What is this fin for?

[Geezer]

I’ve never seen anything g like this. What is the purpose? Is this something that is sold or did the owner do this themselves?

I saw it on the used surfboard Facebook page; I asked the owner these questions but until now he can’t be bothered. It doesn’t come from the shop this way; I had one similar Studer of this model before and was locking them over in the shop just a couple months ago.

[jaffa1949]

An asymmetrical adapter fin probably a later installation to tweak for a specific break! The cuts in the trailing edge of the bigger fin add trailing edge flex, moderate value, the fish design of the board is very knee board profile influenced.
Surfability in the eye of the beholder

[waikikikichan]

Sacrilegious !! Putting a FCS plug on a board that already had Futures Fins boxes. Hmmmph.

Probably he did it that way since old FCS single plugs are much more available than Futures Fins C-5 Twinzer plugs.

Screenshot 2022-03-23 6.12.22 PM.png (54.24 KiB) Viewed 457 times

[Geezer]

I finally got an answer out of the guy. He said it was a stabilizer for bigger days. I guess he mainly surfs one direction.