(London, 17 June 1960)
Entry into force generally: 1 September 1965

PART A
PRELIMINARY AND DEFINITIONS

Rule 1

(a) These Rules shall be followed by all vessels and seaplanes upon the high seas and in all waters connected therewith navigable by seagoing vessels, except as provided in Rule 30. Where, as a result of their special construction, it is not possible for seaplanes to comply fully with the provisions of Rules specifying the carrying of lights and shapes, these provisions shall be followed as closely as circumstances permit.
(b) The Rules concerning lights shall be complied with in all weathers from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the prescribed lights or do not impair their visibility or distinctive character, or interfere with the keeping of a proper look-out. The lights prescribed by these Rules may also be exhibited from sunrise to sunset in restricted visibility and in all other circumstances when it is deemed necessary.
(c) In the following Rules, except where the context otherwise requires:
(i) the word "vessel" includes every description of water craft, other than a seaplane on the water, used or capable of being used as a means of transportation on water;
(ii) the word "seaplane" includes a flying boat and any other aircraft designed to manoeuvre on the water;
(iii) the term "power-driven vessel" means any vessel propelled by machinery;
(iv) every power-driven vessel which is under sail and not under power is to be considered a sailing vessel, and every vessel under power, whether under sail or not, is to be considered a power-driven vessel;
(v) a vessel or seaplane on the water is "under way" when she is not at anchor, or made fast to the shore, or aground;
(vi) the term "height above the hull" means height above the uppermost continuous deck;
(vii) the length and breadth of a vessel shall be her length overall and largest breadth;
(viii) the length and span of a seaplane shall be its maximum length and span as shown in its certificate of airworthiness, or as determined by measurement in the absence of such certificate;
(ix) vessels shall be deemed to be in sight of one another only when one can be observed visually from the other;
(x) the word "visible", when applied to lights, means visible on a dark night with a clear atmosphere;
(xi) the term "short blast" means a blast of about one second's duration;
(xii) the term "prolonged blast" means a blast of from four to six seconds' duration;
(xiii) the word "whistle" means any appliance capable of producing the prescribed short and prolonged blasts;
(xiv) the term "engaged in fishing" means fishing with nets, lines or trawls but does not include fishing with trolling lines.

PART B
LIGHTS AND SHAPES

Rule 2

(a) A power-driven vessel when under way shall carry:
(i) On or in front of the foremast, or if a vessel without a foremast then in the forepart of the vessel, a white light so constructed as to show an unbroken light over an arc of the horizon of 225 degrees (20 points of the compass), so fixed as to show the light 1121/2 degrees (10 points) on each side of the vessel, that is, from right ahead to 221/2 degrees (2 points) abaft the beam on either side, and of such a character as to be visible at a distance of at least 5 miles.
(ii) Either forward or abaft the white light prescribed in sub-section (i) a second white light similar in construction and character to that light. Vessels of less than 150 feet in length shall not be required to carry this second white light but may do so.
(iii) These two white lights shall be so placed in a line with and over the keel that one shall be at least 15 feet higher than the other and in such a position that the forward light shall always be shown lower than the after one. The horizontal distance between the two white lights shall be at least three times the vertical distance. The lower of these two white lights or, if only one is carried, then that light, shall be placed at a height above the hull of not less than 20 feet, and, if the breadth of the vessel exceeds 20 feet, then at a height above the hull not less than such breadth, so however that the light need not be placed at a greater height above the hull than 40 feet. In all circumstances the light or lights, as the case may be, shall be so placed as to be clear of and above all other lights and obstructing superstructures.
(iv) On the starboard side a green light so constructed as to show an unbroken light over an arc of the horizon of 1121/2 degrees (10 points of the compass), so fixed as to show the light from right ahead to 221/2 degrees (2 points) abaft the beam on the starboard side, and of such a character as to be visible at a distance of at least 2 miles.
(v) On the port side a red light so constructed as to show an unbroken light over an arc of the horizon of 1121/2 degrees (10 points of the compass), so fixed as to show the light from right ahead to 221/2 degrees (2 points) abaft the beam on the port side, and of such a character as to be visible at a distance of at least 2 miles.
(vi) The said green and red sidelights shall be fitted with inboard screens projecting at least 3 feet forward from the light, so as to prevent these lights from being seen across the bows.
(b) A seaplane under way on the water shall carry:
(i) In the forepart amidships where it can best be seen a white light, so constructed as to show an unbroken light over an arc of the horizon of 220 degrees of the compass, so fixed as to show the light 110 degrees on each side of the seaplane, namely, from right ahead to 20 degrees abaft the beam on either side, and of such a character as to be visible at a distance of at least 3 miles.
(ii) On the right or starboard wing tip a green light, so constructed as to show an unbroken light over an arc of the horizon of l10 degrees of the compass, so fixed as to show the light from right ahead to 20 degrees abaft the beam on the starboard side, and of such a character as to be visible at a distance of at least 2 miles.
(iii) On the left or port wing tip a red light, so constructed as to show an unbroken light over an arc of the horizon of 110 degrees of the compass, so fixed as to show the light from right ahead to 20 degrees abaft the beam on the port side, and of such a character as to be visible at a distance of at least 2 miles.

Rule 3

(a) A power-driven vessel when towing or pushing another vessel or seaplane shall, in addition to her sidelights, carry two white lights in a vertical line one over the other, not less than 6 feet apart, and when towing and the length of the tow, measuring from the stern of the towing vessel to the stern of the last vessel towed, exceeds 600 feet, shall carry three white lights in a vertical line one over the other, so that the upper and lower lights shall be the same distance from, and not less than 6 feet above or below, the middle light. Each of these lights shall be of the same construction and character and one of them shall be carried in the same position as the white light prescribed in Rule 2(a)(i). None of these lights shall be carried at a height of less than 14 feet above the hull. In a vessel with a single mast, such lights may be carried on the mast.
(b) The towing vessel shall also show either the stern light prescribed in Rule 10 or in lieu of that light a small white light abaft the funnel or aftermast for the tow to steer by, but such light shall not be visible forward of the beam.
(c) Between sunrise and sunset a power-driven vessel engaged in towing, if the length of tow exceeds 600 feet, shall carry, where it can best be seen, a black diamond shape at least 2 feet in diameter.
(d) A seaplane on the water, when towing one or more seaplanes or vessels, shall carry the lights prescribed in Rule 2(b)(i), (ii) and (iii); and, in addition, she shall carry a second white light of the same construction and character as the white light prescribed in Rule 2(b)(i), and in a vertical line at least 6 feet above or below such light.

Rule 4

(a) A vessel which is not under command shall carry, where they can best be seen, and, if a power-driven vessel, in lieu of the lights prescribed in Rule 2(a)(i) and (ii), two red lights in a vertical line one over the other not less than 6 feet apart, and of such a character as to be visible all round the horizon at a distance of at least 2 miles. By day, she shall carry in a vertical line one over the other not less than 6 feet apart, where they can best be seen, two black balls or shapes, each not less than 2 feet in diameter.
(b) A seaplane on the water which is not under command may carry, where they can best be seen, and in lieu of the light prescribed in Rule 2(b)(i), two red lights in a vertical line, one over the other, not less than 3 feet apart, and of such a character as to be visible all round the horizon at a distance of at least 2 miles, and may by day carry in a vertical line one over the other not less than 3 feet apart, where they can best be seen, two black balls or shapes, each not less than 2 feet in diameter.
(c) A vessel engaged in laying or in picking up a submarine cable or navigation mark, or a vessel engaged in surveying or underwater operations, or a vessel engaged in replenishment at sea, or in the launching or recovery of aircraft when from the nature of her work she is unable to get out of the way of approaching vessels, shall carry, in lieu of the lights prescribed in Rule 2(a)(i) and (ii), or Rule 7(a)(i), three lights in a vertical line one over the other so that the upper and lower lights shall be the same distance from, and not less than 6 feet above or below, the middle light. The highest and lowest of these lights shall be red, and the middle light shall be white, and they shall be of such a character as to be visible all round the horizon at a distance of at least 2 miles. By day, she shall carry in a vertical line one over the other not less than 6 feet apart, where they can best be seen, three shapes each not less than 2 feet in diameter, of which the highest and lowest shall be globular in shape and red in colour, and the middle one diamond in shape and white.
(d) (i) A vessel engaged in minesweeping operations shall carry at the fore truck a green light, and at the end or ends of the fore yard on the side or sides on which danger exists, another such light or lights. These lights shall be carried in addition to the light prescribed in Rule 2(a)(i) or Rule 7(a)(i), as appropriate, and shall be of such a character as to be visible all round the horizon at a distance of at least 2 miles. By day she shall carry black balls, not less than 2 feet in diameter, in the same position as the green lights.
(ii) The showing of these lights or balls indicates that it is dangerous for other vessels to approach closer than 3000 feet astern of the minesweeper or 1500 feet on the side or sides on which danger exists.
(e) The vessels and seaplanes referred to in this Rule, when not making way through the water, shall show neither the coloured sidelights nor the stern light, but when making way they shall show them.
(f) The lights and shapes prescribed in this Rule are to be taken by other vessels and seaplanes as signals that the vessel or seaplane showing them is not under command and cannot therefore get out of the way.
(g) These signals are not signals of vessels in distress and requiring assistance. Such signals are contained in Rule 31.

Rule 5

(a) A sailing vessel under way and any vessel or seaplane being towed shall carry the same lights as are prescribed in Rule 2 for a power-driven vessel or a seaplane under way, respectively, with the exception of the white lights prescribed therein, which they shall never carry. They shall also carry stern lights as prescribed in Rule 10, provided that vessels towed, except the last vessel of a tow, may carry, in lieu of such stern light, a small white light as prescribed in Rule 3(b).
(b) In addition to the lights prescribed in section (a), a sailing vessel may carry on the top of the foremast two lights in a vertical line one over the other, sufficiently separated so as to be clearly distinguished. The upper light shall be red and the lower light shall be green. Both lights shall be constructed and fixed as prescribed in Rule 2(a)(i) and shall be visible at a distance of at least 2 miles.
(c) A vessel being pushed ahead shall carry, at the forward end, on the starboard side a green light and on the port side a red light, which shall have the same characteristics as the lights prescribed in Rule 2(a)(iv) and (v) and shall be screened as provided in Rule 2(a)(vi), provided that any number of vessels pushed ahead in a group shall be lighted as one vessel.
(d) Between sunrise and sunset a vessel being towed, if the length of the tow exceeds 600 feet, shall carry where it can best be seen a black diamond shape at least 2 feet in diameter.

Rule 6

(a) When it is not possible on account of bad weather or other sufficient cause to fix the green and red sidelights, these lights shall be kept at hand lighted and ready for immediate use, and shall, on the approach of or to other vessels, be exhibited on their respective sides in sufficient time to prevent collision, in such manner as to make them most visible, and so that the green light shall not be seen on the port side nor the red light on the starboard side, nor, if practicable, more than 221/2 degrees (2 points) abaft the beam on their respective sides.
(b) To make the use of these portable lights more certain and easy, the lanterns containing them shall each be painted outside with the colour of the lights they respectively contain, and shall be provided with proper screens.

Rule 7

Power-driven vessels of less than 65 feet in length, vessels under oars or sails of less than 40 feet in length, and rowing boats, when under way shall not be required to carry the lights prescribed in Rules 2, 3 and 5, but if they do not carry them they shall be provided with the following lights:
(a) Power-driven vessels of less than 65 feet in length, except as provided in sections (b) and (c), shall carry:
(i) In the forepart of the vessel, where it can best be seen, and at a height above the gunwale of not less than 9 feet, a white light constructed and fixed as prescribed in Rule 2(a)(i) and of such a character as to be visible at a distance of at least 3 miles.
(ii) Green and red sidelights constructed and fixed as prescribed in Rule 2(a)(iv) and (v), and of such a character as to be visible at a distance of at least 1 mile, or a combined lantern showing a green light and a red light from right ahead to 221/2 degrees (2 points) abaft the beam on their respective sides. Such lanterns shall be carried not less than 3 feet below the white light.
(b) Power-driven vessels of less than 65 feet in length when towing or pushing another vessel shall carry:
(i) In addition to the sidelights or the combined lantern prescribed in section (a)(ii) two white lights in a vertical line, one over the other not less than 4 feet apart. Each of these lights shall be of the same construction and character as the white light prescribed in section (a)(i) and one of them shall be carried in the same position. In a vessel with a single mast such lights may be carried on the mast.
(ii) Either a stern light as prescribed in Rule l0 or in lieu of that light a small white light abaft the funnel or aftermast for the tow to steer by, but such light shall not be visible forward of the beam.
(c) Power-driven vessels of less than 40 feet in length may carry the white light at a less height than 9 feet above the gunwale but it shall be carried not less than 3 feet above the sidelights or the combined lantern prescribed in section (a)(ii).
(d) Vessels of less than 40 feet in length, under oars or sails, except as provided in section (f), shall, if they do not carry the sidelights, carry, where it can best be seen, a lantern showing a green light on one side and a red light on the other, of such a character as to be visible at a distance of at least 1 mile, and so fixed that the green light shall not be seen on the port side, nor the red light on the starboard side. Where it is not possible to fix this light, it shall be kept ready for immediate use and shall be exhibited in sufficient time to prevent collision and so that the green light shall not be seen on the port side nor the red light on the starboard side.
(e) The vessels referred to in this Rule when being towed shall carry the sidelights or the combined lantern prescribed in sections (a) or (d) of this Rule, as appropriate, and a stern light as prescribed in Rule 10, or, except the last vessel of the tow, a small white light as prescribed in section (b)(ii). When being pushed ahead they shall carry at the forward end the sidelights or combined lantern prescribed in sections (a) or (d) of this Rule, as appropriate, provided that any number of vessels referred to in this Rule when pushed ahead in a group shall be lighted as one vessel under this Rule unless the overall length of the group exceeds 65 feet when the provisions of Rule 5(c) shall apply.
(f) Small rowing boats, whether under oars or sail, shall only be required to have ready at hand an electric torch or a lighted lantern, showing a white light, which shall be exhibited in sufficient time to prevent collision.
(g) The vessels and boats referred to in this Rule shall not be required to carry the lights or shapes prescribed in Rules 4(a) and 11(e) and the size of their day signals may be less than is prescribed in Rules 4(c) and 11(c).

Rule 8

(a) A power-driven pilot-vessel when engaged on pilotage duty and under way:
(i) Shall carry a white light at the masthead at a height of not less than 20 feet above the hull, visible all round the horizon at a distance of at least 3 miles and at a distance of 8 feet below it a red light similar in construction and character. If such a vessel is of less than 65 feet in length she may carry the white light at a height of not less than 9 feet above the gunwale and the red light at a distance of 4 feet below the white light.
(ii) Shall carry the sidelights or lanterns prescribed in Rule 2(a)(iv) and (v) or Rule 7(a)(ii) or (d), as appropriate, and the stern light prescribed in Rule 10.
(iii) Shall show one or more flare-up lights at intervals not exceeding 10 minutes. An intermittent white light visible all round the horizon may be used in lieu of flare-up lights.
(b) A sailing pilot-vessel when engaged on pilotage duty and under way:
(i) Shall carry a white light at the masthead visible all round the horizon at a distance of at least 3 miles.
(ii) Shall be provided with the sidelights or lantern prescribed in Rules 5(a) or 7(d), as appropriate, and shall, on the near approach of or to other vessels, have such lights ready for use, and shall show them at short intervals to indicate the direction in which she is heading, but the green light shall not be shown on the port side nor the red light on the starboard side. She shall also carry the stern light prescribed in Rule 10.
(iii) Shall show one or more flare-up lights at intervals not exceeding 10 minutes.
(c) A pilot-vessel when engaged on pilotage duty and not under way shall carry the lights and show the flares prescribed in sections (a)(i) and (iii) or (b)(i) and (iii), as appropriate, and if at anchor shall also carry the anchor lights prescribed in Rule 11.
(d) A pilot-vessel when not engaged on pilotage duty shall show the lights or shapes for a similar vessel of her length.

Rule 9

(a) Fishing vessels when not engaged in fishing shall show the lights or shapes for similar vessels of their length.
(b) Vessels engaged in fishing, when under way or at anchor, shall show only the lights and shapes prescribed in this Rule, which lights and shapes shall be visible at a distance of at least 2 miles.
(c) (i) Vessels when engaged in trawling, by which is meant the dragging of a dredge net or other apparatus through the water, shall carry two lights in a vertical line, one over the other, not less than 4 feet nor more than 12 feet apart. The upper of these lights shall be green and the lower light white and each shall be visible all round the horizon. The lower of these two lights shall be carried at a height above the sidelights not less than twice the distance between the two vertical lights.
(ii) Such vessels may in addition carry a white light similar in construction to the white light prescribed in Rule 2(a)(i) but such light shall be carried lower than and abaft the all-round green and white lights.
(d) Vessels when engaged in fishing, except vessels engaged in trawling, shall carry the lights prescribed in section (c)(i) except that the upper of the two vertical lights shall be red. Such vessel if of less than 40 feet in length may carry the red light at a height of not less than 9 feet above the gunwale and the white light not less than 3 feet below the red light.
(e) Vessels referred to in sections (c) and (d), when making way through the water, shall carry the sidelights or lanterns prescribed in Rule 2(a)(iv) and (v) or Rule 7(a)(ii) or (d), as appropriate, and the stern light prescribed in Rule 10. When not making way through the water they shall show neither the sidelights nor the stern light.
(f) Vessels referred to in section (d) with outlying gear extending more than 500 feet horizontally into the seaway shall carry an additional all-round white light at a horizontal distance of not less than 6 feet nor more than 20 feet away from the vertical lights in the direction of the outlying gear. This additional white light shall be placed at a height not exceeding that of the white light prescribed in section (c)(i) and not lower than the sidelights.
(g) In addition to the lights which they are required by this Rule to carry, vessels engaged in fishing may, if necessary in order to attract the attention of an approaching vessel, use a flare-up light, or may direct the beam of their searchlight in the direction of a danger threatening the approaching vessel, in such a way as not to embarrass other vessels. They may also use working lights but fishermen shall take into account that specially bright or insufficiently screened working lights may impair the visibility and distinctive character of the lights prescribed in this Rule.
(h) By day vessels when engaged in fishing shall indicate their occupation by displaying where it can best be seen a black shape consisting of two cones each not less than 2 feet in diameter with their points together one above the other. Such vessels if of less than 65 feet in length may substitute a basket for such black shape. If their outlying gear extends more than 500 feet horizontally into the seaway vessels engaged in fishing shall display in addition one black conical shape, point upwards, in the direction of the outlying gear.[1]

Rule 10

(a) Except where otherwise provided in these Rules, a vessel when under way shall carry at her stern a white light, so constructed that it shall show an unbroken light over an arc of the horizon of 135 degrees (12 points of the compass), so fixed as to show the light 671/2 degrees (6 points) from right aft on each side of the vessel, and of such a character as to be visible at a distance of at least 2 miles.
(b) In a small vessel, if it is not possible on account of bad weather or other sufficient cause for this light to be fixed, an electric torch or a lighted lantern showing a white light shall be kept at hand ready for use and shall, on the approach of an overtaking vessel, be shown in sufficient time to prevent collision.
(c) A seaplane on the water when under way shall carry on her tail a white light, so constructed as to show an unbroken light over an arc of the horizon of 140 degrees of the compass, so fixed as to show the light 70 degrees from right aft on each side of the seaplane, and of such a character as to be visible at a distance of at least 2 miles.

Rule 11

(a) A vessel of less than 150 feet in length, when at anchor, shall carry in the forepart of the vessel, where it can best be seen, a white light visible all round the horizon at a distance of at least 2 miles. Such a vessel may also carry a second white light in the position prescribed in section (b) of this Rule but shall not be required to do so. The second white light, if carried, shall be visible at a distance of at least 2 miles and so placed as to be as far as possible visible all round the horizon.
(b) A vessel of 150 feet or more in length, when at anchor, shall carry near the stem of the vessel, at a height of not less than 20 feet above the hull, one such light, and at or near the stern of the vessel and at such a height that it shall be not less than l5 feet lower than the forward light, another such light. Both these lights shall be visible at a distance of at least 3 miles and so placed as to be as far as possible visible all round the horizon.
(c) Between sunrise and sunset every vessel when at anchor shall carry in the forepart of the vessel, where it can best be seen, one black ball not less than 2 feet in diameter.
(d) A vessel engaged in laying or in picking up a submarine cable or navigation mark, or a vessel engaged in surveying or underwater operations, when at anchor, shall carry the lights or shapes prescribed in Rule 4(c) in addition to those prescribed in the appropriate preceding sections of this Rule.
(e) A vessel aground shall carry the light or lights prescribed in sections (a) or (b) and the two red lights prescribed in Rule 4(a). By day she shall carry, where they can best be seen, three black balls, each not less than 2 feet in diameter, placed in a vertical line one over the other, not less than 6 feet apart.
(f) A seaplane on the water under 150 feet in length, when at anchor, shall carry, where it can best be seen, a white light, visible all round the horizon at a distance of at least 2 miles.
(g) A seaplane on the water 150 feet or upwards in length, when at anchor, shall carry, where they can best be seen, a white light forward and a white light aft, both lights visible all round the horizon at a distance of at least 3 miles; and, in addition, if the seaplane is more than 150 feet in span, a white light on each side to indicate the maximum span, and visible, so far as practicable, all round the horizon at a distance of 1 mile.
(h) A seaplane aground shall carry an anchor light or lights as prescribed in sections (f) and (g), and in addition may carry two red lights in a vertical line, at least 3 feet apart, so placed as to be visible all round the horizon.

Rule 12

Every vessel or seaplane on the water may, if necessary in order to attract attention, in addition to the lights which she is by these Rules required to carry, show a flare-up light or use a detonating or other efficient sound signal that cannot be mistaken for any signal authorised elsewhere under these Rules.

Rule 13

(a) Nothing in these Rules shall interfere with the operation of any special rules made by the Government of any nation with respect to additional station and signal lights for ships of war, for vessels sailing under convoy, for fishing vessels engaged in fishing as a fleet or for seaplanes on the water.
(b) Whenever the Government concerned shall have determined that a naval or other military vessel or waterborne seaplane of special construction or purpose cannot comply fully with the provisions of any of these Rules with respect to the number, position, range or arc of visibility of lights or shapes, without interfering with the military function of the vessel or seaplane, such vessel or seaplane shall comply with such other provisions in regard to the number, position, range or arc of visibility of lights or shapes as her Government shall have determined to be the closest possible compliance with these Rules in respect of that vessel or seaplane.

Rule 14

A vessel proceeding under sail, when also being propelled by machinery, shall carry in the daytime forward, where it can best be seen, one black conical shape, point downwards, not less than 2 feet in diameter at its base.

PART C
SOUND SIGNALS AND CONDUCT IN RESTRICTED VISIBILITY

Preliminary
1. The possession of information obtained from radar does not relieve any vessel of the obligation of conforming strictly with the Rules and, in particular, the obligations contained in Rules 15 and 16.
2. The Annex to the Rules contains recommendations intended to assist in the use of radar as an aid to avoiding collision in restricted visibility.

Rule 15

(a) A power-driven vessel of 40 feet or more in length shall be provided with an efficient whistle, sounded by steam or by some substitute for steam, so placed that the sound may not be intercepted by any obstruction, and with an efficient fog horn to be sounded by mechanical means, and also with an efficient bell. A sailing vessel of 40 feet or more in length shall be provided with a similar fog horn and bell.
(b) All signals prescribed in this Rule for vessels under way shall be given:
(i) by power-driven vessels on the whistle;
(ii) by sailing vessels on the fog horn;
(iii) by vessels towed on the whistle or fog horn.
(c) In fog, mist, falling snow, heavy rainstorms, or any other condition similarly restricting visibility, whether by day or night, the signals prescribed in this Rule shall be used as follows:
(i) A power-driven vessel making way through the water shall sound at intervals of not more than 2 minutes a prolonged blast.
(ii) A power-driven vessel under way, but stopped and making no way through the water, shall sound at intervals of not more than 2 minutes two prolonged blasts, with an interval of about 1 second between them.
(iii) A sailing vessel under way shall sound, at intervals of not more than 1 minute, when on the starboard tack one blast, when on the port tack two blasts in succession, and when with the wind abaft the beam three blasts in succession.
(iv) A vessel when at anchor shall at intervals of not more than 1 minute ring the bell rapidly for about 5 seconds. In vessels of more than 350 feet in length the bell shall be sounded in the forepart of the vessel, and in addition there shall be sounded in the after part of the vessel, at intervals of not more than 1 minute for about 5 seconds, a gong or other instrument, the tone and sounding of which cannot be confused with that of the bell. Every vessel at anchor may in addition, in accordance with Rule 12, 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.
(v) A vessel when towing, a vessel engaged in laying or in picking up a submarine cable or navigation mark, and a vessel under way which is unable to get out of the way of an approaching vessel through being not under command or unable to manoeuvre as required by these Rules shall, instead of the signals prescribed in sub-sections (i), (ii) and (iii) sound, at intervals of not more than 1 minute, three blasts in succession, namely, one prolonged blast followed by two short blasts.
(vi) A vessel towed, or, if more than one vessel is towed, only the last vessel of the tow, if manned, shall, at intervals of not more than 1 minute, sound four blasts in succession, namely, one prolonged blast followed by three short blasts. When practicable, this signal shall be made immediately after the signal made by the towing vessel.
(vii) A vessel aground shall give the bell signal and, if required, the gong signal, prescribed in sub-section (iv) and shall, in addition, give 3 separate and distinct strokes on the bell immediately before and after such rapid ringing of the bell.
(viii) A vessel engaged in fishing when under way or at anchor shall at intervals of not more than 1 minute sound the signal prescribed in sub-section (v). A vessel when fishing with trolling lines and under way shall sound the signals prescribed in sub-sections (i), (ii) or (iii) as may be appropriate.
(ix) A vessel of less than 40 feet in length, a rowing boat, or a seaplane on the water, shall not be obliged to give the above-mentioned signals but if she does not, she shall make some other efficient sound signal at intervals of not more than 1 minute.
(x) A power-driven pilot-vessel when engaged on pilotage duty may, in addition to the signals prescribed in sub-sections (i), (ii) and (iv), sound an identity signal consisting of 4 short blasts.
Rule 16
(a) Every vessel, or seaplane when taxi-ing on the water, shall, in fog, mist, falling snow, heavy rainstorms or any other condition similarly restricting visibility, go at a moderate speed, having careful regard to the existing circumstances and conditions.
(b) A power-driven vessel hearing, apparently forward of her beam, the fog-signal of a vessel the position of which is not ascertained, shall, so far as the circumstances of the case admit, stop her engines, and then navigate with caution until danger of collision is over.
(c) A power-driven vessel which detects the presence of another vessel forward of her beam before hearing her fog signal or sighting her visually may take early and substantial action to avoid a close quarters situation but, if this cannot be avoided, she shall, so far as the circumstances of the case admit, stop her engines in proper time to avoid collision and then navigate with caution until danger of collision is over.

PART D
STEERING AND SAILING RULES

Preliminary
1. In obeying and construing these Rules, any action taken should be positive, in ample time, and with due regard to the observance of good seamanship.
2. Risk of collision can, when circumstances permit, be ascertained by carefully watching the compass bearing of an approaching vessel. If the bearing does not appreciably change, such risk should be deemed to exist.
3. Mariners should bear in mind that seaplanes in the act of landing or taking off, or operating under adverse weather conditions, may be unable to change their intended action at the last moment.
4. Rules 17 to 24 apply only to vessels in sight of one another.

Rule 17

(a) When two sailing vessels are approaching one another, so as to involve risk of collision, one of them shall keep out of the way of the other as follows:
(i) When each has the wind on a different side, the vessel which has the wind on the port side shall keep out of the way of the other.
(ii) When both have the wind on the same side, the vessel which is to windward shall keep out of the way of the vessel which is to leeward.
(b) For the purposes of this Rule the windward side shall be deemed to be the side opposite to that on which the mainsail is carried or, in the case of a square-rigged vessel, the side opposite to that on which the largest fore-and-aft sail is carried.

Rule 18

(a) When two power-driven vessels are meeting end on, or nearly end on, so as to involve risk of collision, each shall alter her course to starboard, so that each may pass on the port side of the other. This Rule only applies to cases where vessels are meeting end on, or nearly end on, in such a manner as to involve risk of collision, and does not apply to two vessels which must, if both keep on their respective course, pass clear of each other. The only cases to which it does apply are when each of two vessels is end on, or nearly end on, to the other; in other words, to cases in which, by day, each vessel sees the masts of the other in a line, or nearly in a line, with her own; and by night, to cases in which each vessel is in such a position as to see both the sidelights of the other. It does not apply, by day, to cases in which a vessel sees another ahead crossing her own course; or, by night, to cases where the red light of one vessel is opposed to the red light of the other or where the green light of one vessel is opposed to the green light of the other or where a red light without a green light or a green light without a red light is seen ahead, or where both green and red lights are seen anywhere but ahead.
(b) For the purposes of this Rule and Rules 19 to 29 inclusive, except Rule 20(c) and Rule 28, a seaplane on the water shall be deemed to be a vessel, and the expression "power-driven vessel" shall be construed accordingly.

Rule 19

When two power-driven vessels are crossing, so as to involve risk of collision, the vessel which has the other on her own starboard side shall keep out of the way of the other.

Rule 20

(a) When a power-driven vessel and a sailing vessel are proceeding in such directions as to involve risk of collision, except as provided for in Rules 24 and 26, the power-driven vessel shall keep out of the way of the sailing vessel.
(b) This Rule shall not give to a sailing vessel the right to hamper, in a narrow channel, the safe passage of a power-driven vessel which can navigate only inside such channel.
(c) A seaplane on the water shall, in general, keep well clear of all vessels and avoid impeding their navigation. In circumstances, however, where risk of collision exists, she shall comply with these Rules.

Rule 21

Where by any of these Rules one of two vessels is to keep out of the way, the other shall keep her course and speed. When, from any cause, the latter vessel finds herself so close that collision cannot be avoided by the action of the giving-way vessel alone, she also shall take such action as will best aid to avert collision (see Rules 27 and 29).

Rule 22

Every vessel which is directed by these Rules to keep out of the way of another vessel shall, so far as possible, take positive early action to comply with this obligation, and shall, if the circumstances of the case admit, avoid crossing ahead of the other.

Rule 23

Every power-driven vessel which is directed by these Rules to keep out of the way of another vessel shall, on approaching her, if necessary, slacken her speed or stop or reverse.

Rule 24

(a) Notwithstanding anything contained in these Rules, every vessel overtaking any other shall keep out of the way of the overtaken vessel.
(b) Every vessel coming up with another vessel from any direction more than 221/2 degrees (2 points) abaft her beam, ie, in such a position, with reference to the vessel which she is overtaking, that at night she would be unable to see either of that vessel's sidelights, shall be deemed to be an overtaking vessel; and no subsequent alteration of the bearing between the two vessels shall make the overtaking vessel a crossing vessel within the meaning of these Rules, or relieve her of the duty of keeping clear of the overtaken vessel until she is finally past and clear.
(c) If the overtaking vessel cannot determine with certainty whether she is forward of or abaft this direction from the other vessel, she shall assume that she is an overtaking vessel and keep out of the way.

Rule 25

(a) In a narrow channel every power-driven vessel when proceeding along the course of the channel shall, when it is safe and practicable, keep to that side of the fairway or mid-channel which lies on the starboard side of such vessel.
(b) Whenever a power-driven vessel is nearing a bend in a channel where a vessel approaching from the other direction cannot be seen, such power-driven vessel, when she shall have arrived within one-half (1/2) mile of the bend, shall give a signal by one prolonged blast on her whistle which signal shall be answered by a similar blast given by any approaching power-driven vessel that may be within hearing around the bend. Regardless of whether an approaching vessel on the farther side of the bend is heard, such bend shall be rounded with alertness and caution.
(c) In a narrow channel a power-driven vessel of less than 65 feet in length shall not hamper the safe passage of a vessel which can navigate only inside such channel.

Rule 26

All vessels not engaged in fishing, except vessels to which the provisions of Rule 4 apply, shall, when under way, keep out of the way of vessels engaged in fishing. This Rule shall not give to any vessel engaged in fishing the right of obstructing a fairway used by vessels other than fishing vessels.

Rule 27

In obeying and construing these Rules due regard shall be had to all dangers of navigation and collision, and to any special circumstances, including the limitations of the craft involved, which may render a departure from the above Rules necessary in order to avoid immediate danger.

PART E
SOUND SIGNALS FOR VESSELS IN SIGHT OF ONE ANOTHER

Rule 28
(a) When vessels are in sight of one another, a power-driven vessel under way, in taking any course authorised or required by these Rules, shall indicate that course by the following signals on her whistle, namely:
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 "My engines are going astern".
(b) Whenever a power-driven vessel which, under these Rules, is to keep her course and speed, is in sight of another vessel and is in doubt whether sufficient action is being taken by the other vessel to avert collision, she may indicate such doubt by giving at least five short and rapid blasts on the whistle. The giving of such a signal shall not relieve a vessel of her obligations under Rules 27 and 29 or any other Rule, or of her duty to indicate any action taken under these Rules by giving the appropriate sound signals laid down in this Rule.
(c) Any whistle signal mentioned in this Rule may be further indicated by a visual signal consisting of a white light visible all round the horizon at a distance of at least 5 miles, and so devised that it will operate simultaneously and in conjunction with the whistle-sounding mechanism and remain lighted and visible during the same period as the sound signal.
(d) Nothing in these Rules shall interfere with the operation of any special rules made by the Government of any nation with respect to the use of additional whistle signals between ships of war or vessels sailing under convoy.

PART F
MISCELLANEOUS

Rule 29
Nothing in these Rules shall exonerate any vessel, or the owner, master or crew thereof, from the consequences of any neglect to carry lights or signals, or of any neglect to keep a proper look-out, or of the neglect of any precaution which may be required by the ordinary practice of seamen, or by the special circumstances of the case.
Rule 30
Reservation of rules for harbours and inland navigation
Nothing in these Rules shall interfere with the operation of a special rule duly made by local authority relative to the navigation of any harbour, river, lake, or inland water, including a reserved seaplane area.

Rule 31

Distress signals
(a) When a vessel or seaplane on the water is in distress and requires assistance from other vessels or from the shore, the following shall be the signals to be used or displayed by her, either together or separately, namely:
(i) A gun or other explosive signal fired at intervals of about a minute.
(ii) A continuous sounding with any fog-signalling apparatus.
(iii) Rockets or shells, throwing red stars fired one at a time, at short intervals.
(iv) A signal made by radiotelegraphy or by any other signalling method consisting of the group . . . __ __ __ . . . in the Morse Code.
(v) A signal sent by radiotelephony consisting of the spoken word "Mayday".
(vi) The International Code Signal of distress indicated by N.C.
(vii) A signal consisting of a square flag having above or below it a ball or anything resembling a ball.
(viii) Flames on the vessel (as from a burning tar barrel, oil barrel, etc).
(ix) A rocket parachute flare or a hand flare showing a red light.
(x) A smoke signal giving off a volume of orange-coloured smoke.
(xi) Slowly and repeatedly raising and lowering arms outstretched to each side.
Note: Vessels in distress may use the radiotelegraph alarm signal or the radiotelephone alarm signal to secure attention to distress calls and messages. The radiotelegraph alarm signal, which is designed to actuate the radiotelegraph auto alarms of vessels so fitted, consists of a series of twelve dashes, sent in 1 minute, the duration of each dash being 4 seconds, and the duration of the interval between 2 consecutive dashes being 1 second. The radiotelephone alarm signal consists of 2 tones transmitted alternately over periods of from 30 seconds to 1 minute.
(b) The use of any of the foregoing signals, except for the purpose of indicating that a vessel or seaplane is in distress, and the use of any signals which may be confused with any of the above signals, is prohibited.

ANNEX TO THE RULES
RECOMMENDATIONS ON THE USE OF RADAR INFORMATION AS AN AID TO AVOIDING COLLISIONS AT SEA

(1) Assumptions made on scanty information may be dangerous and should be avoided.
(2) A vessel navigating with the aid of radar in restricted visibility must, in compliance with Rule 16(a), go at a moderate speed. Information obtained from the use of radar is one of the circumstances to be taken into account when determining moderate speed. In this regard it must be recognised that small vessels, small icebergs and similar floating objects may not be detected by radar. Radar indications of one or more vessels in the vicinity may mean that "moderate speed" should be slower than a mariner without radar might consider moderate in the circumstances.
(3) When navigating in restricted visibility the radar range and bearing alone do not constitute ascertainment of the position of the other vessel under Rule 16(b) sufficiently to relieve a vessel of the duty to stop her engines and navigate with caution when a fog signal is heard forward of the beam.
(4) When action has been taken under Rule l6(c) to avoid a close quarters situation, it is essential to make sure that such action is having the desired effect. Alterations of course or speed or both are matters as to which the mariner must be guided by the circumstances of the case.
(5) Alteration of course alone may be the most effective action to avoid close quarters provided that:
(a) There is sufficient sea room.
(b) It is made in good time.
(c) It is substantial. A succession of small alterations of course should be avoided.
(d) It does not result in a close quarters situation with other vessels.
(6) The direction of an alteration of course is a matter in which the mariner must be guided by the circumstances of the case. An alteration to starboard, particularly when vessels are approaching apparently on opposite or nearly opposite courses, is generally preferable to an alteration to port.
(7) An alteration of speed, either alone or in conjunction with an alteration of course, should be substantial. A number of small alterations of speed should be avoided.
(8) If a close quarters situation is imminent, the most prudent action may be to take all way off the vessel.
[1] Note: Vessels fishing with trolling lines are not "engaged in fishing" as defined in Rule 1(c)(xiv). [Footnote appeared in original text.]