I'm working my SOF paddleboard design. For simplicity of the joints I want it flat in the middle and so have the choice flat everywhere or can do something different at the bow and stern. I was thinking of slight V at front of the bow for breaking waves, transitioning to double convex around the "calm" waterline which transitions to flat at midsection and then transition a deep V at the tail. The double-convex in front provides for speed with some stability while the deeper V at the back is good for speed and tracking.

I've seen foam/fiberglass boards with this style of hull but am not sure if the double convex will work on skin-on-frame since the skin effectively follows the convex hull. I've seen Dave Gentry's Lunai which is a single V but wanted to explore the double-convex since its more efficient and allows better turning of the board.

I've attached a simple drawing of what I was invisoning in the cross section, with the thin line below the top representing the skin. My stretch test for my fabric show less than 5% stretch with 200lb load and the convex regions wil be filled it it stretches about 9%. (The white holes at the apex of the convex regions will have a flat support bar running the length of the boat incase it does stretch more than expected over time). The first question is if the skin stretches enough to fill such a void am I just asking for trouble by having cross members that are in contact with the skin?

I did note that in most of the SOF kayak pictures I could fine the longitudinal members (often called ladders) on which present the majority of the skin contact support along the water line with the ribs far enough offset that the skin seems like it would just form long channels along the ladder. It does not seem like it would ever touch a rib. (but the plywood-based SOF kayak I had growing up had ribs were in contact with the skin and so do some I see online, e.g. https://folk.school/wp-content/uploa...ame-boat-2.jpg). Got me wondering, should my cross members (rib/thawlart) members be shorter/****ted line in the bottom version so the longitinitual members (three darker sections) are the only parts in contact with skin hence cause drag by having a lump, or should I maximize support for the skin by having both logitinitual and cross members in contact with skin?