The world has been stunned by the bounce back of the Oracle Team. Obviously, they have a better boat than they did before. The addition of a world champion tactician no doubt helped, but behind the scenes, there is more.
When this started out, the Oracle team obviously didn't stand a chance. Then they used their cancel option and spent some time on their boat. The whole team came back with a smirk and a swagger that has increased with every race, as they licked a winning team within one win of taking the Americas Cup back to NZ.
The confidence shown by the cocky Australian, Jimmy Spithill, at the outset and his smug assurance that the public would see the greatest comeback in racing history, indicates that he knew the changes to his boat would make the difference. The source of his confidence. He has behind him technology and money. .
The answer is in the foils and Team Oracle seems to have solved a tech problem that has given them an unanticpated advantage.
The New Zealand company that built both foils and wings is owned by Larry Ellison. So technical knowledge was accessible, and from the outset, these boats have been a learning curve for all involved. Most likely, the secret of better performance came up from NZ. - with a price tag. And that would explain how Oracle started winning and a winning team of sailors started losing.
As catamarans these boats fly - without foils. When they are on their foils, they achieve even more stunning speeds. However, when they drop speed and are not on the foils, the foils add a drag to the hull, that slows the boat.
If Team Oracle has solved that problem and improved the foils to retract them into the hull, the advantage would be theirs. This could explain the smirk and swagger as Oracle has headed out to compete against Team NZ in the final races.
What they probably did:
Note: I think now the foils are here to stay we will see fully retractable foils & possibly changing the rudder foil angle under way instead of at the dock, where it's fixed at present.