At least one of my readers has been getting herself qualified to drive a personal watercraft and another has been educating us about Admiralty Law. So for the two of you (if nobody else) here is a legal case from the United Kingdom that hinged on the question of, "Is a personal watercraft a ship?"
Apparently the driver of this particular chainsaw-on-water had rammed his weapon-toy into a fellow idiot-jet-skier and severely injured him. An ingenious prosecution charged the miscreant as the master of a sea-going vessel and he was sentenced to six months in prison. (Far too lenient in my opinion).
Unfortunately after what sounds like some expensive legal tap-dancing he won his appeal. I still hate jetskiers. This ultimate PWC repellent is the best way to deal with them as far as I am concerned.