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Jet questions for Dennis



Are there different types of jets? I was told RE: outboard jets that you lose 25% thrust and 25% high end speed given the HP. Is this true? Also that you use alot more thrust to control the boat. What are the advantages of jets other than running in three inches of water?


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There are different types of jets.

Outboard 2 stroke jets.
The disadvantage to these is that you do loose 25 to 30% of the hp at the immpellar.On the right type of hull(flat bottom,jon boat) they will run shallow.Depending on weight and weight distribution you could run as shallow as 6" of water.The only other advantage I can see is that there is less maintanance than a regular outboard.No lower unit to change grease in.I ran one of these on a jon boat for some years and I was very happy with it except that you could not carry any wieght and what weight you had had to be distributed evenly so that the boat would sit perfectly level at rest for the boat to perform properly.

4 stroke outboard jet
Same story but they do get better gas consumption.Allthough I beleive that they are slower to reach top end rpms.Not a good thing when trying to get up on plane in a shallw river.

Inboard Jets.
These boats have tons of power and are very quick and fast.However they usually use large V8 engines and are very heavy and suck up the gas.They are typically not designed to run as shallow.Allthough some west coast boat manufacturers use them in boats designed to run white water.

Mercury Sport Jets.
These are 2 stroke inboard jets.They use the same power heads as large outboards.Much lighter than the V8 inboards and have plenty of power.They reach top end rpms quickly and makes the boat jump on plane very quickly.This is what is in my River Pro.

The jets that loose lots of horse power are outboard jets.They use pressure pumps and the flow of water has to change directions causing them to loose power and increases the gas consumption.
Inboard jets inclucing Merc Sport jets use flow pumps.Very little change in water flow making them much more fuel efficient than outboards.They also do not loose much horse power at the immpellar when compared to a prop.


All jets are steered by usuing propulsion and not a rudder.No propulsion, no steering.If you are coasting you are not going to have control of the boat.That being said they are much more manueverable than baots with rudders.The axis that you turn on is in the center of the boat.A skilled jet driver can turn on a dime by using both the steering wheel and throttle.Its hard to explain but its kind of like sliding the stern of the boat to point the bow in the direction that you want to go and then giving it some gas.Its actually a lot of fun to drive.

Some advantages of jets are they require less maintance than boats with lower units.
Safer than prop boats when used for pleasure.No Prop.
More manueverable.
You never going to nick a prop or knock off the skeg.
Faster accelleration(inboards and Merc Sport Jets only)This is very important on shallow water.Sometimes you only have a few boat lenghts to get the boat up on plane to get over shallow water obstciles.

I Use my River Pro mostly for fishing shallow water,rivers and smaller lakes.I can go where no other boat can go and I don't need to worry about those dead heads floating just uner the surface.The River Pro is the shallowest running boat on the market.
I do however have a 17ft deep vee that I use on larger lakes.Most jet boats need a flat surface to work properly.They are not that comfortable in large waves.

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