marine ply keel fins - how thick?

I cut out a template from a set of fiberglass fins but changed the shape so they’re keel fins. How thick should these be at the thickest point when I foil them? Thanks for any info.

I’m no expert, but I have made several sets and used them. They ranged from 5/8ths to 3/8ths at the base. All have worked well and couldn’t say which worked better because they all have gone on different boards. Check the archives, too. Lots of talk on keel fins. MIke