- Jet drive propulsion systems are used in everything from personal watercrafts (PWCs) to runabouts and commercial ferry boats. Some of their strengths include their versatility, their performance in shallow draft applications, and the use of reverse thrust as a braking system; however, they do not perform well in low-speed environments.
- A jet engine uses an impeller rather than a propeller. Like a propeller, an impeller rotates to move water and create forward thrust. The major difference between them is that an impeller is enclosed inside a pump cavity and a propeller is exposed.
- See all jet drive listings, or read more about Jet Boats in our full-length feature and our Jet Boats explore page.
Jet drives have long had their place in marine propulsion. Here’s a breakdown of their strengths and weaknesses. You will find jet drive propulsion systems on everything from personal watercraft, to family runabouts to giant passenger ferry boats. Jet drives are versatile that way, but if you don’t know much about them, let’s break down some of uses where they excel and some where they do not.
- Simple design
- No exposed propeller blades
- Good for shallow draft applications
- Good for high-performance applications
- Scalable for applications of nearly any size
- Reverse thrust can act as a braking system
- No true neutral gear
- Not good for low-speed environments
- Not good for applications where torque is more important than horsepower
Given that list of strengths and weaknesses, it’s clear that you will not find a jet drive on a tugboat, where torque and low-speed operation are paramount, but you will find them just about everywhere else.
How They Work
A jet drive uses an impeller rather than a propeller. The distinction is subtle because they both perform the same function. Like a propeller, an impeller rotates to move water and create forward thrust. The major difference between them is that an impeller is enclosed inside a pump cavity and a propeller is exposed. Because the impeller is enclosed, there is also a difference in the shape of their blades.
Water enters the pump cavity on the bottom of the boat. The submerged impeller spins to create thrust. Water is directed out the back of the craft through a stator vane. The stator increases the efficiency of the impeller because it removes the “twist” from the water jet created by the impeller.
The stator vane focuses the energy of the thrust. Also, because the impeller is enclosed, that, too focuses the energy, which is why jet drives have such great off-idle acceleration. Greater efficiency occurs because there are no 90-degree gear-to-gear transitions in a jet drive, which increase parasitic drag. A stern drive employs two 90-degree transitions and most outboards have one 90-degree transition. Simply put, a jet drive receives more of an engine’s power than sterndrive or outboard powertrains. Pretty geeky engine stuff, yes, but part of the jet drive’s advantage, for sure.
Obviously, if jet drives didn’t have any drawbacks, they would make up more of the market share. But they do have drawbacks compared with inboards, sterndrives and outboards.
First, the impeller is connected directly to the engine, so when the engine is running, the impeller is moving. That means there is no true neutral gear. Engineers worked around this, creating a neutral setting by employing a combination of forward and reverse thrust. To put a jet boat into reverse is a simple matter of flipping the lever into reverse, which lowers the “reverse bucket” behind the jet nozzle, redirecting thrust forward underneath the boat. Neutral in a jet drive boat is the happy medium between forward and reverse.
The boat usually ends up moving around a little anyway, and some people don’t like that. When a sterndrive, outboard or inboard boat is in neutral, the only movement that occurs stems from wind or current.
Second—and this is probably the bigger obstacle—is that a jet drive needs thrust to steer. If you chop the throttle to nothing, the boat doesn’t steer. It’s so counterintuitive to the way everyone learned to drive—off throttle, turn, resume acceleration. With any other marine propulsion system, you can be off throttle and still have the ability to steer.
It’s gotten better over the years. Some manufacturers, such as Berkeley Jet Drive, now make rudders that mount the bottom of the jet nozzle for improved steering off throttle. PWC manufacturers have used technology to add throttle to help steer even when the rider has lifted off the gas.
As mentioned previously, you’ll find jet drives on lots of different applications. Outboard manufacturers now offer a bevy of jet-drive outboard engines. So, flats-fishing boats that could go in really skinny water can go practically anywhere. Puddles, even. Well, that’s a bit of an exaggeration, but you get the point.
For recreational applications, it’s a matter of personal preference. As previously mentioned, manufacturers have gone to great lengths to minimize the drawbacks, so much so that jet-drive boats are enjoying something of a comeback.
The best way for a buyer to see if a jet boat works for them is to drive it. There’s no other way. We know the powertrain is pretty compact, which allows for more room in the interior. We know it’s safer for swimming behind the boat. We know it has the acceleration to pull skiers. For a cross section of what’s available on the market today, read our full feature on Jet Boats or check out our Jet Boats explore page.
You’ll just have to see if you have what it takes to captain a jet-drive boat—whether it’s a family runabout or a passenger car ferry.
See all our jet-drive powered listings.