Can't really tell from the pics, but the diameter of the bow rake looks like it could be larger.
I like to make my rudders roughly 2/3 the size of the prop for height and 1/4 the size for width. Example: 16" prop = 10 x 4.5 rudder. Then center the rudders with the crankshaft.

The rudders in the pics above are 10" tall and 5" wide at the top and 4" wide at the bottom.

1/4 " Plexiglas?? Hmmm, never thought about it. You could use it, then, sand and shape the plexi to a wing shape, bull nose towards the prop and taper out to the back, then wet sand and buff to clear...that would be cool!