Guide to Jet Outboards and Jet Boats

Marine Parts Warehouse Guide to Jet Outboards and Jet Boats

If you chase steelhead or salmon in any one of our river systems, chances are your sled has an outboard jet drive motor on it or you wish it did. Jet drive outboards are the motor of choice for almost every river fisherman for the simple fact that they allow anglers to motor through skinny water that is too shallow for a propped outboard. 

They also eliminate the chance of damaging a prop and lower unit on unseen hazards such as logs or unexposed rocks. With jet drives becoming more common on rigs in the Midwest, there are a few important factors that should be taken into consideration to achieve the boat's top performance.

There are two options for remedying such situations: Buy a jet outboard or convert an existing motor. Most people don’t know this, but many outboards can be converted to jet propulsion for a few thousand dollars, depending on their size. 

This conversion, along with the proper boat, can allow a boat to run in just a couple of inches of water — and potentially scoot over short sections of land (not recommended), if such an action is required. 

Jet outboards, use a jet drive pump unit to propel boats forward by creating an opposite force in the water. This allows boats to operate in shallow water and other locations where propeller-driven boats cannot, such as ankle deep water. Jet outboards can also provide more usable space inside the boat than inboard motors.

Combining the correct outboard power and boat design is the “secret” of successfully using an outboard jet to run in shallow water. 

These two pieces of information will assist you in selecting the best combination for your needs, thereby giving you the advantages of outboard power for shallow water use.

Most important is the boat. 

Keep it light as possible since, unlike a propeller drive, you can’t change to a lower pitch jet drive impeller to increase load capability.

Aluminum is usually the material of choice. It is light, tough and easy to form in the proper configuration. For outboard jets, the minimum recommended bottom thickness is .100 Gauge but thicker gauge or UHMW reinforcement can be useful in treacherous waters. Just be mindful about weight.

Aluminum is the hands-down winner for a jetboat’s material because of its light weight and durability. Aluminum boats, on average, weigh 25 percent less than fiberglass models, and owners who go skinny tend to occasionally slide over rocks — bad for fiberglass.

The size and shape of the bottom is very important. The object is to ride on top of the water, which requires a good planing surface, and to float as shallow as possible when shut down. Bottom should be at least 48 inches wide and boat length at least 14 feet long. Air entering the jet drive causes slippage, so the boat bottom needs to supply solid water, free of air, to the jet drive intake.

No one boat can satisfy every need, so choices must be made. With this thought in mind, some pros and cons of various boat types are noted below. A flat bottom boat runs shallower than a vee bottom, but slides on the turns more. A vee bottom splits off air bubbles before they reach the jet intake. A flat bottom carries bubbles straight back.

A slight V of 6-10 degrees dead rise will enhance jet boat handling. Deep vee is not desirable for the Outboard Jet, not just because of increased draft and drag, But because the Outboard Jet needs a flat apron of water about 10” wide leaving the hull on which to set the leading edge of the jet intake, to minimize air intake and frontal drag. The dead rise should be fairly constant and not increase to a deep forefoot at the bow. 

A deep forefoot can cause spinout on a sharp turn. Keels can be a problem, introducing air into the jet intake. Center keels vary in size and may introduce air. If this is suspected, the keel should be removed 2-3 feet forward of the transom. Other keel arrangements which tend to funnel air to the jet intake should be avoided. The chines of the boat, where the sides meet the bottom, should be sharp. Round chimes tend to suck the boat down in the water and cause drag. A properly designed tunnel, combined with a slight V bottom hull can greatly enhance jet boat performance. 

It should raise the motor 2-3 inches and place the heel of the jet intake flush or slightly above the bottom of the boat. A jet tunnel doesn’t work well with a flat bottom boat due to air ingestion. It’s imperative that the hull is designed correctly with the tunnel for the boat to operate properly.

The tunnel needs to be just large enough to feed the jet drive its water requirements. A tunnel that is longer, wider or deeper than necessary wastes power in lifting excess water, tends to suck the stern down when planing and sits deeper in the water at rest due to lost buoyancy. The top of the tunnel width should be about 1 ¾ times the width of the jet drive water intake. 

The tunnel length doesn’t have to be longer than about 2 ½ times the water intake width. 

A rigid hull inflatable on the other hand cannot be folded to fit inside your car but steers better and provides solid water to the intake. Unfortunately, the hulls presently available have more than 10 degrees of deadrise. A rigid hull inflatable on the other hand can’t be folded to fit inside your car, but steers better and provides solid water to the intake. Unfortunately, the hulls presently available have more than 10 degrees of deadrise. 

Pontoon boats don’t provide a defined height apron of water ahead of the jet intake. The water level between the pontoons varies with speed and load carried. It’s necessary to build an inclined plane ahead of the jet intake attached to the motor mount, about 16” wide inclined at about 15 degrees with the leading edge above water level, fully loaded at rest, trailing edge lined up with the leading edge of the jet intake.

Boaters who fish debris-strewn bodies of water on a regular basis are probably better served buying a jet outboard from Yamaha, Honda, Mercury or Evinrude. Suzuki doesn’t have one (though there is a way to convert one). Most are considerably less expensive, for the engines themselves, since they don’t have expensive stainless steel shafts, gears and props, but there’s a price to pay: usable power.

Take, for example, the Yamaha F150. It uses a 2.7L in-line four-cylinder four-stroke to make 150 hp — with a prop. 

Equipped with a jet drive, however, Yamaha puts something else on it: a cowling with the number 105, because that’s how much power it generates due to a jet’s relative inefficiency. It goes down the line: F115 (80 hp), F90 (65 hp), F60 (40 hp) and F40 (30 hp).

The other major engine brands experience a similar reduction in thrust, and the selection is limited. Mercury has five but in the narrowest range of horsepower, with models producing 80, 65, 40, 35 and 25 hp. 

There is about a 30% power loss when converting to our jet drive. A suitable outboard jet boat carrying an average load will provide about 80% of propeller speeds. It’s important to decide what load you want to carry how many people, gear, fuel, etc. and add the weight of the boat, motor and battery. Look up this gross weight on the chart below to determine the minimum HP you need. The chart HP is power head horsepower.

It’s important that the boat-motor combination plane the boat quickly. Planning would normally be in the mid 20 MPH range and up. This is necessary for optimum jet performance and shallow water running. At low RPM, when the boat is not planing, you would need about 12 inches of clearance between the bottom of the jet and river bed to maneuver.

A few things things to consider...

Does the boat plane quickly and not cavitate easily?

(listen to the motor for the change in RPM’s) a destructive and negative performance trait. 

Will the boat maneuver through obstacles typically found in your environment without breaking loose or skating? Is handling predictable?

Poor performance will show up in a jet boat taking a long time to get up on a plane, breaking loose early in cornering and cavitation. 

The advantages of Outboard Jet boat include maximum space inside the boat while still having the ability to operate in less than 6” of water, relative ease of cleaning out a clogged pump and adjustment for wear on the impeller and intake liner. So select a suitable boat with sufficient HP to handle your total weight, then enjoy fishing and hunting in areas you couldn’t reach before.

Yamaha has a company division that makes jets for personal watercraft, but it’s interesting that they, along with Mercury, Honda and Tohatsu, source their jet drives from Outboard Jets, which has been making them since 1960 and is the king of jet outboard components. 

Almost every jet drive pump on the water today, no matter what brand motor, is made by a single company: Outboard Jets out of San Leandro, California. The company was started in 1960 by Dick Stallman, who worked closely with the Wooldridge family to form the product that you know today as the jet drive. Today, Outboard Jets build over 80 different models to fit 6 of the top name outboard manufacturers in the marine industry.

They have conversion kits for Suzuki too, but Suzuki doesn’t market them directly to the public like the others. To exactly match the factory motor’s color, Outboard Jets gets paint chip samples from the manufacturer. 

Jet drives aren’t compatible with every type of waterway. Mud, for instance, is a jet killer, so a better solution for going skinny over it is an air-cooled motor such as a propped Mud Buddy. Jets work best on hard bottoms such as rocky riverbeds. 

They work OK over sand, but it, like small rocks, tends to abrade parts such as the impeller and the wear ring that surrounds the impeller. If the impeller doesn’t fit tightly within the wear ring, power is lost, like with a worn ring on a piston in a combustion engine. The impeller can also get dinged up, which costs power, but carefully filing rough spots can bring it back to life. The wear ring is a sacrificial part that costs about $50 to replace when it gets grooved. 

Owners who have an outboard that they want to convert to jet should go to outboardjets.com and see if it’s compatible. The site provides information about how to install them. Surprisingly, it only takes about an hour to change from prop to jet, for anyone who knows which end of a screwdriver to hold. Some outboard owners claim that after a few tries, they can do it in less than half an hour. 

The use of outboard jets is definitely on the rise and we will be seeing a lot more of them on the rivers in the years to come. If you are an angler that is thinking about purchasing an outboard jet, these are some great things to keep in mind when looking.

 What's the difference between a JET OUTBOARD and a JETBOAT?

Jetboats employ a completely different type of propulsion system. Basically, the boat itself isn’t any different than any other, but how it gets around the water is a big departure from a standard motor. 

Jet boats range in size from small personal watercraft all the way up to much larger boats. Here are some of the advantages and disadvantages of jet boats.

Advantages

Security: Jet boats are touted as being far safer than a prop-driven boat since there is no rotation prop exposed externally, without any bulky hardware to potentially strike or injure a swimmer or skier. Truth be told, boating is a very safe activity no matter which type of powerplant you have, but knowing that there is no propeller beneath the waterline certainly does give people -- parents specifically -- an added feeling of security. 

Draft: Boats with jet drives have always touted their exceptional draft edge from 12 inches up to 17 inches. Unlike a stern drive, a jet typical draft is only the depth of the hull itself. That allows them to go in shallower waters with ease, and eliminates a lot of the worry of running aground or undergoing drive-damage in lanky waters. 

Acceleration: Jet boats are also generally quick to plane with very little bow-rise, usually less than 20 degrees. That provides them a superior visibility benefit, as the captain rarely loses sight of what is ahead as the boat comes on airplane. On some propeller-driven ships, a motorist can lose a level of forward vision for as much as three to four seconds. That acceleration is also thrilling, and jets normally have an instantaneous throttle-response that other propulsion systems just can't match. 

Handling: And there's a jet boats unbeatable, sportscar-like handling experience. Grown-up or not, jet boats have a ride which appeals to our inner teenager. Together with the thrust capable to be redirected in a flash, jets are quick and nimble. Give the wheel a fast jerk, punch the throttle, and your average jet will leave other ships in its aftermath. Most jets also don't generally charge as severely, enhancing the driver's feeling of control. It's difficult to express just how amazing jet boat handling can be, but you are going to get a taste of this action if you see our video of the Scarab 165 ID, which we place into some seriously crazy turns.

All of that said, jet boats aren't an ideal selection for all individuals, by any way. Like all types of boats they still have their disadvantages as well. A few of those negative traits may be attributed to experience, since boaters with a backdrop utilizing outboards, inboards, or stern drives will always seem to struggle somewhat when clinging to a jet. Still, you'll observe seasoned jet boat drivers that will deal with their boats with utter precision. Like anything, it takes practice. Less is more!

Disadvantages

Shifting into Reverse and Neutral

Jet boats can't reverse the direction of their impeller (For those of you that don't understand this: "This means that a propeller can reverse it's gears to move right or left in direction to give you the propulsion to move forward or in reverse.") This first sentence does not mean that the article states that jet boats can't go in reverse). The Reverse system is accomplished by dropping a reverse gate or bucket over the stream of water exiting the pump nozzle. These reverse gate buckets basically divert that flowing water, therefore it shoots forward rather than aft pushing the water forward to be able to go in reverse. The reverse gate bucket may be positioned to partially divert the atmosphere, mimicking the true neutral. However, the Scarab jet boats come with an INR module that can be adjusted with a positive number or negative number to offset any conditions with a current pressing the bow or stern. We can literally get out of the boat next to a dock in neutral without any movement. 

Low-speed handling

Certain brand Jet Boats such as Yamaha tend to suffer in low-speed maneuvering around the dock since they have smaller steering nozzles and reverse gates. Driving in a straight line can be difficult for Yamaha jet boats, with the boat drifting off to one side or the other, especially when it's windy, but can be helped for improvement by adding a rudder setup. Inexperienced drivers often get fooled into over-steering as they proceed through slow pace zones or approach the pier. The difference is not huge, but it will mean that the driver may need to create more regular course-corrections. Adding a touch of throttle will straighten the steering aspect if you are they type of person that wants to drive it like a truck by over-steering. The Scarab jet boats drive like a car with an immediate response requiring less input from the Captain. 

Performance

Todays jet boats are all relatively high in horsepower and less in cost over a comparable horse powered outboard. Volume Degree: In no small part because they often rev much higher than propeller-driven boats, 2-stroke jet boats commonly are somewhat louder. Boat makers have mitigated this problem somewhat in newer models, and also have been taking pains to reduce noise levels. But jet boats still remain louder and often high in pitch in the 90's, but not in todays models with the newer 4-stroke models.

Looking for a JET OUTBOARD ENGINE to replace your PROP OUTBOARD ENGINE?

Marine Parts Warehouse order brand new Mercury and Suzuki Outboard jets. Please click here for a quote!

If you are wanting to convert from a jet to a propeller lower unit please click HERE. 

For more information on outboard motors, contact us today!