How Personal Watercraft Work

By: Tracy V. Wilson
Personal watercraft like jet skis are used by millions of Americans each year. Learn how personal watercraft work and about laws and environmental concerns. See more pictures of extreme sports.
Photo courtesy Yamaha Motor Corporation, U.S.A.

When snowmobile manufacturer Bombardier Inc. introduced the SEA-DOO® in 1968, the idea of a motor-driven consumer watercraft with no visible propeller was revolutionary. The idea of passengers standing on a watercraft instead of sitting in a conventional hull was also pretty out there. In fact, the design turned out to be too original. Bombardier's new product was not successful, and the company discontinued it in 1970.

A few years later, Kawasaki Motors introduced the JET-SKI® watercraft, which became so popular that m­any people now refer to all personal watercraft as "jet skis." In the mid-1980s, other manufacturers developed their own models, and Bombardier re-introduced its SEA-DOO design.


­Since then, demand for personal watercraft has skyrocketed. There were 1.48 million personal watercraft registered with the U.S. Coast Guard in 2004. About 28.7 million people rode personal watercraft in U.S. waters in the same year [Source: USDA].

In this article, we will explore how these craft operate, and we'll examine the safety, environmental and legal concern­s related to their use.



How Personal Watercraft Move

A personal watercraft's engine and jet drive

A personal watercraft moves through the water in the same sort of way a rocket moves through the atmosphere. But instead of using high-pressure gas to generate thrust, the craft uses a jet drive to create a powerful stream of water. In the jet drive, an impeller propels a large amount of water from underneath the craft through a steering nozzle at the rear of the craft.

The impeller is a rotor-like device that sits inside a cylindrical passageway in the body of the craft. The craft's engine rotates the impeller via a drive shaft. The impeller's curved blades spin rapidly, forcing water up through the passageway and out through the nozzle.


Yamaha FX High Output impeller and steering
Photo courtesy Yamaha Motor Corporation, U.S.A.

This moves the craft because of the principle described in Isaac Newton's third law of motion. According to Newton's third law, for every action, there is an equal and opposite reaction. In this case, the action is the expulsion of water through the nozzle. The reaction is the movement of the boat in the opposite direction. How Rocket Engines Work explains this principle in detail.

When you steer the craft, a cable linkage connected to the handles swivels the nozzle at the rear of the craft. This changes the direction of the "equal and opposite reaction." If the nozzle directs the water to the right side of the craft, the rear of the craft pushes to the left. That causes the front of the craft to turn to the right.


That's the basic idea of a personal watercraft. Now let's examine the details of this system.


The Engine

Personal watercraft engines are usually two-stroke or four-stroke engines. Learn about personal watercraft engines and how engines are made quieter.
Photo courtesy Yamaha Motor Corporation, U.S.A.

Just like a lawn mower or a car, personal watercraft run on two-stroke or four-stroke engines. Two-stroke models have two or three cylinders. Four-stroke models usually have four cylinders. See How Two-stroke Engines Work and How Car Engines Work (describing the four-stroke engine) to learn all about these mechanisms.

A noticeable difference between marine and automotive engines is the cooling system. Instead of using a radiator, a marine engine uses the surrounding water to control temperature. Water flows through the engine or through a closed system that includes a chemical coolant.


The engine starts the same way a car engine does. The ignition button, usually found on the handlebars, sends a signal to an electric starting motor. The motor turns the engine to get it started. Then, the engine takes over powering the craft.

All newer models of personal watercraft have a pin or key that inserts into a slot near the ignition. The pin is attached to a lanyard that connects to the operator's life vest or wraps around his or her wrist. The boat will not start or run without the pin in place. If the operator falls overboard, the lanyard pulls the pin out, and the craft coasts to a stop. This keeps the boat from traveling very far and reduces the likelihood of a collision.


Steering and Acceleration

Yamaha FX
Photo courtesy Yamaha Motor Corporation, U.S.A.

The steering mechanism of a personal watercraft is very simple.

The handlebars are connected to a steering cable. When the operator turns the handlebars, the cable moves the steering nozzle, which changes the direction of the jet of water. Some models are also designed to allow the operator to lean into turns as they would on a motorcycle.


A trigger on the handlebars controls the throttle, allowing the operator to accelerate. The throttle is as important to steering as it is to acceleration. Without water from the steering nozzle, the boat cannot change direction. Instinctively slowing down to avoid an accident is dangerous and can result in a complete loss of steering power. If this happens, the craft will float in a straight line until friction from the surrounding water brings it to a stop. Newer models use a computer to re-start the jet drive if the operator simultaneously releases the throttle and turns the handlebars hard in one direction.

Some models can go in reverse using a simple shroud that lowers over the steering nozzle. The shroud forces the water into a U-turn, sending it under the boat instead of behind it. Since the rear of the craft always moves in the opposite direction of the flow of water, this makes the craft go backward. This feature can help get the boat into and out of the water or get out of a tight space. It is not designed to slow or stop a craft that is moving at high speeds.

Now that we've covered the mechanical components, let's explore the environmental and legal concerns that surround personal watercraft.


Environmental Concerns

Personal watercraft are small and ride higher in the water than other boats, so they can get into very narrow, shallow spaces. This is particularly helpful for surveyors, search-and-rescue teams and U.S. Homeland Security officials, all of whom use the craft in their work. However, this ability to get into tight spaces can lead to:

  • Disturbance of sediment
  • Destruction of aquatic habitat and plant life
  • Disturbance of or injury to birds, fish and animals

Unlike motorboats, a jet drive has no external propeller to damage coral reefs or injure animals. However, the drive's suction and the force of the jet can still cause damage. Also, if the drive is not flushed thoroughly after every use, "exotic" species, like zebra mussels and invasive plants, can stow away inside the craft. They can then be transported to other bodies of water.


Another environmental concern is pollution. All older models and some newer models of personal watercraft use two-stroke engines, which can vent oil and gasoline into the water with their exhaust. Other motorized boats also use two-stroke engines, but the sheer number of personal watercraft may make their environmental impact greater.

The U.S. Environmental Protection Agency has outlined standards for marine engine emissions and efficiency that take effect in 2006. Virtually all current models of personal watercraft already meet or exceed these standards by incorporating technology such as:

  • Fuel-injection systems
  • Cleaner-running four-stroke engines

A number of government agencies have taken steps to reduce concerns about noise, safety and pollution. We'll look at these in the next section.


Laws and Regulations

Personal watercraft laws and regulations are set by three federal agencies. Learn about personal watercraft laws and regulations and how they affect you.
Photo courtesy Yamaha Motor Corporation, U.S.A.

Several national organizations monitor and regulate personal watercraft in the United States. They include:

The U.S. Coast Guard classifies personal watercraft as inboard boats, so operators and passengers must follow the same laws and guidelines as other boaters. Additional regulations vary by state. The National Association of State Boating Law Administrators has a complete state-by-state listing of personal-watercraft laws. It is up to all operators and passengers to make sure they use their watercraft safely and in compliance with local laws.


For more information on personal watercraft and related topics, check out the links on the next page.


Lots More Information

Related Articles

More Great Links

  • "Boat Smart."
  • Boat/US Clean Water Trust. "Zap the Zebra." Brochure.
  • "Coast Guard Warns Public of Dangers Associated with Underage, Inexperienced Operators of Personal Watercraft."
  • "The Facts About Personal Watercraft." PWIA.
  • "Get the Facts About Today's Personal Watercraft." PWIA.
  • "Information for Boaters - Jet Propelled and Personal Watercraft." Florida
  • Leeworthy, Dr. Vernon R. and Peter Wiley. "Current Participation Patterns in Marine Recreation." U.S. Department of Commerce, National Oceanic and Atmospheric Administration. Silver Spring, 2001.
  • Leeworthy, Dr. Vernon R. National Survey on Recreation and the Environment. "Preliminary Estimates from Versions 1-6: Coastal Recreation Participation." Silver Spring, 2001.
  • "Lift from Flow Turning."
  • National Marine Manufacturers Association Population Estimates
  • "Nautical Know-How - Basic Boating Safety Certification Course."
  • "Newton's Laws: A High School Physics Tutorial."
  • "Personal Watercraft."
  • "Personal Watercraft Background." PWIA.
  • "Personal Watercraft: Fact Sheet." Marshfield Clinic.
  • "Personal Watercraft in the National Parks."
  • "Personal Watercraft Surveying System (PWSS)." Innerspace Technology.
  • "Personal Watercraft Use by Children and Adolescents." American Academy of Pediatrics.;105/2/452
  • Polaris. "2004 Parts Manual No. 9919045: Genesis I." Manitoba: Polaris Sales, Inc., 2003.
  • Polaris. "Owner's Manual for Maintenance and Safety: MSX 110/MSX 160." Manitoba: Polaris Sales, Inc., 2004.
  • "Propeller Thrust."
  • "PWC Builders Shift Focus."
  • "PWC Renter Orientation Checklist." National Association of State Boating Law Administrators.
  • Strum, Madeline. "Summary of Findings from the Boat Manufacturing Process." Environmental Protection Agenc­y Memorandum. January 15, 1997.
  • Tread Lightly. "The Tread Lightly! Guide To Responsible Personal Watercraft Use." Ehlert Publishing Group, Inc., 1999.
  • United States Department of Agriculture. Forest Service. "Recreation Statistics Update. Report No. 1. August 2004." Washington DC. 2004.
  • United States Department of Homeland Security. Coast Guard. "Boating Statistics - 2003." Pub. P16754.17. Washington DC. 2004.
  • United States Environmental Protection Agency. "Draft Regulatory Support Document: Control of Emissions from Spark-Ignition Marine Vessels and Highway Motorcycles." Washington DC: July 2002.
  • United States Environmental Protection Agency. "Regulatory Announcement: Frequently Asked Questions from Snowmobile Owners." Ann Arbor: 2002.
  • United States Environmental Protection Agency. "Regulatory Impact Analysis: Control of Air Pollution Emissions Standards for New Nonroad Spark-Ignition Marine Engines." Washington DC: June 1996.
  • United States National Transportation Safety Board. "Safety Study: Personal Watercraft Safety." Pub. 7002. Washington DC. 1998.
  • "Water Jet Unit Basic Principles and the Consequent Benefits." Castoldi Company.