We too acquired a boat with a rather poor name which needed to be changed. After an appropriate period of contemplation and selection, Neptune was requested to approve the switch and to welcome the newly named vessel. Our request was accompanied by an adequate amount of Mount Gay Eclipse rum, delivered to Neptune directly overboard, all in proper form, of course, with reference to Aeolus, Borealis, etc. We feel this approach was quite effective since we proceeded to win most of the silver at the club that year, and have done well since without additional libations over the side.
Other postings suggest tequila, but IMHO that such an inherently land-based substance (it comes from CACTUS, after all - how far from the ocean can you go??!!?) may not be viewed in as positive a light as the traditional rum by the powers that be. (Or they may not be, but would we be having this discussion if we were sure?) Scotch (single malt, from some lonely rocky isle near Stornoway, if possible) may also work well. I would stay away from tequila. The bugs in it aren''t even weevils, so you won''t garner any credit from Neptune for them either.