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SESK: Stuff Everyone Should Know · sesk.info/boat-fog-signal-powerboat

In fog, a powerboat moving through the water sounds what signal, and how often?

One prolonged blast at least every 2 minutes.

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  1. One prolonged blast at least every 2 minutes ✔
  2. Five short blasts every 30 seconds
  3. Two short blasts every 10 minutes

Why: Rule 35 says a power-driven vessel making way in restricted visibility sounds one prolonged blast at intervals of not more than 2 minutes. If it's stopped and not moving, it sounds two prolonged blasts.

Huh, didn't know that: Sailboats, fishing vessels and towboats in fog use one prolonged blast followed by two short ones instead.

The dad joke
Why did the boat honk in the fog? It wanted to make itself heard, if not seen.
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References

Answer: One prolonged blast at least every 2 minutes. Rule 35 says a power-driven vessel making way in restricted visibility sounds one prolonged blast at intervals of not more than 2 minutes. If it's stopped and not moving, it sounds two prolonged blasts.

  1. 33 CFR 83.35, Sound signals in restricted visibility (Rule 35) www.ecfr.gov/current/title-33/section-83.35
    A power-driven vessel making way through the water shall sound, at intervals of not more than 2 minutes, one prolonged blast.
    Checked 2026-10-09.

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Boating & WaterA boat under 12 meters (39.4 feet) needn't carry a regulation whistle. What must it have?Boating & WaterIn the Navigation Rules, how long is a 'prolonged blast'?Boating & WaterOn inland waters, what does one short blast mean when meeting or crossing another powerboat?

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