What makes a jet ski so different from other boats is that they use a jet pump instead of an exposed propeller.
While a jet ski uses an impeller and a boat uses a propeller, they’re not too different. Each option has its advantages and disadvantages.
In this post, I want to go over jet pumps for jet skis and show you how they work, so you have a better understanding for your own jet ski.
Jet Pump – What It Does
A jet ski and jet boat both use a jet pump to control the movement of the boat.
As covered in the jet ski forward, neutral, reverse and brakes post, a jet ski can be maneuvered quite easily.
What makes a jet pump different from a normal boat’s propeller is that the jet pump is self-contained. With everything in a nice and neat package means there are no exposed spinning blades like there are on regular boats.
With the jet pump, you have a steering nozzle that controls the left and right movements. You also have a reverse bucket that controls the forward, reverse and braking. Lastly, some jet skis have trim that is also controlled at the steering nozzle. Let’s further break down the jet pump and its parts.
The Parts Of A Jet Pump
The heart of a jet pump on a jet ski is the impeller. The impeller looks very similar to a propeller, they’re very similar but have slight differences.
Impeller – Wear Ring – Cables
The impeller is located inside the jet pump housing and a wear ring is wrapped around it to give it tight tolerances. The wear ring is not like the name suggests, it’s not a maintenance item, but something that can wear out if you suck something up. A damaged wear ring can lead to cavitation and poor performance.
The jet pump housing attaches to the jet ski hull and the hull has holes for the steering, reversing and trim cables along with holes that are used to suck out water in the hull using the suction created by the jet pump.
Driveshaft & Direct Drive
The driveshaft connects to the impeller, and bearings on the jet pump hold it in place. Jet skis are direct drive systems, this means if the engine is on the impeller is spinning.
Jet skis 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.
To control the left and right movement of a jet ski, 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 the jet ski to the right.
Backing up in reverse can be confusing on a jet ski because it’s not the direction that many people think, but is easy to get used to.
Since the jet ski is only moving a nozzle that weighs a few pounds, hydraulics are not needed unlike a normal boat. A jet ski uses a long and stiff cable to move the nozzle. Since no hydraulics are used on jet ski 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.
Jet skis do have trim very similar to a boat, but not every jet ski has it, nor is it always needed.
Trim on a boat is used to make up for the prop being so far back, which makes the boat lift up. A jet ski takes in water much sooner and bow rise is not much of a thing on a jet ski, so trim is not a needed feature.
Trim on a jet ski is more of an accessory or upsell for some models.
Trim is nice when racing or tow sports, as you can adjust the PWC to fit your needs. You can trim the jet ski in rough waters, and it helps, but due to the small size of jet skis don’t expect too much.
The adjustment of trim happens at the steering nozzle. If your jet ski has trim its 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 of your jet ski.
Not every jet ski 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.
Just like the name implies, the reverse bucket is a bucket that puts the jet ski in reverse.
The reverse bucket does a little more on modern jet skis, especially ones that have brakes.
A jet ski is a direct drive system, so it’s always in forward. To go in reverse, a bucket drops and forces the water to go forward, which pushes the jet ski backwards.
The reverse bucket does have channels to redirect the water when you turn the handlebars to give you greater control when reversing left or right.
The reverse bucket also acts as a brake, or a parachute, to slow you down. Only jet skis with an electronic reverse will have a brake of some kind. Models with a manual reverse lever should never pull it when above idle, as you will break the reverse bucket. Since you’re essentially putting the jet ski in reverse, if you keep holding the brake lever you will go in reverse, the brake and reverse lever are both the same.
Bailer tubes use the suction that is created by the jet pump to suck out any water that maybe in the hull.
The jet 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 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 jet pump and keep large objects from getting in and damaging the pump.
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.
Jet Drive Pros:
- No exposed prop, no spinning blades out in the open like you have with normal boats.
- Finer grain control, the jet 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.
Jet Drive Cons:
- 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 jet skis because they’re smaller.
- While jet drive boats can float in shallower water, you still can only start your jet ski in 3 feet of water. The jet 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.
A Jet Pump Is NOT A Jet Engine
I’ve noticed that some people think a jet ski’s engine is similar to a jet engine you see on planes.
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.
The jet pump engine in boats are not the same as jet engines on planes.