Jet boats use a central pumping system to draw water from beneath the boat and expel it through a nozzle for propulsion. Developed in the 1950s, they come in mixed flow and axial flow types and are used for recreation, racing, ferries, and naval vessels.
A boat is designated as a jet boat when its means of propulsion is a stream of water escaping from the boat. Some boats move on the water with other methods of energy, such as wind, oars or mechanized propellers. Jet boats use a central pumping system to draw water from beneath the surface of the boat. The water is led through a designed path and then expelled as a stream through a nozzle. The nozzle is located above the water surface at the rear of the boat. Steering is largely accomplished through repositioning of the jet stream.
The central pumping unit of a jet boat is equipped with a propeller system but not for propulsion through the water. The action of a jet boat’s propeller is specifically designed to draw water into the boat and force it into a powerful stream that propels the boat forward. Such propellers are properly designated impellers and typically have smaller blades and faster revolutions than standard propellers.
Developed in the early 1950s by New Zealander Sir William Hamilton, as a shallow water propulsion solution, the jet boat has since undergone multiple transformations. The combined impeller and pump system have evolved into two basic types. Mixed flow is designed to maximize pressure and increase velocity. Compresses water by decreasing the diameter of chamber tubing, forcing water out under pressure through a thin nozzle, resulting in higher velocity. Axial flow type is designed to achieve higher load capacity. The hydraulic chambers remain at a fixed diameter so that the water it emits does so at a greater volume than its mixed flow counterpart.
The engines used to power modern jet boats come in both inboard and outboard configurations. In both cases, there is a measurable decrease in overall horsepower as twenty-five percent to thirty-five percent (25-35%) is used to draw in water, pump water through, and eject it. For example, a one hundred and fifty horsepower (150hp) engine will produce the equivalent of one hundred to one hundred and five horsepower (100-105hp) at the emission point (the nozzle).
Jet boats aren’t limited to popular recreational vehicles. The jet boat design has been applied to racing boats, ferries, and even naval vessels. The increased maneuverability and quick start and stop have contributed to its growing popularity and use.