Maybe this was mentioned in the boat renaming ceremony link post earlier but here's how we were always told to do it:
Write or paint the boat's old name on a small piece of wood and then hide it inside the boat.
By keeping the old name somewhere on the boat, you keep the "boat gods" happy and thus keep yourself and vessel in good standing.
That the gods haven't yet become wise to this trick makes me wonder a bit about their abilities to cause real misfortune, but I assume that they still can if they have just cause. Also, since they appear to have trouble distinguishing real boat names from names scribbled on pieces of wood, I'm pretty sure I'm safe talking about "them" in this post--I hope.