jspr, another thread for you on thick single fins:
“Is this mainly to keep the drag low?”
Not sure why ~1/4" seems to be the defacto thickness for most fins (in context of shortboards).
Hot-take on why it’s that way for injection-molded fins, there’s a point where injection molding has a max wall thickness before you get “sink marks”. My guess is this was a limiting factor?
And they seem to work just fine, there’s so much variability in surfing, even if you could quantify a 15-20% improvement in drag, in the real world that probably isn’t noticeable.
I think of the aerodynamics of a flat plate vs. an airfoil. It’s very counter-intuitive that a flat plate has significantly more drag than an airfoil that is multiple times thicker.
https://www.grc.nasa.gov/www/k-12/VirtualAero/BottleRocket/airplane/shaped.html
Mostly it just matters to us on the fringe who like to tinker around with this stuff.
In my mind the benefits would seem even greater for a single fin longboard though. There are a lots of threads buried in the archives of people making thick fins.
Also, what stoneburner said plays into it… in theory a thicker foiled fin should generate a bit more lift so you could reduce the surface area (ie: reduce the overall template size).