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Boat Design, modeling and material capability

Posted by DavidCline 
Boat Design, modeling and material capability
January 20, 2017 07:07PM
So, I've been modeling a fair amount lately, digitally and in 1:12 with modeling wood. I think I'm about to dive into a build of a 12'x48" McKenzie. I like the shape I'm getting out of taking the lines Roger lays out in his book for the Hindman 16' double ender with transom, and simply reducing the X-axis measurements by 20%. Other measurements remain the same.

Lofting of this design shakes out pretty well, with one or two offending points. One frame (#5), does not fit the model, even though all frames are built to the lofted dimensions. It's warping my brain to figure out why this frame does not conform. Any ideas on how a single frame that matches the lofting would not fit into the assembled boat?

Next question is, when modeling, how do you know or feel when a curve is going to be too radical for the real materials (1/4" marine ply, probably Hydrotek) to make the bend? For this design, since only the length is altered, the sides and floor will have less length to bend to the same width/rocker dimensions as the full sized boat. I think the reduction on the x-axis puts this boat in the same ball park as the HD, in terms of width vs. length, and the bend required in the sides. Other than "listening to the wood," anybody have any comments or suggestions on how tight a bend 1/4" ply will make safely?

Lastly (for now), I plan on oiling this boat in and out for ease of maintenance (I despise sanding flaking paint/varnish). Any sense on how much epoxy I should order to have enough for scarfing, frame assembly, and a bit left for on-river repair?

Re: Boat Design, modeling and material capability
January 20, 2017 07:24PM
RE> "how do you know when a bend is too much?"

That's why I like to design with a full sized model, as outlined in the sticky "design" post at the top of this forum. I try to get a good idea about where I'm headed with foam board and a hot melt glue gun. But I prefer to work full size with adjustable rib-like formers to get what I really want, and to find out how much is too much. I never have much confidence staring at a computer screen. I have a little more confidence looking at a 1/12th scale model. A lot more confidence looking at it full size.

On the other hand you can bend 1/4" plywood a lot. 3/8" plywood not so much but still more than you think, by soaking the bend points for a day or two before bending. Put the panel down on the floor, on top of some wet rags (wet at the bend point anyway). Put some more wet rags on top. Bend it a day or two later.

I wouldn't worry about a frame that doesn't fit. If the shape is what you want the rib dimensions are not good. So change the rib rather than the boat.

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