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