Rule 34(d) — Doubt / Disagreement Signal
POWER-DRIVEN vessels in sight of one another, when in DOUBT whether sufficient action is being taken by the other to avoid collision, shall indicate suc...
Scenario briefing
POWER-DRIVEN vessels in sight of one another, when in DOUBT whether sufficient action is being taken by the other to avoid collision, shall indicate such doubt (Rule 34(d)). A crossing vessel on your starboard bow is not altering as required; you are uncertain of her intentions. What signal must you sound?
Applicable COLREG rule(s)
Key teaching points
- Rule 34(d): when vessels in sight of one another are approaching and either fails to understand the intentions or actions of the other, or is in doubt whether sufficient action is being taken to avoid collision, sound at least FIVE short and rapid blasts.
- May be supplemented by a light signal of at least 5 flashes (Rule 34(d), second sentence).
- The doubt signal is appropriate when the other vessel is approaching close-quarters without apparently taking action.
- After sounding, take your own action — the doubt signal does not absolve you from Rule 8.
Common mistakes to avoid
- Treating the doubt signal as a "rude alarm" and not using it. In court, failure to sound it has been cited against vessels involved in collisions.
- Sounding three or four blasts and considering the duty discharged — the rule says FIVE or more.
Why it matters
Exam relevance
The doubt signal is a popular probe in RYA Yachtmaster Coastal/Offshore and STCW OOW orals — candidates must produce "five short and rapid" without prompting.
Related scenarios
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