Physics of Personal Watercraft

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Personal Watercrafts or "jet skis" are basically Personal Watercraft (PWC) are basically small inboard boats able to travel at high speeds due to large amounts of power and very light weight. Alomst all PWC's are under 600 lbs and most of todays PWC's have at least 90 hp.Not only are PWC's some of the fastest water vehicles they are also some of the most maneuverable water vehicles. This is because PWC's propultion is based on a jet that also is it's turning mechanism. When the driver turns the handlebars the jet (via cables) turns in the direction of the handlebars so the stern is pushed in the opposite direction. This allows the driver to turn at a much tighter angle than traditional boats with keels and rudders.The main drawback to this maneuverability is the fact that if there is no thrust coming from the engine the ability to turn is effictively zero meaning that anytime the driver presses the kill switch (a large red button) they lose all ability to steer. This is extremely dangerous whenever an inexperienced person may drive the PWC back to dock or into shore. PWC's have no brakes and have no ablilty to stop other than turning around. They have an extremely efficient ability to hydroplane (when most of the PWC is above water) and it takes most PWC's a few hundred feet to come to a stop after being at full throttle. This is because 600 lbs + a rider is traveling at a very high speed with only minimal friction to slow them down (since PWC's are made to travel with very little friction).

PWC's also have a problem with turning. When a PWC is at full speed there is a great amount of force produced by the jet and the vehicle is therefor very difficult to turn. The main way to turn sharply during high speeds is to let of the throttle temporarily. This slows the amount of water flowing through the jet so the jet can be turned. Once the jet is turned the driver can depress the throttle again. Although being very effective this tecneque can also be quite dangerous. When the PWC turns it resists it's change in motion, however the driver does not recieve the same change in motion. The driver's body still wants to continue in the previous path of the PWC. Unless the Driver holds on very hard the driver is likely to fall of the PWC at a very high speed.

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