COLREGS Rule 1 — Application

Rule Text

What it means on the water

• →COLREGS apply on the high seas and any connected waters navigable by seagoing vessels.
• →Local authorities may make special rules for harbors, rivers, and inland waterways — this is how the US Inland Rules coexist with COLREGS.
• →Demarcation lines (established by the Coast Guard) separate COLREGS waters from Inland Rules waters in the US.
• →Where local rules exist, they must conform as closely as possible to COLREGS.
• →The rules apply to all vessels, regardless of flag, type, or propulsion.

Common exam mistakes

• ✗Thinking COLREGS only apply in international waters — they also apply on US waters seaward of the demarcation lines.
• ✗Confusing COLREGS with US Inland Rules — different rules apply on each side of the demarcation line.
• ✗Missing that special rules must still conform as closely as possible to the International Rules.

USCG exam questions — Rule 1

These questions are drawn from the same pool used in real USCG licensing exams. Correct answers and explanations are shown.

1. 1. The COLREGS Demarcation Lines define the boundary between which two rulesets?

   • A.Inland Rules and 72 COLREGS✓
   • B.Federal Rules and State Rules
   • C.Inland Rules and U.S. Coast Pilot
   • D.72 COLREGS and the Great Lakes Rules

   Why: The COLREGS Demarcation Lines, published at 33 CFR Part 80, separate the waters where the U.S. Inland Navigation Rules apply (inshore side) from waters where 72 COLREGS apply (seaward side). There are no separate 'Great Lakes Rules' — the Inland Rules cover the Great Lakes.

2. 2. A vessel anchored in a bay on the seaward side of the COLREGS Demarcation Line is governed by which rules?

   • A.U.S. Inland Navigation Rules
   • B.72 COLREGS✓
   • C.Whichever set the master elects
   • D.Both rulesets simultaneously

   Why: Position relative to the COLREGS Demarcation Line determines which ruleset applies — seaward of the line means 72 COLREGS govern, regardless of whether the vessel is underway or anchored.

3. 3. A vessel transiting from the open ocean across the COLREGS Demarcation Line into a harbor must:

   • A.Switch from 72 COLREGS to U.S. Inland Rules at the demarcation line✓
   • B.Continue using 72 COLREGS until anchored
   • C.Apply Great Lakes Rules inside the harbor
   • D.Request a waiver from the Coast Guard before switching rules

   Why: The moment a vessel crosses the COLREGS Demarcation Line from seaward to the harbor side, 72 COLREGS no longer apply and the U.S. Inland Navigation Rules govern. No waiver or notification is required.

4. 4. A U.S.-flagged vessel on the high seas collides with a foreign vessel. Which rules govern the collision?

   • A.U.S. Inland Navigation Rules
   • B.72 COLREGS✓
   • C.The rules of the flag state of the vessel at fault
   • D.U.S. Federal Maritime Law, regardless of position

   Why: 72 COLREGS apply on the high seas and waters connected therewith that are navigable by seagoing vessels (Rule 1(a)). The Inland Rules do not apply on the high seas. Both vessels are subject to 72 COLREGS regardless of flag state.

5. 5. The International Regulations for Preventing Collisions at Sea (COLREGS) apply to:

   • A.All vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels✓
   • B.Only vessels over 20 meters in length operating on the high seas
   • C.Vessels of signatory nations operating beyond the 12-mile territorial sea
   • D.All vessels operating beyond the boundaries established by the US Inland Rules

   Why: COLREGS Rule 1(a) states the rules apply to all vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels. There is no size restriction and the rules cover any navigable connected waters.

6. 6. US Inland Navigation Rules apply to:

   • A.All vessels upon the inland waters of the United States and to vessels of the United States on the Canadian waters of the Great Lakes✓
   • B.All vessels navigating within the 12-nautical-mile territorial sea of the United States
   • C.Only US-flagged vessels operating on US inland waterways
   • D.All vessels operating within state waters, as defined by each individual state

   Why: The US Inland Rules apply to all vessels on US inland waters and extend to US-flagged vessels on the Canadian waters of the Great Lakes, reflecting the bilateral navigation agreement with Canada.

7. 7. Where COLREGS and US Inland Rules differ, which set of rules takes precedence on US inland waters?

   • A.The US Inland Navigation Rules take precedence on inland waters✓
   • B.COLREGS always take precedence as an international treaty obligation
   • C.The rules of the state in whose waters the vessel is operating
   • D.The rules of the vessel's flag state

   Why: On US inland waters, the Inland Navigation Rules (33 CFR Part 83) take precedence over COLREGS. The demarcation lines published by the USCG establish the boundary between COLREGS waters and Inland waters.

8. 8. Which term is defined in the US Inland Navigation Rules but does NOT appear in COLREGS?

   • A.Inland waters✓
   • B.Vessel not under command
   • C.Power-driven vessel
   • D.Seaplane

   Why: 'Inland waters' is defined only in the US Inland Navigation Rules — at Rule 3(q) (33 CFR 83.03(q)) — as the navigable waters of the United States shoreward of the COLREGS demarcation lines (plus the US-side Great Lakes); COLREGS contains no such definition because the International Rules govern the high seas. The other three terms (power-driven vessel, vessel not under command, seaplane) are defined identically in both rule sets.

Frequently asked questions

Where do the 72 COLREGS apply?

The COLREGS apply on the high seas and all waters connected to the high seas that are navigable by seagoing vessels. In the United States, demarcation lines separate COLREGS waters (seaward) from Inland Rules waters (shoreward). Both sets of rules cover all vessels regardless of flag or type.

Can countries make their own rules that override COLREGS?

No. Authorities may make special rules for harbors, rivers, and inland waterways, but those special rules must conform as closely as possible to the International Regulations. They cannot simply override them.

All COLREGS rules