What do you get when you cross a scooter with a Sea-Doo? In Rehoboth Beach, Delaware, you get the “Land-Doo”—a one-of-a-kind custom ride that looks like a personal watercraft but cruises on pavement.

There’s no better time to jam the throttle on a personal watercraft (PWC) than the dog days of July. A jet bike lets you blast through waves, jump wakes and reach speeds more common on the highway ...