Six blasts of a ship's horn does not seem to have a meaning. Five blasts will mean that you are possibly too close to another ship.
Get The Bleep Out Of The Way.
One long honk on the horn
gat out of my way
it is the same right
A warning to other boaters there is danger near by.
I intend to pass you on my starboard (right) side.
Means it's about to turn to port.
Passing on your starboard (right) side.
Three short blasts tell other boaters, “I am operating astern propulsion.” For some vessels, this tells other boaters, “I am backing up.”
They intend to pass starboard side to starboard side.
That you are crossing starboard to starboard or overtaking to port side. (you are passing on YOUR starboard side)