1.2 General Definitions (Rules 1-3)

Rule 1 — Application

Rule 1 states that the rules apply to all vessels upon the high seas and in all waters connected therewith navigable by seagoing vessels. It also authorizes local authorities to make special rules for harbors, roadsteads, rivers, and inland waters — which is exactly how the Inland Rules and local pilot rules exist alongside the international text. For the OUPV you only need the headline: the rules bind every vessel, and a lack of specific instruction never excuses a collision.

Rule 2 — Responsibility (the most-tested short rule)

Rule 2 is only two sentences long but appears constantly on the exam because it contains two powerful ideas:

• Rule 2(a) — the Rule of Good Seamanship. Nothing in the rules exonerates any vessel, owner, master, or crew from the consequences of neglect to comply with the rules or of neglect of any precaution which the ordinary practice of seamen or the special circumstances of the case may require. In plain terms: following the letter of a rule does not protect you if a prudent mariner would have done more.
• Rule 2(b) — the General Prudential Rule. In construing and complying with the rules, due regard shall be had to all dangers of navigation and collision and to any special circumstances, including the limitations of the vessels involved, which may make a departure from these rules necessary to avoid immediate danger.

That second clause is the legal basis for breaking a rule in extremis. If obeying the give-way/stand-on assignment would cause the collision, Rule 2(b) not only permits but requires you to depart from the rules to avoid immediate danger.

Rule 3 — General Definitions

Rule 3 defines the vocabulary the rest of the book depends on. These definitions decide who gives way to whom, so memorize them precisely.

Vessel categories:

• Power-driven vessel — any vessel propelled by machinery.
• Sailing vessel — under sail, provided that propelling machinery, if fitted, is not being used. The moment you start the engine, a sailboat becomes a power-driven vessel even with sails up.
• Vessel engaged in fishing — fishing with nets, lines, trawls, or other apparatus that restrict maneuverability. This does NOT include a vessel fishing with trolling lines, which do not restrict maneuverability. This distinction is a classic trap: a sportfisher dragging trolling lines is not "engaged in fishing" under the rules and gets no special privilege.
• Vessel not under command (NUC) — through some exceptional circumstance (engine failure, lost rudder) is unable to maneuver as required and therefore cannot keep out of the way.
• Vessel restricted in her ability to maneuver (RAM) — from the nature of her work is unable to keep out of the way. Examples named in the rule include laying or servicing a navigation mark, cable, or pipeline; dredging, surveying, or underwater operations; replenishment or transferring people/cargo while underway; launching or recovering aircraft; mine-clearance; and a towing operation that severely restricts the tug and tow in their ability to deviate from course.
• Vessel constrained by her draught (CBD) — 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. CBD exists only under the International Rules.

Movement and condition terms:

• Underway — not at anchor, not made fast to the shore, and not aground. A vessel drifting with her engine off is still underway.
• Making way — underway and moving through the water. A vessel can be underway but not making way (e.g., stopped and drifting). This underway-versus-making-way distinction governs several light and sound-signal rules.
• In sight of one another — vessels are in sight only when one can be observed visually from the other. This matters enormously: the steering rules of Section II (Rules 11-18) apply only when vessels are in sight; if you can see each other only by radar, you are in restricted visibility and Rule 19 governs instead.
• Restricted visibility — any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms, or any similar cause.
• Length and breadth of a vessel mean her length overall and greatest breadth.

A note on 'vessel' itself: Rule 3 defines a vessel broadly as every description of water craft, including non-displacement craft, WIG (wing-in-ground) craft, and seaplanes, used or capable of being used as a means of transportation on water. So a seaplane taxiing on the surface is a vessel and must obey the rules like any other.

These categories are not just labels — they set a priority order that Rule 18 spells out in full (Section 1.10). As a preview, a rough hierarchy of who keeps clear of whom runs: power-driven gives way to sailing; sailing gives way to fishing; fishing gives way to a vessel restricted in her ability to maneuver or not under command. Establishing a vessel's category is therefore the first move in any encounter, because it fixes which end of the give-way relationship you occupy before you ever look at the geometry.

Why These Definitions Win Points

Many "who gives way" questions are really definition questions in disguise. If the exam says a sailboat is motoring, the correct reasoning is that she is a power-driven vessel; if it describes a boat with trolling lines out, she is not engaged in fishing; if it says a vessel lost her engine, she may be not under command. Nail Rule 3 and a large share of the module answers itself.