# jet boat



## lilpropane (Dec 5, 2011)

im constructing a jet jon the boat is 17'x50 wide just wondering how big of a jet ski motor i would need to push it up some shallow water at a good rate i have a motor and pump out of a GTX seadoo 650 motor do u think it will be enough to plan it out??


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## lilpropane (Dec 5, 2011)

just any tips would be nice just starting out in this


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## bulldog (Dec 5, 2011)

I think a 650 would do just fine pushing that sized boat. The best thing you have going for you with the boat is how wide it is. It will plane easier and run shallower. Post some pics. We love pics.


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## lilpropane (Dec 5, 2011)

glad to here im working on pictures now.I got a friend thats in the fab biz he is giving me a bunch of aircraft aluminum so i dont have to put heavy wood back in it. I spent about six hours saturday rewelding all the crappy welds from factory the boat alone with out motor only weighs in at 223 pounds didnt think that was to bad going to pick up my seadoo saturday hopefully have it in the boat sunday.


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## lilpropane (Dec 5, 2011)

what would be ur guess on the top speed of this thing?Ive been told by a mecanhic that i need a after market pipe and water box yall no anything about that


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## PSG-1 (Dec 5, 2011)

Hope you don't plan on welding that aircraft aluminum....as most of it is non-weldable.

As for the top speed with a 650 pushing the boat at 250 pounds, you should expect at least 40 MPH for the top speed, perhaps 45 MPH.


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## bulldog (Dec 5, 2011)

40 mph probably. Maybe more depending on weight. I'm not sure what a water box is but I'm assuming it has something to do with the exhaust. If you can find an aftermarket pipe, that never hurt any motor. What year sea doo are you using?


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## PSG-1 (Dec 5, 2011)

There is no need for the aftermarket exhaust system. An aftermarket head pipe and waterbox may give it some more HP, but at the expense of being much louder. I'd run factory exhaust, and see how that goes. It should be just fine.


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## lovedr79 (Dec 6, 2011)

Should do pretty good


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## lilpropane (Dec 6, 2011)

just trying to figure out how to seal it off it the back of the boat


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## PSG-1 (Dec 6, 2011)

Not sure what you mean by sealing it off at the back of the boat.

If you mean by running the exhaust out of the hull, you should be able to do this with a flange, right out the back of the transom, as low as possible.

Of course, the best method, if you have the room inside the jet tunnel, is to route the exhaust into this, and then use some rubber skirting around the back, notched to fit around the jet pump....this reduces the noise signature like you wouldn't believe, in fact that's what Yamaha does with all their 4 stroke jet skis now.


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## bulldog (Dec 6, 2011)

What year Sea Doo are you using?


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## lilpropane (Dec 6, 2011)

bulldog said:


> What year Sea Doo are you using?


1994


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## bulldog (Dec 6, 2011)

lilpropane said:


> bulldog said:
> 
> 
> > What year Sea Doo are you using?
> ...



I believe the years around that year, the oil tank feeds via gravity to the motor. When you mount the oil tank for your build, make sure you mount it high enough to not get any air in the tube leading from the bottom of the oil tank to the bottom of the motor. The oil tank keeps the bearings in the bottom of the motor lubricated and if they don't get enough oil you will have an expensive repair on your hands. I had the same motor, I believe, in my jet jon and I mounted the oil tank as high as I could. Look at where it is mounted in the Sea Doo and mount it atleast that high with the tube at the same angle.

If your motor is not like this, disregaurd this post.


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## montanaman (Dec 6, 2011)

650 engine you might see 32-34 mph. i hope you have a better jet pump to use other then the stock seedoo watercraft jet unit
the intake grill has only a cpl bars and they are to far apart to stop any rocks/stones . the liner in that seadoo is nylon/plastic and will not hold up to pumping any sand/gravel/stones. then the impellers is also way to thin to stand up to the same thing. on that size jet intake your intake grill should look more like this 1


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## lilpropane (Dec 7, 2011)

what kind of pump should i use im new to all this jet stuff. If you would brand model thankful for any info.


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## PSG-1 (Dec 7, 2011)

If it were me, I'd use a Yamaha XL700 pump. It's closely matched to the 650 engine.

Something like a Yamaha XL1200, with its 155mm bore, would be too much for the 650, it would overlug the engine. I think the XL700 pump is a 144mm bore.

The yamaha pumps use a stainless steel wear ring, instead of plastic like the sea doo pumps use. PLastic wear ring liners get chewed up really quick if they hit sand, gravel, etc.


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## montanaman (Dec 7, 2011)

lilpropane said:


> what kind of pump should i use im new to all this jet stuff. If you would brand model thankful for any info.



a pump that is made for jet boats is going to serve you much better in the long fun the a watercraft/jet ski pump
here is a pic of an impeller we have custom made to match our 6" jet pumps to the yamaha 650/701/800 2 strokes
these impellers are very thick and strong to hold up to a shallow running jet boat thats pumping alot of sand/gravel/stones
this is something that a watercraft impeller just can not do and hold up for very long.


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## montanaman (Dec 7, 2011)

here is the jet pump that impeller goes to
it is a 6" aquajet from new zealand and works very well with the smaller watercraft type engines in 2 and 4 stroke
we have used it with engines up to 143 turbo hp and in new zealand they have used it with subaru's up to 180hp


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## bulldog (Dec 7, 2011)

That impeller is beefy to say the least. I like it. What is is constructed of?


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## montanaman (Dec 7, 2011)

bulldog said:


> That impeller is beefy to say the least. I like it. What is is constructed of?



stainless steel. this is why an inboard jet pumps can hold up to the extreme shallow running with sand and gravel pumping all day
an outboard jet is fine for some shallow running but when you start pumping alot of trash they just can not do the job and last very long
i have looked back at the nozzle when we are running over a gravel bar and there is as much gravel coming out the nozzle as there is water. after a trip like that when we get back to the shop i have taken the impeller out to inspect it and all is fine and right back in it goes for more thrashing lol.


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## lilpropane (Dec 7, 2011)

so if i do run factory stuff i need impeller what kind should i get??


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## lilpropane (Dec 7, 2011)

would that 6 inch aqua jet work with my 650 gtx motor


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## montanaman (Dec 7, 2011)

lilpropane said:


> so if i do run factory stuff i need impeller what kind should i get??



i have never seen anybody that makes thick strong replacement impellers for watercraft jet pumps
watercraft jet pumps are not made for this type of use so nobody makes impellers for them that will work very well pumping gravel
thats why you need a true river jet pump. yes i know there are guys that use watercraft type jet pumps for making a small river boat
but the truth is they just do not hold up if you are going to run the extreme shallow pumping trash and thats just the truth of it
so if you would like to build a boat that you can take out and run the shallow stuff pumping trash without the worry of the jet pump leaving you stranded then you need to step up and use the right jet pump for the job. yes they cost more then a free or next to free watercraft jet pump but if you do a good build it should give you years of great service.just think how good you will feel every time you head out on the river and you pass those jon boats with junk jet pumps in them.

here is the intake grill of the 6" jet pump and you can see how much better it is then a watercraft intake grill


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## montanaman (Dec 7, 2011)

lilpropane said:


> would that 6 inch aqua jet work with my 650 gtx motor



yes it would work very well if it is set up with the right impeller.
this is a yamaha 800cc set up with the aquajet 6" jet pump


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## lilpropane (Dec 8, 2011)

What price does the Aqua 6inch start at??


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## PSG-1 (Dec 8, 2011)

montanaman said:


> lilpropane said:
> 
> 
> > what kind of pump should i use im new to all this jet stuff. If you would brand model thankful for any info.
> ...





WOW! Good lord, those are some thick blades on that impeller!! It would take me several years to wear one of those things down, even the way I run a boat. Any chance they make those for the XL1200 Yamaha pump?


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## montanaman (Dec 8, 2011)

PSG-1 said:


> montanaman said:
> 
> 
> > lilpropane said:
> ...



give us a call about making custom impellers for your yamaha
thanks bill 406-677-4242


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## montanaman (Dec 8, 2011)

lilpropane said:


> What price does the Aqua 6inch start at??



these jet pumps range from $2500 on up
depends on impeller, intake grate, stomp grate , and so on.
i hope you can see in the impeller pix that these jet pumps are not toys. i know there are some guys that like to build there own jet boat
and that is very good. but if you start with some better parts you will end up with a much better shallow running jet boat in the end.
a boat that you will use for years and will hold its value much longer then a cheap jon boat with cheap parts. the engine and jet pump are key factors in making a jet boat that runs,drives,and holds up well to the shallow running where you are pumping gravel all the time.
i do not think you guys are packing that much wt. in your boats like we do hunting. so the engine you use can be a little less H.P. then what we need to get our boats up on step very fast when we have them loaded full of dead critters like moose.


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## PSG-1 (Dec 8, 2011)

Yeah, the pics of the pump and components look like they are built VERY stout. I like the multiple tines on the intake grate, that's about what I need for running around oyster shells, etc. 

Also, the housing of the pump looks pretty thick. What is the approximate thickness of the duct?

The yamaha intake duct is a very thin casting, like maybe 3/32" of an inch. One good rock could easily bust a hole in that, and this is the one thing I always worry about.

And then the impeller thickness, that is really impressive. 

The edges of the factory Yamaha and aftermarket Solas impellers are pretty thin, one good rock or oyster shell is all it takes to put a nick in the leading edge. And being that thin, it doesn't take long to wear one down by running through sand, etc.

I'll be in touch with you soon about getting a custom impeller made for my Yamaha pump, though. And when it comes time to build another jetboat, I'll probably go with an Aqua Jet pump. Like the saying goes, buy quality, and only cry once.


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## bulldog (Dec 8, 2011)

PSG-1 said:


> Like the saying goes, buy quality, and only cry once.



If you can swing it, very good advice.


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## lilpropane (Dec 9, 2011)

What all due you'll know about the mercury sport jet 90????


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## montanaman (Dec 9, 2011)

they are a good idea for small lite set up but thats where it ends. they suck on fuel and the jet pumps are not that strong and do not hold up to the extreme shallow running if you are sucking up alot of sand and gravel.


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## lilpropane (Jan 10, 2012)

Well just so yall know im still alive been working on my boat just about finished. I ordered a 4 foot x 10 foot sheet of 1/4 alum. i took most of the back end out using my plasma cutter and replaced in with 1/4 inch built tunnel to spec. Replaced the transome as well with 1/4 welded it all together for added strength today i will be welding my ski deck and working on my steering console any suggestions where i should put my console?? I'm using the 90 hp mercury sport jet any idea how fast this thing may run?? Hopefully the profit of this boat will allow me to order my new pump from montana man and start my new right already got the motor i found a wrecked wrx im thinking bout..


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