4 short blasts are the letter H is morse. On the River Clyde in Scotland a local bye law allows it to be signalled by a vessel going astern from a berth, generally a paddle steamer, indicating that it is going astern, it has difficulty in manoeuvring and warning other vessels to keep clear.
"I am about to turn to starboard".
three short blast
It means a vessel is going to back up.
A boat is using astern propulsion and is in the act of backing up.
Two short horn blast from a vessel means that she is turning port and one short horn blast that she is turning starboard
Three short blasts means you are operating in reverse. One prolonged blast followed by 3 short blasts means boat under tow in redcued visibility conditions.
One short blast of a horn mean while boating may mean a couple of things depending on where you are. Some of the meanings of the short blast include request for drawbridge to open, intention to pass of the left side and intention to change course to starboard among others.
You could 'toot' your horn...
Toot
toot
When two boats approach each other, they use horn blasts to signal the other about their intentions when it comes to moving to avoid collision. 5 short blasts indicates that the signaling boat is unsure about what the other boat is doing.
The danger signal