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 blast
A. Three long blast of the ships whistle or general alarm at an interval of three, means a man overboard. This is dismissed by three short whistle blast. B. Three Short blast can also be Rule 34 (Inland and International) "Maneuvering and Warning Signals." Three short blast means "I am operating astern propulsion."
It means a vessel is going to back up.
A boat is astern propulsion and is in the act of backing up
You could 'toot' your horn...
Toot
toot
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.
It means "I am altering my course to starboard"
"I am about to turn to starboard".
When altering your course to port, you should sound one short blast on your horn to indicate your intentions to nearby vessels. This signal is commonly used to indicate that you are changing your course to the left (port side).