The Rule:

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

(a) The word "vessel" includes every description of watercraft, 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 term "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 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 Only (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 Only (n) "Western Rivers" means the Mississippi River, its tributaries, South Pass, and Southwest Pass, to the navigational demarcation lines {30 CFR 80} 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.

Inland Only (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.

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

Inland Only (q) "Inland Waters" means the navigable waters of the United States shoreward of the navigational demarcation lines {30 CFR 80} 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.

Discussion: This rule is quite long but very important to the remainder of the book. Students should refer often to Rule 3 when studying other sections of the rules. Here are some key points from Rule 3:

Vessels are anything that can be used to carry people or cargo on the water. Presumably, this includes autonomous vehicles. 

Power Driven Vessels are those propelled by machinery. Sailing Vessels are those propelled by sails. When a sailboat uses its engine, even if the sails are up and filling, it is a power-driven vessel.

Vessels Engaged in Fishing are those whose maneuverability is restricted by its fishing gear. However these vessels show specific lights and shapes for fishing to separate them from other vessels restricted in maneuverability. Trolling vessels, such as a typical sportfishing boat, is a power-driven vessel. 

Vessels Restricted in their Ability to Maneuver (VRAM) are those who cannot maneuver easily due to the nature of their work.

Vessels Not Under Command (NUC) are those who cannot maneuver easily due to some exceptional circumstance. 

Restricted Visibility is anything that reduces vision such as snow, rain, fog, etc. It does not include night.

In Sight means that vessels can actually see each other and does not include detection by radar.

Underway means not anchored, aground, or tied to a pier. Drifting without propulsion engaged is still “underway.”

Constrained by Draft vessels are only found in international rules and are only power-driven vessels. Presumably this is because inland waters are generally shallower and most vessels are constrained by draft in these cases.  

Test Strategy: It is very important to memorize these definitions, particularly the key definitions listed above. When prompted with “VRAM” your brain should go immediately to “Nature of Her Work.” When prompted with “NUC” your brain should go immediately to “Some Exceptional Circumstance.” Test questions are plentiful and varied regarding this rule; there are over 50 in the database and you will certainly see some questions on your exam