The same breach of warranty laws that apply to cars apply to boats, but there is not a  lemon law for new boats or used boats; there is a general breach of warranty law for boats.  The boat and the engines must work as promised according to the specific warranty.  If there is an express-written-warranty and the boat cannot be fixed as promised you can sue for damages.  You can sue for breach of warranty and if it takes them too long to fix the boat you can sue for damages.  You can recover attorney's fees under certain circumstances with cost of the lawsuit.

Key Questions

Is there a warranty, written or implied?

What does it cover?

Can the boat be fixed in a reasonable time?

What are your damages, slip rental, boat payments, etc.?