Fog Signals (Rule 35)

A power-driven vessel making way through the water sounds one prolonged blast at intervals of not more than two minutes. A power-driven vessel underway but stopped and making no way sounds two prolonged blasts in succession, about two seconds apart, at intervals of not more than two minutes. 'Underway' means not at anchor, made fast to the shore or aground; 'making way' means moving through the water.

A vessel not under command, restricted in ability to manoeuvre, constrained by draught, sailing, fishing, or towing or pushing another vessel sounds one prolonged followed by two short blasts at intervals of not more than two minutes instead of the power-driven signals. A yacht is a sailing vessel for this purpose only when under sail and not using propulsion machinery. If the engine is being used for propulsion, apply the power-driven status and signal.

A vessel at anchor rings the bell rapidly for about five seconds at intervals of not more than one minute. At 100 metres or more, the bell is sounded in the forepart and a gong rapidly aft for about five seconds immediately afterward. A vessel aground adds three separate and distinct bell strokes immediately before and after the rapid ringing. A vessel under 12 metres is not obliged to give those prescribed Rule 35 signals, but if it does not, it must make another efficient sound signal at intervals of not more than two minutes; Rule 33 also requires an efficient means of making sound.