Naval architect...
usually a degree, placement, then keep your nose clean and work your way up through a few companies and if you are lucky you get to be known and desirable.
I did it the other way, apprenticeship (boat builder), night school, read lots of books, lots of application forms then a lucky break. Then I kept my nose clean, absorbed the knowledge from older wiser ones than I, and one day I was asked if I fancied a bit more responsibility. I took it on and went from there.
Styling and design....
Basically the same, although you need a bit of flair to get noticed. Again, luck plays a big part as oportunities are rare and if you get one and it goes down well, you will probably be asked to carry on.