I know that both of these are available at Orient Beach (my boys already figured that out, and I am sure it is the parasailing and waverunning rather than the prospect of seeing naked people that made them decide that we will spend our day at Orient Beach).
I went Jet-skiing in St. Maarten. I dont know what the beach was called, but we took a water taxi over to the main city part thing and there was a beach there. There are a few people offering Jet Skiing. I payed 45 bucks for half an hour. IT WAS A BLAST!!!! You can see the ships and all and basically go wherever you want. They didnt try to short me of my 30 minutes either... i think i came in a few minutes late actually lol! It was AWESOME!! What ship are you going on? We were on the glory, docked next to the Caribbean princess, and explorer.