Who the rules apply to, and key definitions

The rule in plain words

Who and where?Every vessel, of any size or flag, on the high seas and in connected waters: coasts, harbours, estuaries, rivers… COLREG does not switch off near land.
What about local rules?A harbour, river or lake can have special rules from its authority. They apply there, but must conform as closely as possible to COLREG.
Extra signals?Governments may add signals for warships, convoys and vessels fishing as a fleet. They must never be mistakable for COLREG signals.
Traffic and special vessels?Traffic separation schemes are adopted by the IMO. A special vessel that cannot fully comply on the number, position, range or arc of visibility of lights or shapes, or the disposition and characteristics of sound-signalling appliances, follows the closest compliance her Government determines.

A seagoing ship coming in from the open sea through the harbour entrance: COLREG applies on the high seas and in all connected waters navigable by seagoing vessels. Photorealistic image generated from a public-domain photo by Editor5807 (Wikimedia Commons).

Before you read on: what would you do?

Question 1/1

Where does COLREG apply?

Frequent mistakes

Wrong: "COLREG only applies on the high seas."
Right: It also applies in connected navigable waters: coasts, harbours, rivers…
Wrong: "Vessels fishing as a fleet may use additional whistle signals."
Right: Extra whistle signals are only for warships and convoys. Fleet fishing: lights or shapes only.
Wrong: "Paragraph (e) exempts special vessels."
Right: It only adapts lights, shapes and sound appliances. Everything else still applies.

Exam keys & interpretation

Options with "only", "exclusively", "cancels" or "exempts" are usually the trap.
Scope question → "all vessels, on the high seas and connected navigable waters".
When you read "the Organization", think IMO.

How to read it

Connection is the key: an inland lake with no connection to the high seas is outside COLREG.

COLREG is the common baseline; local rules complete it in their area without contradicting it.

Key points

All vessels · high seas + connected navigable waters.
Local rules: yes, but as close as possible to COLREG.
"The Organization" = IMO → adopts traffic separation schemes.
Special vessel → closest possible compliance, only for lights, shapes and sound-signalling appliances.

Test your knowledge

3 questions to check it. Pick an answer to see why.

Question 1/3

A harbour has special rules from its authority. What happens?

Official text

IMO COLREG 1972 U.S. Coast Guard — International Navigation Rules (2024)

Full wording of the rule, reproduced from the official source below.

(a) These Rules shall apply to all vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels. (b) Nothing in these Rules shall interfere with the operation of special rules made by an appropriate authority for roadsteads, harbors, rivers, lakes or inland waterways connected with the high seas and navigable by seagoing vessels. Such special rules shall conform as closely as possible to these Rules. (c) Nothing in these Rules shall interfere with the operation of any special rules made by the Government of any State with respect to additional station or signal lights, shapes or whistle signals for ships of war and vessels proceeding under convoy, or with respect to additional station or signal lights or shapes for fishing vessels engaged in fishing as a fleet. These additional station or signal lights, shapes or whistle signals shall, so far as possible, be such that they cannot be mistaken for any light, shape or signal authorized elsewhere under these Rules. (d) Traffic separation schemes may be adopted by the Organization for the purpose of these Rules. (e) Whenever the Government concerned shall have determined that a vessel of special construction or purpose cannot comply fully with the provisions of any of these Rules with respect to the number, position, range or arc of visibility of lights or shapes, as well as to the disposition and characteristics of sound-signaling appliances, such vessel shall comply with such other provisions in regard to the number, position, range or arc of visibility of lights or shapes, as well as to the disposition and characteristics of sound-signaling appliances, as her Government shall have determined to be the closest possible compliance with these Rules in respect to that vessel.

Source:

U.S. Coast Guard — International Navigation Rules (2024)