Hello Fred,
Some time ago, I built this model with a balsa hull. My rudder was a sheet of brass shim, cut to shape and folded over the brass rod. It was then epoxied together and clamped. Any tidying up of the edges was done with filler, then finished with the smooth file and emery cloth before painting.
The size was approx. 3mm over what the design shows. This was not really necessary as the handling is good whilst moving forward and what has already been said earlier is correct.
The problems I had with the rudder were not the shape, but the linkage. It took three attempts to get it right and they were due to me not removing enough balsa from the stern end bread and butter construction. This won't be a problem with a moulded hull.
Attached is a link to my build. I still have the model stored in the shed and must give it a clean up.
**LINK**
Wishing you every success with the build.