Sound signal

A sound signal is a signal made by a vessel’s whistle, bell, or gong to convey a maneuvering or warning message under the COLREGs, audible when sight is restricted. Annex III sets the technical detail: the whistle’s frequency band and audibility range scale with vessel length, a vessel of 200 m or more carrying a whistle audible up to 2 nautical miles, and vessels of 100 m or more also carrying a bell and a gong. Rules 34 and 35 fix the meanings, the maneuvering signals in sight of one another and the fog signals in restricted visibility at intervals not exceeding two minutes. The mariner reads the blast count and rhythm to know another ship’s action or status.