Outboard Jet Drive

topgun3690

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Need some info/advice about these outboard jet motors.....am considering getting a 17-18 foot all aluminum tunnel hull jet for running up rivers and creeks, places you wouldn't want to take a conventional prop boat. Engines like a Merc or Yamaha 90/65 Jet. Besides the loss of 25 HP due to the jet drive, was wondering if there were any maintenance issues or other problems associated with operating these engines? Would the jet drive require less maintenance than a regular lower unit/prop motor? Or more? Would kinda like to know what I might be getting into before i got "into" it if you know what I mean.....Have never driven a jet nor do I know anyone who has one.....so anybody who has experience with this type of setup I would appreciate your input. Thanks.
 

FunInDuhSun

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Apr 25, 2010
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Need some info/advice about these outboard jet motors.........Have never driven a jet nor do I know anyone who has one.....so anybody who has experience with this type of setup I would appreciate your input. Thanks.
Jet outboards don’t have the same ‘grip’ on the water that props have. If you’ve ever run a SeaDoo you should understand. If you’re willing to trade off the relatively firm grip of a prop for the shallow water ability, go for it.
 

topgun3690

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Jet outboards don’t have the same ‘grip’ on the water that props have. If you’ve ever run a SeaDoo you should understand. If you’re willing to trade off the relatively firm grip of a prop for the shallow water ability, go for it.
That's what this is all about, shallow water ability....and not breaking off a lower unit or destroying a prop. Definitely a trade off for sure, with the loss of HP for the jet drive, loss of steering control if engine stops, and loosing the "grip" that props have. Thanks F.I.D.S. for the reply.
 

dwco5051

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Sep 14, 2008
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Have run both and a jet will have a different feel the first few times you run it. If most of my fishing was on the river I would have a jet. You can buy a lot of gas for the price of a prop or lower end gear set. Plus it will get you places you would want to fish but would pass on with a prop final drive.
 

topgun3690

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"Plus it will get you places you would want to fish but would pass on with a prop final drive." Exactly what I'm talkin about.....thanks dwco for the input. (y)
 

Sea Rider

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Sep 20, 2008
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A jet system is not the panacea motor, have certain parameters you have to fulfill to work as intended. The water flow at speed must pass right under the protruding plate (1) There's a certain distance 1 to 2 that will need to check on the motor you intend to buy to know the lower leg clearance.

In other words if you thought that those jets works while sitting very high on transom the answer is no. Before venturing on any jet motor, measure the height distance from your current motor from AV plate to the tail and compare it to the jet parameters. If both are near same stay with a prop motor and don't go running like crazy on water cond you don't know anything about.

Being a jet propulsion system won't free you from smashing the unit against a hidden, tree, rock whatever lying under water. Although having a lower water intake screen won't guaranteed to be 100% safe, anything can get there and tangle around the impeller, cancel water propulsion, screw your boating/fishing day as will need to count with tools to disassemble the lower unit to get rid of whatever tangled there. So think it twice if going for a jet powered motor...

Happy Boating
 

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topgun3690

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I understand totally what you are saying Sea Rider....my intent was not to simply slap a jet onto my existing fiberglass fishing boat. Rather, I would be getting an all aluminum boat with built in tunnel hull, taller transom height, and hydraulic jack plate for the engine......a rig designed for a jet drive. From what I understand, if set up properly, the intake will be above the lowest portion of the hull while underway, so if you hit anything the hull will take the punishment not the engine. But like you said, the intake can suck up debris and stop the flow.....especially aquatic vegetation....but a prop boat doesn't do very well in heavy weeds either. Just gathering info at this point....have not purchased anything. Thanks for the info SR. (y) BTW....have seen the youtube videos of these daredevils going 60 MPH through just inches of water, narrowly missing rocks and trees with their hair on fire! Lol....not what I intend to do if I get one.
 
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Sea Rider

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If you install a Jet powered motor for the intake to ride above the lowest portion of the hull will cancel the jet propulsion while the jet nozzle delives water on air. These motors needs to work with the large round bulb and the jet nozzle fully submerged as is pic 1 post 9 to achieve their max HP cowl rated for while the motor revs middle to its max wot rpm range factory stated depending on the motor brand. A motor with an Hydraulic Jack Plate tested at different heights will surely dial best jet thrust performance.

Happy Boating
 

topgun3690

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If you install a Jet powered motor for the intake to ride above the lowest portion of the hull will cancel the jet propulsion while the jet nozzle delives water on air. These motors needs to work with the large round bulb and the jet nozzle fully submerged as is pic 1 post 9 to achieve their max HP cowl rated for while the motor revs middle to its max wot rpm range factory stated depending on the motor brand. A motor with an Hydraulic Jack Plate tested at different heights will surely dial best jet thrust performance.

Happy Boating
I am no expert on this subject Sea Rider.....but it is my understanding that the tunnel hull creates a column of water for the jet drive to operate in while underway....allowing the intake and large round bulb to be above the bottom of the hull while staying fully submerged and supplying thrust. The faster the boat goes, the higher the engine can be raised with the jack plate. The tunnel creates a low pressure area which draws water into a column which the jet drive operates in. In other words, the intake is below the top of the tunnel, but above the bottom of the hull. This is my understanding of the jet drive/tunnel system.....just from what I have read and seen.
 

Faztbullet

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Mar 2, 2008
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If you install a Jet powered motor for the intake to ride above the lowest portion of the hull will cancel the jet propulsion while the jet nozzle delives water on air. These motors needs to work with the large round bulb and the jet nozzle fully submerged as is pic 1 post 9 to achieve their HP
You have absolutely no idea of what your talking about....
From Outboard Jets website..

13. How far does the jet go down into the water?

The water intake grill slopes down to the rear to give a scooping effect. The leading edge is flush with the bottom of the boat. The trailing edge is about two inches lower.

7. How high exactly do you have to raise the transom?

The height is approximately six inches higher than with a propeller. It varies between different motors and boats. When the jet drive is on the motor, set the height so that the leading edge of the intake is flush with the boat bottom. Then test the boat and adjust the height, if necessary, as high as possible without air entering the pump and causing cavitation (slippage).

1610412830903.png


This motor seems to be doing pretty good since it is delivering water on air........
1610413032403.png

Read pages 5 and 19-21 of the manual you posted....might learn something.
 
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topgun3690

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With a proper tunnel-hull setup.....NOTHING should be below the hull while underway, with the jackplate set correctly....as I understand it.
 
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