First off, of course, you really should be talking to a California tax professional. Taking tax
advice from a bunch of strangers on an
internet forum is a really bad idea.
Second, if the owner has skipped, how do you expect to be able to legally buy the boat? Are you in touch with him? Even if you are, I can't imagine what sort of a
contract you would write that would leave you stuck with the back taxes. Heck! California might even pay you a bounty to help them track him down.
Thirdly, just don't. This sounds like such a bad idea right from start to finish that I would walk away and never look back. There is just no way that I see this ending well.
Good luck, whatever you do.