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What is a Jet Boat?

A jet boat is a thrilling watercraft, propelled by a jet of water ejected from the back of the vessel. Unlike traditional boats with external propellers, jet boats have an internal impeller, offering enhanced maneuverability and the ability to navigate shallow waters. Intrigued by how jet propulsion provides such an exhilarating ride? Let's examine the mechanics that make jet boats so dynamic.
Jonathan Stevens
Jonathan Stevens

A boat is designated as a jet boat when its means of propulsion is a stream of water jetted out from the boat. Some boats move atop the water by other methods of energy, such as wind, oars or mechanized propellers. Jet boats utilize a central pump system to draw water up from beneath the surface of the craft. The water is channeled through a designed route and then is expelled in streaming form through a nozzle. The nozzle is situated above the water's surface at the rear of the jet boat. Steering is largely accomplished through the repositioning of the jet stream.

The central pumping unit of a jet boat features a propeller system but not for propulsion through the water. The propeller action of a jet boat is specifically designed to draw water into the craft and force it into a powerful stream that moves the boat forward. Such propellers are properly designated as impellers and typically feature smaller blades and faster revolutions than standard propellers.

Ferries are often jet boats.
Ferries are often jet boats.

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 combination impeller and pump system have evolved into two basic types. The mixed flow is designed to maximize pressure and increase speed. It compresses the water by diminishing the diameter of the chamber plumbing, forcing the water to emit under pressure through a thin nozzle, resulting in greater speed. The axial flow type is designed to result in greater load carrying capacity. The plumbing chambers remain at a fixed diameter so that the emitting water does so at a greater volume than its mixed flow counterpart.

The engines used to power modern jet boats are available in both inboard and outboard configurations. In both instances, there is a measurable decrease in overall horsepower since anywhere from twenty-five per cent to thirty-five per cent (25-35%) is utilized to draw the water in, pump the water through, and emit the water out. For example, a one hundred and fifty horsepower (150HP) engine will produce the equivalent of one hundred horsepower to one hundred and five horsepower (100-105HP) at the point of emission (the nozzle).

Jet boats are not limited to popular recreational type vehicles. The jet boat design has been applied to racing boats, ferries and even military vessels. The increased maneuverability and quickness in starting and stopping have added to its growing popularity and use.

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Discussion Comments

David09

@SkyWhisperer - I don’t think a jet ski is the most thrilling ride you can ever experience. You can go on jet boat tours across the rapids of the Niagara Falls, if you want to experience that wonder firsthand.

These tours use massive jet boats that accommodate a number of people and they make sure you have plenty of opportunities to get wet and experience adventure. It’s kind of like the water boat rides you see in some theme parks, except with some turbo charged action.

Mammmood

@SkyWhisperer - Since you used a jet ski and not a jet boat, I’m willing to bet that it used the mixed flow design.

That design is meant to increase pressure and emit greater bursts of water out of a smaller nozzle. I think that’s the design that a jet ski would need to increase greater speed, as opposed to needing a design meant to take on a greater load, like you would with a boat.

SkyWhisperer

I’ve never ridden on a jet boat, but I did ride on a jet ski once. Like a jet boat, ski technology works the same way, pulling water into the jet and then expelling it out the boat.

All I can tell you is that those jet skis are powerful! I rode with my friend on the Potomac river one summer. We were both strapped with life vests and I stood in the back and held on to him for dear life, as that thing sliced through the waves and slammed and pounded the water, making my head shake.

It was quite a thrill ride and it was certainly more wild than any roller coaster I had been on! For some people, it’s the only way to travel on the lake.

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    • Ferries are often jet boats.
      Ferries are often jet boats.