Rule 3 Explained.

General definitions
For the purpose of these Rules, except where the context otherwise requires:
(a) 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.
(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 manoeuvrability, but does not include a vessel fishing with trolling lines or other fishing apparatus which do not restrict manoeuvrability.
(e) The word “seaplane” includes any aircraft designed to manoeuvre on the water.
(f) The term “vessel not under command” means a vessel which through some exceptional
circumstance is unable to manoeuvre 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 manoeuvre” means a vessel which from the nature of her work is restricted in her ability to manoeuvre 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 manoeuvre” shall include but not be limited to:
(i) a vessel engaged in laying, servicing or picking up a navigation 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.
(h) The term “vessel constrained by her draught” means a power-driven vessel which, because of her draught 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.

Explanation
Rule 3 gives the general definitions used in the COLREGS. It is important that the definitions are fully understood so that the correct actions are taken by all vessels when they meet.

Questions and Answers

Describe the term “not under command”?
The term “vessel not under command” means a vessel which through some exceptional circumstance is unable to manoeuvre as required by these Rules and is therefore unable to keep out of the way of another vessel.

Describe the term” vessel restricted in her ability to manoeuvre”?
Is a vessel through the nature of her work; she is unable to deviate from her course she is following or comply with the rules.

Describe a “vessel constrained by her draught”?
Is a power-driven vessel, because of her draught in relation to the depth of water she is in, cannot deviate from the course she is following.

Describe the word “Underway”?
When a vessel is not at anchor, aground or made fast to the shore, and is only going through the water by tide and/or wind.

Describe the word “Making way”?
When a vessel is being propelled through the water by engine propulsion, sails or oars.

Describe a power-driven vessel?
Any vessel that has an engine to propel herself through the water.

Describe a sailing vessel?
A vessel using sails and not using engine propulsion to push her through the water.

Describe the word “seaplane”?
Any aircraft that can land on water.

How would you describe the “Length and Breadth” of your vessel?
The longest length of your vessel and the widest part of the vessel, you’ll get this from your “Stability book” and the “Record of particulars“.

The term “when vessels are in sight of one another” what does this mean?
When you can see the vessel visually by the naked eye during daylight or at night, Rule 34 explains the sound signals used “When vessels are in sight of one another“.