COLREGs Rule 3: General definitions in the Navigation Rules

Last reviewed: October 14, 2026

Rule 3 defines terms used in the Navigation Rules, such as vessel, power-driven vessel, sailing vessel and underway. The International and Inland versions are mostly the same. The Inland rule reserves paragraph (h) and adds definitions in paragraphs (n) through (s).

Applies toThe definitions apply for the purpose of these Rules, except where the context otherwise requires; the Inland rule also applies them for Subchapter E.

What it says

  1. The word vessel includes every description of water craft used or capable of being used as a means of transportation on water, including non-displacement craft, WIG craft and seaplanes.

    COLREGs Rule 3(a)“The word vessel includes every description of water craft, including non- displacement craft, WIG craft and seaplanes, used or capable of being used as a means of transportation on water.”
  2. A sailing vessel is a vessel under sail, provided that any propelling machinery is not being used.

    COLREGs Rule 3(c)“The term sailing vessel means any vessel under sail provided that propelling machinery, if fitted, is not being used.”
  3. A vessel not under command is a vessel that, through some exceptional circumstance, cannot maneuver as the Rules require and so cannot keep out of the way of another vessel.

    COLREGs Rule 3(f)“The term vessel not under command means a vessel which through some exceptional circumstance is unable to maneuver as required by these Rules”
  4. International: A vessel constrained by her draft is a power-driven vessel that, because of her draft in relation to the available depth and width of navigable water, is severely restricted in her ability to deviate from her course. The Inland rule reserves paragraph (h).

    COLREGs Rule 3(h)“The term vessel constrained by her draft means a power-driven vessel which, because of her draft in relation to the available depth and width of navigable water”
  5. A vessel is underway when it is not at anchor, made fast to the shore, or aground.

    COLREGs Rule 3(i)“The word underway means that a vessel is not at anchor, or made fast to the shore, or aground.”
  6. Vessels are deemed to be in sight of one another only when one can be observed visually from the other.

    COLREGs Rule 3(k)“Vessels shall be deemed to be in sight of one another only when one can be observed visually from the other.”
  7. Restricted visibility means any condition in which fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes restrict visibility.

    COLREGs Rule 3(l)“The term restricted visibility means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.”
  8. Inland: Inland Waters means the navigable waters of the United States shoreward of the navigational demarcation lines, and the waters of the Great Lakes on the United States side of the International Boundary.

    COLREGs Rule 3(q)“Inland Waters means the navigable waters of the United States shoreward of the navigational demarcation lines dividing the high seas from harbors, rivers, and other inland waters of the United States”

Common questions

What does underway mean in the Navigation Rules?

A vessel is underway when it is not at anchor, or made fast to the shore, or aground.

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

What counts as restricted visibility?

It means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.

“The term restricted visibility means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.”

When are two vessels in sight of one another?

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

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

Does a vessel fishing with trolling lines count as a vessel engaged in fishing?

No. The term does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability.

“but does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability.”

The text of COLREGs Rule 3

U.S. Coast Guard, Navigation Rules and Regulations Handbook

Rule 3: General Definitions

International (COLREGs)

For the purpose of these Rules, except where the context otherwise requires:

(a) The word vessel includes every description of water craft, including non- displacement craft, WIG craft and seaplanes, used or capable of being used as a means of transportation on water.

(b) The term power-driven vessel means any vessel propelled by machinery.

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

(d) The term vessel engaged in fishing means any vessel fishing with nets, lines, trawls or other fishing apparatus which restrict maneuverability, but does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability.

(e) The word seaplane includes any aircraft designed to maneuver on the water.

(f) The term vessel not under command means a vessel which through some exceptional circumstance is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel.

(g) The term vessel restricted in her ability to maneuver means a vessel which from the nature of her work is restricted in her ability to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel. The term vessels restricted in their ability to maneuver shall include but not be limited to:

(i) a vessel engaged in laying, servicing or picking up a navigation mark, submarine cable or pipeline;

(ii) a vessel engaged in dredging, surveying or underwater operations;

(iii) a vessel engaged in replenishment or transferring persons, provisions or cargo while underway;

(iv) a vessel engaged in the launching or recovery of aircraft;

(v) a vessel engaged in mine clearance operations;

(vi) a vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course.

(h) The term vessel constrained by her draft means a power-driven vessel which, because of her draft in relation to the available depth and width of navigable water is severely restricted in her ability to deviate from the course she is following.

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

(j) The words length and breadth of a vessel mean her length overall and greatest breadth.

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

(l) The term restricted visibility means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes.

(m) The term Wing-In-Ground (WIG) craft means a multimodal craft which, in its main operational mode, flies in close proximity to the surface by utilizing surface-effect action. Condition of Visibility

Inland Rules

General definitions For the purpose of these Rules and Subchapter E ‡, except where the context otherwise requires:

(a) The word vessel includes every description of water craft, including non- displacement craft, WIG craft and seaplanes, used or capable of being used as a means of transportation on water.

(b) The term power-driven vessel means any vessel propelled by machinery.

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

(d) The term vessel engaged in fishing means any vessel fishing with nets, lines, trawls, or other fishing apparatus which restricts maneuverability, but does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict maneuverability.

(e) The word seaplane includes any aircraft designed to maneuver on the water.

(f) The term vessel not under command means a vessel which through some exceptional circumstance is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel.

(g) The term vessel restricted in her ability to maneuver means a vessel which, from the nature of her work, is restricted in her ability to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel. The term vessels restricted in their ability to maneuver include, but are not limited to:

(i) A vessel engaged in laying, servicing or picking up a navigation mark, submarine cable, or pipeline;

(ii) a vessel engaged in dredging, surveying, or underwater operations;

(iii) a vessel engaged in replenishment or transferring persons, provisions, or cargo while underway;

(iv) a vessel engaged in the launching or recovery of aircraft;

(v) a vessel engaged in mine clearance operations;

(vi) a vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course.

(h) [Reserved] ‡ Parts 83-90 of Title 33 Code of Federal Regulations.

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

(j) The words length and breadth of a vessel mean her length overall and greatest breadth.

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

(l) The term restricted visibility means any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms, or any other similar causes.

(m) The term Wing-In-Ground (WIG) craft means a multimodal craft which, in its main operational mode, flies in close proximity to the surface by utilizing surface-effect action.

(n) Western Rivers means the Mississippi River, its tributaries, South Pass, and Southwest Pass, to the navigational demarcation lines dividing the high seas from harbors, rivers, and other inland waters of the United States, and the Port Allen- Morgan City Alternate Route, and that part of the Atchafalaya River above its junction with the Port Allen-Morgan City Alternate Route including the Old River and the Red River.

(o) Great Lakes means the Great Lakes and their connecting and tributary waters including the Calumet River as far as the Thomas J. O’Brien Lock and Controlling Works (between mile 326 and 327), the Chicago River as far as the east side of the Ashland Avenue Bridge (between mile 321 and 322), and the Saint Lawrence River as far east as the lower exit of Saint Lambert Lock.

(p) Secretary means the Secretary of the Department in which the Coast Guard is operating.

(q) Inland Waters means the navigable waters of the United States shoreward of the navigational demarcation lines dividing the high seas from harbors, rivers, and other inland waters of the United States and the waters of the Great Lakes on the United States side of the International Boundary.

(r) Inland Rules or Rules means these Inland Navigational Rules and the annexes thereto, which govern the conduct of vessels and specify the lights, shapes, and sound signals that apply on inland waters.

(s) International Regulations means the International Regulations for Preventing Collisions at Sea, 1972, including annexes currently in force for the United States.

The plain-English explanation on this page was written with AI from the regulation text above and checked automatically before publishing: every quote appears in the text, every number comes from it, and a second model confirmed each statement adds nothing the text doesn't say. Regulation text current as of August 12, 2024. The regulation text governs. RegKnot is not affiliated with the U.S. Coast Guard.