This skeg was spotted by Jeff out at Montauk a few days ago. It’s called the Turbo Tunnel Fin, and there are surfers who say the thing does many wonderful things…helps maintain speed through turns, improves nose riding, provides lots of drive and so on.
Back when I started windsurfing there used to be some experimental or otherwise unusual fins advertised in the back of windsurfing magazine. I remember a fin with small holes running through the fin (to “channel water to prevent cavitation,”) a asymmetrical fin that would change shape depending on the reach it was on, an aluminum fin and so on. But this is the freakiest thing I’ve seen since the football fin, but unlike the football fin, it seems to have some fans.
(Top photo by Peconic Jeff. Bottom photo from the Turbo Tunnel web site.