The Duke and Duchess of Cambridge perched on the front of a high-speed catamaran as they cheered on Sir Ben Ainslie's America's Cup team to victory.
The royal couple joined thousands of spectators to support Sir Ben's Land Rover BAR team in the Portsmouth leg of the America's Cup World Series (ACWS).
William and Kate, wearing the shirts of the Olympic champion's team, sat at the front of the twin-engine boat as it chased after the racing catamarans at speeds in excess of 40 knots during the three races of the afternoon.
Prior to climbing on to the deck, Kate tied her hair into a ponytail and put on a baseball cap to prevent it being swept around in the sea winds.
At the end of the final race which secured Land Rover BAR's victory, the couple's boat, bearing the royal standard, sailed alongside Sir Ben's catamaran as the team and their support vessel cheered and began their celebrations.
William congratulated the team by applauding them as they sailed past.
When the teams arrived back at the event village, William and Kate presented the winner's trophy and medals to Sir Ben and his team in front of cheering crowds.
Sir Ben said to the crowds: "The guys did an incredible job with the boat handling and to be able to do that in front of you guys is what it's all about for us, so thank you."
After the royals had left the stage, the winners celebrated their victory with the traditional spraying of champagne.
The couple began the day by visiting the home crew's base in Old Portsmouth, where they were shown the team's state-of-the-art testing boats.
They were met by a group of youngsters who had been out with the team ahead of the racing through The 1851 Trust, the Land Rover BAR-affiliated charity which Kate is the royal patron of and which is aimed at getting children involved in the maritime industry.
They also met 10-year-old Zak Kay, from St Paul's Catholic Primary School in Portsmouth, who won a competition to design the trophy for the Portsmouth ACWS event.
When he asked William what George had received for his birthday on Friday, the prince replied: "I am not telling, he got too many things, he's far too spoilt, he's not into boats yet."
Sir Ben was not present for the tour of the headquarters as he was on the water preparing for the day's racing.
The teams were competing for points to take forward to the finals being held in Bermuda 2017 and Sir Ben is hoping to be the first British team to win the prestigious event in its 165-year history.
Oracle Team USA are the defending champions. The Duke of Edinburgh also visited the base on Friday before watching a practice race from the water.