How Does a Jet Ski Work?

how does a jet ski work

How Do You Get Your High-Speed Personal Watercraft Moving?

Your car is able to move across the pavement because the grip of your tires grasps the asphalt. When the engine supplies power to the wheels, the tires “bite” the pavement and propel you forward. If you live in an area that gets snow, you know that trying to propel your car across icy or wet surfaces is much more difficult, and sometimes impossible. Of course, your personal watercraft doesn’t have wheels. And it certainly can’t grip the water’s surface, so how does it move?  Keep reading to find out exactly how your jet ski works. 

understanding how your personal watercraft sources its power

Understanding Your Sea-Doo’s Power Source

The first steps in understanding how your personal watercraft works are to understand what powers your personal watercraft (PWC). It doesn’t usually matter if it’s a Sea-Doo, Jet Ski, or any other model. Your PWC is powered by an internal combustion engine, which usually runs on gasoline.

The gasoline engines in most PWC’s are four-stroke, four-cylinder engines, comparable to the power of a small car. The largest models can have 1500cc engines and 20-gallon tanks. This might seem like a lot for a vehicle only a little bit bigger than a motorcycle. But your PWC actually needs a lot of power to get itself going, and a big fuel tank so you don’t get stranded in the middle of the lake or ocean. 

Just like your car engine, most PWC’s have an electric start that enables easy activation. The big difference in the engines is how a PWC’s cooling system works. Instead of a car radiator, which transfers heat, your PWC uses the temperature of the water around you to cool the system.

So now that we know a little bit about our engine, let’s talk about what all that power is doing.

how does your PWC move?

How Does Your PWC Move?

So, as we said earlier, there’s nothing for your PWC to “push” on to move it forward. So how does it do it? Well, let’s head back to school for a minute. Let’s talk about Newton’s 3 Laws of Motion!

Law #1: A body in motion will stay in motion unless an external force acts on it

Law #2: Force equals mass multiplied by acceleration

Law #3: For every action, there is an equal and opposite reaction

Now, all of these certainly affect how your PWC moves. But it’s not all pertinent to understanding how your jet ski works. While it would help you understand how much force your PWC needs to move, it doesn’t help us to understand why it moves. So we’re just going to focus on the laws most relevant to what we’re discussing. 

A Body (or Personal Watercraft) in Motion Will Stay In Motion

Well, first of all, let’s finally discuss how we get that body (your PWC) in motion. Your engine pulls water into your PWC through a grate in the bottom. Once it has entered your PWC, the engine shoots a jet of water out of the nozzle in the back of your vehicle. 

a PWC in motion will stay in motion

This first law specifically says “motion”, however, it makes the opposite true as well. A body at rest will stay at rest. You probably remember that line, too. On its own, a PWC has no propulsion power. However, your car’s round tires would allow it to move on a sloped surface (if the brakes weren’t on). Alternatively, for your PWC, the water is always “level”. 

So how does your PWC move when it can’t grip the water’s surface like your car grips the asphalt, and it has no ability to “roll”? Well, here comes Newton’s second law! It comes from the engine and its ability to push water behind you. All of which brings us to Newton’s third law.

For Every Action, There is an Equal and Opposite Reaction

To understand this one, let’s imagine a person on a skateboard. Let’s say this person is on a completely flat surface, and they’re just standing on the skateboard. No movement, not even wind to push them. So how do they start moving? In order to move forward on your skateboard, you have to push your foot backward.

understanding that for every action there is an equal and opposite reaction

This is just like we talked about before with the jet stream of water that your PWC pushes behind you. Just like when a skateboard kicks off from the ground, your PWC “pushes” water behind you from the nozzle and the jet drive propels you forward.

Of course, you can angle the nozzle via the handlebars and push water to the left or right of you, enabling you to turn. 

time to get on the water with your favorite Personal watercraft

For a PWC, “braking” in the same sense that you would brake in your car isn’t exactly possible.  PWC’s have their own alternative in reverse bucketing as a way to “brake”. Reverse bucketing systems use the same physics to reduce your speed by pushing water out of the front of your PWC. While this isn’t a bullet-proof safety system, it is a big improvement over the PWC’s of yesteryear which had no stopping power!

Now You’re Ready for Your Ph.D. in Physics

ready for a PHD in personal watercraft physics?

Well, maybe we didn’t go into that level of detail. But hopefully, now you understand a little bit more about the science that moves us! Of course, you don’t need to know how or why your PWC moves. The fun part is actually riding the sucker. But we hope you found this interesting! 

If you did, pass it along to your personal watercraft buddies and learn ‘em something! And if you’re looking to buy your own jet ski, check out our recent blog! We’ve got plenty of reasons you should get yourself a PWC.

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