Team New Zealand appear to be trialling a new set-up on their AC75 vessel, as their preparation for the America's Cup match ramps up.
The Kiwis have been enjoying extra time to train and experiment since the conclusion of the World Series regatta in December, and won't be needed on the competitive waters for another two and a half weeks.
Team New Zealand will be keeping a close eye on the Prada Cup final series to see who out of Luna Rossa and Ineos Team UK will advance to face them for the Auld Mug.
But that extra time the defenders have to improve their boat appears to have been well-spent, with one eyewitness believing the design of Te Rehutai is different when spotting the vessel out on water today.
"[They're] trialling an American Magic-type mainsail for heavy winds. They must see some value in testing this," a source told the Herald.
"The concept makes sense. When it's 15 knots plus, the extra sail area up high is just drag and slows the yacht down going upwind. So [it's] a good option to have for windy conditions."
Several other sources confirmed to the Herald that Team NZ's new sail design - referred to as the "batwing main" due to its likeness to the comic book superhero's craft - has not been seen before.
The Kiwis were spotted this afternoon, parked up not far off Motuihe Island and surrounded by chase boats, with a crew member out on the end of one of the foils in the water, and others on deck nearby.
At one stage, a crew member could be seen climbing to the top of the mast in order to pull the sail back up.
It has been reported that Te Rehutai has been reaching never-before-seen speeds while training on the Hauraki Gulf.
The Italians look the more likely opponent in the America's Cup match, leading the Prada Cup final 4-0 and needing three more wins to advance.
The Cup match begins on March 6.
Team NZ did not respond to requests for comment.