Sorry for my two cents, but I like the subject ! As Nathan already explained, these features may produce small vortex in order to delay the flux separation and increase efficiency with large angle and avoiding entering in Stall, more or less similar to the "turbolators" on wings and masts and eventually Fins when the speed is decreasing. Reynolds oblige !! Very often rudders are entering into 'stall condition' in particular around the buoy, but rarely admitted by the skippers ! Merry Christmas ClaudioD
