Building my first jet john.. need pointers

[derek03]

I am a 19 year old kid that wants a cool boat that not many people have, and I am in the process of planning out my first jet john (I have moderate mechanical experience, but youtube and reading forums are my friend). I have a flat bottom 17ft bass tracker that I have completely gutted, and currently working on buying a rotax 951cc seadoo motor. I was hoping some of you guys that have built a jet john could give me a few pointers. I am planning on leaving the motor on the original jet ski motor mounts and cutting the bottom of the jet ski then dropping it in the boat (if this is the easiest way). I would like to make a center console with a steering wheel instead of using a steering stick thats right by the motor. I have seen that some of you guys have created a "spoon" and was wondering what the purpose of this is? like I said any words of advice and pointers such as what obstacles you came across and what you did to overcome them will be greatly appreciated!

 

[derek03]

And I am also new to this website so Im trying to figure it all out as I go!

 

[amk]

The spoon is for cavitation you may or may not need one you wont need to worry about that until after you put it in the water and test it. I didn't on either of my boats just depends on how smooth your transition is from the aluminum boat bottom to the jet bottom. Building these boats are like the old saying of how you eat an elephant... one bite at a time. Once you get the ski take your time disassembling and make sure your ready to cut. I cut the bottom out of the second boat I built if I could do it over again it would look more like cedarriverscooters I used a lot more ski than I needed to. His build for the most part is what I would mimic only thing I would really do different is I would put a few bolts instead of only 5200 to adhere the boat to the ski bottom.

 

[derek03]

How will I know if I have to make a "spoon" or not?

 

[CedarRiverScooter]

Thanks for the compliment AMK!

Derek - I would read every build thread you can find (Ranchero 50, PSG-1. etc). That helped me a bunch.

The spoon is supposed to create a negative pressure area that sweeps air away from the intake (that is somewhat counter-intuitive). I didn't put one on mine, but will scab one on later if it cavitates. I did, however, flatten out the center rib several feet before the intake so as to not have that turbulence.

One more piece of advice - always be thinking 3 steps ahead. (I assume you will be like me & have no drawings 8). There were several steps that I had to take apart because I had painted myself into a corner.

Plan on several hundred hours of work - If you want to use it this summer, start now.

 

[derek03]

Thanks these comments helped a lot! Once I start on the boat I'll post pics as I go!

 

[amk]

you will know if you need a spoon or your cavitating when you try to go but it sounds like crud and your motors wide open and your not going anywhere. Its like spinning your tires in mud.

 

[Ranchero50]

Ditto, post up some pics of what you have. Also, make sure your donor is good to go before cutting up the hulls.

Plan 20-30 steps ahead and be sure to spend a lot of time sitting in the boat making motor noises and mock casting with your fishing gear. Sounds dumb but it helped make a lot of important design decisions. Also plan your build so you can take it apart (in a hurry if needed) when you poke a hole in it.

Plastic worms will save the day. #-o

 

[CedarRiverScooter]

be sure to spend a lot of time sitting in the boat making motor noises and mock casting with your fishing gear. Sounds dumb but it helped make a lot of important design decisions.

Funny you entioned this Ranchero - Several times I climbed in, with seat & controls barely mocked up, to get a feel for the layout. I changed it quite a bit. My original layout was going to be too cramped - seats too close together & the stick to close to my leg.

 

[PSG-1]

The best pointer I can give, from my own experience, is to build the boat around the parts. By that I mean have the specific part on hand before you start working on that section of the boat.

It sounds simple enough, but in the excitement of a build, it's easy to get ahead of yourself, or get impatient waiting on a part to be shipped to you...and decide to go ahead and "wing it" and build that part of the boat, guesstimating how the part will interface, hoping you're right, then having to go back and build it a second time, modify it, or the part, when stuff doesn't work correctly. A good example would be building the jet tunnel without having control cables (Been there,done it) Then when you get the cables, you realize the position of your bulkhead fitting doesn't coincide with the travel of the cable to work the steering/reverse gate, and you have to start modifying, or re-doing it #-o #-o

 

[Flat_Bottum]

As said above, go slow and build it right the first time. I sped through the first build of my jet jon and took a lot of short cuts and corners. Needless to say, less than a year later I am ripping the boat back down to a bare hull, ripping the engine and pump out so I can do it properly this time around. In the end, it will have taken me twice as long to complete and cost hundreds of dollars more than what it should have if I would have just done it right to begin with. Good luck.