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Rule 3(f)-(s)
Two different reasons a vessel cannot get out of your way
Official rule text as published in the U.S. Coast Guard Navigation Rules
Source: USCG NavCen / eCFR Navigation Rules · Last updated September 7, 2026

(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 navigational 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.

International
(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.

Inland
(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 tributary waters including the Calumet River as far as the Thomas J. O'Brien Lock and Controlling Waters (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.
MyCOLREGS explanation
Summary
Rule 3 separates two categories that are easy to blur. A vessel "not under command" is one that some exceptional circumstance has left unable to maneuver as the Rules require — think steering-gear failure or a fouled propeller. A vessel "restricted in her ability to maneuver" is limited by the nature of the work it is doing — the Rule lists examples including cable-laying, dredging, replenishment at sea, aircraft recovery, mine clearance, and certain towing operations. The same caution is warranted around both, but the reason for the limitation is different.
Real World Example
A steering casualty drifting broadside to the channel can often be fixed by shifting to neutral and calling for a tow; a cable-layer with divers over the side or an anchor handler mid-deployment cannot simply disengage, which is exactly why Rule 3 treats "restricted in her ability to maneuver" as its own category instead of folding it into "not under command."

Practice Questions

Q1. A dredge is actively working in a channel, its gear limiting how it can move. Based on Rule 3(f) and (g), is the dredge best described as "not under command" or "restricted in her ability to maneuver"?
A. Restricted in her ability to maneuver, because Rule 3(g) specifically lists dredging as an example of that category.
B. Not under command, because it has no engine running.
C. Not under command, because it cannot get out of the way of another vessel.
D. Neither category applies to vessels engaged in dredging.
Q2. What is the key difference between a vessel "not under command" (Rule 3(f)) and one "restricted in her ability to maneuver" (Rule 3(g))?
A. There is no meaningful difference; the terms are interchangeable, and the Rules use whichever phrase happens to read more naturally in a given provision without any distinction in status or effect.
B. "Not under command" arises from an exceptional circumstance that leaves the vessel unable to maneuver as required; "restricted in her ability to maneuver" arises from the nature of the work the vessel is doing.
C. 'Restricted in her ability to maneuver' only applies to vessels over 100 meters, since Rule 3(g)'s listed examples like dredging and cable-laying are typically performed by larger commercial vessels.
D. 'Not under command' only applies to sailing vessels, since power-driven vessels are assumed to always retain the ability to maneuver as long as their engine is running.

Practice Question Answers

Q1.
A. Restricted in her ability to maneuver, because Rule 3(g) specifically lists dredging as an example of that category. Rule 3(g)(ii) names "a vessel engaged in dredging, surveying or underwater operations" as an example of a vessel restricted in her ability to maneuver by the nature of her work — a distinct category from "not under command," which covers an exceptional, usually unexpected inability to maneuver such as a steering failure. B and C describe symptoms that could sound like "not under command," but that category is for an exceptional, abnormal inability to maneuver - a dredge's limitation comes from the nature of its work, which is exactly what "restricted in ability to maneuver" covers instead. D denies a category that clearly applies.
Q2.
B. "Not under command" arises from an exceptional circumstance that leaves the vessel unable to maneuver as required; "restricted in her ability to maneuver" arises from the nature of the work the vessel is doing. Rule 3(f) ties "not under command" to an exceptional circumstance (e.g., mechanical failure); Rule 3(g) ties "restricted in her ability to maneuver" to the nature of the work being performed, such as the enumerated dredging, cable-laying, or mine-clearance examples. A collapses a meaningful legal distinction into nothing. C and D each attach a restriction - vessel size or type - that Rule 3(f)/(g) doesn't actually impose; the real distinction is exceptional circumstance versus the nature of the work.