One thing that has been stated over and over is that these rudders "must" have more drag than a non-T foil rudder and this seems to be one of the main arguments against them. One preson alluded to the fact the A Cup boats use end plates on their keels and it was noted almost all new airliners use winglet foils on the ends of their wings. The SOLE purpose of these is to reduce the drag of the attached keel/wing. It has also been mentioned that the rudders are almost never in a perfectly neutral position in regard to the boat- they are almost constantly at an angle (ie loaded). Going upwind they are certainly loaded. The "endplate" effect of the foils in these conditions serves to decrease the tip vortices and drag and could even potentially result in a rudder with less drag than one without the foils. This would completely negate all the "They have more drag" arguments against them and may explain why even in light air T foil equipped boats seem to be at least comparable to non-T foil equipped boats.

Kirt