# Kansas JetJon build



## sulfurburner (May 1, 2014)

Hey guys. Been a member for a little while but mostly just lurking and taking notes. I finally finished up enough of my other projects to start on my jetjon build. It's not going to be fancy or pretty or anything else like the nice ones on here, but for what I'm going to be doing in it it's going to be just fine. The boat is an old 14' Larson mod-V, and the ski was an 01 Polaris Virage 700cc rated at 95hp.

I'm going to be going the less desirable route of grafting the glass hull into the aluminium boat. Mainly because of the lack of the right tools, time, and most importantly skill. So far I've got the ski cut up, motor and pump have been taken off. I've cut the hole in the jon and set the glass hull in. I'm wanting some advice on how low I'm setting the pump intake before I glass it together. I've got some pictures of where I'm at on my phone that I'll upload in the morning.


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## sulfurburner (May 2, 2014)

as promised here are a few pictures of the progress so far. I need to start trying to take more pictures.

Here's what I'm starting with: 14' Larson modified V. year unknown but I would guess it's existed more than twice as long as I have. Picked it up off Clist for $100 last year. 





I don't have a picture of the complete Ski as I was overly gung-ho and forgot to take pictures of that. Anyhow here's whats left of it minus the motor/pump:





Alright found the center and drew some lines! All downhill from here right?


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## sulfurburner (May 2, 2014)

And just like that it's in! (after 3 hours of cutting, lifting, re-measure, more lifting, cut again, lift some more, measure again, draw new lines to fix the last cut, replace broken saw-zaw blade, cut some more)













So here's where I'm looking for input before I go too far. I measured and cut so that the lowest point of the V from the ski hull would be even with the two outer strakes (I still need to take out more of the middle strake I know), but once I got it in I realized that the actual intake/ride plate sits a little higher. 





I don't think I want to go any lower with the front part of the Ski hull, but I'm worried about the angle of the jet if I widen the cut to drop the intake/ride plate another couple inches. Do you think I will have issues with cavitation if I glass it in the way it sits now?


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## PSG-1 (May 2, 2014)

Although I have never built one using the fiberglass hull method, I can confirm that it's imperative to have a smooth transition from aluminum to glass hull in front of that pump intake. Anything sticking up is going to cause cavitation. 

Nice work so far! You seem to be on the right track. Be sure to post pics as you move along, and if you hit a snag, post a question on the forum. It's much easier to correct an issue BEFORE you build something, rather than AFTER, where you have to go back and modify it.... what a PITA (take it from someone who's been there, done that) 

There are a few here who have done it with the glass hull method who can better advise on how to proceed.


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## sulfurburner (May 2, 2014)

Thanks for the quick reply! I feel pretty good about how the actual transition will be. Actually the reason I left as much of the ski hull was because it's actually molded similar to the spoon design on another build on here. I will end up taking out another 12" at least of the center strake and glass in the front of the spoon. I agree with the fix it now not later approach, especially doing it the ultra cheapo glass route I'm going. Do you think it would hurt more than help if I opened the rear of the hole a little to drop the intake/ride plate a little further? Right now the entire ski hull is pretty much level. I'm not sure if angling it down will help or hurt me.

I'd love to have the ability and means of putting together something like you did some day. This project will be more of a learning experience than anything else though. I spend a lot of time on the river throughout the year. Right now I've got 5 boats, the one I like best (for fishing) is very similar to this one except it's a 16' with a 15hp tiller steer. It goes everywhere I want to go for the most part but I hate cringing every time I need to pass through a spot with lots of things to bounce the prop off of. I plan to sell off two of the 5, a 17' bass tracker flat bottom and a 1236 Lowe flat bottom. 

I always had the idea of building one of these in the back of my mind until last year when the girlfriend wanted to pick up a bigger nicer boat to take to the lake for tubing. I ended up picking up a Seadoo Speedster with twin 85hp jet drives. I had no idea what a jet boat could do so needless to say that thing has opened my eyes :shock: 

Right now total I've got $350 into this thing. I'm hoping for two things out of this build: A) keep the total budget under $1000, and B) keep enough motivation going to get it done before summer ends.


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## PSG-1 (May 2, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=350950#p350950 said:


> sulfurburner » Today, 10:00[/url]"]Thanks for the quick reply! I feel pretty good about how the actual transition will be. Actually the reason I left as much of the ski hull was because it's actually molded similar to the spoon design on another build on here. I will end up taking out another 12" at least of the center strake and glass in the front of the spoon. I agree with the fix it now not later approach, especially doing it the ultra cheapo glass route I'm going. Do you think it would hurt more than help if I opened the rear of the hole a little to drop the intake/ride plate a little further? Right now the entire ski hull is pretty much level. I'm not sure if angling it down will help or hurt me.





I don't see where it would hurt to have it angled just a slight bit, in fact, that would probably help with cavitation, as it would feed more water to the pump. But you don't want to over-do it, either, then it's just dragging, or over-loading the pump, not to mention the angle of the pump changes the angle of the nozzle and will likely require a positive degree nozzle, or trimming all the way up (if equipped with a trim nozzle) to compensate for it, to keep the bow from digging in. IMHO, you don't want the back end of the pump to be more than 1/2" below the bottom of the boat. And while you don't want the front end sticking down causing cavitation, you also don't want to have it being inset, because this will create an air pocket, which will also lead to cavitation.

Ranchero50 seems to have the best understanding of the dynamics of water flow under a jet john, as he fabricated his own spoon from aluminum, so, maybe he can impart some advice here.






> I'd love to have the ability and means of putting together something like you did some day. This project will be more of a learning experience than anything else though. I spend a lot of time on the river throughout the year. Right now I've got 5 boats, the one I like best (for fishing) is very similar to this one except it's a 16' with a 15hp tiller steer. It goes everywhere I want to go for the most part but I hate cringing every time I need to pass through a spot with lots of things to bounce the prop off of. I plan to sell off two of the 5, a 17' bass tracker flat bottom and a 1236 Lowe flat bottom.
> 
> I always had the idea of building one of these in the back of my mind until last year when the girlfriend wanted to pick up a bigger nicer boat to take to the lake for tubing. I ended up picking up a Seadoo Speedster with twin 85hp jet drives. I had no idea what a jet boat could do so needless to say that thing has opened my eyes :shock:
> 
> Right now total I've got $350 into this thing. I'm hoping for two things out of this build: A) keep the total budget under $1000, and B) keep enough motivation going to get it done before summer ends.



Right now, I have 2 boats, my jet, and my Triton 1650SC with a 50 Merc. Also have a Yamaha VX110, and a Superjet, and of course, my little Hobie Bravo sailboat. Anyhow, back in 2003, I bought a used SeaDoo Speedster with the twin 85 HP engines. Like you, it opened my eyes to how fun jet boats can be! Of course, I never pressed the envelope with the SeaDoo and tried to run any shallow water, but I sure had fun waterskiing with it, and cutting 180 turns, as well as running all those switchback creeks. 

By the end of 2004, I was determined that I wanted an aluminum hull jet boat, and by January of '05, I had begun building mine, with a Tigershark 2 stroke engine, later changed to a Yamaha 4 stroke. 

After having built my jet boat, and seeing how shallow it could run, and with my SeaDoo being 10 years old, with age beginning to cause some issues here and there, I parted with that boat, somewhat reluctantly. But it wasn't like I was boat-poor or anything! And, because I had maintained it and re-upholstered it, and installed brand new hydro-turf mats, I managed to sell it for just about the amount I had paid for it, not to mention having used the boat for about 5 years.

In any case, when I built my jet boat, there was no tin boats forum. My "blueprint" was my Sea Doo jet boat. I would look at how things were put together on that boat, and try to interpolate how to do it with a johnboat. All things considered, I think I did pretty good for the first time around. When the boat was upgraded to the 4 stroke engine, a few things were improved, such as the jet tunnel being made wider, and the cowling taking on a more streamlined shape, but for the most part, everything else stayed the same.


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## sulfurburner (May 2, 2014)

For some reason it seems those seadoo boats get a bad wrap. Mine was actually "given" to us because my girlfriend's dad was tired of dumping money into it. Lucky for me he replaced some of the big wear items (impellers, wear rings, driveshafts). We did fry the ECM on the first trip out though. It had been setting and both batteries were gone, so in order to show me how it ran he hooked the two electronic systems to one 12v battery. Learned the hard way you can't do that. Luckily I was able to find a guy in Texas that fixes them when that happens, but it wasn't cheap. Anyhow we like it so far. It needs new upholstery and I'd love to get some hydro turf for it, but unfortunately I have a feeling the port side engine is weak and will need fixed before anything else. I'm getting ready to pull it out of the shop in the next couple weeks. I intentionally put it away last fall without running a compression check so I didn't have to dread fixing it this year [-o<


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## sulfurburner (May 2, 2014)

Almost forgot to ask, I was reading through some other posts and I saw where you mentioned using spray foam was a no no because of crevice corrosion. I was actually planning on using spray foam as a filler for the gaps around the ski hull and the jon hull, then shaping it and glassing it in. I saw on another site (sorry can't remember which build now) where a guy did that. I do plan on using SS bolts every 2-3" to mate the actual hulls together for structural integrity. Do you have any suggestions for alternatives to filling the gaps and forming the front of the "spoon" other than foam?


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## PSG-1 (May 2, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=350991#p350991 said:


> sulfurburner » 18 minutes ago[/url]"]For some reason it seems those seadoo boats get a bad wrap. Mine was actually "given" to us because my girlfriend's dad was tired of dumping money into it. Lucky for me he replaced some of the big wear items (impellers, wear rings, driveshafts). We did fry the ECM on the first trip out though. It had been setting and both batteries were gone, so in order to show me how it ran he hooked the two electronic systems to one 12v battery. Learned the hard way you can't do that. Luckily I was able to find a guy in Texas that fixes them when that happens, but it wasn't cheap. Anyhow we like it so far. It needs new upholstery and I'd love to get some hydro turf for it, but unfortunately I have a feeling the port side engine is weak and will need fixed before anything else. I'm getting ready to pull it out of the shop in the next couple weeks. I intentionally put it away last fall without running a compression check so I didn't have to dread fixing it this year [-o<



If the compression is shot and it needs a re-build, try SBT, you can't go wrong. They have a no-fault 2 year warranty on their short block rebuilds. I think you can get a SeaDoo 717 engine done for around 800 dollars or so.

When I bought mine, they had failed to pull the plug, and the boat had sat at an angle, filling the engine compartments with rain water, so the first issue I had was a dead battery. Then my starboard side carb kept being sticky, because of corrosion. Had it re-built. Then the magnetos started going out. But, this is the kind of stuff that is typical with ANY PWC or jet boat. It's just more of a PITA and a PITW (Pain In The Wallet) when there are TWO engines to deal with, instead of one!

But hey, they run great, and they are so much fun. What I loved about mine in the serpentine curves was showing people how I could run through some serious turns and barely have to use the steering wheel, by simply using my throttles to turn. LOADS of fun!!


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## PSG-1 (May 2, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=350994#p350994 said:


> sulfurburner » 19 minutes ago[/url]"]Almost forgot to ask, I was reading through some other posts and I saw where you mentioned using spray foam was a no no because of crevice corrosion. I was actually planning on using spray foam as a filler for the gaps around the ski hull and the jon hull, then shaping it and glassing it in. I saw on another site (sorry can't remember which build now) where a guy did that. I do plan on using SS bolts every 2-3" to mate the actual hulls together for structural integrity. Do you have any suggestions for alternatives to filling the gaps and forming the front of the "spoon" other than foam?




Are you operating in salt water? If not, then, crevice corrosion isn't really so much of an issue to contend with.

That said, if you are glassing in the foam and completely sealing it before final installation, I don't see where it would be an issue. The issue with the foam arises when it's unsealed, and it soaks up water like a sponge. But I do wonder if the resin of the glass will melt that foam? You might want to try a sample first before you go through all that work! 

Other materials to consider besides spray foam: composites, such as star board cut into strips. Or, closed-cell foam board, cut to shape.


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## sulfurburner (May 2, 2014)

I can almost guarantee this thing will never see salt water as long as I own it. I'm in NE KS and don't plan on leaving any time soon. I'll definitely do a test piece to see if it eats the foam first, I didn't think about that - this is why I'm glad I found this board!

As far as the seadoo boat I'll probably just have a buddy of mine go through the engine if it needs it. I do a little powder coating work for him now and then so he's been really good to me when I've had him work on small engines for me in the past, plus it's what he does day in and day out. But I'll keep SBT in mind if mine isn't saveable. I'm excited to get that thing back on the water though. Last fall we met some friends at the lake that had just spent countless hours getting this old cuddy cabin style boat going. It had twin small blocks, not sure what outdrives but they were dialed in to run and drink lots of fuel. The look on their faces when we got the jet boat out and pulled away from them wide open was priceless :LOL2:


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## sulfurburner (May 12, 2014)

No pictures to update yet. I've had to take a break from making any big progress on this for a couple weeks as I just had eye surgery. I figure fiberglass, aluminium, and wood particles flying through the air would be a bad idea as my eyes heal. I was able to get the throttle and steering setup built though. I also gathered all of the stainless bolts and black RTV needed to seal the two hulls together. Hopefully I can get that part finished up this week.


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## He Reigns (May 12, 2014)

I am waiting patiently to see how you graft it all together. I am about a week out from cutting mine. Do you plan on putting some flat bar aluminum around the cut in the hull?


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## sulfurburner (May 13, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=352111#p352111 said:


> He Reigns » Yesterday, 20:31[/url]"]I am waiting patiently to see how you graft it all together. I am about a week out from cutting mine. Do you plan on putting some flat bar aluminum around the cut in the hull?



That sounds like a good idea, and if I had some flat stock laying around I probably would go that route. This build however is all about keeping costs low and being resourceful by using what I can find laying around. The way it sits now I've got about a 2.5" gap between the flat part of the ski hull where I'm going to run the SS bolts through to the boat hull. I'm planning on cutting some 5/8" plywood into strips and stacking them to fill that gap. I'll RTV seal each surface and run the bolts every ~4" through the ski hull, plywood, and boat hull. once that's done I plan to fill the remaining gaps with an expanding foam that I can shape and glass over that. Pictures will help explain once I can get some up.


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## wlockerb (May 18, 2014)

I did the exact same thing here. I used spray foam in the gaps and then glassed around it. Used 3 coats of fiber glass. I have some pics in my thread but not many of the early stages where I glasses over the foam. It works fine and I have no leaks but the 3m 5200 sealant is pretty high. I think I paid $25 a tube and 3 or 4 tubes.


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## Ranchero50 (May 19, 2014)

Do you still have the front of the ski? I'd trim the ski nose to fit the boat and graft it to match the hull profile. Gonna be a bear doing the front transition with that much of a difference.


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## sulfurburner (May 30, 2014)

[url=https://www.tinboats.net/forum/viewtopic.php?p=352775#p352775 said:


> Ranchero50 » 19 May 2014, 13:05[/url]"]Do you still have the front of the ski? I'd trim the ski nose to fit the boat and graft it to match the hull profile. Gonna be a bear doing the front transition with that much of a difference.



yeah I had that thought myself about a week after I'd cut up the rest of the ski hull into little pieces for the garbage can


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## sulfurburner (Jun 13, 2014)

figured I'd post an update since it's been a couple weeks. I've worked several hours on it but I'm no further progress wise than I have been, other than finally having a plan. I need to get to the metal shop and have them break two pieces of aluminum to about 20 degrees to mount between the ski and jon hulls. this will give me more surface area for both hulls to mount to. 

Aside from that most of my efforts have been going towards my seadoo jet boat. After finding low compression on all 4 cylinders we tore into them. I'm surprised either motor ran at all  . So now I get to spend a bunch of money with SBT on that one. Hopefully while I'm waiting on the new motors to show up I can make some progress on the jetjon.


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