if you want the boat then sounds like they are trying to do the right thing for you, unfortunately you bought a boat that ya wanted to use right away and couldn't, which Stinks.
If you have no confidence in the way it needs to be repaired will last and want to get out of the deal, then you should find a lawyer with marine experience and have him give them a call, he will know all the right things to say to put the fear in them. Maybe they'll refund your money and transfer the boat back out of your name.

Call some of the big yaht dealers, surely they know some good attorneys.