During a casual conversation in mixed company about strange sailing tech I mentioned flappers (properly known as anti-ventilation skirts, those semi-silly plastic tongues that allowed raceboard designers to chop off the tails.) This immediately sparked the imagination of Bonnie Queen of the Kayak Bloggers (see Frogma). Bonnie can draw, and so here we are. Awesome, I say!
(Click on the art above for Bonnie's original post. To the right we have the best photo I could find of an AVS flapper. Not an ideal photo, so if you're new to flappers, the white tongue is a rubbery material that extends several inches behind the fin. The idea is it prevents air from getting sucked down behind the fin where it would induce spinout. I never raced, but I sailed a few AVS-equipped boards. They worked, but gave the overwhelming impression of It's Not Going To Work For Long.)