One version of the story
The lore I heard concerning this is that a vessel becomes a personality and obtains a soul from King Neptune during christening. To change the name of a boat is bad luck because the vessel's soul is still there but has been insulted/shamed with a new name that does not match the personality of the christened name. To avenge the original vessel's soul, King Neptune, or the vessel itself, would plague the owners with numerous minor problems that eventually turned into major problems, then into a sinking usually of the gruesome, horrific kind with all hands on board and lost. To prevent this nightmarish series of events, the owner should properly advise King Neptune that the owner respects the soul provided to the vessel, but needs to change the name to also respect the wishes of the landlubbers. King Neptune, wanting to maintain proper relations with the landlubbers and the associated gods, allows two means of doing this: 1) Rechristening the same soul with a new name that is somewhat related to the same personality. 2) Recommit the vessel's soul/name to King Neptune and respectfully request a new soul/name be given to the honorable vessel.In either case a proper ceremony is required with either champagne or appropriate wine. Appropriate is determined by both season and the reception dinner main course.Complete instructions are available at: http://www.48north.com/aug97/denaming.htm