I faced a similar situation when I built a Sea Rider a couple of years ago. I am 5'9, 170 lbs, and at 65 I'm much stiffer than I was years ago when I was paddling whitewater frequently. I'm not sure if I would describe myself as having short legs. I find it hard to sit for a long time with my legs straight out.

I raised the frame at the front of the cockpit, but I'll have to look back at my section profiles to see how much. The profile is still attractive.

I used TurboCad to draw the frames, so somewhere I have drawings in both DFX and PDF formats if you would like to see them. I could send you photos as well.

I am used to, and like, the tight fit of my 1980's Perception Dancer white water kayak where I can lock myself in with knees against pads that protrude into the cockpit, and feet against foot braces. I found that the frame at the front of the Sea Rider cockpit is in the wrong place for me as it is just about where my kneecaps are. When I first tried my Sea Rider I did not have foot braces in place and I found it to be a twitchy ride as the frame at the front of the cockpit didn't provide a good spot for me to engage my knees and my legs were straight out. Later, I installed adjustable foot braces (salvaged from a destroyed Dancer kayak). Foot braces made the Sea Rider feel much more stable and comfortable, but the legs almost straight out seating position becomes uncomfortable after more than an hour or so.

If I were rebuilding my Sea Rider for comfort I would build a keyhole cockpit as that would allow me to draw my legs up and change position. I also might reconsider the position of the frame at the front of the cockpit and/or change the shape at the top of the frame or add padding so that there would be a place to press my knees against.

I lashed my Sea Rider with artificial sinew (no glue). It has proved to be very strong. I covered it with 8 oz polyester from Dyson and coated it with tinted polyurethane. The cloth is drum tight.

I know I haven't directly answered your questions, but I hope my comments are helpful. I'll have to go back and look at the design and my Sea Rider to answer your questions about section 4.

Good luck, Steve Bartlett