I have wanted to redesign a race boat using one of my favorite modern "river runner"; the Pintail.
After shoulder surgery I chose the Pintail for it's combination of down river speed, stability, easy rolling, and playability to ease the transition from physical therapy to boating at the best of my abilities again. I quickly fell in love with the boat and paddled it whenever I was not creeking or doing park and play missions. Long after my full recovery I was still using the Pintail for nearly 50% of my paddling.
The image on the top and the bottom of the stack is the original Pintail. All the others have been modified with Photoshop (as I'll explain below) to see how the boat can be stretched into a new model. It's quick and simple, but gives enough information for the home builder to use (instead of going through tons of uncomprehensible engineering programs)
the Pintail is 7 feet 4 inches long. So, I cropped the image exactly at the ends of the boat, then scaled the whole image to the equivalent size in pixels. Since 7'4" is 7.33 feet I just changed the width of the image (which is the length of the boat) to 7.33 inches. That was the hardest part. The fun started right after that.
I made the canvas size really long so I could make lots of copies of the Pintail stacked on itself. Then I copied the boat and pasted a bunch of them on top and bottom.
The second boat from the top was made in four steps.
1. expand the canvas width to 9 inches (to keep with the 1" = 1' scale) so that I could see what a 9 foot boat looked like
2. select the bow of the boat from the tip of the cockpit to the very tip of the bow, copy it, paste it.
3. stretch the new pasted bow part out to the edge of the new canvas size
4. repeat step 2 and 3 to the stern
that stretches the bow and stern without changing the cockpit size. If you want to just stretch the entire boat, without worrying about the cockpit area until you are done then all you need to do is copy the entire boat, paste it, then strech each end out to the sides of the canvas.
I repeated this process for 10, 11, and 11something (can't remember right now what the conversion for the scaled 350cm slalom "legal" size was)
I really like the looks of the 9 and 10 foot boats. If I have time this winter I'll glue up some foam and project the template and rocker with a slide projector (easy to get digital images made into slides and that allows you to keep the scale fairly accurate.)