Kenshin posted:

Not from a legal standpoint for private boats (aside from boating licenses in some places, the Washington State one is basically passing a simple online test and also having a driver's license and they send you a boating permit card).

If you ever want to rent/charter sailboats though they'll require some certifications. Your basic day-sailing certs are ASA 101 and 103. 104 is for multi-day chartering trips (where you are captain of the boat), and 114 is lots of specific stuff on catamarans. I'd highly recommend at least doing those four. They are all on-the-water classes that also have written exams and books to study.

Even if you just want your own boat it's probably a good idea to do classes. That said there is the (relatively) famous experience of the couple who circumnavigated on "Bumfuzzle", a ~40ft catamaran, back in the mid 2000s, who took the first day of their ASA 101 class, decided they didn't like taking classes, and then just went sailing. They made it, though as I read through their blog even near the end of their trip around the world 2-handing their boat they were still doing things that made me facepalm because I'd learned those things in my classes and they didn't do them while sailing around the world.