By: Captain Bill Jennings
With the many different 'types' of boats on the market, and it is hard to know which type is best for you. Most information that you see is advertising driven, so while the benefits are easy to find the downsides are not. To help boaters navigate through the realities of boat types, I present this series of articles that reveal some of the not frequently advertised characteristics of different boat types in order to help you, the boat buyer, select a boat type that is best for your needs. In this article, we discuss jet powered boats.
In a jet boat, the drive shaft from an internal combustion engine turns an impeller housed in a tube inside the boat. This impeller sucks up water from under the boat and shoots it through a nozzle out the back of the boat in a high pressure stream, or jet. This stream propels the boat forward through both the "equal and opposite action" physics formula, and the jet itself pushes on the water behind the boat.
Actually, jet boats are not a 'type' of boat, but rather a type of drive. The reason jets are referred to as a 'boat type' is because they are a specialized form of boating and represent a relatively small number of total boat sales. There are many examples of jet boats, and nearly every boater knows about personal water craft (PWCs as they are referred to). These are perfect examples of popular small jet drives. You may also have seen large ocean going passenger ferries with commercial jet drives powered by large diesel engines. But when it comes to recreational pleasure boats, we see many more outboard, sterndrive, and inboard systems than we do jets. In theory, you can buy a jet drive to fit most internal combustion engines -- and this includes outboard motors. So why we don't see more of them on our lakes is an interesting question.
Why would a boater want appendages hanging below the bottom of his/her boat if they were not necessary? With no lower units or prop shafts, jet boats have a shallow draft as well as less drag. With no external propeller there can be no propeller damage from striking the bottom, or worse, a person in the water. When running at full throttle, some jet boats can operate in just 3 inches of water. You can almost drive it to work on a rainy day.
Acceleration and turning ability in jet boats is recognized as being better than in other equivalent length pleasure boats. There have been many tests that certify this fact. The top-speed of a jet boat is based upon the motor installed and its horsepower rating. As a testimonial to this, there are several classes of racing specifically designed for jet boats. A few years back I did some river racing in a jet. It was a five day race on Mexico's treacherous Balsas River with 52 jet boats entered from several countries. When I won, the 'federales' informed me that I would "take dinner with the President of Mexico." It was not an invitation, it was an order. Turned out to be just another political opportunity for the president, but he seemed like a nice guy and the food was pretty good.
Okay -- before we all jump up to sell our current boat and buy a jet, lets take a look at some of the possible disadvantages. Engine durability and wear can be more of a problem with a jet than with a sterndrive or outboard. This is mostly due to the higher rpm levels in which jets operate. These higher rpm's also impact fuel consumption, and poor fuel economy can be a deal breaker for many of us. These same high rpm levels also account for jets being much louder than today's quiet outboard motors. Several jet boat owners I know have added sound insulation to the engine compartment, in attempts to rectify the louder engine noise.
Jets are ideal for running in shallow water, but when you do the water being sucked into the impeller can also introduce foreign objects. Some of this will build on the screen or "grate" covering the water intake opening and can be simply raked off, but some things such as paper or sand can enter the drive and damage the impeller. To counter this concern, most jet drives provide access from inside the boat to remove any debris that made it past the grate.
Jet drives and how they are installed result in significant differences in how the boat handles. It will take a few turns at the helm before first time drivers are comfortable with jet characteristics. For example, some older jets would continue to creep forward, when placed in neutral. Not good for docking. Others will move differently than expected when placed in reverse. These situations along with a torque difference make sterndrives a better bet for pulling skiers and wakeboarders.
Whether you are running a propeller or an impeller, you need it to be in the water in order to have thrust. Propellers usually have plenty of water because of their location, so they are usually under load. The water intake for a jet impeller is very close to the surface, so when you jump a large wave in a jet, you will momentarily suck air and the impeller will lose its load. The resulting engine over-rev can damage your engine. The possibility of 'air time' requires special attention when driving on large bodies of water.
I would peg the greatest drawback to owning a jet drive boat to be the limited availability of specialized service. There are many conveniently located boat dealers that will not work on jet drives.
If you are searching for jet boats, be sure to check online. There you will find a good number of jet boat manufacturers. Also, jet drive manufacturers will help boat manufacturers (where applicable) install their drives in a boat you choose. Ride comfort and storage capacity factors will depend on the boat in which you choose to attach your jet drive. For a very nice 27-foot twin engine cruising jet boat, look to spend around $140k. Smaller single engines are considerably cheaper.
Boats powered by a jet drive can be a great choice. They’re quick and sporty, and a good bang for the buck. If your boating includes very shallow lakes or rivers, jets are the "go to" unit. Just be sure to evaluate how the above noted disadvantages will affect your usage, and most importantly, take a test drive before buying.
You can check out the rest of our 'Pros and Cons' series below: