Rule 35 - Sound signals in restricted visibility
In or near restricted visibility, day or night:
- A power-driven vessel making way: one prolonged blast, at intervals of not more than 2 minutes.
- A power-driven vessel underway but stopped, making no way: two prolonged blasts, about 2 seconds apart, at the same interval.
- A vessel not under command, restricted in ability to manoeuvre, constrained by draught, a sailing vessel, a vessel fishing, or one towing/pushing: one prolonged followed by two short blasts, at the same interval, instead of the signals above.
- A vessel being towed (or the last vessel if more than one), if manned: one prolonged followed by three short blasts, at the same interval, sounded as soon as practicable after the towing vessel's signal.
- A fishing vessel at anchor, and a RAM vessel carrying out her work at anchor, sound this signal (one prolonged + two short) instead of the anchor signal.
- A composite unit (pushing vessel rigidly connected) sounds as a single power-driven vessel.
- A vessel at anchor: rapid bell ringing for about 5 seconds at intervals of not more than 1 minute; vessels 100 metres or more also sound a gong aft immediately after the bell; a short-long-short blast may additionally be sounded as a warning.
- A vessel aground: the bell (and gong) signal, plus three separate strokes immediately before and after the rapid ringing; an appropriate whistle signal may additionally be sounded.
- Vessels under 12 metres need not give the above signals but must make some other efficient sound signal at intervals of not more than 2 minutes.
- A pilot vessel on duty may add an identity signal of four short blasts.
Rule 36 - Signals to attract attention
Any vessel may, if necessary, make light or sound signals that cannot be mistaken for any signal authorised elsewhere in these Rules, or direct her searchlight toward the danger without embarrassing another vessel. Such a light must not be mistaken for an aid to navigation; high-intensity intermittent or revolving lights such as strobes should be avoided.
Rule 37 - Distress signals
A vessel in distress requiring assistance uses or exhibits the signals described in Annex IV.
Rule 38 - Exemptions
Vessels (or classes of vessel) complying with the 1960 Collision Regulations, whose keel was laid before this Convention (COLREG 1972) entered into force, are granted certain temporary or permanent exemptions from specific light-range, colour, and positioning requirements (see the official text for the full list). This rule is largely historical and has limited practical relevance for vessels in service today.
Part D (Rules 32-38) as a whole is built on one idea: announcing by sound what cannot be seen.
