How it happened
I was surfing at Torrance beach and pondering how fins help surfing. I thought about how they keep the tail of the board from sliding sideways when the surfer is standing near the tail. I realized that if the fin were to be rotated a bit when on the wave it would act like a sail and add forward speed.
What I did
I met with Hap Jacobs at is shop in Hermosa Beach while he was shaping a board for me and I told him about my idea. His response was very bland. I took that as a sign that my idea had little merit. I did, however, investigate materials that might make this work. I tried cutting a regular fin very thin to let it bend but fiberglass is a poor material for that. I then experimented with attaching a thin stainless steel plate between the fin post and the fin. That appeared to be a solution but I dropped the whole idea.