Not at all. Lemon laws apply to all sorts of vehicles, including boats, as well as motorcycles, trailers, trucks, and more. The biggest issue for your boat situation, however, is that only 7 of the 50 US states extend lemon law protections to used vehicles. And not all used vehicles will necessarily qualify — it’ll depend on how it was bought, whether or not the manufacturer’s warranty is still valid, and more.
I’m being vague because lemon laws are regulated at the state level, so you’ll need to look at your local regulations to get the details. The 7 states that extend lemon law protection to used vehicles are Minnesota, New Mexico, New Jersey, New York, California, Connecticut, and Massachusetts. Your chances of getting a successful lemon law claim are better in those states. But even if you aren’t in one of them, it can still be a good idea to look up a “Lemon law attorney near me” and get a consultation.