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Chris Riley by Chris Riley Updated on June 28, 2020. In nauticalknowhow

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You’re operating at night when you see a white light flashing this pattern: a short flash and brief dark interval, then a longer flash and a longer interval of darkness, repeated every 8 seconds. What is it?

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The answer is: the white light is sending the morse code equivalent of the letter “A” which in the IALA-B system are used only on mid-channel and fairway buoys.

You’re on the water at night and you see the lights below: an amber light that flashes once each second for three seconds and then is off for three seconds, indicates what? What are you looking at?

What are you looking at?

Port side of a submarine [on the surface], under way, making way. He is the stand-on vessel, you must give way.

The flashing light sequence spells out in Morse code the letter “s” for submarine. This is prescribed in 72 COLREGS (Rule1[c] footnote).



What is it?

A power driven vessel towing astern.
The towing vessel is less than 50 meters in length and the length of tow (from stern of towing vessel to stern of vessel being towed)
is 200 meters or less.


If stuff like this interests you – you should be taking the boating course!

About Chris

Outdoors, I’m in my element, especially in the water. I know the importance of being geared up for anything. I do the deep digital dive, researching gear, boats and knowhow and love keeping my readership at the helm of their passions.


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