… there’s many different grades of ply out there …suits all budgets and purposes . Some companies will custom make a sheet for ya ($$$$'s). Standard skin thick is a bit lean @ .6mm , and doesn’t leave much tolerance for finish sanding . Great stuff for building furniture Stoneburner , it doesn’t shrink or warp in weather like a solid bench top can over time .
If you’re talking about shortboard fins and you’re going to use with a fin system like FCS, I added several layers of fiberglass to the “flat” side of the fin panel prior to templating. That serves as the halo. I also add a layer over the foiled side to protect the wood. So if you intend to put tabs for a fin system you need to start out with a ply panel that’s thinner than 1/4". I think I used 3/16, so 10 plys in 3/16 with a fiberglass back is going to be pretty strong. We haven’t broken any of those fins yet.
I was experimenting and made a longboard centerfin with the stuff by sandwiching a 6 or 8 layers of 6oz (I forget exactly how many) between 2 layers of the 3/16. The fiberglass in the center serves as the spine and halo. I had to mill down the tab portion in order to it to fit the finbox but I ended up with a fatter fin at the base. Someday I aspire to do a 1" thick fin that way.
I haven’t tried it yet but I’ve had an idea for a couple years of using vacuum infusion to “fill” the wood prior to finishing and then skipping the outer fiberglass altogether. I’m a little concerned what that might do to the remaining flex of the ply, but as long as the effect was consistent I guess that would be okay.
I sourced my aircraft ply directly from a SoCal company called “Aircraft Spruce” in Corona, Calif.