Jesse, I would say yes. And if the kid were going to read to himself or herself, I'd probably offer a one-sheet for knot and sailing terms (and a few others) unless kid was keen on dictionaries.
I know the author posts here (hee) but other than the protagonists being adolescent, I don't feel like the books are YA at all. They're not written with vocabulary chosen for teens and I had to look some of the terms up when I was reading (which I like). But the content and story and themes are absolutely appropriate I would think, especially if kid made it through the darker Harry Potter books.