Part C: Lights and Shapes (Rules 20 to 31)
Parts C and D are the input side of the conduct Rules: the lights and shapes say what a vessel is and which way she heads, the sound signals say what she is doing, so the steering Rules can act on the answer (Chapter 5). The annotation here surfaces the key wording and the traps; the exact lights, arcs, shapes and ranges are carried by the recognition tables in the visuals pass, which this section points to rather than duplicates.
Rule 20: Application
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(a) Rules in this Part shall be complied with in all weathers.
(b) The Rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the lights specified in these Rules or do not impair their visibility or distinctive character, or interfere with the keeping of a proper look-out.
(c) The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary.
(d) The Rules concerning shapes shall be complied with by day.
(e) The lights and shapes specified in these Rules shall comply with the provisions of Annex I to these Regulations.
ANNOTATION
The framing Rule for Part C. Lights and shapes are complied with “in all weathers” (a). Lights are shown “from sunset to sunrise,” and during that time no other lights may be shown that could be mistaken for the prescribed lights or impair their visibility or distinctive character (b). Lights are also shown “from sunrise to sunset in restricted visibility,” and may be shown “in all other circumstances when it is deemed necessary” (c). Shapes are shown by day (d). The Rule also makes the technical detail of “Annex I” binding (e). The key idea is that the prescribed lights are a fixed set: nothing may be shown that could be confused with them. See Chapter 5; the Parts C and D recognition tables.
Rule 21: Definitions
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(a) “Masthead light” means a white light placed over the fore and aft centreline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either side of the vessel.
(b) “Sidelights” means a green light on the starboard side and a red light on the port side each showing an unbroken light over an arc of the horizon of 112.5 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on its respective side. In a vessel of less than 20 metres in length the sidelights may be combined in one lantern carried on the fore and aft centreline of the vessel.
(c) “Sternlight” means a white light placed as nearly as practicable at the stern showing an unbroken light over an arc of the horizon of 135 degrees and so fixed as to show the light 67.5 degrees from right aft on each side of the vessel.
(d) “Towing light” means a yellow light having the same characteristics as the “sternlight” defined in paragraph (c) of this Rule.
(e) “All-round light” means a light showing an unbroken light over an arc of the horizon of 360 degrees.
(f) “Flashing light” means a light flashing at regular intervals at a frequency of 120 flashes or more per minute.
ANNOTATION
The arcs are the thing to learn, because the conduct Rules are built on them. The masthead light shows an unbroken arc of “225 degrees,” from right ahead to 22.5 degrees abaft each beam (a); each sidelight shows “112.5 degrees” on its side (b); the sternlight shows “135 degrees,” centred right aft (c). A towing light is “a yellow light” with the same characteristics as the sternlight (d); an all-round light shows “360 degrees” (e); a flashing light flashes at regular intervals (f). The numbers interlock: masthead plus sternlight totals 360, and the two sidelights plus the sternlight total 360. The 22.5-degrees-abaft-the-beam line, where a sidelight gives way to the sternlight, is the exact boundary Rule 13(b) uses to define overtaking, which is why a vessel seeing only your sternlight is astern of your beam and overtaking. See Rule 13; abaft the beam in the Glossary; the light-arc figure in the visuals pass.
Rule 22: Visibility of Lights
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The lights prescribed in these Rules shall have an intensity as specified in Section 8 of Annex I to these Regulations so as to be visible at the following minimum ranges:
(a) In vessels of 50 metres or more in length:
a masthead light, 6 miles; a sidelight, 3 miles; a sternlight, 3 miles; a towing light, 3 miles; a white, red, green or yellow all-round light, 3 miles.
(b) In vessels of 12 metres or more in length but less than 50 metres in length:
a masthead light, 5 miles; except that where the length of the vessel is less than 20 metres, 3 miles; a sidelight, 2 miles; a sternlight, 2 miles; a towing light, 2 miles; a white, red, green or yellow all-round light, 2 miles.
(c) In vessels of less than 12 metres in length:
a masthead light, 2 miles; a sidelight, 1 mile; a sternlight, 2 miles; a towing light, 2 miles; a white, red, green, or yellow all-round light, 2 miles.
(d) In inconspicuous, partly submerged vessels or objects being towed:
a white all-round light, 3 miles.
ANNOTATION
Sets the minimum ranges at which lights must be visible in clear air, scaled by vessel length, which fix the distance at which a vessel should be picked up at night. Reference detail; an OOW needs the principle (bigger vessels, longer ranges) rather than the table by heart, and the figures bear on safe speed at night (Rule 6). See Rule 6; the recognition tables.
Rule 23: Power-driven Vessels Underway
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(a) A power-driven vessel underway shall exhibit:
(i) a masthead light forward;
(ii) a second masthead light abaft of and higher than the forward one; except that a vessel of less than 50 metres in length shall not be obliged to exhibit such light but may do so;
(iii) sidelights;
(iv) a sternlight.
(b) An air-cushion vessel when operating in the non-displacement mode shall, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit an all-round flashing yellow light.
(c) A WIG craft only when taking off, landing and in flight near the surface shall, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit a high intensity all-round flashing red light.
(d)
(i) A power-driven vessel of less than 12 metres in length may in lieu of the lights prescribed in paragraph (a) of this Rule exhibit an all-round white light, and sidelights;
(ii) A power-driven vessel of less than 7 metres in length whose maximum speed does not exceed 7 knots may in lieu of the lights prescribed in paragraph (a) of this Rule exhibit an all-round white light and shall, if practicable, also exhibit sidelights;
(iii) The masthead light or all-round white light on a power-driven vessel of less than 12 metres in length may be displaced from the fore and aft centreline of the vessel if centreline fitting is not practicable, provided that the sidelights are combined in one lantern which shall be carried on the fore and aft centreline of the vessel or located as nearly as practicable in the same fore and aft line as the masthead light or the all-round white light.
ANNOTATION
A power-driven vessel underway shows a masthead light, sidelights and a sternlight, with a “second masthead light abaft of and higher than the forward one” on vessels of 50 metres or more (a). The two masthead lights are a heading indicator: their separation and relative position let an observer read which way she is pointing, and when they come into line she is heading straight towards or away. Special provisions cover air-cushion vessels in non-displacement mode and WIG craft (b, c) and small craft (d). See Rule 21; Chapter 7; the recognition tables.
Rule 24: Towing and Pushing
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(a) A power-driven vessel when towing shall exhibit:
(i) instead of the light prescribed in Rule 23(a)(i) or (a)(ii), two masthead lights in a vertical line. When the length of the tow, measuring from the stern of the towing vessel to the after end of the tow exceeds 200 metres, three such lights in a vertical line;
(ii) sidelights;
(iii) a sternlight;
(iv) a towing light in a vertical line above the sternlight;
(v) when the length of the tow exceeds 200 metres, a diamond shape where it can best be seen.
(b) When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit they shall be regarded as a power-driven vessel and exhibit the lights prescribed in Rule 23.
(c) A power-driven vessel when pushing ahead or towing alongside, except in the case of a composite unit, shall exhibit:
(i) instead of the light prescribed in Rule 23(a)(i) or (a)(ii), two masthead lights in a vertical line;
(ii) sidelights;
(iii) a sternlight.
(d) A power-driven vessel to which paragraph (a) or (c) of this Rule apply shall also comply with Rule 23(a)(ii).
(e) A vessel or object being towed, other than those mentioned in paragraph (g) of this Rule, shall exhibit:
(i) sidelights;
(ii) a sternlight;
(iii) when the length of the tow exceeds 200 metres, a diamond shape where it can best be seen.
(f) Provided that any number of vessels being towed alongside or pushed in a group shall be lighted as one vessel:
(i) a vessel being pushed ahead, not being part of a composite unit, shall exhibit at the forward end, sidelights;
(ii) a vessel being towed alongside shall exhibit a sternlight and at the forward end, sidelights.
(g) An inconspicuous, partly submerged vessel or object, or combination of such vessels or objects being towed, shall exhibit:
(i) if it is less than 25 metres in breadth, one all-round white light at or near the forward end and one at or near the after end except that dracones need not exhibit a light at or near the forward end;
(ii) if it is 25 metres or more in breadth, two additional all-round white lights at or near the extremities of its breadth;
(iii) if it exceeds 100 metres in length, additional all-round white lights between the lights prescribed in sub-paragraphs (i) and (ii) so that the distance between the lights shall not exceed 100 metres;
(iv) a diamond shape at or near the aftermost extremity of the last vessel or object being towed and if the length of the tow exceeds 200 metres an additional diamond shape where it can best be seen and located as far forward as is practicable.
(h) Where from any sufficient cause it is impracticable for a vessel or object being towed to exhibit the lights or shapes prescribed in paragraph (e) or (g) of this Rule, all possible measures shall be taken to light the vessel or object towed or at least to indicate the presence of such vessel or object.
(i)
(i) Where from any sufficient cause it is impracticable for a vessel not normally engaged in towing operations to display the lights prescribed in paragraph (a) or (c) of this Rule, such vessel shall not be required to exhibit those lights when engaged in towing another vessel in distress or otherwise in need of assistance.
(ii) All possible measures shall be taken to indicate the nature of the relationship between the towing vessel and the vessel being towed as authorised by Rule 36, in particular by illuminating the towline.
ANNOTATION
A vessel towing shows an extra masthead light or lights in a vertical line (“two” normally, “three” when “the length of the tow… exceeds 200 metres”), sidelights, a sternlight, a towing light above the sternlight, and a diamond shape by day “where the length of the tow exceeds 200 metres” (a). The point of the signal is to warn of a long, poorly-lit obstruction strung out astern, and the 200-metre threshold marks when that hazard is treated as serious. Further paragraphs cover pushing and being pushed, composite units, and partly submerged tows. See Rule 35; Chapter 7 (RAM where a tow severely restricts the tug); the recognition tables.
Rule 25: Sailing Vessels Underway and Vessels Under Oars
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(a) A sailing vessel underway shall exhibit:
(i) sidelights;
(ii) a sternlight.
(b) In a sailing vessel of less than 20 metres in length the lights prescribed in paragraph (a) of this Rule may be combined in one lantern carried at or near the top of the mast where it can best be seen.
(c) A sailing vessel underway may, in addition to the lights prescribed in paragraph (a) of this Rule, exhibit at or near the top of the mast, where they can best be seen, two all-round lights in a vertical line, the upper being red and the lower being green, but these lights shall not be exhibited in conjunction with the combined lantern permitted by paragraph (b) of this Rule.
(d)
(i) A sailing vessel of less than 7 metres in length shall, if practicable, exhibit the lights prescribed in paragraph (a) or (b) of this Rule, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision.
(ii) A vessel under oars may exhibit the lights prescribed in this Rule for sailing vessels, but if she does not, she shall have ready at hand an electric torch or lighted lantern showing a white light which shall be exhibited in sufficient time to prevent collision.
(e) A vessel proceeding under sail when also being propelled by machinery shall exhibit forward where it can best be seen a conical shape, apex downwards.
ANNOTATION
A sailing vessel underway shows sidelights and a sternlight (a), with the small-craft and optional masthead red-over-green variations at (b) and (c). A vessel under oars may show those lights or have a torch ready to show in time to prevent collision (d). The trap is (e): “a vessel proceeding under sail when also being propelled by machinery shall exhibit forward… a conical shape, apex downwards.” A motor-sailer is a power-driven vessel (Rule 3(c)) and must show power-driven lights by night and the cone by day. See Chapter 7; Rule 3(c); the recognition tables.
Rule 26: Fishing Vessels
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(a) A vessel engaged in fishing, whether underway or at anchor, shall exhibit only the lights and shapes prescribed in this Rule.
(b) A vessel when engaged in trawling, by which is meant the dragging through the water of a dredge net or other apparatus used as a fishing appliance, shall exhibit:
(i) two all-round lights in a vertical line, the upper being green and the lower white, or a shape consisting of two cones with their apexes together in a vertical line one above the other.
(ii) a masthead light abaft of and higher than the all-round green light; a vessel of less than 50 metres in length shall not be obliged to exhibit such a light but may do so;
(iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.
(c) A vessel engaged in fishing, other than trawling, shall exhibit:
(i) two all-round lights in a vertical line, the upper being red and the lower white, or a shape consisting of two cones with apexes together in a vertical line one above the other.
(ii) when there is outlying gear extending more than 150 metres horizontally from the vessel, an all-round white light or a cone apex upwards in the direction of the gear;
(iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.
(d) The additional signals described in Annex II to these regulations apply to a vessel engaged in fishing in close proximity to other vessels engaged in fishing.
(e) A vessel when not engaged in fishing shall not exhibit the lights or shapes prescribed in this rule, but only those prescribed for a vessel of her length.
ANNOTATION
A vessel “engaged in trawling” shows all-round green-over-white (b); a vessel “engaged in fishing, other than trawling” shows all-round red-over-white, with a signal for gear extending more than 150 metres horizontally (c). The qualifying idea is the one from Rule 3(d): these signals belong only to a vessel whose gear “restricts manoeuvrability,” so a vessel trolling shows ordinary power-driven or sailing lights, not the fishing signal. Paragraph (d) covers proximity to other fishing vessels; (e) covers a vessel not engaged in fishing showing none of this. See Chapter 7; Rule 3(d); trolling lines in the Glossary; the recognition tables.
Rule 27: Vessels Not Under Command or Restricted in Their Ability to Manoeuvre
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(a) A vessel not under command shall exhibit:
(i) two all-round red lights in a vertical line where they can best be seen;
(ii) two balls or similar shapes in a vertical line where they can best be seen;
(iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight.
(b) A vessel restricted in her ability to manoeuvre, except a vessel engaged in mineclearance operations, shall exhibit:
(i) three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;
(ii) three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond;
(iii) when making way through the water, a masthead light or lights, sidelights and a sternlight, in addition to the lights prescribed in sub-paragraph (i);
(iv) when at anchor, in addition to the lights or shapes prescribed in sub-paragraphs (i) and (ii), the light, lights or shape prescribed in Rule 30.
(c) A power-driven vessel engaged in a towing operation such as severely restricts the towing vessel and her tow in their ability to deviate from their course shall, in addition to the lights or shape prescribed in Rule 24(a), exhibit the lights or shapes prescribed in sub-paragraphs (b)(i) and (ii) of this Rule.
(d) A vessel engaged in dredging or underwater operations, when restricted in her ability to manoeuvre, shall exhibit the lights and shapes prescribed in sub-paragraphs (b)(i), (ii) and (iii) of this Rule and shall in addition, when an obstruction exists, exhibit:
(i) two all-round red lights or two balls in a vertical line to indicate the side on which the obstruction exists;
(ii) two all-round green lights or two diamonds in a vertical line to indicate the side on which another vessel may pass;
(iii) when at anchor, the lights or shapes prescribed in this paragraph instead of the lights or shape prescribed in Rule 30.
(e) Whenever the size of a vessel engaged in diving operations makes it impracticable to exhibit all lights and shapes prescribed in paragraph (d) of this Rule, the following shall be exhibited:
(i) three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white;
(ii) a rigid replica of the International Code flag “A” not less than 1 metre in height. Measures shall be taken to ensure its all-round visibility.
(f) A vessel engaged in mineclearance operations shall in addition to the lights prescribed for a power-driven vessel in Rule 23 or to the lights or shape prescribed for a vessel at anchor in Rule 30 as appropriate, exhibit three all-round green lights or three balls. One of these lights or shapes shall be exhibited near the foremast head and one at each end of the fore yard. These lights or shapes indicate that it is dangerous for another vessel to approach within 1000 metres of the mineclearance vessel.
(g) Vessels of less than 12 metres in length, except those engaged in diving operations, shall not be required to exhibit the lights and shapes prescribed in this Rule.
(h) The signals prescribed in this Rule are not signals of vessels in distress and requiring assistance. Such signals are contained in Annex IV to these Regulations.
ANNOTATION
A vessel not under command shows “two all-round red lights in a vertical line” and, when making way, sidelights and a sternlight (a). A vessel restricted in her ability to manoeuvre shows “red, white, red in a vertical line” (b), and where the work is dredging or underwater operations adds “two all-round red lights” on the obstructed side and “two all-round green lights” on the clear side, telling others which side is safe to pass (d). The two-light versus three-light distinction marks the difference between the involuntary NUC and the work-driven RAM (Rule 3(f), (g)). See Chapter 7; Rule 18; Rule 3(f) and (g); the recognition tables.
Rule 28: Vessels Constrained by Their Draught
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A vessel constrained by her draught may, in addition to the lights prescribed for power-driven vessels in Rule 23, exhibit where they can best be seen three all-round red lights in a vertical line, or a cylinder.
ANNOTATION
A vessel constrained by her draught may show, in addition to her power-driven lights, “three all-round red lights in a vertical line” or “a cylinder” by day. The signal says she cannot deviate because the water itself constrains her, so give her a wide berth, but recall the Rule 3(h) trap: she is still a power-driven vessel and an ordinary crossing can develop with her. See Chapter 7; Rule 3(h); Rule 18(d); constrained by her draught in the Glossary; the recognition tables.
Rule 29: Pilot Vessels
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(a) A vessel engaged on pilotage duty shall exhibit:
(i) at or near the masthead, two all-round lights in a vertical line, the upper being white and the lower red;
(ii) when underway, in addition, sidelights and a sternlight;
(iii) when at anchor, in addition to the lights prescribed in sub-paragraph (i), the light, lights or shape prescribed in Rule 30 for vessels at anchor.
(b) A pilot vessel when not engaged on pilotage duty shall exhibit the lights or shapes prescribed for a similar vessel of her length.
ANNOTATION
A vessel “engaged on pilotage duty” shows “white over red” all-round lights at the masthead, plus the appropriate underway or anchor lights (a). Off duty she shows only the latter (b). The mnemonic is “white over red, pilot ahead.” See Rule 30; the recognition tables.
Rule 30: Anchored Vessels and Vessels Aground
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(a) A vessel at anchor shall exhibit where it can best be seen:
(i) in the fore part, an all-round white light or one ball;
(ii) at or near the stern and at a lower level than the light prescribed in sub-paragraph (i), an all-round white light.
(b) A vessel of less than 50 metres in length may exhibit an all-round white light where it can best be seen instead of the lights prescribed in paragraph (a) of this Rule.
(c) A vessel at anchor may, and a vessel of 100 metres and more in length shall, also use the available working or equivalent lights to illuminate her decks.
(d) A vessel aground shall exhibit the lights prescribed in paragraph (a) or (b) of this Rule and in addition, where they can best be seen:
(i) two all-round red lights in a vertical line;
(ii) three balls in a vertical line.
(e) A vessel of less than 7 metres in length, when at anchor, not in or near a narrow channel, fairway or anchorage, or where other vessels normally navigate, shall not be required to exhibit the lights or shape prescribed in paragraphs (a) and (b) of this Rule.
(f) A vessel of less than 12 metres in length, when aground, shall not be required to exhibit the lights or shapes prescribed in sub-paragraphs (d)(i) and (ii) of this Rule.
ANNOTATION
An anchored vessel shows an all-round white light forward and, on vessels of 50 metres or more, a second one aft “at or near the stern… lower than the forward light,” and a ball by day (a, b). The forward-and-aft arrangement indicates heading and rough length. A vessel aground shows the anchor lights plus “two all-round red lights in a vertical line” and “three balls” by day (d). An anchored vessel is no longer underway (Rule 3(i)): others manoeuvre around her. See Chapter 7; Rule 35 (anchor and aground sound signals); the recognition tables.
Rule 31: Seaplanes
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Where it is impracticable for a seaplane or a WIG craft to exhibit lights and shapes of the characteristics or in the positions prescribed in the Rules of this Part she shall exhibit lights and shapes as closely similar in characteristics and position as is possible.
ANNOTATION
Where it is impracticable for a seaplane (or a WIG craft) to exhibit lights and shapes “of the characteristics or in the positions prescribed,” she shows them “as closely similar in characteristics and position as is possible.” The same as-close-as-possible logic as Rule 1(e), reflecting that her configuration may make exact compliance impossible. She is a vessel (Rule 3(e)) and keeps well clear of all vessels (Rule 18(e)). See Rule 1(e); Rule 3(e); Rule 18(e).
Part D: Sound and Light Signals (Rules 32 to 37)
Rule 32: Definitions
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(a) The word “whistle” means any sound signalling appliance capable of producing the prescribed blasts and which complies with the specifications in Annex III to these Regulations.
(b) The term “short blast” means a blast of about one second’s duration.
(c) The term “prolonged blast” means a blast of from four to six seconds’ duration.
ANNOTATION
Defines the building blocks. A “whistle” is any sound-signalling appliance capable of producing the prescribed blasts (a). A “short blast” is “about one second” (b); a “prolonged blast” is “from four to six seconds” (c). Every signal in Part D is built from these two, so the short-versus-prolonged distinction is the key to reading all of them. See Rules 34 and 35; short blast and prolonged blast in the Glossary.
Rule 33: Equipment for Sound Signals
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(a) A vessel of 12 metres or more in length shall be provided with a whistle, a vessel of 20 metres or more in length shall be provided with a bell in addition to a whistle, and a vessel of 100 metres or more in length shall, in addition, be provided with a gong, the tone and sound of which cannot be confused with that of the bell. The whistle, bell and gong shall comply with the specifications in Annex III to these Regulations. The bell or gong or both may be replaced by other equipment having the same respective sound characteristics, provided that manual sounding of the required signals shall always be possible.
(b) A vessel of less than 12 metres in length shall not be obliged to carry the sound signalling appliances prescribed in paragraph (a) of this Rule but if she does not, she shall be provided with some other means of making an efficient sound signal.
ANNOTATION
Sets what each vessel must carry, scaled by length: a vessel of “12 metres or more” carries a whistle, a vessel of “20 metres or more” a bell in addition, and a vessel of “100 metres or more” a gong as well, “the tone and sound of which cannot be confused with that of the bell” (a). On a large anchored vessel the bell sounded forward and the gong aft give an approaching vessel a sense of her length and orientation in fog. A vessel of less than 12 metres is excused the equipment but must have some other means of making an efficient sound signal (b). See Rule 35; the recognition tables.
Rule 34: Manoeuvring and Warning Signals
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(a) When vessels are in sight of one another, a power-driven vessel underway, when manoeuvring as authorised or required by these Rules, shall indicate that manoeuvre by the following signals on her whistle:
one short blast to mean “I am altering my course to starboard”; two short blasts to mean “I am altering my course to port”; three short blasts to mean “I am operating astern propulsion”.
(b) Any vessel may supplement the whistle signals prescribed in paragraph (a) of this Rule by light signals, repeated as appropriate, whilst the manoeuvre is being carried out:
(i) these light signals shall have the following significance: one flash to mean “I am altering my course to starboard”; two flashes to mean “I am altering my course to port”; three flashes to mean “I am operating astern propulsion”;
(ii) the duration of each flash shall be about one second, the interval between flashes shall be about one second, and the interval between successive signals shall be not less than ten seconds;
(iii) the light used for this signal shall, if fitted, be an all-round white light, visible at a minimum range of 5 miles, and shall comply with the provisions of Annex I to these Regulations.
(c) When in sight of one another in a narrow channel or fairway:
(i) a vessel intending to overtake another shall in compliance with Rule 9(e)(i) indicate her intention by the following signals on her whistle: two prolonged blasts followed by one short blast to mean “I intend to overtake you on your starboard side”; two prolonged blasts followed by two short blasts to mean “I intend to overtake you on your port side”;
(ii) the vessel about to be overtaken when acting in accordance with Rule 9(e)(i) shall indicate her agreement by the following signal on her whistle: one prolonged, one short, one prolonged and one short blast, in that order.
(d) When vessels in sight of one another are approaching each other and from any cause either vessel fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken by the other to avoid collision, the vessel in doubt shall immediately indicate such doubt by giving at least five short and rapid blasts on the whistle. Such signal may be supplemented by a light signal of at least five short and rapid flashes.
(e) A vessel nearing a bend or an area of a channel or fairway where other vessels may be obscured by an intervening obstruction shall sound one prolonged blast. Such signal shall be answered with a prolonged blast by any approaching vessel that may be within hearing around the bend or behind the intervening obstruction.
(f) If whistles are fitted on a vessel at a distance apart of more than 100 metres, one whistle only shall be used for giving manoeuvring and warning signals.
ANNOTATION
The signals for vessels “in sight of one another.” A power-driven vessel altering course indicates it by whistle: “one short blast” for a turn to starboard, “two short blasts” for a turn to port, and “three short blasts” when operating astern propulsion (a), with matching light signals available (b). Paragraph (c) gives the overtaking signals in a narrow channel (Rule 9(e)). The warning signal at (d) is the important one: a vessel in doubt whether another is taking sufficient action to avoid collision “shall… give at least five short and rapid blasts,” the signal a stand-on vessel sounds when the give-way vessel is not acting (Rule 17). Paragraph (e) gives the bend signal of “one prolonged blast” (Rule 9(f)). See Rule 9; Rule 17; the recognition tables.
Rule 35: Sound Signals in Restricted Visibility
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In or near an area of restricted visibility, whether by day or night, the signals prescribed in this Rule shall be used as follows:
(a) A power-driven vessel making way through the water shall sound at intervals of not more than 2 minutes one prolonged blast.
(b) A power-driven vessel underway but stopped and making no way through the water shall sound at intervals of not more than 2 minutes two prolonged blasts in succession with an interval of about 2 seconds between them.
(c) A vessel not under command, a vessel restricted in her ability to manoeuvre, a vessel constrained by her draught, a sailing vessel, a vessel engaged in fishing and a vessel engaged in towing or pushing another vessel shall, instead of the signals prescribed in paragraphs (a) or (b) of this Rule, sound at intervals of not more than 2 minutes three blasts in succession, namely one prolonged followed by two short blasts.
(d) A vessel engaged in fishing, when at anchor, and a vessel restricted in her ability to manoeuvre when carrying out her work at anchor, shall instead of the signals prescribed in paragraph (g) of this Rule sound the signal prescribed in paragraph (c) of this Rule.
(e) A vessel towed or if more than one vessel is towed the last vessel of the tow, if manned, shall at intervals of not more than 2 minutes sound four blasts in succession, namely one prolonged followed by three short blasts. When practicable, this signal shall be made immediately after the signal made by the towing vessel.
(f) When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit they shall be regarded as a power-driven vessel and shall give the signals prescribed in paragraphs (a) or (b) of this Rule.
(g) A vessel at anchor shall at intervals of not more than one minute ring the bell rapidly for about 5 seconds. In a vessel of 100 metres or more in length the bell shall be sounded in the forepart of the vessel and immediately after the ringing of the bell the gong shall be sounded rapidly for about 5 seconds in the after part of the vessel. A vessel at anchor may in addition sound three blasts in succession, namely one short, one prolonged and one short blast, to give warning of her position and of the possibility of collision to an approaching vessel.
(h) A vessel aground shall give the bell signal and if required the gong signal prescribed in paragraph (g) of this Rule and shall, in addition, give three separate and distinct strokes on the bell immediately before and after the rapid ringing of the bell. A vessel aground may in addition sound an appropriate whistle signal.
(i) A vessel of 12 metres or more but less than 20 metres in length shall not be obliged to give the bell signals prescribed in paragraphs (g) and (h) of this Rule. However, if she does not, she shall make some other efficient sound signal at intervals of not more than 2 minutes.
(j) A vessel of less than 12 metres in length shall not be obliged to give the above mentioned signals but, if she does not, shall make some other efficient sound signal at intervals of not more than 2 minutes.
(k) A pilot vessel when engaged on pilotage duty may in addition to the signals prescribed in paragraphs (a), (b) or (g) of this Rule sound an identity signal consisting of four short blasts.
ANNOTATION
The fog signals, sounded “in or near an area of restricted visibility” by day or night. The distinctions to read are by state. A power-driven vessel “making way through the water” sounds “one prolonged blast” at intervals; a power-driven vessel “underway but stopped and making no way” sounds “two prolonged blasts” (the underway-but-not-making-way distinction of Rule 3(i) made audible). A vessel not under command, restricted in her ability to manoeuvre, constrained by her draught, sailing, fishing, or towing sounds “one prolonged followed by two short blasts.” An anchored vessel rings the bell; aground, she gives bell and gong signals with the additional strokes. The signal tells you the state of a vessel you cannot see. See Chapter 7; Rule 3(i); Rule 33; the recognition tables.
Rule 36: Signals to Attract Attention
THE RULE · MISCPUB 0127
If necessary to attract the attention of another vessel any vessel may make light or sound signals that cannot be mistaken for any signal authorised elsewhere in these Rules, or may direct the beam of her searchlight in the direction of the danger, in such a way as not to embarrass any vessel. Any light to attract the attention of another vessel shall be such that it cannot be mistaken for any aid to navigation. For the purpose of this Rule the use of high intensity intermittent or revolving lights, such as strobe lights, shall be avoided.
ANNOTATION
A vessel may make “light or sound signals that cannot be mistaken for any signal authorised elsewhere,” or direct a searchlight, to attract attention, provided the signal cannot be mistaken for an aid to navigation and a searchlight is not used so as to embarrass another vessel. The constraint is that an attention signal must not be confusable with a prescribed one, the same closed-vocabulary logic as Rule 20(b). See Rule 20.
Rule 37: Distress Signals
THE RULE · MISCPUB 0127
When a vessel is in distress and requires assistance she shall use or exhibit the signals described in Annex IV to these Regulations.
ANNOTATION
When a vessel is “in distress and requires assistance” she uses or exhibits the signals set out in “Annex IV.” A pointer Rule: the actual list (the gun fired at intervals, the SOS, the flames, the orange smoke, and the rest) lives in the Annex. See Annex IV; the recognition tables.
Parts E and F (Rules 38 to 41) follow. They are administrative: exemptions and the verification regime, with no live bridge content (Chapter 5).