River boat

[Superfly Silverfox]

Hey folks I have a 700 cc two stroke jet ski engine and jet. I also got a 14’ x 4.6”aluminum Jon boat !

I cut down the ski , it runs now.
Time to take the center rib out about mid ship and start my build.

Sure would like advice, info , builds to look at to help?

Thanks and here she is.
The SuperFly Silverfox

[CedarRiverScooter]

I would plan out the position of everything before you start cutting.

Make cardboard templates for the big items. Plan out your wire & cable routings too. It will save some frustration later.

My biggest issue was the thrust angle of the jet pump. If you have power trim that would be best. If not, you might have to add trim tabs or worse reset the jet ski insert.

Check with your DNR about getting it legit registered. I got mine converted to 'homemade' status & is fully legal & insured.

[Superfly Silverfox]

I would plan out the position of everything before you start cutting.

Make cardboard templates for the big items. Plan out your wire & cable routings too. It will save some frustration later.

My biggest issue was the thrust angle of the jet pump. If you have power trim that would be best. If not, you might have to add trim tabs or worse reset the jet ski insert.

Check with your DNR about getting it legit registered. I got mine converted to 'homemade' status & is fully legal & insured.

Thank you!
How do you get the engine to separate the jet shaft?

[CedarRiverScooter]

The best advice I can give you on that is to buy a shop manual for your particular jet ski. Sometimes you can find a freebie on web. Is that a Polaris? Try Greenhulk. They have lots of info.

[Superfly Silverfox]

The best advice I can give you on that is to buy a shop manual for your particular jet ski. Sometimes you can find a freebie on web. Is that a Polaris? Try Greenhulk. They have lots of info.

Thanks for the info


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[Superfly Silverfox]

Ok got it all apart without tearing anything up. Got the mock up photo

Not sure how to proceed but I will.

[CedarRiverScooter]

Find a source of reasonably priced aluminium angle. Your going to need a bunch of it.

You will want to attach the jet ski tunnel insert to angles running fore-aft. Those need to be attached to the existing cross ribs & the transom if possible. The more you can tie the structure together the better.

You will have 80 hp pushing on the transom & it needs to transmit that force to the rest of the boat without the engine/pump alignment flexing.

A suggestion is to rivet your bracing in & then take it to a weld shop to have them run some beads.

[Superfly Silverfox]

Find a source of reasonably priced aluminium angle. Your going to need a bunch of it.

You will want to attach the jet ski tunnel insert to angles running fore-aft. Those need to be attached to the existing cross ribs & the transom if possible. The more you can tie the structure together the better.

You will have 80 hp pushing on the transom & it needs to transmit that force to the rest of the boat without the engine/pump alignment flexing.

A suggestion is to rivet your bracing in & then take it to a weld shop to have them run some beads.

Thanks again for the sage advice!

I have a aluminum spool gun so I’ll weld it up. The rivet / screw idea USA good one.

You think that the jet ski insert needs to be attached to both runners? Hmmm.

I had in my head to cut it down small to just the jet drive? I need to see more pics I guess.

Thanks again and please if you are reading this and you have knowledge let me know! I’ve done a fair bit of work but always appreciate the advice of been there done that!

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[CedarRiverScooter]

Probably 100 ways to put your boat together. The advantage of using enough of the jet ski bottom to include motor mounts is that you don't have to engineer the motor mount positions. The engine needs to be in exact alignment with pump. You will need an alignment rod to check this as you are screwing & gluing the insert down. The insert won't have near the stiffness as it did in entire molded hull & so it would be easy to lock in a warp if you aren't careful. It took me forever to shim the alignment on mine (Polaris).

You can buy alignment rod for about $60 on Ebay or rent one from a guy in Wisc., He is a jet ski aftermarket shop, forget the name.

The pump inlet needs to be the lowest point on the bottom. If you make your own mounts & limit the plastic insert to just the intake & pump that would be a much smaller hole in bottom, which is a good thing.

Not sure of your question regarding attaching to both stringers. I put them on both sides of insert. I notched the cross ribs back so the angle is down tight with hull skin & welded the rib ends to angle. Front of angles make tee joint with unmolested cross rib in front of engine. I cross bolted the insert to the stringers in about 6 places each side. The plastic insert is sealed to hull with 3m5200. The jet pump 'box' is screwed & glued really well to the transom.

Hope this makes sense. I had pictures until my phone went swimming.

[Superfly Silverfox]

Probably 100 ways to put your boat together. The advantage of using enough of the jet ski bottom to include motor mounts is that you don't have to engineer the motor mount positions. The engine needs to be in exact alignment with pump. You will need an alignment rod to check this as you are screwing & gluing the insert down. The insert won't have near the stiffness as it did in entire molded hull & so it would be easy to lock in a warp if you aren't careful. It took me forever to shim the alignment on mine (Polaris).

You can buy alignment rod for about $60 on Ebay or rent one from a guy in Wisc., He is a jet ski aftermarket shop, forget the name.

The pump inlet needs to be the lowest point on the bottom. If you make your own mounts & limit the plastic insert to just the intake & pump that would be a much smaller hole in bottom, which is a good thing.

Not sure of your question regarding attaching to both stringers. I put them on both sides of insert. I notched the cross ribs back so the angle is down tight with hull skin & welded the rib ends to angle. Front of angles make tee joint with unmolested cross rib in front of engine. I cross bolted the insert to the stringers in about 6 places each side. The plastic insert is sealed to hull with 3m5200. The jet pump 'box' is screwed & glued really well to the transom.

Hope this makes sense. I had pictures until my phone went swimming.

Well you answered my next question- what adhesives !

I have and maintain a Airboat and live on the river. I’m considering using poly after the fact to toughen her up too.

So I’m gonna just say this is what I’ve done today and how I see it.
I took that advice to tie to those stringers and to use as much ski plug as possible. So I cut and measured and here is the project this
So I’d like to get some aluminum and make a cover for the ski bottom.

I have no idea what needs to be replaced or repaired as I reassemble the jet and engine components?

SS fasteners trough the cover , ski and nutted with a sealing washer.

The transom needs angle , glued and screwed. Wood or heavy aluminum bracing ?

Dear lord what have I done, hahahahaha!

[CedarRiverScooter]

That is a great start. Shoot for 1/8 inch gap for the 5200 sealant. I primed & painted the aluminium for 5200 adhesion. The plastic is fine as is. 5200 doesn't stick to bare aluminium very well.

[Superfly Silverfox]

That is a great start. Shoot for 1/8 inch gap for the 5200 sealant. I primed & painted the aluminium for 5200 adhesion. The plastic is fine as is. 5200 doesn't stick to bare aluminium very well.

10-4! 1/8” gap!

[CedarRiverScooter]

I see now that your boat already has fore aft stringers. So no need for the angles I mentioned. Just tie the sled down to what you have. Of course extra bracing is not a bad thing either.

[CedarRiverScooter]

"So I’d like to get some aluminum and make a cover for the ski bottom."

I have a flatbottom boat & had to make a V shape from about 8 foot in front of transom back to jet ski insert. Before that any wave I hit would feed air to the pump. Made slow going in a chop.

So a suggestion is to use the pc that you cut out as a cover. Maybe bend as much V into it as you can. Just need a smooth transition right before the pump inlet. The bottom keel rib is a plus.

Sorry for the kibitizing, getting slow here in the Covid Midwest.

[Superfly Silverfox]

"So I’d like to get some aluminum and make a cover for the ski bottom."

I have a flatbottom boat & had to make a V shape from about 8 foot in front of transom back to jet ski insert. Before that any wave I hit would feed air to the pump. Made slow going in a chop.

So a suggestion is to use the pc that you cut out as a cover. Maybe bend as much V into it as you can. Just need a smooth transition right before the pump inlet. The bottom keel rib is a plus.

Sorry for the kibitizing, getting slow here in the Covid Midwest.

That’s the plan is the old cut out. Remove the center rib and weld them back in. Maybe build a keel from angle.

Ordered the 5200
Gotta get welding gas, wire, fiberglass
And lots of aluminum scrap.

Merry Christmas y’all!

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