVCEN explains that the Inland Navigational Rules Act of 1980 unified the old Inland Rules, Western Rivers Rules, Great Lakes Rules, and their pilot rules, and that the Inland Rules took effect on December 24, 1981, except on the Great Lakes, where they took effect on March 1, 1983.

The two rule sets use the same numbering and are very similar. Inland Rule 1 says the Inland Rules are the "special rules made by an appropriate authority" that International Rule 1(b) allows. Where they differ, the differences matter, especially in Rule 9 (narrow channels), Rule 14 and Rule 15 on the Great Lakes and Western Rivers, Rule 24 (pushing ahead), and Rule 34 (maneuvering signals). Our Inland vs International guide covers them in detail.

Which set applies depends on where you are. The COLREGS demarcation lines in 33 CFR Part 80 mark the boundary: inside the lines, Inland Rules apply, and outside them, the 72 COLREGS apply.

Who has to follow COLREGS?

International Rule 1(a) says the rules apply "to all vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels." And Rule 3 defines "vessel" broadly, to include "every description of watercraft, including non-displacement craft, WIG craft, and seaplanes," used or capable of being used as a means of transportation on water.

So it isn't just ships. A kayak, a sailboat, and a container ship are all vessels under the rules. That's why boaters, not only professional mariners, benefit from knowing them.

Test yourself

Here are real questions from our 1,272-question bank, word for word.

How to start learning COLREGS

1. Get the official text. It's free. See our COLREGS PDF and free resources page for the NAVCEN and eCFR links.
2. Learn the structure first. Knowing that Part B is steering, Part C is lights, and Part D is sounds makes everything else easier to file away.
3. Practice with real questions. Our free web study tool has 1,272 Coast Guard style questions.
4. If you're testing for a license, read our USCG Rules of the Road test guide.

Ready for exam-style practice? Drill your weak spots with missed-question review in COLREGS: Rules of the Road for iPhone and iPad. Download on the App Store

Frequently asked questions

What does COLREGS stand for?

COLREGS stands for the International Regulations for Preventing Collisions at Sea. The full name of the current version is the International Regulations for Preventing Collisions at Sea, 1972, often called the 72 COLREGS.

What are the 72 COLREGS?

They're the international navigation rules formalized in the 1972 Convention on the International Regulations for Preventing Collisions at Sea, which became effective on July 15, 1977. They set the steering and sailing rules, lights and shapes, and sound signals for vessels.

What is IRPCS?

IRPCS is short for International Regulations for Preventing Collisions at Sea. It's another name for the same rules as COLREGS.

Are COLREGS the same as the U.S. Inland Rules?

No, but they're very similar and use the same rule numbers. The U.S. Inland Navigation Rules (33 CFR Part 83) apply shoreward of the COLREGS demarcation lines, and the 72 COLREGS apply outside them.

How many rules are in COLREGS?

The 72 COLREGS have 41 rules in Parts A to F, plus four Annexes. Rules 1 to 38 cover how vessels operate, and Rules 39 to 41 cover verification of compliance with the Convention.

Keep studying

• All 38 rules explained
• COLREGS demarcation lines explained
• COLREGS PDF and free study resources
• USCG Rules of the Road test guide
• Free web study tool with 1,272 questions