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COLREGs · Rule 3 · 33 CFR §83.03

General Definitions

Defines the key vocabulary used throughout the rules: 'vessel', 'power-driven vessel', 'sailing vessel', 'restricted in ability to maneuver', 'not under command', 'underway', 'restricted visibility', etc.

What does Rule 3 actually say?#

Source

Verbatim 33 CFR §83.03, public domain. The international COLREGs text is published by the IMO and cannot be reproduced here; this U.S. wording tracks it closely.
For the purpose of these Rules and Subchapter E, except where the context otherwise requires:
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.
The term power-driven vessel means any vessel propelled by machinery.
The term sailing vessel means any vessel under sail provided that propelling machinery, if fitted, is not being used.
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.
The word seaplane includes any aircraft designed to maneuver on the water.
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.
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:
A vessel engaged in laying, servicing, or picking up a navigation mark, submarine cable, or pipeline;
a vessel engaged in dredging, surveying, or underwater operations;
a vessel engaged in replenishment or transferring persons, provisions, or cargo while underway;
a vessel engaged in the launching or recovery of aircraft;
a vessel engaged in mine clearance operations;
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.
[Reserved]
The word underway means that a vessel is not at anchor, or made fast to the shore, or aground.
The words length and breadth of a vessel mean her length overall and greatest breadth.
Vessels shall be deemed to be in sight of one another only when one can be observed visually from the other.
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.
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.
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.
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.
Secretary means the Secretary of the Department in which the Coast Guard is operating.
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.
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.
International Regulations means the International Regulations for Preventing Collisions at Sea, 1972, including annexes currently in force for the United States.
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.
The term power-driven vessel means any vessel propelled by machinery.
The term sailing vessel means any vessel under sail provided that propelling machinery, if fitted, is not being used.
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.
The word seaplane includes any aircraft designed to maneuver on the water.
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.
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:
A vessel engaged in laying, servicing, or picking up a navigation mark, submarine cable, or pipeline;
a vessel engaged in dredging, surveying, or underwater operations;
a vessel engaged in replenishment or transferring persons, provisions, or cargo while underway;
a vessel engaged in the launching or recovery of aircraft;
a vessel engaged in mine clearance operations;
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.
[Reserved]
The word underway means that a vessel is not at anchor, or made fast to the shore, or aground.
The words length and breadth of a vessel mean her length overall and greatest breadth.
Vessels shall be deemed to be in sight of one another only when one can be observed visually from the other.
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.
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.
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.
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.
Secretary means the Secretary of the Department in which the Coast Guard is operating.
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.
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.
International Regulations means the International Regulations for Preventing Collisions at Sea, 1972, including annexes currently in force for the United States.

Practice this rule#

One real exam question on this rule, cited to source. No sign-up.

Rule 3 — General Definitions

Under the Inland Navigation Rules, a vessel is considered 'underway' when she is in which condition?

How does Inland Rule 3 differ from COLREGs?#

Rule 3 is where the Inland and International definition lists part company. The Inland text adds definitions the international rules have no need for — Western Rivers, Great Lakes, inland waters, Secretary, and the demarcation-line boundary at §83.03(q) — because those terms carry the Inland-only provisions in Rules 9, 14, 15 and 30. The operational definitions the exam leans on (underway, engaged in fishing, not under command, restricted in her ability to maneuver, in sight of one another, restricted visibility) read the same in both sets.

21 of 38 rules differ somewhere; the five the exam leans on are Rule 9, Rule 10, Rule 24, Rule 28 and Rule 34, side by side on Inland vs International Rules.

Why it shows up on the exam#

Most exam questions on definitions test 'vessel restricted in ability to maneuver' (RAM) vs 'not under command' (NUC) vs 'constrained by draft' (CBD).

What does the exam actually test here?#

  1. Underway

    Not anchored, moored, or aground

    Underway means only that the vessel is not at anchor, not made fast to the shore, and not aground. A vessel stopped dead in the water with no way on is still underway — the distinction between 'underway' and 'making way' decides which fog signal Rule 35 requires.

  2. Engaged in fishing

    Gear that restricts maneuverability

    The term covers vessels fishing with nets, lines, trawls, or other apparatus that restricts maneuverability. It expressly excludes a vessel trolling — trolling lines do not restrict maneuverability, so a trolling vessel is just a power-driven or sailing vessel under Rule 18.

  3. NUC vs RAM

    Exceptional circumstance vs nature of the work

    A vessel not under command is unable to maneuver through some exceptional circumstance — a breakdown. A vessel restricted in her ability to maneuver is unable to maneuver because of the nature of her work: dredging, surveying, cable work, replenishment underway, launching or recovering aircraft, mine clearance, or a tow that severely restricts deviation.

Rule 3 — common exam questions#

What does 'underway' mean in the Rules?

Underway means a vessel is not at anchor, not made fast to the shore, and not aground (33 CFR §83.03(i)). It does not require movement through the water — a vessel drifting with engines stopped is underway but not making way.

Is a vessel trolling 'engaged in fishing'?

No. Rule 3(d) covers fishing with nets, lines, trawls, or other apparatus that restricts maneuverability, and expressly excludes vessels fishing with trolling lines or other apparatus that do not restrict maneuverability (33 CFR §83.03(d)).

What is the difference between 'not under command' and 'restricted in her ability to maneuver'?

Not under command means the vessel cannot maneuver as required because of some exceptional circumstance, such as a breakdown. Restricted in her ability to maneuver means the nature of her work prevents it — dredging, surveying, cable or pipeline work, underwater operations, replenishment underway, aircraft operations, mine clearance, or a severely restricting tow (33 CFR §83.03(f) and (g)).

When are two vessels 'in sight of one another'?

Only when one can be observed visually from the other (33 CFR §83.03(k)). Radar or AIS contact is not being in sight — which is what decides whether Rules 11–18 or Rule 19 govern the encounter.

What counts as restricted visibility?

Any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms, or any other similar cause (33 CFR §83.03(l)).

Authoritative source#

  • 33 CFR §83.03 — this section with its neighbours. 33 CFR Part 83 is public domain; checked 2026-05-16.
  • COLREGs Rule 3 is published by the IMO and is authoritative internationally.

Practise this rule against the real exam.

Real exam questions. No signup, no card.

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