Warnings, International and Inland

Danger or doubt

I don't understand your intentions or actions, or I doubt you're doing enough to avoid collision.

At least five short, rapid blasts

Press play. One signal at a time.

Danger or doubtInternational and Inland
I don't understand your intentions or actions, or I doubt you're doing enough to avoid collision.
Rule 34(d); Inland Rule 34(d), 33 CFR 83.34(d)

Who sounds it

Any vessel in sight of another and approaching it.

How it's sounded

"At least five short and rapid blasts." No exact speed is set. Five blasts of about 1 second with 0.4 second gaps are used here.

A short blast is about 1 second. A prolonged blast is 4 to 6 seconds. Clips use 1 and 5 seconds.

Worth remembering

At least five, so more is fine. It may be backed up by at least five short and rapid flashes. In a narrow channel, a vessel doubting a crossing vessel's intent may sound it under International Rule 9(d) and must under Inland Rule 9(d).

The same sound elsewhere

These use the same pattern, so the rules you’re under and the situation decide what it means.

Study more

See every sound signal, try the free Rules of the Road practice test, or read who gives way, and how Inland differs.

Learn the whole set

Helm drills every signal with flashcards and spaced review, on the web and iPhone.

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Sources

Rule 34(d); Inland Rule 34(d), 33 CFR 83.34(d)

Helm is an independent study aid, not affiliated with or endorsed by the U.S. Coast Guard or the National Maritime Center. This page is for study, not navigation guidance or legal advice. Check the current rules before you rely on anything here.