JEM Watercraft

I began my cutting today. The plans are very easy to follow, thanks for that Matt. Everything measured out easily on my first peice and I got most of it cut out. Sorry no photos yet, my digi-cam is in the shop at the moment. Funny, it looked like it could take more abuse but I guess they are quite fragile. Anyhow, I will start posting pics of my progress as soon as I can.
--Garrett

A quick question for Matt. Is it possible or worth the effort to laminate 2 peices of 4 mm okoume together in place of the 6 mm bottom peices? I am a little concerned about oil canning, and I think I will have enough ply left over to make 2 extra pannels. Any thoughts would be appreciated. --Garrett

It's possible but I'd wait until you get her on the water at least once. I think you may only need a few strips in key places, if any at all.

I cut some more peices today, I have to call RAKA tomarrow to order my epoxy and glass. So far I am enjoying this project, although I am just getting started. Matt, I forgot to tell you that I am building this boat for my Wife as a congrats present. She doesnt weigh all that much, will that be better as far as the oil canning goes? Im not sure if the weight of the paddler has anything to do with it or not. More later --Garrett

well it kinda does. The bottom of the hull can flex down as well as up. But it doesn't matter much.

Gken,

It's pressure of the boat against the water that causes oil canning. Gross vehicle weight (tare plus pay loads) total some factor, and the boat presses that many pounds of water out of the way. This causes pressure against the hull - that's what holds it up and keeps it from sinking.

If you get flexing, simple strips running parallel to your keel (longitudinal centerline of the boat) are a good place to start. Say, one on each side of the keel line, running over the areas of maximum flexure. These can be the same plywood from which you built the boat. Say, 1/8" think X 2" wide for as long as you think is needed.

After you try this, if you still get flexing (oil canning), a couple of shorter, auxiliary strips would add additional stiffness if needed spaced near the longer ones, over any area of flexure.

All of these strips should be placed symmetrically, so the left and right sides of your boat match. These can be placed either inside or outside the bottom. I'd place them inside unless you feel your boat isn't tracking well. then, strips along the outside would aid that. Otherwise, a clean, slick bottom will give less drag and best performance.

I'd advise against strips inside the boat, running crossways. These would inevitably trap water and debris. This makes the boat more difficult to clean up, and could eventually lead to damage.

Oh - I forgot to say that, If Matt tells you anything different than what I say, follow his advice.

I generally recommend strips from left to right because of the nature of thin plywood and the laminated layers. You generally have less grain strength go from left to right in an assembled boat.

The best solution is additional layer(s) of fiberglass but that is not always practical.

I am going to place my order for my glass tomarrow, should I ask for more than is reccomended so I can put 2 layers on the hull? Should I put it inside, or on the bottom? I promise next time around I will know more. Thanks again for your help. --Garrett

no worries. I bet 10 other people will read this and wonder the same thing.

If you want to go with extra glass, order 3 yards extra. That should be more than enough. Glass inside and out.

I should put more than one layer inside and out? Will three more yards be enough?