The multi-purpose SISSY DO isn't fancy or streamlined, just a sturdy, basic boat that gets the job done. Learn how to fiberglass the easy way, by looking over the shoulder of an expert who is working on actual boats. 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. A couple of fellows working on a long weekend should be able to slap her together without problem. 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. The plans and patterns are especially complete with step-by-step building photos of exactly how the original was built, including written text and material list. Up to 10% by re-spacing the frames from the aft end of the stem to the transom a proportional amount. 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.
With an older sister that frequently was called on to "do" things for her little sister, I immediately said, "Sissy Do". As for riding ability, it will bring you back on any type of water a boat of this size and power should be out in. 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. 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.
You can draw it up on the beach and walk ashore, something that's not so easy with a vee bottom hull.




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