Talking With Sound: Signals & Fog

When boats are close, words don't carry — so the COLREGs let you "talk" with your horn. A short blast lasts about 1 second; a prolonged blast lasts 4–6 seconds. Under Rule 34 (maneuvering signals), when vessels are in sight of one another and you change course, you announce it: one short blast = "I am turning to starboard," two short = "turning to port," and three short = "I am operating astern propulsion" (reversing — not necessarily moving backward yet). If you don't understand another vessel's intentions or doubt they're taking enough action to avoid you, sound the doubt/danger signal: five or more short, rapid blasts.

When fog, heavy rain, or darkness rolls in, you switch to Rule 35 (restricted visibility) signals, sounded roughly every 2 minutes — and here you may be blind to other traffic, so these are heard, not seen. A power-driven vessel making way sounds one prolonged blast. If it's underway but stopped and not making way through the water, it sounds two prolonged blasts (a short gap between them). A sailing vessel, or one fishing, towing, or restricted in ability to maneuver, sounds one prolonged followed by two short blasts — one signal covering several "I have limited options" cases.

The logic: in sight of each other you signal intentions (Rule 34); when you can't see each other you signal presence and status (Rule 35). Recall from earlier cards that fog also demands a safe speed and extra lookout — the sound signals don't replace those, they layer on top.