A personal water craft (PWC), also called water scooter, is a recreational watercraft that the rider sits or stands on, rather than inside of, as in a boat. PWCs have two style categories. The first and most popular being a "sit down", where the rider uses the watercraft mainly sitting down and typically holds two or more people. The second style is a "stand up", where the rider uses the watercraft standing up. The stand up styles are built for one rider and is used more for doing tricks, racing, and are used in competitions. Both styles have an inboard engine driving a pump jet that has a screw-shaped impeller to create thrust for propulsion and steering. They are often referred by the trademarked brand names Jet Ski, WaveRunner, or Sea-Doo. Most are designed for two or three people, though four-passenger models exist. The United States Coast Guard defines a personal watercraft, amongst other criteria, as a jet drive boat less than 13 feet (4 m) in length, in order to exclude from that definition more conventional sized jet boats. There is a wide variety of "jet boats" many of which exceed 30–40 feet (9–12 m) in length. Companies such as UK based *DJR Ltd specialise in building high end luxury freestyle machines based on the Yamaha superjet combined with an aftermarket hull, such.