COLREG / ARPA / AIS Bridge
Rule 35(a)
Rule 35(b)
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Rule 35(a) — PDV Underway in Fog
FOG. Visibility 0.3 NM. You are a power-driven vessel MAKING WAY through the water.
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Scenario briefing
FOG. Visibility 0.3 NM. You are a power-driven vessel MAKING WAY through the water. Rule 35 requires you to sound specific signals at intervals of NOT MORE than 2 minutes. Which signal applies?
Applicable COLREG rule(s)
Rule 35(a) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.
Rule 35(b) — referenced in this scenario. Practising this scenario reinforces correct application under realistic time pressure.
Key teaching points
- Rule 35(a): a power-driven vessel making way through the water sounds ONE prolonged blast every ≤2 minutes.
- Rule 35(b): a power-driven vessel under way but stopped and making no way sounds TWO prolonged blasts every ≤2 minutes.
- A prolonged blast is 4–6 seconds (Annex III).
- Sound signals must be made even when the vessel believes she has been seen — Rule 35 applies in or near an area of restricted visibility.
Common mistakes to avoid
- Sounding short blasts instead of prolonged — wrong duration, wrong meaning.
- Stopping the signal when the radar shows targets are clear — the rule asks for continuous signalling while in or near reduced visibility.
Why it matters
Rule 35 fog signals are the only legal way to declare your status when vessels cannot see each other. Skipping them or sounding the wrong one has been a contributing factor in dozens of fog collisions investigated by MAIB and NTSB.
Exam relevance
Rule 35(a) and (b) are routinely tested in Yachtmaster Coastal/Offshore and STCW OOW orals — candidates produce the rhythm verbally and state the maximum interval.
Related scenarios
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