Whatever the theory was, it looks like they no longer market/use them, at least not as a separate item on their website - www.425pro.com/fins

I do see though that they still have a notch at the base of the fin - maybe as a flex point? Maybe the mid-fin notch was a trial on flexing the fin at the centre to promote more drive out of turns? Or possibly a way to try disrupting flow off the trailing edge to create a small vortex to increase speed? No real clue, just guessing! Maybe just to give it a different appearance!

The owner (Jerry) appears to come from an outrigger background - www.425pro.com/about-us - maybe the notch was inspired by something in that space

justaddwater said..

808-Obsession said..
Whatever the theory was, it looks like they no longer market/use them, at least not as a separate item on their website - www.425pro.com/fins

I do see though that they still have a notch at the base of the fin - maybe as a flex point? Maybe the mid-fin notch was a trial on flexing the fin at the centre to promote more drive out of turns? Or possibly a way to try disrupting flow off the trailing edge to create a small vortex to increase speed? No real clue, just guessing! Maybe just to give it a different appearance!

The owner (Jerry) appears to come from an outrigger background - www.425pro.com/about-us - maybe the notch was inspired by something in that space

Leg rope slicer

I've seen them do that with the long base futures fins, because they go in on an angle you can not get them in without the little cut out on the back.

Bighugg said..
Hi riverider, agree with you on the base for mounting. It was the notches over half way up the back edge that puzzled me ??

The other board was running 3D fins

Possibly for tip flex Michael Cundith/GG were doing it in the early 80's in Byron/Broken area,some times it was as crude as hacksaw cuts in the trailing edge,gotta love the innovators of or lifestyle /sport

Bighugg said..
Hi riverider, agree with you on the base for mounting. It was the notches over half way up the back edge that puzzled me ??

The other board was running 3D fins

Haha, I just thought that was black painted triangles, should of gone to spec savers!

I meet the 425 man the other day but didn't know ask about the fins, hopefully will see him at the Bali Longboard Sup Revolution Event