Back Matter
Appendix A: A-to-Z Glossary
A reference list of the words and phrases the Rules use that a first-time reader needs glossed: the terms Rule 3 defines, the plain vocabulary the Rules never explain, the legalistic phrasing that carries force, and the deliberately open terms the Rules leave to judgement. Each entry gives a plain reading, the Rule it sits in, and where in the guide it is treated at length. Defined terms are marked as such. Quotations are verbatim from MISCPUB 0127 (the December 2013 edition); commentary glosses are from Cockcroft & Lameijer, 7th ed. Lights, shapes and sound entries are kept brief here; the recognition tables in the visuals pass carry the detail.
A
Abaft the beam. Behind the line drawn square out from the ship’s side. The point 22.5 degrees abaft the beam is the boundary that defines overtaking: a vessel coming up from more than 22.5 degrees abaft another’s beam is overtaking (Rule 13(b)), and at night this is the arc from which only the sternlight, not a sidelight, can be seen (Rule 21). See Chapter 7; Rule 13.
All-round light. A light showing an unbroken arc of 360 degrees (Rule 21(e)). The colour and combination signal a vessel’s state: two all-round reds for not under command, red-white-red for restricted in her ability to manoeuvre, and so on. Detail in the Parts C and D recognition tables; Rule 27, Rule 30.
Ample time. The standard Rule 8(a) sets for avoiding action: “any action taken to avoid collision shall… be taken in ample time.” It is undefined as a distance; it means early enough that the action is obvious and effective without becoming an emergency manoeuvre (Cockcroft & Lameijer, 7th ed, comment on Rule 8). Compare good time, used at Rule 8(c), which reads as a near-synonym; ample is the stronger of the two. See Chapter 6; Chapter 8.
At all times. A marker of a continuous duty that does not depend on the situation. Used for the look-out (Rule 5) and safe speed (Rule 6): both are owed at all times, not only when a contact appears. See Chapter 7.
At anchor. A vessel is at anchor, and therefore not underway, when she is held by her anchor (and not aground or made fast to the shore). She is no longer bound by the give-way and stand-on Rules in the way an underway vessel is; others manoeuvre around her, and she shows anchor lights and a ball (Rule 30). See underway; Chapter 7.
B
Breadth. A vessel’s width; paired with length in Rule 3(j), which states that “length and breadth of a vessel mean her length overall and greatest breadth.” The figures matter because many lights, shapes and sound-signal requirements are scaled by length. Defined term, Rule 3(j).
C
Close-quarters situation. The undefined zone between risk of collision developing and a collision occurring, where vessels are near enough that ordinary action may no longer suffice. The Rules name it (Rule 8(c), Rule 19(d) and (e)) without fixing a distance, because the distance depends on the ships and the conditions. The whole thrust of Rule 8 is to act in ample time so a close-quarters situation never develops. See Chapter 8.
Constrained by her draught (CBD). A defined term: “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” (Rule 3(h)). The trap is in the opening words: she is a power-driven vessel, not a privileged class in the Rule 18 order. Others must not impede her safe passage (Rule 18(d)) and she shows the Rule 28 lights, but an ordinary crossing or head-on can still develop with her, and she herself must navigate with particular caution. Defined term, Rule 3(h); see Chapter 7; Rule 18(d); Rule 28.
Crossing situation. Two power-driven vessels in sight of one another on courses that cross so as to involve risk of collision (Rule 15). The vessel that has the other on her own starboard side gives way and, if the circumstances admit, avoids crossing ahead of the other. See Rule 15; Part III scenarios.
D
Danger of collision. A phrase used once, at Rule 19(e), where a vessel in restricted visibility must navigate with extreme caution “until danger of collision is over.” It is not a second defined trigger alongside risk of collision; it reads as the closing phase of an encounter, the point at which the danger has passed. Compare risk of collision, which is the defined concept (Rule 7). See Chapter 6; Rule 19.
Deemed (shall be deemed to). A drafting device that creates a presumption and forecloses argument. Where the Rules say a state “shall be deemed” to exist, they force a conservative default rather than leave it to be argued. Risk of collision “shall be deemed to exist” if the compass bearing of an approaching vessel does not appreciably change (Rule 7(d)(i)); if there is any doubt whether a situation is overtaking, “the vessel concerned shall assume that it is” and act accordingly (Rule 13(c) reasoning, and the deeming at Rule 13(b)). See Chapter 6.
Due regard. A duty to weigh something and take it into account, short of an absolute command. Used at Rule 2(b) (due regard to all dangers of navigation and to any special circumstances), Rule 8(a) and Rule 19(c). See Chapter 6.
E
Engaged in fishing. A defined term: “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” (Rule 3(d)). The status comes from the gear restricting the vessel, not from the act of fishing; a vessel trolling is not engaged in fishing for the purposes of the Rules. Defined term, Rule 3(d); see Chapter 7; trolling lines.
Exonerate. To clear of blame. Used in the savings clause at Rule 2(a): nothing in the Rules shall exonerate any vessel, owner, master or crew from the consequences of neglecting to comply with the Rules or to take any precaution required by the ordinary practice of seamen. The word preserves liability that the letter of the Rules might otherwise seem to remove. See Chapter 6; Chapter 10.
Extreme caution. The strongest of the Rules’ caution gradings, required of a vessel in restricted visibility that hears a fog signal apparently forward of the beam, or cannot avoid a close-quarters situation with a vessel forward of the beam (Rule 19(e)). Compare particular caution (Rule 10(f), Rule 18(d)) and “particular alertness and caution” (Rule 9(f)). The text plainly escalates, though whether the three are a deliberate ladder is open. See Chapter 7; Rule 19.
F
Fairway. A navigable channel; the part of the water where vessels can pass. Undefined in the Rules but used throughout Rule 9. See narrow channel; Rule 9.
Finally past and clear. The point at which an overtaking vessel is released from her duty: she remains the overtaking vessel, bound to keep clear, “until she is finally past and clear” (Rule 13(d)). All three words are undefined and the test is only judgeable in hindsight, which is why the overtaking classification persists through any apparent change in bearing. See Chapter 9; Rule 13.
Fore-and-aft sail. A sail set along the line of the keel rather than across it (the opposite of square-rigged). The distinction is needed to read Rule 12(b), which fixes which side a fore-and-aft rigged sailing vessel’s “windward side” is for the purposes of the sailing-vessel right-of-way test. See windward; Rule 12.
G
Give-way vessel. The vessel directed to keep out of the way in a given encounter; she must, so far as possible, take early and substantial action to keep well clear (Rule 16). The term is defined by function, not by class: which vessel gives way is set by the governing Rule (13, 14, 15, 18). See Rule 16; stand-on vessel.
Good seamanship / ordinary practice of seamen. The body of accepted seafaring practice the Rules assume but do not write down. Rule 2(a) preserves it: nothing in the Rules exonerates anyone from the consequences of neglecting “any precaution which may be required by the ordinary practice of seamen.” It is the standard against which judgement in the gaps is measured. See Chapter 10.
Good time. The standard at Rule 8(c) for action taken to avoid a close-quarters situation: an alteration “made in good time.” It reads as a near-synonym of ample time (Rule 8(a)); Cockcroft discusses both without drawing a hard legal line between them. See Chapter 6; Chapter 8.
H
Head-on situation. Two power-driven vessels meeting on reciprocal or nearly reciprocal courses so as to involve risk of collision (Rule 14). Each alters to starboard to pass port to port. Where there is any doubt whether the situation is head-on, it must be assumed to exist (Rule 14(c)). See Rule 14; Part III scenarios.
I
If the circumstances of the case admit. A phrase that conditions the manner of compliance rather than whether the duty binds. It allows for situations where the ordinary way of complying is not available, while leaving the obligation itself in place. Used at Rule 8(a) and (b), Rule 15, Rule 17(c) and Rule 18(d), among others. See Chapter 6.
Immediate danger. One of the two conditions, with special circumstances, that together gate a lawful departure from the Rules under Rule 2(b): a departure is permitted only where necessary to avoid immediate danger and special circumstances exist. See Chapter 10; Rule 2.
In sight of one another. A defined term: vessels “shall be deemed to be in sight of one another only when one can be observed visually from the other” (Rule 3(k)). The word that does the work is visually: a radar contact in fog is not in sight, so the give-way and stand-on Rules of Section II do not apply and Rule 19 governs instead. Defined term, Rule 3(k); see Chapter 5; Chapter 9; Rule 19.
Inshore traffic zone. The water between the landward boundary of a traffic separation scheme and the coast (Rule 10(d)), normally to be avoided by through traffic. See traffic separation scheme; Rule 10.
K
Keep clear / keep well clear / keep out of the way / not impede. A family of clearing duties of different strengths, not synonyms. “Keep out of the way” (Rules 12 to 18) is the give-way vessel’s core duty. “Keep well clear” (Rule 16, and the seaplane at Rule 31) demands a wider margin. “Keep clear” appears in the narrow-channel context (Rule 10(b)(ii)). “Not impede” (Rules 9 and 10) is different again: it is a duty to leave room early so that risk of collision does not develop, and was never a grant of right of way (Rule 8(f)). See Chapter 8; Rule 8(f); Rule 16.
L
Length and breadth. “Length and breadth of a vessel mean her length overall and greatest breadth” (Rule 3(j)). Used throughout Parts C and D, where light, shape and sound-signal requirements change at length thresholds (typically 7, 12, 20, 50 and 100 metres). Defined term, Rule 3(j).
Leeward. The sheltered side, the side away from the wind. See windward; Rule 12.
M
Making way. Moving through the water under her own power or momentum. A vessel can be underway but not making way (stopped and drifting); she is still underway and still owes the Rules. The distinction drives several sound signals (Rule 35). See underway; Chapter 7.
Masthead light. A white light over the fore-and-aft centreline showing an unbroken arc of 225 degrees, from right ahead to 22.5 degrees abaft each beam (Rule 21(a)). A power-driven vessel of 50 metres or more shows a second, after masthead light, and the pair reads as a heading indicator. Detail in the Parts C and D tables; Rule 21; Rule 23.
N
Narrow channel. A constrained navigable waterway, undefined as to width because it is local and size dependent. A vessel proceeding along one keeps as near to her starboard-side outer limit as is safe and practicable (Rule 9(a)). See fairway; Rule 9.
Not impede. See keep clear / keep well clear / keep out of the way / not impede. A duty to leave sea room early so risk of collision does not arise; if risk of collision does develop, the not-impede duty does not disappear and the ordinary encounter Rules apply on top of it (Rule 8(f)). See Chapter 8; Rule 8(f); Rule 9; Rule 10.
Not under command (NUC). A defined term: “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” (Rule 3(f)). She shows two all-round red lights (Rule 27(a)) and sits at the top of the Rule 18 order. The status is involuntary, the result of a breakdown or similar, not of the work she is doing. Compare restricted in her ability to manoeuvre. Defined term, Rule 3(f); see Rule 18; Rule 27.
Notwithstanding. The strongest override word in the Rules: “despite, or regardless of, anything said elsewhere.” Rule 13(a) opens “notwithstanding anything contained in the Rules of Part B, Sections I and II,” which makes the overtaking duty override every other steering and sailing Rule. An overtaking fishing vessel still keeps clear of the power-driven vessel she is overtaking, and the duty persists even if the bearing later looks like a crossing (Rule 13(d)). See Chapter 6; Rule 13.
O
Officer of the Watch (OOW). The officer in charge of the navigational watch, to whom this guide is addressed throughout. Convention; see Front Matter.
Ordinary practice of seamen. See good seamanship / ordinary practice of seamen.
Overtaking. Coming up with another vessel from more than 22.5 degrees abaft her beam (Rule 13(b)). An overtaking vessel keeps out of the way of the vessel being overtaken, and the duty overrides all other steering Rules (Rule 13(a)) and persists until she is finally past and clear (Rule 13(d)). See Rule 13; abaft the beam; finally past and clear.
P
Passage / safe passage. Related phrases in the not-impede Rules. A vessel must not impede “the passage” of another in a narrow channel (Rule 9(b), (c)) or a traffic lane (Rule 10(i)); “safe passage” attaches to a vessel constrained by her draught (Rule 18(d)) and to a power-driven vessel using a lane (Rule 10(j)). The wording differs; whether the two carry a different legal weight is left open in the text. See Chapter 6; Rule 8(f).
Power-driven vessel. A defined term: “any vessel propelled by machinery” (Rule 3(b)). The default class: a vessel is power-driven unless one of the other Rule 3 states applies, and several states that feel special (constrained by her draught, a motor-sailer) are power-driven vessels underneath. Defined term, Rule 3(b); see Chapter 7.
Prolonged blast. A blast of four to six seconds (Rule 32(c)). Paired with the short blast, it builds every signal in Part D. See short blast; Rule 32; Rule 35.
R
Replenishment (RAS). Replenishment at sea, the transfer of fuel or stores between ships under way; one of the activities that can make a vessel restricted in her ability to manoeuvre (Rule 3(g)(iii)). See restricted in her ability to manoeuvre; Rule 3(g).
Restricted in her ability to manoeuvre (RAM). A defined term: 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” (Rule 3(g)). The status flows from the work being done, so it can come and go through the day; a tug is RAM only while a tow severely restricts her, not in transit (BR45 Vol 4, para 1014c). Compare not under command, which is involuntary. Defined term, Rule 3(g); see Rule 18; Rule 27.
Restricted visibility. A defined term: “any condition in which visibility is restricted by fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes” (Rule 3(l)). When vessels are not in sight of one another in or near an area of restricted visibility, Rule 19 governs and the give-way and stand-on Rules do not apply. Defined term, Rule 3(l); see Chapter 5; Rule 19.
Risk of collision. The defined trigger for the steering and sailing Rules, governed by Rule 7. It shall be deemed to exist if the compass bearing of an approaching vessel does not appreciably change (Rule 7(d)(i)), and if there is any doubt, it shall be deemed to exist (Rule 7(a)). The Rules do not fix the range at which it begins, leaving that to judgement. Compare danger of collision (Rule 19(e)). See Chapter 8; Rule 7.
Roadstead. An open anchorage offshore, generally given some protection by shoals but offering less shelter than a harbour (Cockcroft & Lameijer, 7th ed, comment on Rule 1). Named in Rule 1(b) among the waters local authorities may make special rules for. See Rule 1.
S
Safe distance. The passing distance an avoiding action should achieve: action taken to avoid collision should result in passing “at a safe distance” (Rule 8(d)). Undefined, because it depends on the size and speed of the vessels and on interaction effects. See Chapter 8; Rule 8.
Safe speed. The speed at which a vessel can take proper and effective action to avoid collision and be stopped within a distance appropriate to the circumstances (Rule 6). The Rule lists factors to weigh, including visibility, traffic density, manoeuvrability, and at night the presence of background light, plus further radar factors, but fixes no number. See Chapter 7; Rule 6.
Sailing vessel. A defined term: “any vessel under sail provided that propelling machinery, if fitted, is not being used” (Rule 3(c)). The proviso is the trap: a yacht motor-sailing is a power-driven vessel, loses sailing-vessel priority, and must show power-driven lights and a cone by day (Rule 25(e)). Defined term, Rule 3(c); see Chapter 7; Rule 12; Rule 25.
Seaplane. A defined term: “any aircraft designed to manoeuvre on the water” (Rule 3(e)). She is a vessel for the purposes of the Rules and is required, in general, to keep well clear of all vessels and avoid impeding their navigation (Rule 18(e)); her lights are shown as close as practicable to those prescribed (Rule 31). Defined term, Rule 3(e); see Rule 18; Rule 31.
Separation zone / separation line. The strip or line in a traffic separation scheme that divides streams of opposing traffic (Rule 10(b) and (e)); normally not to be entered or crossed except as the Rule allows. See traffic separation scheme; Rule 10.
Shall. The mandatory operator. Where the Rules say “shall,” there is no discretion; it is the default form of every duty in the instrument, and the qualifying phrases (“so far as possible,” “if the circumstances admit”) soften only the manner, not the obligation. See Chapter 6.
Short blast. A blast of about one second (Rule 32(b)); the basic unit, with the prolonged blast, of the Part D signals. See prolonged blast; Rule 32; Rule 34.
Sidelights. A green light to starboard and a red light to port, each showing an unbroken arc of 112.5 degrees, from right ahead to 22.5 degrees abaft the beam on its side (Rule 21(b)). They show another vessel which way you are heading and which side she is seeing. Detail in the Parts C and D tables; Rule 21; Rule 23.
So far as possible. A strong qualifier that yields only to genuine impossibility. Used where the duty is meant to bind hard, as at Rule 16 (the give-way vessel shall, so far as possible, take early and substantial action) and Rule 18(c). Compare so far as practicable, which is more forgiving. See Chapter 6.
So far as practicable. A qualifier of reasonableness and feasibility, more forgiving than “so far as possible.” Used at Rule 9(a) (“as is safe and practicable”) and through Rule 10. The ranking of possible above practicable is the guide’s synthesis for teaching; Cockcroft gives no side-by-side definition of the two. See Chapter 6.
Special circumstances. With immediate danger, one of the two conditions that gate a lawful departure from the Rules under Rule 2(b). Both must hold: special circumstances, including the limitations of the vessels involved, and the necessity to avoid immediate danger. See Chapter 10; Rule 2.
Square-rigged. Carrying sails set across the line of the keel. See fore-and-aft sail; Rule 12.
Stand-on vessel. The vessel required to keep her course and speed in an encounter (Rule 17(a)(i)), so that the give-way vessel can plan around a predictable target. She may take action when it becomes apparent the give-way vessel is not acting (Rule 17(a)(ii)), and must act when collision cannot be avoided by the give-way vessel’s action alone (Rule 17(b)). See Rule 17; give-way vessel.
Sternlight. A white light at the stern showing an arc of 135 degrees, 67.5 degrees from right aft on each side (Rule 21(c)). A vessel who can see only your sternlight, and neither sidelight, is by definition abaft your beam and therefore overtaking. Detail in the Parts C and D tables; Rule 21; Rule 13.
T
Traffic separation scheme (TSS). A routeing measure that separates opposing streams of traffic into lanes, governed by Rule 10. A vessel using a lane proceeds in the established direction, keeps clear of the separation zone, and joins or leaves at the ends or at a small angle. See separation zone; inshore traffic zone; Rule 10.
Towing light. A yellow light with the same characteristics as the sternlight, shown above it by a vessel towing (Rule 21(d), Rule 24(a)). It warns of a tow strung out astern. Detail in the Parts C and D tables; Rule 24.
Trolling lines. Fishing lines drawn through the water behind a moving vessel, which do not restrict her manoeuvrability. A vessel fishing with trolling lines is expressly not a vessel engaged in fishing (Rule 3(d)); she keeps her ordinary status. See engaged in fishing; Rule 3(d).
U
Underway. A defined term: a vessel is underway when she is “not at anchor, or made fast to the shore, or aground” (Rule 3(i)). The point first-time readers miss is that underway does not mean moving: a vessel stopped and drifting is still underway, still bound by the Rules, and cannot rely on others to keep clear of her. A vessel that is underway and also moving through the water is making way. Defined term, Rule 3(i); see Chapter 7; making way; at anchor.
V
Vessel. A defined term, drawn deliberately wide: “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” (Rule 3(a)). The breadth means the Rules reach craft that are not ordinary ships. Defined term, Rule 3(a); see Chapter 3.
W
Way / take all way off. “Way” is movement through the water. To “take all way off” (Rule 8(e)) is to stop, by slackening, stopping or reversing the means of propulsion, as a permitted form of avoiding action. See making way; Rule 8.
Windward / leeward. The windward side is the side from which the wind blows; the leeward side is the sheltered side opposite. Rule 12 uses windward to allocate the duty between two sailing vessels with the wind on the same side: the windward vessel keeps out of the way of the leeward vessel. See fore-and-aft sail; Rule 12.
WIG craft (wing-in-ground craft). A defined term: “a multimodal craft which, in its main operational mode, flies in close proximity to the surface by utilising surface-effect action” (Rule 3(m)). When taking off, landing and in flight near the surface she keeps well clear of all vessels and avoids impeding their navigation; when operating on the water surface she complies with the steering and sailing Rules as a power-driven vessel (Rule 18(f)). Defined term, Rule 3(m); see Rule 18.
The full text of each Rule, with these terms surfaced and annotated inline, follows in The Rules, Annotated.