Low tide find

I found this fin on One of those negative tides a few weeks ago in North county San Diego, wedged upright against a piece of reef.

HOw Old could it be?

Any guestimations how long it was down there?

There’s a spot in my town that’s notorious for breaking fins. I once snapped a 3rd of a fin off at that spot and a year later while wading out through the rocks I looked down and there was the part that broke off.
If you were to go snorkelling there on a calm day you could find hundreds of fins.

Looks like a 70s or 80s at the latest fin, but the hole was an early solution for leash attachment.
I doubt it’s been down there since then- it would be encrusted with gunk.

Photo of thruster fins encrusted in gunk:

W-Cool find, neat fin. Interesting how some of the iron leeched out of the roll pin.
Let me know via PM if you want to try a FR-4 tab to repair it.
Tabs are 1.5" L x .345" W x .255" thick with a .203" diameter hole approx .300" center to end.

I thought the rust stain was neat too. I increased the saturation to make that pop in the photo. I think it had not moved in quite some time for the rust streak to be so defined like that. It did require a surprising amount of force to extract, considering it was just sand holding it upright against the reef. I did search for more fins at the time with no luck.

In the general area where I found the fin , I have also scraped up my own fins, and broke one fin’s forward tab, and rebuilt the fin nearly 6 years ago, moving the tab to the trailing edge and roll pin to the front, using carbon fiber roving and epoxy, and perhaps a degree or 3 of overkill, but it has survived all impacts since. I heavily reinforced the box in the board too as it was leeching salt from between box and epoxy.

While I have no real desire to personally put any effort into restoring the found fin to functionany time soon, if ever, I do have some interest into its past. I wonder if it destroyed the fin box. The roll pin is not centered in the fin, but hard to imagine it exited the box’s slot.

Seems like a leash attached to the fin itself would put a lot of force on the finbox in a way not really intended when designed. By all the wear on the trailing edge where the leash’s finrope would have resided, it appears it lasted for quite a while before the reef took it out.

That’s a very cool find. That’d be something if it was stuck down there since 71 or 72! I’d make a board just for that fin. Mike