Sound Signals

Rule 34 — Manoeuvring & warning signals

Used by power-driven vessels in sight of one another — to announce a course or speed change, to warn another vessel of doubt, or to request passage in narrow channels.

• One short blast (•) — "I am altering my course to starboard."
• Two short blasts (• •) — "I am altering my course to port."
• Three short blasts (• • •) — "I am operating astern propulsion." (Backing engines — does not necessarily mean the vessel is making sternway.)
• Five or more short rapid blasts (• • • • •) — "I am in doubt as to your intentions" — or, in plain language: danger. Often called the "wake-up signal."
• One prolonged blast (—) — sounded by a vessel approaching a bend or section of channel where view of other vessels may be obscured. Answered by any approaching vessel within hearing.
• Two prolonged + one short (— — •) — "I intend to overtake you on your starboard side" (in a narrow channel).
• Two prolonged + two short (— — • •) — "I intend to overtake you on your port side."
• Long-short-long-short (— • — •) — agreement signal from the vessel about to be overtaken.

"Short" blast = about 1 second. "Prolonged" blast = 4 to 6 seconds.

Rule 35 — Sound signals in restricted visibility

Sounded every 2 minutes or less in or near an area of restricted visibility, by day or by night:

• Power-driven vessel making way — one prolonged blast (—).
• Power-driven vessel under way but stopped — two prolonged blasts (— —) with about 2 seconds between.
• Vessel not under command, restricted in ability to manoeuvre, constrained by draught, sailing, fishing, or towing/pushing — one prolonged + two short (— • •).
• Vessel being towed (or last vessel of tow if manned) — one prolonged + three short (— • • •) immediately after the tug's signal.
• Vessel at anchor — bell rapid ringing for 5 seconds, every minute. (Vessels > 100m: bell forward + gong aft, 5 sec each.) May supplement with one short + one prolonged + one short whistle to warn an approaching vessel.
• Vessel aground — bell signal of an at-anchor vessel + three separate strokes of the bell before and after.
• Pilot vessel — may sound, in addition to the above, identity signal of four short blasts.

The simulator scenarios

Two formats:

1. Audio → identify. The simulator plays a fog signal or whistle pattern. You select the vessel type and status from a list. Each correct answer drives your score; wrong answers are explained.
2. Situation → select signal. The simulator describes a scenario ("you are a power-driven vessel under way in fog"). You choose which signal to sound.

The free demo includes the most-tested patterns: • (altering starboard), — (under way in fog), — • • (sailing or RAM in fog), • • • • • (danger). Full course adds bell/gong combinations, towing-vessel signals, anchor warnings, and the rare four-short pilot signal.

Common mistakes

• Confusing "altering starboard" with "altering port" — one blast vs two. Mnemonic: one blast for the one word direction (starboard? right? short?). Find a memory hook that works for you.
• Thinking three short = stopping — it means astern propulsion; the ship may still be moving forward.
• Sounding fog signals less often than every 2 min — Rule 35 sets 2 minutes as the maximum interval.
• Not knowing the danger signal — five short rapid blasts is the most important signal a yacht skipper can recognise. If a ship sounds it at you, take immediate action.
• Forgetting that bell and gong replace whistle for anchored / aground vessels — a rapid bell in fog is not a wake-up call, it's a "ship anchored ahead" warning.