Rudder configuration

For the most part the winglets used on A-Cat rudders are there to provide automatic attitude adjustment for the boat. They act to reduce pitching, not to act as a fence or to reduce tip vortex generation. Some of the newer L and T foils are designed to do that, but come with major structural problems so I doubt they will be adopted widely, at least for some time.

My thought was that it probably doesn't matter much where vertically on the rudder they are placed, though traditionally they have been about 2/3 down the rudder (why that was chosen I have no idea). If instead they were placed much higher, then they may also act as a ventalation fence, preventing aeration.