ColRegs Sound Signals

One prolonged blast at intervals of not more than 2 minutes. The default fog signal for power-driven vessels moving through the water.

Two prolonged blasts, ~2 seconds between them, every ≤2 minutes. Tells listeners the vessel is dead in the water but not anchored — engines stopped, drifting.

One prolonged followed by two short, every ≤2 minutes. The catch-all signal for vessels with restricted manoeuvrability — covers not-under-command, restricted-in-manoeuvre, constrained-by-draught, sailing vessels, fishing vessels, and any vessel towing or pushing.

One prolonged followed by three short, given immediately after the towing vessel's signal. If practicable, the manned last vessel of the tow sounds this so listeners know the tow extends astern.

Four short blasts, in addition to the usual underway or anchor signal for her type. Identifies a vessel engaged in pilotage duty.

Rapid ringing of the bell for about 5 seconds, at intervals of not more than 1 minute. Forward where it can best be heard.

Same rapid bell forward as smaller vessels, plus immediately after — the gong rung rapidly for ~5 seconds at the after end of the vessel. Signals the vessel's length to listeners.

May additionally sound this short + prolonged + short on the whistle to warn an approaching vessel of her position and the possibility of collision.

Three distinct strokes of the bell + rapid bell + three distinct strokes, every ≤1 minute. The three-strokes-rapid-three-strokes pattern is unique to a vessel aground and must not be confused with an anchored vessel.

One short blast. Given by a power-driven vessel in sight of another when actually taking the action authorised by these Rules.

Two short blasts. Same context — visible to and within hearing of another vessel.

Three short blasts. Signals the engines are running astern — regardless of whether the vessel is actually moving astern through the water yet.

Used in a narrow channel where the overtaken vessel must take action to permit safe passing. Asks for permission to overtake to starboard.

Same context — overtaking signal in a narrow channel, but on the port side.

The vessel about to be overtaken signals agreement. If she doubts the safety of the manoeuvre, she instead sounds five short (Rule 34(d)).

At least five short and rapid blasts. Required when one vessel doubts whether the other is taking sufficient action to avoid collision. Always preferable to silence.

One prolonged blast as the vessel approaches a bend in the channel or any place where intervening obstructions may obscure other vessels. Any vessel within hearing on the other side answers with one prolonged blast.