Manoeuvring and Warning Signals.
(a) When vessels are in sight of one another, a power driven vessel under way, when manoeuvring as authorized 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 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 not be 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 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 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 meters, one whistle only shall be used for giving manoeuvring and warning signals.
The signals described in paragraphs (a), (b), (c) and (d) are only to be given by vessels in visual sight of one another. Paragraph (e) is obviously intended to apply in clear visibility. Manoeuvring signals should not be given when taking avoiding action for a vessel detected by radar and CAN NOT be seen visually, due to restricted visibility. This does not mean that just because a poor visual lookout is being kept, sounding of these signals is excused.
Note also that paragraph (a) applies only to a power driven vessel and not to sailing vessels. Sailing vessels are not permitted to give manoeuvring signals when taking action to avoid collision. However, the remaining paragraphs of this rule apply to ALL vessels. Even a small alteration of course, if it is authorised or required under these Rules, must generally be indicated by the appropriate whistle signal.
Note also, that the sound signal is the one required to be given by the Rules and not the light signal. The light is signal purely supplementary to the sound signal and logically, would be shown at night, to visually indicate which vessel had just given the whistle signal. It must be emphasised that the light signal is not the “night” signal with the whistle signal being the “day” one.
These signals are only to be used when taking action that is authorised or required by these Rules and not for indicating alterations of course to counter the effect of tide, or to check the swing of a vessel.
Sound signals need not be given if action is taken for a vessel in sight, but at long range, before a risk of collision exists. But if the Rules do apply, the signals must be sounded even if it is thought that they will not be heard.
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