If you're tired of hitting rocks in the river, switching to a 40 hp jet outboard might be the best move you ever make. There's a specific kind of freedom that comes with knowing you can skim across six inches of water without worrying about your lower unit ending up at the bottom of the stream. For anyone who spends their weekends chasing smallmouth bass in rocky shallows or navigating skinny creeks where a traditional prop just won't survive, this power range is often considered the "sweet spot."
But before you go out and bolt one onto your transom, there are a few things you really need to understand about how these machines work. It isn't just a regular motor with a different bottom; it's a completely different animal when it comes to performance and handling.
Why the 40 hp range is the magic number
You might wonder why so many people settle on the 40 hp mark. Most of the time, it comes down to the weight-to-power ratio. A lot of the boats used in shallow water—like 14 to 16-foot aluminum jon boats—don't need a massive V6, but they do need enough "omph" to get on plane quickly.
When you're running a 40 hp jet outboard, you're usually getting a motor that's light enough for one or two guys to manage on a trailer, yet strong enough to haul a decent amount of gear, a full livewell, and a buddy. If you go much smaller, you might struggle to get the boat up on top of the water, especially if the current is pushing against you. If you go much larger, you start adding so much weight to the back of the boat that you actually sit deeper in the water, which kind of defeats the purpose of having a jet in the first place.
The truth about horsepower loss
One thing that catches people off guard is the "jet tax." If you take a standard 40 hp powerhead and slap a jet pump on it, you aren't actually getting 40 hp at the nozzle. Because of the friction and the physics of moving water through an impeller rather than spinning a prop in open water, you lose about 30% of your power.
Essentially, a 40 hp jet outboard performs more like a 28 or 30 hp prop motor in terms of actual thrust. This is why you'll often see these motors labeled with two numbers, or why some manufacturers build them on larger blocks. If you need 40 hp of actual "push," you might actually be looking for a motor that has a 60 hp powerhead but is rated as a 40 at the pump. It sounds a bit confusing, but it's just the nature of the beast.
Handling and the learning curve
Driving a jet boat is a lot like driving on ice. Since there's no skeg or propeller acting like a rudder in the water, you don't have much directional control when you're at idle or if you kill the throttle. This can lead to some pretty "exciting" moments when you're trying to approach a dock or navigate a tight bend in a fast-moving river.
Steering with thrust
The most important thing to remember is that you only have steering when you have water moving through the pump. If you're heading for a rock and your instinct is to cut the gas, you've just lost your ability to steer away from it. You actually have to give it gas to turn. It takes a few trips to get used to, but once you do, you can slide a jet boat around corners in a way that's honestly a ton of fun.
The "drifting" sensation
Because the bottom of the boat is usually flat and there's nothing sticking down into the water, these boats tend to slide or drift during turns. You won't "bite" into the water like a V-hull with a prop. It's a very loose feeling, almost like a sports car on a gravel road. It's part of the charm, but it's something to be aware of if you're used to more traditional setups.
Maintenance that actually matters
Owning a 40 hp jet outboard isn't necessarily harder than owning a prop motor, but the "to-do" list is a little different. You aren't worried about dings in a prop, but you are very worried about the gap between your impeller and the liner.
Keeping the impeller sharp
The impeller is the heart of the system. Over time, as you suck up sand, small pebbles, and silt, the edges of the impeller will get rounded off. When this happens, your performance drops off a cliff. You'll notice the motor revving high but the boat not moving as fast. Most jet owners learn how to take the pump housing apart and file the impeller blades back to a sharp edge to keep things running tight.
The dreaded intake grate
The intake grate is your first line of defense. It keeps the big rocks out, but it's a magnet for weeds, leaves, and plastic bags. If you're running through a patch of floating grass and your motor suddenly starts screaming and losing power, you've probably "sucked a rug." Most guys keep a long-handled rake or a specialized tool on board to reach under the boat and clear the grate without having to jump in the water.
Choosing the right boat for your motor
A 40 hp jet outboard is only as good as the hull it's attached to. If you put it on a heavy, deep-V fiberglass boat, you're going to be disappointed. These motors are designed for flat-bottom or very slight mod-V aluminum boats.
- Weight distribution: Since jet boats are sensitive to how they sit in the water, you want to keep the weight balanced. If everything (batteries, fuel tank, you, and the motor) is in the back, the stern will squat, and you'll need more water to get on plane.
- Transom height: This is a big one. A jet motor needs to be mounted higher than a prop motor. The intake should be roughly flush with the bottom of the boat. If it's too low, it creates drag; if it's too high, it sucks in air and "cavitates." Many people use a jack plate to get the height exactly where it needs to be.
Is it worth the switch?
If you're a lake fisherman who stays in deep water, honestly, stay with a prop. It's more efficient, faster, and uses less fuel. But if you've ever felt that pit in your stomach as you watched your depth finder drop to two feet, or if you've spent hundreds of dollars replacing mangled props, the 40 hp jet outboard is a total game-changer.
Sure, it's a bit louder, and it's not as fast as its prop-driven cousins, but it opens up miles of river that other people simply can't reach. There's nothing quite like the feeling of zooming over a gravel bar that would have ripped the transom off a standard boat. It's about access, and in the world of fishing and exploring, access is everything.
In the end, it's about picking the right tool for the job. For the river runner, the 40 hp jet is often that perfect balance of utility, power, and reliability. Just keep your impeller sharp, your grate clean, and your eyes on the water ahead, and you'll be set for years of skinny-water adventures.