At Anchor, It is used addition to the required rapid ringing of the bell for five seconds (not to exceed one minute interval) to let other vessels know her location.
One long blast can mean one of many things:
1) I am turning to starboard2) In a situation of restricted view (ie turning a blind corner on a river) it's a warning signal to warn other vessels of...
3 prolonged blasts followed by one short blast on the ships' whistle has no meaning in everyday use. A prolonged blast is about 4-6 seconds long, while a short blast is about 1 second long. The...