How Do Jet Skis Work?

While most jet ski riders are content to just enjoy the speed and leisure offered by a jet ski without needing to know how the magic happens, those with an affection for physics might wonder at some point during their ride “How do jet skis work exactly?”

Like a boat, a jet ski, or PWC (personal watercraft), can float on water whether it’s moving or sitting still.

That has everything to do with its boat-like hull, which is specifically designed to maintain buoyancy.

A PWC doesn’t move like a traditional boat, though. (Although boats have been designed using the same propulsion method that PWC use.)

Where a boat uses propellers to displace water and move forward through the water, jet skis rely on thrust.

How does a jet ski create that thrust?

It takes several components working together to turn still water into momentum.

How does a jet ski engine work?

Like in a car, a jet ski engine (powered by fuel and a battery) provides the PWC with its power.

The engine is started with a key and idles when the jet ski is not actively in motion.

But even an idling jet ski starts moving water through its drive shaft, so most models will move forward as soon as they are turned on.

Once the engine is running, the jet ski can be operated using the throttle and handlebars.

The engine itself only provides power. It will not move the PWC forward without any additional signals to the craft.

Jet Ski Throttle Lever Operation

While the power in a jet ski lies in its engine, determining how fast it can go and how easily it can pull a skier or tuber, implementation of that power lies entirely in a PWC’s handlebars.

More specifically in the jet ski throttle lever.

When driving a jet ski, pulling the throttle lever sets the internal components inside the jet ski into motion.

The throttle turns the impeller inside a jet ski, which is how a jet ski pulls in water and pushes it out the back end, creating thrust.

How does a jet ski impeller work?

The impeller on a jet ski is the jet ski’s main attraction.

It sits inside pipe that has an intake grate to pull in water on the underside of the jet ski and a nozzle to push the water out on the back of the jet ski.

A PWC impeller looks much like a standard propeller, but instead of the blades being placed apart at an even level all around the hub, the blades are tightly wrapped, overlapping each other, but not touching.

Here is a photo of each for comparison –

When the PWC throttle is operated the impeller turns.

When the impeller turns, it pulls water from below the craft up into its intake grate and expels it out the nozzle.

The harder the throttle lever is pressed, the faster the impeller turns and the faster and harder the water is moved through the craft, increasing its speed.

Jet Ski Propeller

A jet ski impeller IS a jet ski’s propeller. It does not have the same type of external propellers that create movement in boats.

This is why, traditionally, jet skis have not been able to reverse.

While a propeller can be operated either way to go either forward or backward, an impeller works only one way to move water through the jet ski – in through the intake grate, out through the nozzle.

Changing the direction of the nozzle is how a jet ski is steered.

Since a jet ski impeller sits inside the body of the jet ski and is inaccessible during riding, it is safer than a traditional propeller.

However, jet ski thrust is very powerful and poses dangers of its own.

Jet Ski Handlebar

When you turn the handlebar on a jet ski, what you are actually controlling is the nozzle that expels water from the PWC’s back.

The nozzle changes the direction of the thrust created by the impeller to propel you in the direction you want to go.

The fact that a jet ski is steered on thrust means a jet ski can’t be steered when the throttle is not engaged.

This makes it a completely different animal than other watercraft and any vehicle that operates on land.

Traditionally, jet skis also haven’t had brakes, which makes letting off the throttle the only means of slowing down.

You can see how this creates a problem in steering your way out of an accident.

Today, more and more manufacturers are creating PWC with brakes or reverse systems, which do provide a means of slowing a jet ski without losing the ability to steer.

Jet Ski Reverse and Jet Ski Brakes

Despite all the new technology and abilities in personal watercraft, one things remains true – jet ski impellers and intake systems only work one way.

What that means in operational terms is that a jet ski’s impeller alone cannot cause a PWC to reverse or to brake.

Instead, the water the impeller pulls in and pushes out must be redirected inside the intake channel.

To accomplish this, a small dam, known as a bucket, is installed on the nozzle of the jet ski.

When engaged, the bucket prevents the water from escaping the back of the PWC and pushes it back toward the front.

When braking, this slows the jet ski more rapidly than just letting up on the throttle alone.

When reversing, this causes the jet ski to move backward when the throttle is applied.

How does a jet ski cooling system work?

Just like a car’s engine needs a radiator to keep from overheating, a PWC engine needs a cooling system to prevent it from getting too hot while in use and becoming non-operational or damaging the internal components.

Jet skis use two different types of cooling systems – open loop and closed loop.

Open Loop Cooling System

The majority of jet skis use an open loop system, including models by Kawasaki and Yamaha.

An open loop cooling system pulls in water from outside the craft, passes it through the water jacket around the engine, and expels it with the rest of the water moving through the craft.

Closed Loop Cooling System

Sea-Doo uses a closed loop cooling system on their crafts.

In a closed loop cooling system, a PWC still pulls in water to aid in its cooling, but instead of this water going into the engine compartment directly, the water goes into the jet ski’s version of a radiator.

Here, the water cools down the antifreeze in the jet ski, and that cooled antifreeze moves through the engine compartment.

Open Loop vs Closed Loop Water Cooling

Both open loop and closed loop cooling systems have their advantages.

An open loop system is more efficient. A closed loop system protects the engine.

The main advantage of a closed loop system is that it keeps saltwater out of the engine compartment.

Saltwater is hard on a jet ski’s engine and can cause corrosion.

After riding in the ocean, a PWC with an open cooling system must be flushed to prevent damage to the engine.

his is why Sea-Doo likely opted for a closed loop system, since they market themselves as the oceangoing PWC company.

How a Jet Ski Works

While a jet ski requires many components to work, the everyday operation isn’t all that complicated.

Turn a key to start the engine, press the throttle, the impeller inside the jet ski turns, which pulls in water and pushes it out a nozzle at the back.

This expulsion creates thrust, which propels the jet ski forward.

Turn the handlebar, the nozzle turns and redirects the thrust, which changes the jet ski’s direction.

Block the thrust, and the water pushes back toward the front of the jet ski, causing the machine to stop or go in reverse.

It took many years of tinkering to invent such a method of propulsion, but, in the end, it’s pretty simple really.

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