Whistle signals in sight: International vs Inland (Rules 32 and 34)

Navigation Rules, lights & bridges · Power & sail

When vessels are in sight, horn signals announce maneuvers and warn of danger. Under the COLREGS a power-driven vessel's signal reports what it is doing now; under the Inland Rules it states an intention that the other vessel must answer. The danger and bend signals are the same in both.

Blasts and whistles

• A short blast lasts about 1 second; a prolonged blast lasts 4 to 6 seconds (Rule 32(b), (c)).
• In the Rules a 'whistle' is any sound-signaling appliance that can make the prescribed blasts and meets the Annex III specifications (33 CFR 86), so a compliant horn counts (Rule 32(a)).

International (COLREGS): signals of action

• A power-driven vessel in sight of another signals each maneuver as she makes it: 1 short = 'I am altering my course to starboard'; 2 short = 'to port'; 3 short = 'I am operating astern propulsion' (COLREGS Rule 34(a)).
• The COLREGS signal needs no reply and has no distance limit: it reports an action under way, not a proposal.
• Light flashes may back up the whistle: flashes of about 1 second, about 1 second apart, at least 10 seconds between signals, from an all-round white light visible at least 5 miles (COLREGS Rule 34(b)).

Inland: signals of intent and agreement

• Power-driven vessels in sight and meeting or crossing within half a mile signal when maneuvering: 1 short = 'I intend to leave you on my port side'; 2 short = 'on my starboard side'; 3 short = 'I am operating astern propulsion' (Inland Rule 34(a)(i)).
• If the other vessel agrees, it answers with the same signal and both act to pass safely. If it doubts the plan, it sounds the danger signal and both take precautions until they agree (Inland Rule 34(a)(ii)).
• Overtaking, in any waters: 1 short = 'I intend to overtake you on your starboard side'; 2 short = 'on your port side'. The overtaken vessel repeats the signal if she agrees, or sounds the danger signal if in doubt (Inland Rule 34(c)).
• If vessels agree by radio, such as bridge-to-bridge VHF, whistle signals become optional. If they can't agree, they must exchange whistle signals in good time, and the whistle signals prevail (Inland Rule 34(h)).
• A power-driven vessel leaving a dock or berth sounds one prolonged blast (Inland Rule 34(g)). The COLREGS have no such signal.

International overtaking in a narrow channel

• When the vessel ahead must move over to let you pass: 2 prolonged + 1 short = 'I intend to overtake you on your starboard side'; 2 prolonged + 2 short = 'on your port side'. Agreement is prolonged, short, prolonged, short (COLREGS Rule 34(c)).
• These signals are used only when overtaking is possible only if the vessel ahead takes action. If she is in doubt, she may sound the danger signal (COLREGS Rule 9(e)(i)).

Danger and bend signals (both rule sets)

• If you don't understand another vessel's intentions, or doubt it is doing enough to avoid a collision, immediately sound at least five short, rapid blasts (Rule 34(d)).
• Nearing a bend or obstruction that may hide other vessels, sound one prolonged blast. Any vessel around the bend that hears it answers with one prolonged blast (Rule 34(e)).

The rules: COLREGS Rule 32 · COLREGS Rule 34 · Inland Rule 34 · 33 CFR 83.32 · 33 CFR 83.34

A plain-language summary of federal rules for recreational boats, checked against the rules’ own text and a second source, and written in our own words. It isn’t legal advice. States add rules of their own, and rules change — the links above go to the current official text.