Jet Ski is the brand name of a personal water craft (PWC)  manufactured by Kawasaki,  a Japanese company.  The term is often used generically to refer to any type of personal watercraft used mainly for recreation, and it is also used as a verb to describe the use of any type of PWC. 
A runabout style PWC typically carries 1–3 people seated in a configuration like a typical bicycle or motorcycle.
"Jet Ski" is a proper noun and registered trademark of Kawasaki. The stand-up Kawasaki Jet Ski was the first "commercially successful" personal watercraft in America, having been released in 1972 (after reaching a license agreement with the inventor of the Sea-doo, Clayton Jacobson II when his license agreement with Bombardier expired).  The Kawasaki Jet Ski was the only commercial successful PWC for almost 16 years, from the introduction of the WSAA in October 1972 through the re-introduction of the sit-down, runabout style Bombardier Sea-Doo in 1988.  
With the introduction of the Jet Ski, Kawasaki, in cooperation with aftermarket companies and enthusiasts, helped in creating the United States Jet Ski Boating Association (USJSBA). In 1982 the name was changed to the International Jet Sports Boating Association (IJSBA). At the start, only JS440 stand-ups were raced. After Kawasaki introduced the runabout style X2 in 1986 it gained its own class, later to be renamed the "Sport Class". 
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Kawasaki introduces the first production stand-up PWC in October 1972. The WSAA and follow-on WSAB were powered by modified 400cc 2-stroke twin cylinder engines. The WSAA was designed with a flat hull and the WSAB came with a concave design. The design concepts distinctive of these original craft were a fully enclosed impeller for safety and self-righting, self-circling features. Without a lanyard the self circling allowed the rider to swim back to the idling craft after falling off. Kawasaki called them "Water Jet" and "Power Skis" before they settled on the name Jet Ski. 
The 1976 JS400 was popular among thrill seeking recreational riders and racers. The 1977 JS440 offered more power and performance. It was one of Kawasaki's longest selling models. In 1982, Kawasaki responded to market demand for more performance with the JS550. The 550 featured a newly designed high capacity mixed flow pump driven by more powerful 531cc engine. The 550 introduced an automatic rev limiter to prevent engine damage when the pump cavitates.
Kawasaki continued to improve the JS550 well into the 1990s. In 1986 the JS440 was replaced in the line-up by the JS300, a single cylinder 294cc two-stroke engine featuring automatic fuel /oil mixing.
Kawasaki introduces the completely redesigned JS650-A. It featured an even higher capacity axial flow pump and a powerful 635cc two-stroke twin engine in a modified V-hull design for increased maneuverability and stability.
In 1992, the company introduced a stand-up JS750-A. The engine was a twin cylinder 743cc two-stroke with reed valves and automatic oil injection. The redesigned hull was lighter weight and more maneuverable. The 750 introduced underwater exhaust for quieter operation to the stand-up kawasaki.
The JS750-B is the first stand-up JetSki with dual carbs.
Kawasaki releases a commemorative edition JS550-C. The high performance JS750-C is released featuring a lower center of gravity due to its hand-laminated fiberglass hull.
Kawasaki introduces the JS800A a 781cc two-stroke stand-up. It has a fiberglass reinforced plastic (FRP) hull and top deck, along with an 781cc in-line twin 2-stroke engine generating 80 hp.
Due to US EPA restrictions, Kawasaki releases their final two-stroke stand-up, and the last year of the JS800 SX-R, to recognize the 37-year history of the stand-up JetSki. The model designation was JS800ABF, with an MSRP of $7899.00. 
On October 6, 2016 Kawasaki reintroduced the stand-up JetSki. The 8 ft. 9 in., 550+ lb. SX-R 1500 shared little with its predecessors. Powered by a 160HP inline 4-cylinder four-stroke engine, the SX-R was described by one author as "on steroids" and having "lost some of the playfulness of early standup models".  It holds 6.1 gallons of fuel, measures 104.5" long, 30.1" wide and 33.1" high. 
Kawasaki produced various models of the Jet Ski starting in 1972, beginning with the JS400 and leading up to the current JS1500.
The 800 SX-R was introduced for the 2003 model year, and remained unchanged until it was discontinued in 2011.
- Common name: 800 SX-R
- Displacement: 781cc, Inline 2-Cylinder, 2-Stroke
- Bore x stroke: 82 x 74mm
- Compression ratio: 7.2:1
- Rated Power Output: 80 hp, 59.7 kW
- Dual carb (Mikuni SBN40) with reed valves
- Premix ratio, gas/oil: 50:1
- Max fuel consumption (US gal/h): 7.7
- Range at full throttle: 0.6 hrs
- Spark plug: BR8ES Solid (NGK 3961)
- RPM Limiter: 8,000 rpm
- Fuel capacity (gal): 4.5
- Length (in): 90.6
- Width (in): 28.7
- Height (in): 28.9
- Weight, dry (lb): 369.9
- Displacement (cc) to weight ratio: 2.11
- Max speed (mph): 47
- Impeller: Stainless steel 3 blade
In 1990 Yamaha introduced the Super Jet. It was designed in consultation with Clayton Jacobson II. It is still in production today, with various updates throughout the model years.
In 1994-1995 Yamaha introduced the FX-1, which had a limited production of 1500 units.
In 2004 Bombardier introduced the SeaDoo 3D. Unfortunately it had an ill-fated life and was only sold as 2005-2007 model years.
Various manufacturers produce a range of aftermarket competition hulls for stand-up PWCs.
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