International regulations for
preventing collisions at sea (1972)
Manoeuvring and warning signals
(a) When vessels are in sight of one
another, a power-driven vessel underway, 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 light signals shall have the
- one flash to mean "I am altering my course
- 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
(c) When in sight of one another in a narrow
channel or fairway.
(i) a vessel intending to overtake another
shall in compliance with
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.