It's entirely legal to design and build your own boat and put it in the water pretty much anywhere in the world. If you want to carry paying passengers then th

It's entirely legal to design and build your own boat and put it in the water pretty much anywhere in the world. If you want to carry paying passengers then things are different, but that's why they were officially crew. (Crew members who are paying to be there has a very long history. One of the last lines operating sailing ships, in the 1920s and 30s, made money from merchant marine cadets whose countries still required them to have a certain amount of experience as crew of a sailing vessel to get their ticket.)