Over ambitious 12' Sea King jet jon

[deadkitty]

Hello All-

I've been lurking these forums for quite awhile, and now I finally own a jon boat. Went out and got some good deals on the boat and ski. It's a Sea King 12 footer, 32" wide; the ski is a 94 kawasaki xi with a ported 650 engine. My brother and I are taking on quite a project this winter in hopes to have her seaworthy by spring. We are essentially combining a couple builds we've seen on here and across the web. The first thing we want to do is widen it to around 50" to make her nice and stable. From there we plan on dropping the ski motor into to it :lol: then decking it out and adding all the creature comforts and pretties. We know there's the possibility of complete and utter failure. But we say "go big or go home", lol.

Anyway, should be fun. If it fails it will be a good experience to learn from.

Any words of wisdom as we embark on this journey?

do's and don'ts? (and no don't do it is not an option... we are goin for it!) :LOL2:

I'm sure we will have questions along the way and we'll be sure to ask.

sea king 12'

kawasaki xi

motorguide stealth 300

 

[PSG-1]

Always nice to see another jet john project!

OK, as for how to widen, this is what I would do......

You first need to make the hull rigid where you're going to cut, or it will fold like a beer can, you will have a helluva mess. So, the first thing you have to do is place a longitudinal structural member on each side of the cut. This structural member needs to be one solid piece, and it needs to be welded along its length, with numerous stitch welds. It can be made from square or rectangular tubing.

For the boat you're working on, I would put the tube about where the first gutter is on each side. Get ready to scrap the middle section. Cut a few inches on the inside of the first gutter, and on the inside of where you put the longitudinal member, on each side, all the way down the boat.

Now, you'll measure the 2 halves of the boat, add up their width, then see how much more you'll need to make your boat the desired width. Using some .090" or .125" aluminum sheet, make the center piece that will run the full length of the boat. You'll have to cut and weld, or brake it for the bow and transom, and of course, there will also be a splice or two someplace, as sheets are only 8-10 feet in length.

Wherever you make the splices, you need to back it up on the inside with an additional piece of material, for added strength. The hull plate joints/splices will be butt welds, which is not the strongest weld in the world, therefore, it needs to be reinforced anywhere you have it spliced.

Where the hull plate joins to the 2 halves of the existing hull, you can either cut it 4 inches wider than the gap, then do a 2" X 90 degree brake on either side, this will allow it to come up and meet the edge of the longitudinal square tubing that you put in earlier, and you can weld to this. If you don't have a brake, you could always weld some aluminum angle to the inside of the hull splice plate, then weld this angle to the square tube inside the hull.

Either way, once you have it stitched to the square tube, then you'll have to run your continuous seam from bow to stern, on either side. BE SURE TO PROPERLY CLEAN THE METAL BEFORE MAKING THIS WELD. This weld needs to be watertight, and if you have any paint, corrosion, or other contamination in the base metal, it's going to compromise the welds.

Your center hull plate/splice, whatever we want to call it, does NOT need a strake. In fact, putting one on there is the worst thing you can do if you intent to run a jet. Leave it flat, don't put any strakes on it, this will help to eliminate cavitation issues.

Well, that's about it as far as how to splice your hull. When it comes time to start installing the engine, etc. check out my aluma-jet thread, or ranchero's jet boat build, for some ideas. Ranchero's build is probably the best fiberglass pump build I've seen yet, and mine is probably one of very few bolt-in aluminum pump builds out there. So, whichever route you go, one of these 2 boats will be a good example to use as a guide.

 

[lckstckn2smknbrls]

No don't do it, at least with that hull. This is a very light duty boat see how the ribs don't go up the sides. You should look for a stronger hull to start with.

 

[deadkitty]

Thanks for your input PSG-1. We will definitely be reinforcing the snot out of the whole boat before we are finished no need to worry lckstck. Will update once we get some work done, soon as we can find the always elusive time and money....

 

[PSG-1]

As far as the boat not having vertical ribs.....that's not a problem if you have some 2x2x 1/8" square aluminum tube. :wink:

You can either notch/bend, or angle cut each rib where the gunwale meets the floor, and once you are satisfied with the angle and fitup, weld the notched or bent section, reinforce it with a piece of 1/8" X 1& 1/2" square aluminum plate, to fish-plate the area where you bent or cut it to make the angle.

In fact, I'd go ahead and shi+ - can those existing ribs, and replace all of it with the square tubing, making each rib to specifically fit where required. If you do that, along with the vertical sections, you will have a strong hull, no question about it.

There are no problems with building boats, only solutions. There's a way to do anything....of course, it should be noted, there IS a right way, and a wrong way.

That said......I've met and screwed enough goats of different varieties, colors, sizes, shapes, dispositions, etc, I can pretty much tell you the difference in how to do it the right way and the wrong way, because each goat in life comes with its own specific detailed set of instructions on how it is to be screwed, and those instructions are not to be deviated from in any way, shape, fashion, or form, or there will be consequences! :LOL2: :mrgreen:

 

[veedubfreak86]

Looks like it should be a good project hope it turns out well

 

[deadkitty]

Little update, we've finally cut the jet ski down to just the part that will be installed in the boat. Next up is widening the boat once we go out and get some aluminum. Here are some slicing and dicing pics:

 

[TxTightLiner]

These type of mods really interest me.
I have been thinking about building one myself.
I will be following this one!

 

[PSG-1]

Just curious if you've made some progress on your build? Looking forward to some updates, and some pics!

 

[deadkitty]

We have made some progress and decisions had to be made we scored some awesome 12'x4' .050 aircraft aluminum sheets for $10 a pop at a scrap yard to fill the center of our wide barge of a jon boat. However because of the thin sheets, we decided to nix the "jet" part of our build because even when we doubled the sheets we just didn't feel comfortable mounting it in the boat. We were able to get some 1/8th inch thick diamond plate for the transom and some thinner diamond for the bow. My uncle donated a fiberglass boat with trailer to our cause, we then stripped it of its 18hp johnson as well as all the controls. The trailer will be nice once I get around to overhauling it, but definitely gotta finish the boat first. My brother is moving much further away than the 6hrs away he lives now at the end of the month, so we want to get the boat water worthy in the next 30 days. The current goal of the boat is to be a 1263 with center console steering decked front and back. Wish us luck [-o<
Here are a couple pics of the in progress work:
I only got a few on my phone, my brother has a bunch more that I will post later.

 

[PSG-1]

Nice work on the widening of the boat! Looks really good from what I can see in the picture. 8)

Sorry to hear you scrapped the idea for the jet, but you're right, trying to mount it to .050" isn't the strongest design. And doubling up on .050" isn't the same strength as a sheet of .080-.100" material.

In order to install a jet, you'd need to build a framework to support the engine and pump, and that's a good bit more work.

 

[deadkitty]

Well, apparently the title of this thread was a self-fulfilling prophecy....
My brother moved far away, and I ended up moving about an hour and a half from where I used to live to the suburbs with much less "project" room. Essentially, I gave up the project and sold the whole thing to a very enthusiastic guy who was stoked to get it, plus I gave him a great deal compare to what I put into the project. I took the money and went out and bought something fishable. I will finish out this season with it as is and probably over the winter start fiddling with it. It's a 12' Valco that came with a non-functional '62 Johnson seahorse (with major overhaul needing to be done), sold that and picked up a '72 9.8hp Merc 110, it's red an black and matches the boat
Thanks for all the advice on the other project, I think I will be a bit less ambitious with this boat, that way I can keep on fishing with it even if it is mid project.

 

[DrNip]

Man that sucks. Good luck on the new boat.