Would it be possible to make the rudder and the shaft as one piece from flat stock? I’ve seen some dagger rudders on small people sailboats that go through a slot in a rotating block through the deck.
It was just a thought to lighten or thin the rudder by removing the 3.2mm (1/8 inch) shaft so the blade is thinner. I don’t think a shaft smaller than 3.2mm would be strong enough? You could also hammer the (brass) shaft flatter or grind flats on the sides to make it thinner.
Simplest and strongest method to do a metal rudder is to cut a longitunal slot in the shaft and solder it to the flat stock. You could, then, thin out the two sides to a lower profile. If you stepped the shaft down to a thinner diameter to attach a thinner rudder; you would still have a serious weak spot where the step meets the rudder.
Bob
I’m not sure I want to do the entire rudder in metal- just get the shaft thinner, because when you add the two sides of the rudder blade to the shaft, the frontal area can get large.