Rule 32 - Definitions
- Whistle: any sound-signalling appliance capable of the prescribed blasts, complying with Annex III.
- Short blast: a blast of about one second.
- Prolonged blast: a blast of four to six seconds.
Rule 33 - Equipment for sound signals
Vessels 12 metres or more in length carry a whistle and a bell; those 100 metres or more also carry a gong distinguishable in tone from the bell. All must comply with Annex III; the bell and/or gong may be replaced by other equipment with the same sound characteristics, provided manual sounding remains possible. Vessels under 12 metres are not obliged to carry this equipment but must have some other means of making an efficient signal.
Rule 34 - Manoeuvring and warning signals
When vessels are in sight of one another, a power-driven vessel underway, manoeuvring as authorised or required, signals on her whistle: one short blast = "I am altering course to starboard"; two short blasts = "I am altering course to port"; three short blasts = "I am operating astern propulsion". These may be supplemented by light signals with the same meanings: each flash about one second, interval about one second, successive signals at least ten seconds apart; the light, if fitted, must be an all-round white light visible at least 5 miles, per Annex I. In a narrow channel, in sight of one another: a vessel intending to overtake signals under Rule 9(e)(i) — two prolonged + one short = "I intend to overtake on your starboard side"; two prolonged + two short = "I intend to overtake on your port side"; the vessel to be overtaken, if agreeing, answers with one prolonged, one short, one prolonged, one short. When a vessel is in doubt about another's intentions or whether sufficient action is being taken, she immediately signals at least five short and rapid blasts (may be supplemented by at least five short and rapid flashes). A vessel nearing a bend or obstruction sounds one prolonged blast, answered in kind by any vessel that may be within hearing around the bend. If whistles are more than 100 metres apart, only one is used for manoeuvring and warning signals.
These three rules give the signals referenced in Rule 9(e) and Rule 17 an actual sound - "I am altering course" now has a voice.
