Basics of Jet Boat propulsion
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Basics of Jet Boat propulsion

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    Lightbulb Basics of Jet Boat propulsion

    I am really wanting to understand how my boat works. Would someone take the time to tell me which parts do what to move the boat, and why some parts/materials are better than others?

    I am probably not going to be changing mine a bunch to try and keep up with everyone but I want to understand what I am piloting in the water and take good care of it.

    Thank you.

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    Senior Member jetboatperformance's Avatar
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    Basically , the Engine crankshaft turns the Jet drive pump shaft , the impeller on the jet pump shaft turns (in similar fashion to a propeller) and draws water from under the boat hull, that water is passed thru the axial line of the pump shaft into and thru the jet bowl and expelled via the bowl thru a directional nozzle creating thrust which moves the craft forward reverse is obtained bt deflection or redirection of water flow at the directional nozzle as is turning ...

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    Senior Member 74Bonneville's Avatar
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    Go through and read all of the jet boat posts for a while and you will learn tons.

    Simple answer: The hole in the bottom of your boat allows the water to be forced through a turbine out the back pushing the boat. You steer with the gas pedal.

    Tom popped up as I was typing - What he said, this guy is good!
    Last edited by 74Bonneville; 04-02-2014 at 08:40 AM.


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    I will do some more research in the other threads.

    just trying to figure out what some things are, like a bowl, loader grate, etc.

    I see people talking about them but don't know what they are for.
    Last edited by SuperTiger77; 04-02-2014 at 10:20 AM.

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    Quote Originally Posted by SuperTiger77 View Post
    I will do some more research in the other threads.

    just trying to figure out what some things are, like a bowl, loader grate, etc.

    I see people talking about them but don't know what they are for.

    A pump has a suction housing that is at the bottom of the baot. It feeds water into the impellar that is in the bowl. The bowl looks just like that and is attached to your suction housing. (big round deal in front of your pump outlet) It moves water out the back of your boat propelling it forward. A loader grate fits into your suction housing and loads the face of the impellar with water. The better you load your pump the more water you can move through the faster you'll go up to a point of diminishing return.

    That boat of yours looks very familiar!

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    Quote Originally Posted by SuperTiger77 View Post
    I will do some more research in the other threads.

    just trying to figure out what some things are, like a bowl, loader grate, etc.

    I see people talking about them but don't know what they are for.

    The search function on these sites is your friend, there is endless threads and articles with differing opinons and solid information available here

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    its like a vacuum. a motor turns nickelback... nickelback sucks. then then they blow out the back. kinda like a vacuum.




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    Quote Originally Posted by SuperTiger77 View Post
    I am really wanting to understand how my boat works. Would someone take the time to tell me which parts do what to move the boat, and why some parts/materials are better than others?

    I am probably not going to be changing mine a bunch to try and keep up with everyone but I want to understand what I am piloting in the water and take good care of it.

    Thank you.
    there are two "basic" types of pumps. if you know what brand it is, the basic way it operates can be described.

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    My Jet is a Berkely.

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    Quote Originally Posted by SuperTiger77 View Post
    I am really wanting to understand how my boat works. Would someone take the time to tell me which parts do what to move the boat, and why some parts/materials are better than others?
    just the first part of your question. the engine functions the same way as any other engine. it is connected via a pto, through a driveshaft/hbar/u-joint, to the Berkeley pump shaft. you can find a parts breakdown of a typical Berkeley pump at their website, like this one Berkeley Jet Drive - Model 12JG Parts.
    a Berkeley pump is an axial flow, single stage, centrifugal pump. the impeller is keyed to the pump shaft, spinning at the same rpm as the engine. water enters through the intake (hole in the bottom), through the suction piece, to the suction side of the impeller. water entering the suction side of the impeller is discharged outward at high velocity and some pressure. as the water travels through the bowl volute sections, velocity energy is converted to even more pressure energy (Bernoulli's equation, conservation of energy, blah blah). pressure continues to slightly increase until it exits the nozzle. the force, or thrust, is the result of the volume of water and the velocity of the water exiting the nozzle. lbm/hr X ft/sec/sec2 = force. as you increase engine speed, water volume through the pump increases.
    the intake is bolted/epoxied to the bottom of the boat, which is where the force is applied. the boat moves in reaction to the force.

    this is "basically" how the pump works. there are many factors that can affect each one of the characteristics that make the boat move. they have been hashed, re-hashed and hashed again all over this forum. if you have very specific questions, much easier to answer.

    Quote Originally Posted by SuperTiger77 View Post
    I am probably not going to be changing mine a bunch to try and keep up with everyone but I want to understand what I am piloting in the water and take good care of it.

    Thank you.
    depending how anal you are about caring for it. don't run the engine connected to the pump on the trailer (dry). when you go to launch, make sure the bucket is open. there are pros that will recommend backing the boat into the water, pulling it back out, to flush the pump before launching. make sure the keel pump intake is in 5'-6' of water before starting the engine. if it is a foot or 2 feet deep, you suck a hole in the bottom and every piece of rock, sand or gravel will be sucked through the pump. there are clearances involving the impeller/suction piece/bowl that are important to the performance of the pump. leading edges of the impeller need to remain straight and sharp.

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    Wow, thank you.

    I am really hoping to go run into some of you all up at the lake this summer. There are a lot of valves for moderating the amount of water flow to various places for temperature and such that I don't really know about. I am glad someone told me about starting the boat out of the water. I had been thinking about it. There is a small body of water above a damn that is only a couple miles from my house. If I want to hear it run I better at least put the trailer in the water.

    You guys have all been a very big help, thanks again.


    John

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    Senior Member 74Bonneville's Avatar
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    Quote Originally Posted by SuperTiger77 View Post
    Wow, thank you.

    I am really hoping to go run into some of you all up at the lake this summer. There are a lot of valves for moderating the amount of water flow to various places for temperature and such that I don't really know about. I am glad someone told me about starting the boat out of the water. I had been thinking about it. There is a small body of water above a damn that is only a couple miles from my house. If I want to hear it run I better at least put the trailer in the water.

    You guys have all been a very big help, thanks again.


    John
    One more thing - Make sure all of those water regulating valves are wide open! Do some serious research before thinking about restricting water flow.

    Have Fun


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    Here's a simplified picture of how the pump works. Granted, this isn't a Berkely pump.....but they all work basically the same and this will give you a basic idea of the internal workings of a pump.
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    Cliff
    1978 21' Crusader, 466 CID BBF, Berkely Jet
    1966 13' Boston Whaler sport, 40 HP Yamaha Two Smoker

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