At the dock out show yesterday I talked to one of the Oracle designers. I asked him why they didn't go with a self tracker on the jib and he said that it was a decision made early in the design process to help keep weight down and he said that the sailors wanted the option of backwinding it for maneuverability. Unfortunately it appears to be a major downfall off the boat. You can see the whole rig move when the pop the jib during a tack. I also asked if the kiwis can tack faster because of the additional rocker in their hulls and he mentioned that the boats had "almost the same amount of rocker but the tacks are all about foil work." Maybe if the jib grinders were able to adjust foils instead you'd see similar performance.