Game Development Reference
In-Depth Information
Jet Skis
Jet skis, or more generally personal watercraft (PWC), are small, highly maneuverable water-
craft that offer a lot of possibilities for game simulations. Although different manufacturers
refer to them by different names, in this section we will use the term “jet ski.” As shown in
Figure 9-11, jet skis are powerful, highly maneuverable watercraft. They are usually designed to
carry from 1 to 3 people and are ridden like a motorcycle. Jet skis have V-shaped planing hulls,
and as such they rise out of the water when they reach a certain speed.
Figure 9-11.
Masao Fujisama goes airborne in his jet ski. (Photo courtesy of JetSkiNews,
www.jetskinews.com)
Jet Drives
Jet skis and other personal watercraft are powered by jet drives. A low-pressure water pump
sucks in water from an opening in the bottom of the hull and accelerates the water backwards
through a nozzle out the back of the hull. The acceleration of the water generates a thrust that
propels the jet ski forward. Typically, the exit velocity of the water coming out of the nozzle will
be about twice the top speed of the jet ski.
The water is accelerated inside the pump by means of an
impeller
, which can be thought
of as an internal propeller. The function of an impeller is exactly the same as an external propeller.
The impeller blades push the water back and down, which sets up a pressure difference between
the forward and rearward faces of the blades. Impellers are safer than external propellers for the
obvious reason that they operate inside the jet ski so riders or swimmers aren't exposed to
the blades.
Optimum performance of a jet drive depends on getting a clean, steady supply of water
into the pump. The flow can be disrupted, for example, if the jet ski makes sharp, high-speed
turns. Another risk to performance is if seaweed or other water-borne debris gets sucked up
into the pump.
