Sled Boat Bow rise

No, I'm going to build it as close as possible to the pictures shown, I don't really see those plates as frames as they are put in after the fact and the sheeting is formed first. I know the strait parts are easy that's why I am posting looking for some advice on the rise, but it doesn't sound like anyone here knows much more then I do about the subject other then to buy plans or have it designed by a architect. There are several builders in Oregon doing this and they post these pictures all the time on facebook.

 

I think this would be very easy to figure out using free software such as FreeShip. Even the old DOS program "Hulls" could manage it. They both will output the developed panels in dxf format.

 

In the photos shown, do the builders join the bottom plates while upside down or right side up as the first step? I would assume they need some sort of frame or strongback to maintain alignment and prevent warp and twist.

Since you seem to have already found the shape that you are seeking with your plywood models, you can derive your curve off of them. When you say “radius” you’re by definition assuming that the curve is a simple arc of a circle. But the curve you created with your plywood model is likely more complex than that (parabola, etc.). There is no single formula that will define every shape you might produce. You’ll need to plot a few of the points along your curve using your original plywood edges as the x-y axis. Once you have those points plotted you can put them in Excel or any number of free online calculators to generate the formula that best represents that curve. I’m assuming that’s what you need to feed the CNC, but I don’t work with that equipment. That’s the mathematical (sort of) answer to your original question. Using software like W9GFO suggested is the practical answer.

It really comes back to Ad Hoc’s original answer. There is no fixed rule, that’s why you keep finding different curves on each boat you measure. Either try to match the boat shape you like the best, or come up with a shape that turns your crank and derive the curve from that.