Fog

Most of the time the view at the Bitter End Marina, Bayview Idaho - on Lake Pend Oreille - looks like this.

This morning at 8:30, it looked like this.  Pretty, eh???
Then the atmospheric conditions changed very quickly.  Humidity and dew point got together.

By 9:45, the fog started to set in and it looked like this.  Visibility around 1,000 feet.

By 10:15 the fog was so thick that visibility had been reduced to ~300 feet.
We had seen two boats head out fishing about an hour earlier.  There was almost no breeze and virtually no sound from the water.  CERTAINLY no fog horns.  I had to imagine that if I was sailing along in those conditions whether I would be able to see the fishermen before I plowed into their silent boat in the fog......
If you were in the fog, would you know the proper fog horn signals to use for your boat?

If you are motoring (including fishing) =  one prolonged blast
If you are sailing  =  one prolonged blast followed by two short blasts