Why not make a rudder by laminating marine plywood sheets with epoxy on the 'fingers' welded to the rudder stock? Give it an appropiate NACA profile. Then some layers of epoxy and glass.
I think that is stronger and more durable.
I couldn't find the link to descriptions by Il Cigno. Il Cigno and FriendlySailor made their own rudders, amongst others. Years ago I gave my rudder a NACA profile following Il Cigno's description.
Recently there was
this discussion. GMDV already mentioned Modus Marine in Lelystad.
Edit: I haven't found IlCigno's original thread about his new ruddder, but I found his
thread of repairing a windvane, including the description and pictures of making a new rudder for that windvane (on pages 3-5). Same principle.