I don't know.
This is great. Japan, even more so than the rest of the world, has some warped ideas about the permissibility of bodies, (AKA "Those things we all have") particularly if those bodies happen to be female. Censorship is rampant, even in pornography. It's a weird way to highlight the problem, but it obviously works - I've seen the vagina-boat on a couple different websites so far. I hope most people get what she's trying to do. Cheers! Edit: Hey, she successfully made the boat! ...And was arrested for it.
Good question! But I don't think it matters - The actual interesting-looking bits are likely to be on top, with the person paddling the boat sitting in the, er, hole. The underside of the boat would be analogous to the interior of the person, and therefore doesn't have any 3d modeling - Most likely it'll end up being something pretty traditional for a boat of this size.
edit: I don't even want to be a part of this but it'll look bad if I delete my comment, so here. Now you'll never know.