After renovating a historic home in Philadelphia, then building new construction, then later building three bakeries, I learned a lot from previous mistakes.
It can't be said enough that everything should be in writing, even if something simple like through a text message, and should always be 100% clear. There could be several back and forth texts or conversations with negotiations, so it can be muddy towards the end. Before beginning work, I always text or e-mail with, "my understanding is blah blah blah <very specific work, prices, terms and penalties>. Please confirm if this is correct." If it isn't in writing, it's a "he said/she said". (Being a contractor means you can hopefully do the agreed upon work, but it doesn't necessarily mean you're any good at admin, negotiations, or running a business. They're two different skill sets.)
I'm not sure how it plays out with boat yards, but one thing I build into negotiations now is the increasing penalties for not completing specific parts of the work on time. It's very common for contractors to take on more work than they can do and then try to ride it all out and get it done on their own time. This is no fun when it's delaying your business opening (or boating season) but without penalties they know they have you by the balls because it would take you just as long to find someone else to do the work.