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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 02:03 

Joined: 22 Aug 2017, 16:03
Posts: 15
Ok, here we go. I am excited to get this under way, but nervous as all get out.

I picked up the jet ski today. It is a 1988 seadoo sp with a 587 rotax. I got it for $75

The motor is torn down already, and it looks like everything is there except the front cover for the flywheel/stator housing. The impeller shaft looks like it might be bent a bit, but I will check that later.
I should be able to get it straight again.

I think gluing the hull in will be the best route. There is a natural flat on either side of the jet ski "keel" that will mate up with my flat aluminum hull. I think using it in this way should eliminate the need for any spoon, since the jetski hull will do it's job of displacing turbulent water and bring up solid water for the jet. The jet already has a gravel grate on it, so I am excited about that. The impeller is chipped, so it will need dressing.

I wanted to buy a different unit that had trim, but it was pushing the budget for this week. I figure I can at least get things planned out with this $75 unit, and if I get it back in good shape, I will use it until I find something better.

I will try to get some pics in the morning. I drove for 10 hours today, trying to turn 3 trips into one. I had to pick up stainless for my hangers anyway, so I picked up some oil and the jet ski on the same trip.

If anybody has some really good tips, I'm all ears.


IMG_5726.JPG


Last edited by IkeCarlson on 19 Sep 2017, 14:41, edited 1 time in total.
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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 09:06 

Joined: 13 Nov 2014, 08:01
Posts: 734
Ike - Sounds like you have a good start on your project.

What size boat are you building?

I would keep it as light as possible.

Sound proofing will go a long way.

Also, they tend to porpoise, so install your fuel tank & driver station as far forward as you can.

Good luck!


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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 09:59 

Joined: 22 Aug 2017, 16:03
Posts: 15
It is 14' semi v with flat bottom in the rear.

I figured it would try to porpoise, and that is why I wanted the trim nozzle. I want to keep the bow planted if I can. I am building this boat for river/shalliw water use, since I live on rivers in WI, and they can go from 15' to 6" in a blink. I discovered that last week when I tried to fish the Red Cedar with my outboard. Even with it tipped up, I was kicking rocks. The prop is beat up a bit, and I almost didn't make it back upstream with it so shallow/fast. A jet is the only good answer I can find.

My idea to prevent porpoising is to angle the thrust down about 7* from level. I am still working on this, but figure I can either redrill the steering nozzle so it points down, or install an extra 1-2" on the nozzle that points down a bit. Has anyone with trim actually measured the angle to know what it is on plane without porpoising? I am guessing at the angle here. If someone could measure their angle with it set to cruising trim, that would be great. I am hoping for 20-25 mph from this setup, since the river can hit 15 mph in the shallows.

I may put the battery and fuel tank up front under a short deck. My biggest problem is space. At 14', this boat is on the small side. I want to fit 3 peeps for fishing. The motor takes up 3' in the stern, so that leaves 11' for feet, tackle, possible livewell, battery, fuel, etc... I plan on taking out some seats and installing a low floor with foam under it. This will help with flotation and will give more room.

The rear may get decked over to make storage next to the motor, or I might just use the jet ski seat for the engine cover and sit on it. Not sure how that will go yet. I do need to cut away the parts of the jet that I know I won't be using. I do know that the jet ski hull weighs as much as my whole boat. :shock:

I do like that the weight will be more balanced with a jet vs an outboard, but it takes up so much space. It is like laying the outboard down in the boat to use it. I will be clearing space in the shop today and doing some measuring/figuring. I don't want to cut up my new boat and ruin it. :oops:

I see lots of jon boats online like this but not many semi v hulls. The semi v should help with cavitation in the first place.

If anyone knows where I can get a cover for the stator housing on a yellow motor, please let me know.


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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 15:59 
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Joined: 05 Feb 2016, 03:42
Posts: 399
Location: Langley, BC
Couple of FaceBook groups that will be helpful. Franken Jet Jons and JetJon unlimited. Lots of useful info there and I'd be dubious about glueing fiberglass in there. One good hit on a rock and you are swimming.


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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 17:25 

Joined: 22 Aug 2017, 16:03
Posts: 15
I plan on using 3M 5200 adhesive and some stainless carriage bolts. From what I hear, 5200 does not let go.


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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 17:57 

Joined: 13 Nov 2014, 08:01
Posts: 734
Sounds like a good plan.

I will measure the thrust angle of mine - I modified the pump mount to be able to push down more. Works fine but was lots of work.

You should get 30 MPH+ with that boat.

Hope you get it done in time to use it this fall. Mine took me all winter.


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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 18:09 

Joined: 22 Aug 2017, 16:03
Posts: 15
I am in the process of planning, tearing it all apart, checking things out, and figuring how to rig the steering so I can still fish without a big control pole in the boat, lol. I don't really want a console, but may end up with one. I will continue to use the boat as is until I am completely ready to cut the hull. I am hoping to have it done in a few days once I start cutting.


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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 20:08 

Joined: 13 Nov 2014, 08:01
Posts: 734
I measured my tail cone, it is just shy of 5* down. I have 1648/750 polaris with no weight up front. The other day, I was alone in boat & at WOT (about 35 mph) it was just starting to porpoise going into the wind.

Stick steer is really easy to rig & also easy to get used to. You could use PWC seat & straddle the engine if you want to save space, but I would think that would get old on a long trek.

One thing that might help - 3M5200 is kinda runny & I had problem with it running out, esp on vertical seams. The last revision I used tape on seams to contain it, worked well.

Good luck.


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 Post subject: Alumacraft F Jet Build
PostPosted: 26 Aug 2017, 20:15 

Joined: 22 Aug 2017, 16:03
Posts: 15
CedarRiverScooter wrote:
I measured my tail cone, it is just shy of 5* down. I have 1648/750 polaris with no weight up front. The other day, I was alone in boat & at WOT (about 35 mph) it was just starting to porpoise going into the wind.

Stick steer is really easy to rig & also easy to get used to. You could use PWC seat & straddle the engine if you want to save space, but I would think that would get old on a long trek.

One thing that might help - 3M5200 is kinda runny & I had problem with it running out, esp on vertical seams. The last revision I used tape on seams to contain it, worked well.

Good luck.


So your fuel and battery are in the rear? I have thought about using the seat, but it would be better to use my swivel seat mounted over the motor. Thanks for the tip on the steering and 5200/tape.

I am still trying to move things around in the shop so I can get some decent pics and some more working space. I have an 80 foot shop and it is full of junk, has been since before we got this place. I just finished replacing the old fuse box with a proper breaker box that should have enough breakers to keep me busy for a while, lol. The floor is mostly dirt, with 16 feet of concrete on one end.
Insulating and putting in concrete are on my list.


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 Post subject: Alumacraft F Jet Build
PostPosted: 27 Aug 2017, 01:43 

Joined: 22 Aug 2017, 16:03
Posts: 15
I drilled out every rivet on the jet ski to separate the hull, but it looks like they are epoxied together.
Can you tell this is my first jet ski rodeo?

I will have to cut the top off. I am not looking forward to fiberglass everywhere. I will have to drag it out in the grass and do it. :( I will set up my dust deputy and shop vac to keep the dust down.
This is why I like aluminum boats, lol.

Sorry for no pictures yet. I have some but need to know how to post them. Can anyone tell me the procedure for posting pictures on here?
Maybe I should just make vids and upload them to youtube. :?:
Let me know what you prefer.

Once I get the hull apart, I will be able to do some more planning. I measured and jet ski hull and the boat hull, and it looks like the jet ski hull will sit about 3/4-1" below the boat hull or even with the original keel. Perfect. Some of this is going to be seat-of-the-pants fabricating, but that is how a lot of my projects go. I have a general plan in my head and make it work as I go along.

I plan to weld/braze the gunwales where they meet to help stiffen the boat. The joints on the bow move a bit. I need to get some alumaweld or break out the torch. I have not welded aluminum in years, and I haven't done it much to begin with. :o

Anyway, I should have more progress, and hopefully some video to share, on Monday.


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 Post subject: Alumacraft F Jet Build
PostPosted: 27 Aug 2017, 08:40 

Joined: 13 Nov 2014, 08:01
Posts: 734
Yes, all weight is in last 4 feet of boat.

I used a sawzall with xtra long blade to cut ski hull apart.

Do it outside with long clothes, eye & respirator protection.

I have found pop rivets to be pretty effective. I tabbed the alum angle by notching, then bent tab over to attach to the boat's ribs. Also used extra laps, overkill is good when you haven't done any strength calculations!

Alum brazing is not good, too much heat, warps badly & isn't strong. If you are removing bench seat, that structural strength needs to be replaced.

Sealing up the vertical transom joint was a challenge.

I wish I had thought more about serviceability during design phase, as I have to take things apart to get to other stuff.

Edit - Another game plan would be to rivet your braces for position, then haul it to a weld shop to have the welding done. TIG or Mig is great if you have the right equipment & skills.


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PostPosted: 28 Aug 2017, 02:35 

Joined: 05 Jun 2017, 18:20
Posts: 3
To combat porpusing, have you considered adding sponsons to add flotation behind the center of thrust or have you considered a trim tab system?

Sent from my SAMSUNG-SM-G930A using Tapatalk


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 Post subject: Alumacraft F Jet Build
PostPosted: 28 Aug 2017, 10:26 

Joined: 22 Aug 2017, 16:03
Posts: 15
I have considered sponsons, but I am not sure how I would attach them. I don't really want to use trim tabs because it is another thing to get caught on. I go throung some crazy places and I think the trim tabs would get caught on something or my line would get caught in them.


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 Post subject: Alumacraft F Jet Build
PostPosted: 28 Aug 2017, 10:30 

Joined: 22 Aug 2017, 16:03
Posts: 15
Does anyone know if an adhesive primer is required with 5200?

Would u-418 work as well? It has the same strength, elongation, and durability specs as 5200, but is a bit thicker, which worries me some.


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 Post subject: Alumacraft F Jet Build
PostPosted: 28 Aug 2017, 12:22 

Joined: 13 Nov 2014, 08:01
Posts: 734
Glass urethane is not something I have personally used. If it is much cheaper, it might be worth trying. I used S30 roofing urethane on part of my build & can say it is not as tough as the 3M5200.

No primer needed with 5200 but do ruff up the surface with 80 grit. If you want to prime it 1st (this is OK too), then use a self etching primer.


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