|1 short blast (Morse E)||I am altering course to Starboard (Flag E)|
|I intend to leave you on my Port side|
|2 short blasts (Morse I)||I am altering course to Port (Flag I)|
|I intend to leave you on my Starboard|
|3 short blasts (Morse S)||I am operating in reverse (Flag S)|
|5 short blasts||Danger ..or.. Message Not Understood|
|1 prolonged blast||Entering a blind turn or leaving a dock|
|1 long blast every 2 minutes||Power-driven vessel operating in poor visibility|
|1 long blast + 2 short blasts
every 2 minutes
|Sailing vessel operating in poor visibility|
Short blast is a blast of 1 second duration. A prolonged (long) blast is 4 to 6 seconds. (One very long blast used to mean abandon ship -- maybe still does.)
1 long blast + 3 short blasts is made by the last vessel in a tow (usually in reply to a signal made by towing vessel). I did not include this above because I could not confirm it's an international signal.
When a vessel in a narrow channel or tidal stream is meeting another vessel, the vessel that is heading with the current makes 1 short blast if altering to starboard (the norm) and 2 short blasts if altering to port. The vessel that must "give way" to the first vessel replies WITH THE SAME SIGNAL if in agreement or with the danger signal (5 short blasts) if in doubt.
Pleasure boats do not generally use these signals when passing normally (port to port) but if a large ship signals you, be sure to answer back -- and get out of his way! You must always give way to large ships!
And then there's train signals, which have nothing in common with boats: 3 short toots + one long toot means a level crossing with lights but no barriers.
When approaching a lockstation, you must use a slightly different sound signal. 3 long blasts means you wish to lock through. 4 long blasts means you need both gates opened (don't do this if you are in a small cruiser unless it's your first lock or you're having trouble). You don't need to signal if the doors are open and you are making a course to enter. If you are not going to enter the lock, indicate your intensions by changing course. (In Canadian heritage canals, the edge of the approach dock is usually painted "blue" and reserved for boats waiting for the next lockage.)