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Rule 3: General Definitions (COLREGS)

Last reviewed October 21, 2026

The short answer

Rule 3 defines the terms the rest of the rules depend on: vessel, power-driven vessel, sailing vessel, engaged in fishing, not under command, restricted in ability to maneuver, constrained by draft, underway, length, in sight, and restricted visibility. A sailing vessel using her engine counts as power-driven.

The rule text

The term sailing vessel means any vessel under sail provided that propelling machinery, if fitted, is not being used.

International Rules, U.S. Coast Guard Navigation Rules and Regulations Handbook (NAVCEN, 2024 corrected edition), Rule 3

The word underway means that a vessel is not at anchor, or made fast to the shore, or aground.

International Rules, U.S. Coast Guard Navigation Rules and Regulations Handbook (NAVCEN, 2024 corrected edition), Rule 3

Vessels shall be deemed to be in sight of one another only when one can be observed visually from the other.

International Rules, U.S. Coast Guard Navigation Rules and Regulations Handbook (NAVCEN, 2024 corrected edition), Rule 3

What it means on the water

  • Power-driven: any vessel propelled by machinery (3(b)).
  • Engaged in fishing excludes trolling lines and gear that doesn't restrict maneuverability (3(d)).
  • NUC: exceptional circumstance; RAM: nature of her work (3(f), 3(g)).
  • Underway includes drifting: not anchored, made fast, or aground (3(i)).
  • In sight means visually observed, not radar (3(k)).

International vs Inland

Inland 3(h) (constrained by her draft) is reserved. Inland adds definitions such as Western Rivers (3(n)), Great Lakes (3(o)), Secretary, Inland Waters, Inland Rules, and International Regulations.

Common exam traps

  • Calling a sailboat motorsailing a sailing vessel. She's power-driven.
  • Counting a radar contact as in sight.
  • Calling a drifting vessel not underway.

Try 3 questions on Rule 3

  1. A sailboat with sails up and engine running is a:

    1. Sailing vessel
    2. Power-driven vessel
    3. Vessel RAM
    4. Vessel NUC
    Show answer

    B. Power-driven vessel Rule 3(b) and (c).

  2. A vessel drifting with engines off, not anchored, is:

    1. Underway
    2. Not underway
    3. At anchor
    4. Aground
    Show answer

    A. Underway Rule 3(i).

  3. A vessel trolling lines is:

    1. Engaged in fishing
    2. Not engaged in fishing under Rule 3(d)
    3. RAM
    4. NUC
    Show answer

    B. Not engaged in fishing under Rule 3(d) Rule 3(d).

Frequently asked questions

What's the difference between NUC and RAM?

NUC is unable to maneuver through some exceptional circumstance; RAM is restricted by the nature of her work (Rule 3(f) and (g)).

Does radar count as in sight?

No. In sight means one can be observed visually from the other (Rule 3(k)).

What are the Western Rivers?

An Inland term (Inland 3(n)) covering the Mississippi River, its tributaries, South Pass, Southwest Pass, and related waters.

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