"Wayne.B" wrote
http://tinyurl.com/3ymzod
It is reported that a 24' Mako ran between a tug and a barge being
towed astern. The Mako hit the tow wire and was capsized, throwing the
passengers into the water.

"The captain tried in vain to warn the powerboat, blowing his whistle four
times, but the Mako continued."

Isn't five blasts the standard danger signal? Or maybe the tug sounded a
five blast signal four times and the above is the reporter's interpretation.
Not that someone putting himself in that situation might necessarily be
expected to understand the signal anyway.