Rules of the Road · Sound Signals — Doubt Signal
When a vessel fails to understand the intentions of another, or is in doubt whether sufficient action is being taken to avoid collision, she shall sound:
- AOne short blast
- BTwo prolonged blasts
- CAt least five short and rapid blasts✓ Correct
- DOne prolonged and three short blasts
Explanation
The danger/doubt signal is at least five short and rapid blasts on the whistle, which may be supplemented by at least five short and rapid flashes of a light.
Authority: COLREGS/Navigation Rules, Rule 34(d)
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