Printable reference
Sound signals table
Maneuvering, warning, fog, anchor, and aground signals.
Timing key: a short blast is about 1 second; a prolonged blast is 4–6 seconds. Maneuvering signals are for vessels in sight; restricted-visibility signals are a different system and repeat at prescribed intervals. International and US Inland meanings can differ—use the detailed page where noted.
In sight: maneuvering, passing, and doubt
| Signal | Pattern | Meaning |
|---|---|---|
| One short blastRule 34(a) | · | International: “I am altering my course to starboard.” Inland: “I intend to leave you on my port side” — a proposal that must be answered. |
| Two short blastsRule 34(a) | · · | International: “I am altering my course to port.” Inland: “I intend to leave you on my starboard side” — a proposal that must be answered. |
| Three short blastsRule 34(a) | · · · | “I am operating astern propulsion” — the engines are going astern (which is not the same as actually moving astern). |
| Overtake on your starboard side (International)Rule 34(c)(i) | — — · | Two prolonged + one short: “I intend to overtake you on your starboard side” — narrow channel, International Rules. |
| Overtake on your port side (International)Rule 34(c)(i) | — — · · | Two prolonged + two short: “I intend to overtake you on your port side” — narrow channel, International Rules. |
| Overtaking agreement (International)Rule 34(c)(ii) | — · — · | Prolonged, short, prolonged, short — Morse “C” — sounded by the vessel about to be overtaken to say “agreed, come past.” |
| Overtake on your starboard side (Inland)Rule 34(c)(i) | · | One short blast from an overtaking vessel: “I intend to overtake you on your starboard side” — Inland Rules. |
| Overtake on your port side (Inland)Rule 34(c)(i) | · · | Two short blasts from an overtaking vessel: “I intend to overtake you on your port side” — Inland Rules. |
| Danger / doubt signalRule 34(d) | · · · · · | At least five short and rapid blasts: “I doubt your intentions — or I see danger.” The most important signal to recognize instantly. |
| Bend / obstruction signalRule 34(e) | — | One prolonged blast when nearing a blind bend or obstruction; any approaching vessel around the bend answers with one prolonged blast. |
| Leaving a dock or berth (Inland)Rule 34(g) | — | One prolonged blast sounded by a power-driven vessel when leaving a dock or berth — Inland Rules only. |
Restricted visibility
| Signal | Pattern | Meaning |
|---|---|---|
| Power-driven vessel making way (fog)Rule 35(a) | — | One prolonged blast at intervals of not more than 2 minutes — a power-driven vessel making way through the water in restricted visibility. |
| Power-driven vessel underway but stopped (fog)Rule 35(b) | — — | Two prolonged blasts, about 2 seconds apart, every 2 minutes — underway but stopped and making no way through the water. |
| Hampered vessel (fog)Rule 35(c) | — · · | One prolonged + two short blasts every 2 minutes — not under command, restricted in ability to maneuver, constrained by draft (International), sailing, fishing, or towing/pushing. |
| Manned vessel being towed (fog)Rule 35(e) | — · · · | One prolonged + three short blasts every 2 minutes — a manned towed vessel (the last of the tow), sounded right after the towing vessel's signal when practicable. |
| Pilot vessel identity signal (fog)Rule 35(k) | · · · · | Four short blasts — an optional identity signal a pilot vessel on duty may add to her normal fog signal. |
At anchor and aground
| Signal | Pattern | Meaning |
|---|---|---|
| Vessel at anchor (fog)Rule 35(g) | rapid bell (5 s) | Rapid ringing of the bell for about 5 seconds, at intervals of not more than 1 minute — a vessel at anchor in restricted visibility. |
| Vessel of 100 m or more at anchor (fog)Rule 35(g) | rapid bell (5 s) + rapid gong (5 s) | Rapid bell forward for 5 seconds, then rapid gong aft for 5 seconds, every minute — large vessels at anchor mark both ends. |
| Vessel aground (fog)Rule 35(h) | 3 strokes + rapid bell (5 s) + 3 strokes | Three distinct bell strokes, rapid ringing for 5 seconds, then three more strokes, every minute — “stuck – stuck – stuck” around the anchor signal. |
| Anchored vessel warning (whistle)Rule 35(g) | · — · | One short, one prolonged, one short — an optional whistle warning an anchored vessel may sound at an approaching vessel. |
Attention and distress
| Signal | Pattern | Meaning |
|---|---|---|
| Continuous sounding (distress)Rule 37 & Annex IV | — — — … (continuous) | Continuous sounding with any fog-signalling apparatus indicates distress and need of assistance — Annex IV. |
| SOS / Mayday (distress)Rule 37 & Annex IV | · · · — — — · · · | The Morse group · · · — — — · · · (SOS) by any signalling method, or the spoken word “Mayday” by radiotelephone — Annex IV distress signals. |
Learning aid only — not for navigation. Confirm current rules and local requirements with the relevant authority.