Hi John, you will want a 500 Series Nuvi. They are touchscreen so they'll work great in a car, and waterproof so they'll work great on the jet ski. You'll want to buy a G2 Vision card for Lakes to get Lake Maps if required. This unit is not even out yet, worth waiting for though. Here is a link:
https://buy.garmin.com/shop/shop.do?...SERIES_NUVI500
Call me to order. We are a Factory Garmin dealer so we can get them right at release. You'll probably want a universal mounting cradle for the jet ski
https://buy.garmin.com/shop/shop.do?pID=27931#