Probably using a smaller spin cut like the Viper's sail plan. Watching the AC45s do the speed trials in San Diego, I now understand how a smaller chute can be faster (speed)....don't know relative to VMG on a truly leeward mark. The speed trial was set up with a 135 wind direction.

BTW, the 3rd fastest was Bundy running without a spin and squeezing the pins at both ends. I wonder if Oracle had only 1 small spin available for the speed trial? All of the rest had large chutes. One even tried the larger chute without the jib.