Ever wondered how jet skis and jet boats work? Well, they both rely on something called a “jet pump” for propulsion, which sets them apart from regular boats with traditional propellers.
So, what’s this jet pump all about? It’s an interesting system that includes a steering nozzle, which lets you control the left-right movement, a reverse bucket for handling forward, reverse, and even braking, and if you’re feeling fancy, there’s also the option for trim control.
Now, let’s dive deeper into jet pumps and bust some common myths about them in this post below!
The heart of a jet pump is the impeller, which closely resembles a propeller, with only slight differences.
Impeller – Wear Ring – Cables
The impeller, enclosed by a wear ring with tight tolerances, isn’t a maintenance item but can wear out if debris is sucked up. The wear ring is designed to protect the jet pump.
A damaged wear ring can cause cavitation and performance issues.
The pump housing connects to the hull, which has cable holes and water-suction (bailer tubes) openings driven by the pump’s suction.
Direct Drive = When The Engine is On, It’s Moving
The driveshaft connects to the impeller, and bearings on the pump hold it in place. Watercraft are direct drive systems, this means if the engine is on the impeller is spinning.
I find this concept often confuses new riders, as they think it’s like a boat and all motion stops when in neutral.
Jet drive systems don’t have a true neutral.
It’s only putting the reverse bucket between forward and reverse. When it comes to jet drive boats, you want to turn the engine off when docked.
How the Steering Works
To control the left and right movement, a steering nozzle is used.
The steering nozzle is super simple, it’s a metal cone that pivots and controls the direction the water flows out. Turn the handle bars right, the nozzle goes right and pushes it to the right.
New riders can find backing up in reverse to be confusing because it’s not the direction that many people think, but is easy to get used to.
Since you’re only moving a nozzle that weighs a few pounds, hydraulics are not needed, unlike a normal boat. A long and stiff cable is used to move the nozzle. Since no hydraulics are used on the steering, you can move the handlebars freely when the engine is off and won’t hurt anything, so long as the nozzle is not caught on something.
You Can Trim A JetSki
PWCs can have trim, but not every model has or needs it.
Unlike boats, PWCs have their pump intake forward, minimizing bow rise, so trim isn’t necessary and is more of an upsell by manufacturers. (My opinion.)
Trim is nice when racing or tow sports, as you can adjust the PWC to fit your needs.
The adjustment of trim happens at the steering nozzle. If your watercraft has trim, it’s most often done by an electric motor (all 4-stroke use electric trim) and it raises and lowers the nozzle. Not only does the steering nozzle control left and right, but can also control the bow rise.
Not every model has trim, and the ones that don’t have it can’t always add it either. To be honest, trim is nice, but not a must-have if you don’t already have it.
How Reverse Works On A Jet Ski
The reverse bucket, as the name suggests, moves you in the reverse direction.
It’s also used for braking in some models.
A jet ski is a direct drive system, it’s always in forward. To go in reverse, the bucket drops, redirecting water to push the craft backward. Channels in the reverse bucket aid in turning left or right when reversing.
Reverse Bucket Is The Brake
The reverse bucket doubles as a brake, but only electronic reverse units have brakes. Manual reverse lever models should never be pulled above idle, as it can damage the reverse bucket.
The Bailer Tubes keep you Afloat
Bailer tubes use the suction that is created by the pump to suck out any water that maybe in the hull.
The pump creates a negative vacuum and using small hoses bent the right way, you have a very simple bilge pump.
The downside is that the bailer tubes only work when the engine is on, but you can learn more about bailer tubes here.
The Intake Grate Takes In The Water
The intake grate is not attached to the jet pump but is needed for the jet pump to work properly.
The intake grate is to help focus water into the pump and keep large objects from getting in and damaging the pump.
A common misconception I see about the intake grate is that people want to remove right away when they suck something up…
DO NOT DO THIS!
The intake grate is often through bolted, you may get a few bolts off, but you won’t get them all. You also need to seal the grate back up if you do remove it and wait 24 hours for it to dry, I find it best to avoid removing as much as possible.
Jet Pump Vs Propeller
Jet pumps and outdrive/outboards or anything that uses a propeller both have their advantages and disadvantages.
To better understand each, I’m going to list the pros and cons of a jet drive.
- No exposed prop, no spinning blades out in the open like you have with normal boats. I find this as a huge plus, especially if you have kids.
- Finer grain control, the pump is always processing water and pushing it where it needs to go, which gives you far greater control over the boat.
- Brakes – Brakes are not a thing on normal boats, but a thing on some jet drive boats.
- Jet drive boats can float in shallower water as there is no lower hanging unit.
- You don’t have to worry about trim as much as jet drive engines take in water closer to the center of the boat, so less bow rise.
- Jet drive systems are simpler and have fewer moving parts than other boat’s drive systems. This also means less maintenance on a jet drive system compared to other boats.
- A jet drive is basically a large vacuum and will suck up anything that gets in the way. That means ropes, rocks, sticks and so on. The wear ring is made to protect the pump, but things happen. And no, you can’t put a screen over the intake.
- Jet drive engines tend to use more gas than a normal boat, though it’s not much more, and all boats suck at gas mileage. It’s less noticeable on waverunners because they’re smaller.
- While jet drive boats can float in shallower water, you still can only start your machine in 3 feet of water. The pump is a powerful vacuum that will suck up anything too close to it, and that goes for sand and rocks on the water floor.
NOT A Jet-Engine!
I’ve noticed that some people think a watercraft engine is similar to a jet engine you see on planes. Even big name boating magazines call jet drive engines “jet engines”, super annoying and very wrong!
It gets even more confusing when people conflate the Rotax engine used in planes with the Rotax engine used in Sea-Doo’s. Rotax is own by BRP, who also own Sea-Doo, but the engines are very different.