I was wondering if I could get a bit of feedback, or a few questions I have answered about building a small ( 4' x 11') flat bottom boat. If I make no seats in the boat, will just the epoxy coating and the 'but joints' with cloth be strong enough? From a structural stand point, not having a midship thwart and a bow piece (breast hook, foredeck or thwart) the sides of the boat will likely flop around a good bit.
It would be possible to have a small thwart at each end of the boat with reinforced sheer clamp and maybe a topside stringer, to provide the open layout you desire. Location: maine A 4 foot wide boat as described would have quite a wide bottom, and it's strength (to resist transverse flexing) would be achieved by having a reasonable amount of rocker or making the seats full boxes for flotation and a set of transverse beams. In your case, wanting to have a clear open area, you can't just modify an existing plan without help from someone knowledgable. PAR will, I'm sure, provide you with a good set of plans or modify to suit, but by all means maske sure the bottom is rigid enough and that the connection to the sides is well braced.
In the future, I may purchase plans and modify them to suit my own design, but for this first project, I think I'm going to just go with this basic design and consider purchasing plans in the future for something a bit more complex, even though I have questions about this 'simple' design!
One of the goals of this little project is to just keep it as simple and cheap as possible for now. In the attached picture, there is the rough outline and dimensions, as well as the proposed 'skeleton' of the boat made from 2x2s. I would be putting cloth and epoxy on the outside and inside of all seams, but should the entire boat surface be coated as well, or just the seams? Again, the boat will be used for shallow, calm water, and will have rub strips along the underside for added stability and for protection from rocks etc.
Location: Alliston, Ontario, Canada At the very least put a bit of curvature in the bottom as it will help stiffen it and prevent oil-canning.
A bit of a curve will do the same thing for the sides: they do not have to come all the way in to a point at the bow. It is actually easier to do it this way than the way you have sketched: ply bends easily and it will save you have to make joints that are strong enough and waterproof.
Use seats as frames, and hide flotation in them Three cavities, both bow and stern shelves and the center thwart (seat).
Location: Ontario Hey, It's been awhile, and I thought I'd update this thread with what I ended up doing.


First, thank you to everyone who gave their advice and input in this thread, it was much appreciated, and much needed. I decided not to put seats in it, because I want the space for carrying things I have in it, but I included a 2x2 across the top and bottom near the middle of the boat. I have more pictures I could show, but it seems that I'm at my size limit here with the 3 pics I've already posted in this thread. Anyways, I wanted to come back to say thanks, and also to show you guys what I ended up doing. When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Well, I can get this on top of the car by myself, but it works a lot better when Matthew or my girlfriend helps me.
We let the paint dry in the summer air for a day or two, and then Matthew and I decided we would take it on its maiden voyage to a nearby lake in the Columbia River Gorge near Portland, Oregon.
This boat is meant for protected waterways, which means hardly any waves or wake, and no a lot of heavy current, so this little lake (some might call it a big pond) would be a fairly safe place in case it sprung a leak.
We placed it in the lake, and anxiously looked inside to see if any spouts of water were welling up.  Nothing. I let Matthew get in first.  No water, and the boat seemed remarkably stable for such a small craft. My son, Matthew, and I learned how to fiberglass via youtube instructional videos, a few websites explaining it, and just plain ol’ following the directions on the resin container. But, we had put in too much work for me to scrap it, so I figured I would go back out, mix a little bit of resin with a large amount of catalyst and then quickly add that to the stuff already on the boat and maybe it would all kind of mix wet-on-wet, like one of my watercolor paintings.  Obviously, this is something I would never do again, but I had to salvage it, right?
So, the next section of fiberglass worked a LOT better once I mixed it correctly with the catalyst. We added Bondo to the cracks and seams.Here is a bow-view of the hull with the keel and runners to protect it from underwater rocks and trees. After I showed him how to measure, and use the chop saw, I let Matthew do the seats by himself.  He did a very good job, and I think it gave him a boost in self-confidence.
You could make one from your own design and it would perform to some expectations, but you could also get a set of plans (I have low cost plans for just the boat you describe) that will optimize the shapes, keep it simple to build and answer your questions about how thick things need to be, plus where to precisely put them. I've spent a bit of time reading the forum and looking at other 'jon boat' plans on the net, and I've modified my initial design.


Does this plan look stable enough now, or are the few 'extra' transverse beams that I've now included overkill since it will be epoxied? The entire underside would be epoxied of course, but does the entire inside need it as well, or just the seams?
Curvature can make the ply act as if it was twice as thick, without the weight and cost, and it will go faster and smoother. If you make the front plate (pram transom) slope a bit the boat won't come to an abrupt stop when you run into a wave form a bigger boat (see PDRacer again). Well, I realized that my square design that I had initially come up with wasn't going to cut it, so I took the advice to make some curves in it. I used a lot of epoxy on the bottom, more than I should have, but it was my inexperience at 'fiberglassing' that caused me to use so much.
I also made sure we both had PFDs (or, personal flotation devices) in the form of life vests. I plan to put narrow 'runners' on the bottom of the boat for extra stability and protection from rocks etc. I know it dries very hard, but I want to know if the way I'm picturing doing it will be ok. An added benefit would be better performance from the little outboard and improved maneuverability as a result of the shapes employed in the design.
Most ply boats have a stiffening member along the top (sheer) of the side planks which is called a gunnel. You may find that it will be fairly easy to twist it without any bulkheads to give it rigidity so a couple of knees from side to bottom might be in order to help with this. New 18% over drive gears, all new bearings, gaskets, and seals 800Hp - New front carpet installed - New adapter plate custom made for leveling carburetor on intake manifold Holly 780 CFM D pump Moved power train forward 9 in. 4 hp is just on the border of enough to get you planning if the boat is light enough but I bet not so internal framing is not so necessary.



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