Personal watercraft ownership has grown rapidly in recent years. Some new owners may be unfamiliar with some key details of jet ski operation. There are several differences that make operating a jet ski different from driving or riding other vehicles such as boats, cars, motorcycle and ATV’s.
Most modern jet skis have a reverse feature that allows them to move backward. It works by moving the steering nozzle cover over the water outflow tube at the rear of the ski. This redirects the flow of the water jet forward under the ski to move it backward. PWC impellers can’t reverse spin direction.
Although jet skis do not have a transmission system, the engine and drive system are impressive. The jet ski can be put into neutral, reverse and forward for docking or better maneuverability. Riders should become familiar with operation of these functions to become safer and better riders. Let’s look at how a jet ski works and how a personal watercraft achieves its neutral and reverse features.
How does a jet ski work?
For the most part, a jet ski, also commonly known as a PWC (Personal Water Craft), has an engine based similar to that of any motorized vehicle. That means that it has a piston-cylinder based engine that is placed underneath the seat of the jet ski. Modern skis use standard 4-stroke motors while some older skis are powered by 2-stroke engines.
When the jet ski is running, the torque from the engine is thrust directly onto a drive shaft that has an impeller attached towards the end of it. As the engine runs, the driveshaft is always rotating, and so does the impeller. The shaft and impeller on PWC’s rotates only in one direction at all times (except for the newly introduced flushing system used to clear debris available on a limited number of Sea Doo models.)
How does the jet ski move forward?
Jet skis have water intakes positioned at the bottom or sides that allows the turning impeller to pull in water. No matter what design a jet ski has, the movement principle is the same. As the impeller starts to rotate, it sucks water through the bottom that is pushed through a tube and out of the rear of the ski to propel it forward. The throttle controls the speed of impeller rotation which controls water flow, and thus determines the speed of travel of the jet ski.
Due to the fact that the force is pushing the water out the back end of the jet ski, the resulting opposite force pushes the jet ski in a forward direction.
The type of engine that a jet ski has is thus known as a direct drive system because of the fact that the engine is connected directly to the impeller.
The water used to drive the ski is also used to cool the motor, impeller shaft, exhaust and other moving parts, at least in part. The engine’s heat is dissipated by the water flowing through the impeller tube, and the engine does not overheat. Sea Doos also have a separate closed loop cooling system that uses standard coolant like a car.
Does a jet ski have a transmission?
Although the principle of a jet ski’s engine works very similar to that of any motor vehicle, the one difference is that a jet ski does not have a transmission and thus does not have gears. This again is due to its direct drive nature. (Source)
What is a transmission, and do you need one for reverse?
A transmission is a mechanical device used in engines that transfers rotation speeds between engine and drive components. It allows for differing degrees of engine rotation to be transferred to the drive shaft in varying speeds. This just means that the gearbox uses gears and components at various points to supply variable speed and torque from the rotating power source to the final moving parts.
A transmission thus comprises of gears which include variable sizes to control speed of rotation as well as gears to move in reverse or neutral by disengaging the gears. The transmission will reverse the direction of the drive shaft to allow the axle of the car rotate in the opposite direction.
Does a jet ski have a reverse gear?
Although a jet ski does not have a transmission that changes speed and direction of the impeller and shaft, it can still reverse or be placed in neutral.
How does a jet ski reverse work?
Situated at the back of the jet ski is what is called a steering nozzle. This nozzle directs the flow of water in a certain direction which is controlled by the handlebars. Therefore if you move the handlebars, the nozzle will direct the flow of water in that same direction to move the jet ski left or right.
The steering nozzle also controls the forward, neutral, and reverse of the jet ski. We now know that the jet ski is propelled forward because of the direct-drive system ( the water is forced past the impeller out the back, pushing the jet ski forward). Due to the fact that this is the only force by which the jet ski can move, the steering nozzle has has to redirect the water jet output to allow for neutral or reverse.
When the jet ski is placed in neutral, the steering nozzle will cover the thrust nozzle and will not allow the water to be forced out in any direction. Therefore the jet ski will stay in place even when it is on, and the motor is running. When a jet ski is running at idle speed, there is still some rotation of the impeller and shaft. So it cannot maintain its position unless the jet flow is controlled. Even though the flow is slow, it is still always there. Partially covering the output allows the ski to effectively be placed in neutral to keep positions steady.
When the jet ski is placed in reverse, the curved steering nozzle plate will fully cover the thrust nozzle, and it will actually be positioned in such a way that the water will be directed towards the bottom and front of the jet ski. This means that because the water is being thrust in a direction that is in a forward direction, the jet ski will move in a backward direction (reverse).
It is important to note that technically, a jet ski does not have a reverse gear because a jet ski does not have a transmission. However, due to the direct drive system’s simplistic workaround and the steering nozzle, a “reverse gear” can be accomplished, allowing the jet ski to move backward.
If this concept of the thrust nozzle is a bit difficult to grasp, take a look at the videos throughout this post which will demonstrate how each brand works.
Do all jet skis have reverse?
For the most part, most modern designed jet skis now come with reverse. However, It is important to note that older models and some models designed to be “stand up” jet skis do not come with reverse.
Why do jet skis have reverse?
When jet skis were first designed, the features of reverse were not included, and what you would need to do is turn around if you needed to go back to a particular location.
The “reverse gear” was introduced because of various safety reasons and for practicality. The first is that water hobbies and especially jet skis have become very popular and most individuals who ride a jet ski are novices and hence need more safety features. A lot of new jet ski owners aren’t aware that there is constant impeller rotation and jet flow even at idle speeds. So many new owners found themselves striking other boats or docks when they thought their ski was stopped. Boats do stop rotation of their propellers when the throttle is closed, so this characteristic of jet skis isn’t intuitive to new owners who may be used to boat operation.
Another reason for the reverse feature is that it is much easier to get the jet ski back into position when trying to dock it safely. Using neutral and reverse judiciously around docks makes them very controllable at slow speeds, and prevents unwanted scratches, scuffs and dents. It also makes you look like a pro once you’ve mastered the art of docking without having to grab onto part of the dock or another boat to stop.
To summarize, jet skis technically do not have a reverse gear because a gearbox is a part of a transmission system that a jet ski does not have. Remember a jet ski is based on a direct drive system that always rotates in one direction and always pushes water through the rear output, even at idle.
However, a jet ski has a neutral and reverse feature that allows it to stay in place or move backward because of the direction of the impeller’s water which is positioned by the steering nozzle.
The last thing to note is that most modern jet skis do have this feature, but some older models may not.