Jet Drive Propulsion Basics

Blow up a balloon.  Let it go.  What happens?

According to a famous law of motion: "For every action there is an equal and opposite reaction."  This theory applies to the jet drive propulsion system of personal watercraft.  Your PWC is pushed through the water by the action of an engine-driven jet pump.  Just as air exiting a blown up and released balloon pushes the balloon in the opposite direction around the room, water leaving the jet pump pushes your personal watercraft through the water.

Personal watercraft have certain, common characteristics. They have an inboard engine with jet drive and they are designed for the operator to safely fall overboard and re-board the vessel. These two features are related. The jet drive system eliminates parts, such as a propeller or rudder, on the outside of the hull.

The pump works by drawing water into the housing ahead of an impeller.  The impeller (a type of precision propeller contained within the housing) pressurizes the water and forces it, in a high-pressure stream, behind and away from the back of the boat.  The force of the exiting water pushes the boat in the opposite direction. A handlebar controls nozzle direction.

Reverse is available on some of these types of personal watercraft.  This is accomplished by a "clam-shell" type device, often called a reverse bucket, which can be moved over the end of the directional nozzle to reverse the water flow.  This enables the personal watercraft to “back-up.”