A reply was quickly flashed back... "You change course 10 degrees North."
The captain was somewhat annoyed and sent another message... "I am a captain. Change course 10 degrees South."
Back came the reply... "I am an able-seaman. Change course 10 degrees North."
By now the captain was outraged and flashed the message... "I am a 240,000 ton tanker! Change course 10 degrees South!"
Back came the reply... "I am a LIGHTHOUSE! Change course 10 degrees North!!!"