Internet advice:

Naming boats is a tradition since it is believed long ago that naming boats after god and goddess' name would bring luck to travel and good fortune. The wrong name was the difference between good luck and being lost at sea. Changing the name of a ship has historically been considered bad luck.

Why is it bad luck to change the name of a vessel? Boats change hands all the time, and what was a perfect name for one owner can't possibly be the perfect name for you. Many boaters and sailors, though, insist changing the name brings bad luck. If you must change it, you should perform a ceremony first to ensure good luck.