Have to express my gratitude to Elmo today for his help in my efforts in my first venture in urethane moulding. Absolutely stuffed the first attempt but with some useful tips I think I can rectify the mould itself. I'm trying to replicate Fangy's fin in a carbon / glass and silicone carbide foil. Needless to say the attempt was a learning experience. If you don't make any mistakes in life, you're not learning anything.
cheers, mate

If you can get CNC code for the fin mould I may be able to get it CNC cut in SE Asia

Great idea Col, We'd need to get the fin scanned. I have no idea how to do it as I've done it by eye. But any help would be welcome

So, after my third attempt, it's been a bit of a success. Not completely sure my neighbours like the sound of the router any more but, it had to be done. Both sides done and it's starting to look like a split mold..

AUS 808, the cad that Fangy has are for his fins, mine are a little different. Like his, the chord ratio is still 8% through the profile, however I've made the fillet shorter as I believe it's done it's work on entry and may not be needed at the rear. This may of course be completely wrong, but after testing I found it worked, and worked well. Mine are carbon, which may be lighter but do not wear well, especially where the sand particles are suspended in the weed. I'm trying to coat the leading edge (in the mold) with silicone carbide which Elmo had success with. 6 months of wear and tear and the leading edge looks like one trip to Albany. However, after handing me a jar, he had an evil snigger happening, which I'm sure has to do with final sanding.
Anyway, I've made three of them, a 24cm, a 21 and a 19. The leading edge is 49 through to 53 degrees, which should of been 51 but ended up at 53 from some estuary bed profiling. Why mess with mother nature...

Looks amazing, wish I had your skills.