Great suggestions, here is what I do. A sorta multi pronged approach. Eliminate any bridge that would allow them access. They can jump fairly good distances. Second, seal up any access, this includes the prop exhaust(they luv exhaust manifolds). Put down trays of bait, sticky trays, and spring traps. Dryer sheets may be beneficial, but not sure of there effectiveness, but likely couldn't hurt, The last thing is vigilance, check the boat on a regular basis, one thing they don't like is activity.