I can see her wanting a boat. Especially being in the Miami/Bahama area. I think she would want it as a status symbol. I also think Peter Nygurd her lover from the late 80's said that she loved going out on the water. So I can buy that part of the story.
LOL @ Forked tongue comment
I don't know why she wanted a boat.
Didn' she ever read about what happened to Natalie Wood?