Ted Brewer (the designer of the Whitby 42) wrote in a letter in '98
"Re rudders: I do recommend a small increase in size as an aid to steering. My suggestion is to add 3" to the trailing edge, and to square of the bottom of the rudder parallel to the waterline. This should not create any problems with strength and, indeed, I have heard of no problems from owners who have done this. Problems seem to occur in shafts where the stock has been shaved to make it easier for the builder to bend it around the aperture, or in stocks where the bend has created a fracture because it was not done properly."
Having read all the other available information, most hidden deeply in the bowels of the "owners group", and having cut into the rudder in two places I have decided to leave the size of the rudder as is, for the moment. I agree with Ted that a small increase would help but I may go the bow thruster route when time and money permits. The only factor that might change my mind would be how the vessel handles under sail in heavy winds.
The next bite of the elephant is........ the center fuel tank!!!! Fun Fun, NOT.