This looks good. love your designs, what are you going to make your foot pocket out of? for your triangular piece i would suggest you create it in fiberglass. I have used fiberglass for some attempts on my tail. depending on how thick you make it will depend on how it feels in the water. it will not shatter at all, which is great for things that require high performance. I hope your extension works. I started my tail 7 years ago, and i'm finally on my last attempt of the extension. i will state this to you though. its not as easy as you might think to create. I wish you luck.