Get them to take the measurement of the bullet wholes. You will have to determine which side would have been the facing the shooter, but it sould give you a guess on what the caliber of the weapon was.
If it was a rifle, and they could get off a long shot, you could be looking anywhere from 200-500 yds. back for shells. If it was a pistol, it would only be 50-100 yds., unless they are trying to be Superman and really reach out and touch someone.
Hate to hear that about your boat. Next time, get Progressive Insurance on it, and see if they would get you a new boat. Just an idea.