Tinny widening options

[SailingFan]

Ok, all, this one is a doozie, and I realize I am doing something that is not normal.

I have a 12 foot jonboat that I am trying to bring to a greater buoyancy, and have arrived on a plan of sorts. The plan involves attaching two side-hugging pontoons of sorts against the hull (one on each side of course) and then compartmentalizing them to hold rods, various cold drinks, etc., but mostly they calculate to extend the gross buoyancy of the empty jonboat an additional 800-ish pounds! As this is a tiny tinny, the thing is light, but the bigger issue is that as a jon she has about 4-6 inches of freeboard with just my fat butt in there, no outboard, and a battery/trolling motor. She is also over plate capacity at that point. I don't have the resources at the moment to get a larger boat, but I do have enough to add those saddlebags (that are 9 feet long each) and boost the stability as well (her beam before hand is 32 inches!), and she becomes more jet-ski resistant at the new beam of 44 inches and a boost of more reserve buoyancy addition than she has in the factory state WITHOUT my butt on the pilot's bench.

So, I have a question that I am hoping someone can offer insight on. I have MANY sheets of 6 MM ply I was hoping to dedicate to a launch for my sailboat later on. I have about 2 gallons of useful epoxy on hand. It won't be enough to seal and glass the ply in the normal manner so I am thinking that material is out.

I have ability to snag a couple sheets of 1/2 nominal inch CDX and have all the structural support (2x4 pine!) plus fasteners to assemble the pontoons with that thicker ply and bolt it to the hull with fender washer backing plates.

I need to figure out how to seal the ply for intermittent interaction with water and how to bond the seam between the hull and the 2 box shells (a side above, one below, and a fore and aft) to the jonboat aluminum.

The boat will not live in the freshwater, and will not be in saltwater most likely at all. It will be used at most overnight on shallow water inland areas. I just know what the ski boats and jetskiers around here are like when I had a v-hull tinny, and they will try to drown me if I am in a jonboat.

Oh, and this is definitely a Frankenboat, and I will be uploading pics as we go if I can work out the method. Can I still use photobucket, moderator?

The end result will be a far safer and more useful jonboat for maybe 2-300 bucks expenditure (maybe a LOT less). Interestingly, my title says it is a 154 footer, so if I need to extend something to make it more accurate it is actually a good thing. Otherwise I have to get it retitled! I don't remember how that happened, but I think it was because I did not have accurate info from the guy I bought it from several years ago. It was stolen and I just got it back!

I am not equipped or knowledgeable in welding aluminum. I can wire-weld steel, so I may be able to use steel sheet instead of plywood? I don't know what to do...

So, what can I do to make this redneck construction work for occasional immersion of plywood, or of some other material within my poor budget (any more and I would just buy a bigger boat)? Right now, she is a dented canvas that can be made into something far more useful without having to toss her aside. She does not leak much either!

[Wotname]

Use the epoxy to edge seal the ply and any joins, use paint to cover the external surface of the ply.

Back in the day, dinghies were built in ply without epoxy edge sealing and they lasted pretty well.

[SailingFan]

Wotname, I was considering using oil-based Kilz if I went the paint route as a primer, then hitting it up with an oil-based cover paint, something of about three coats thickness. That would be pretty cheap.

So what would you suggest for a sealant/adhesive to make the seal around where the "pontoons" meet the hull? They would be throughbolted through the gunnels with vertical and horizontal 2 x 4s. and that would allow me to compartmentalize them for putting in storage for rods and the like (plus makes me feel more comfortable about potential leaks in any particular part of a pontoon). I really don't want to use 5200 at 24 bucks a caulking tube. I was considering siliconized caulk, but not sure how it would respond to UV..

I currently can seal all the edges with epoxy, but don't have enough to completely seal the plywood, I don't think. I am thinking the oil based primer in combination with the paint might do it, but not sure..

[SailingFan]

Now I think about it, I could laminate two or three layers of the Luan (6mm each) with a layer of Titebond 3 between each lamination, finish with a layer of Titebond 3 on the surfaces and edges as well but cover that with something like muslin, then paint the result with an oilbase Kilz layer and then a couple or so layers of more oil base. That would harden things, keep intrusion at lower risk. I still need a way to lock water out between the hull and the contact edge of each box though. I don't think Titebond 3 sticks to aluminum... Oh this thing is going to be "something" to "behold"... Trying to keep a workboat finish on it and just get some life out of a 1970s or older jonboat on weekends while still stuck at home.

[SailingFan]

Just wait until the mast goes up.. Will be an occasional catboat too!! HA HA HA!!

[Simi 60]

https://boatcollar.com.au/

[SailingFan]

Simi, that is the effect, more or less, that I am seeking, but it is $1200 AUS prior to shipping costs to Florida from Australia. What I have in mind also gains a crap-ton of storage for light items like tackle boxes, rods, float-coats, wire runs in 1" pvc pipe, whatever. So more boxy and tall for me, but yes, that is pretty much what I have in mind, but hollow and lidded, broken up in compartments for use as storage and to prevent progressive flooding while boosting buoyancy by something like 800 pounds. As the boat this size only has about 600 pounds to being with, that is a substantial increase in flotation with an additional boost to stability through widening the hull form as well. Thanks for the link regardless as it confirms to me that I am not entirely off my nut...