The Duke and Duchess of Cambridge were among the disappointed crowd as the America's Cup World Series was abandoned due to extreme weather.
William and Kate left the kids at home and travelled to Portsmouth to watch the second day of racing at the event.
They were hoping to cheer on Olympic champion Sir Ben Ainslie in his bid to be the first British challenger to win the trophy.
But with winds in excess of 30mph on site, the race was abandoned.
The America's Cup is being held in Britain for the first time since the very first one was held off the Isle of Wight in 1851, the year that William's great-great-great-great-grandmother Queen Victoria was on the throne and Britain held the Great Exhibition.
America's Cup racing cancelled: William and Kate's day out dashed
26 July 2015
BBC News
William and Kate hoped to watch the first of two races from a boat and tour the festival site
The Duke and Duchess of Cambridge were among the disappointed crowd as the America's Cup World Series was abandoned due to extreme weather.
William and Kate travelled to Portsmouth to watch the second day of racing at the event.
They were hoping to cheer on Olympic champion Sir Ben Ainslie in his bid to be the first British challenger to win the trophy.
But with winds in excess of 30mph on site, the race was abandoned.
The Duke and Duchess will leave Portsmouth disappointed
The races were called off and spectators were asked to leave the waterfront as winds reached in excess of 30mph on the South Coast
An official statement from the organisers said: "After discussions with the America's Cup organising committee, due to extreme weather we had to take the difficult decision to cancel today's racing and Louis Vuitton America's Cup World Series event programme, and the site has been closed for the day.
"We had hoped to go ahead with early racing, but with winds gusting in excess of 30mph we could not risk the safety of the crews and public, and their welfare is paramount.
"Due to high winds, the Waterfront Festival Arena and Fanzone Arena closed and we asked the public to leave the event site.
"For everyone who booked tickets in the Fanzone Arena and Grandstand today, refunds will be issued through Ticketmaster."
Waterlogged
The royal couple were hoping to cheer on Olympic champion Sir Ben Ainslie in his bid to be the first British challenger to win the trophy
The royal couple were due to watch the first of two races from a boat and tour the festival site, but the ground had become waterlogged.
Sir Ben, who has won four Olympic golds and a silver, was joined by the Duchess as he launched Britain's bid to win the 35th America's Cup in June last year.
The Duchess, a keen sailor herself, is also royal patron of the 1851 Trust which provides training for young people who want to learn about sailing and the marine industry.
"The English summer, you just can't count on it," Sir Ben said, after the race was called off.
"Yesterday was the most amazing day of my sailing career. There were so many people out, everyone had a fantastic time.
"Today was a shame, but we will get that sorted out and book the weather in for next year."
'Deeply disappointing'
Donna Jones, leader of Portsmouth City Council, called the cancellation "deeply disappointing".
She added: "While this is incredibly sad news for the thousands who were due to experience another spectacular event, the safety of the crews and spectators is paramount.
"The race village will remain closed for the rest of the day.
"While this has been a tough difficult announcement for the organisers, who don't want to let anyone down, it was the right choice given the circumstances."
The first America's Cup race took place off the Isle of Wight in 1851 but a British team has never won it.
The four-day World Series event in Portsmouth opened on Thursday with a sailing parade.
The weekend's racing was the start of a lengthy qualification process that will count towards the 2017 America's Cup Challenger Series, the winner of which will take on holders Oracle Team USA in the 2017 America's Cup.
The abandonment meant Sir Ben Ainslie and his Land Rover BAR Racing team secured the overall victory across the weekend.
America's Cup racing cancelled: William and Kate's day out dashed - BBC News
William and Kate left the kids at home and travelled to Portsmouth to watch the second day of racing at the event.
They were hoping to cheer on Olympic champion Sir Ben Ainslie in his bid to be the first British challenger to win the trophy.
But with winds in excess of 30mph on site, the race was abandoned.
The America's Cup is being held in Britain for the first time since the very first one was held off the Isle of Wight in 1851, the year that William's great-great-great-great-grandmother Queen Victoria was on the throne and Britain held the Great Exhibition.
America's Cup racing cancelled: William and Kate's day out dashed
26 July 2015
BBC News
William and Kate hoped to watch the first of two races from a boat and tour the festival site
The Duke and Duchess of Cambridge were among the disappointed crowd as the America's Cup World Series was abandoned due to extreme weather.
William and Kate travelled to Portsmouth to watch the second day of racing at the event.
They were hoping to cheer on Olympic champion Sir Ben Ainslie in his bid to be the first British challenger to win the trophy.
But with winds in excess of 30mph on site, the race was abandoned.
The Duke and Duchess will leave Portsmouth disappointed
The races were called off and spectators were asked to leave the waterfront as winds reached in excess of 30mph on the South Coast
An official statement from the organisers said: "After discussions with the America's Cup organising committee, due to extreme weather we had to take the difficult decision to cancel today's racing and Louis Vuitton America's Cup World Series event programme, and the site has been closed for the day.
"We had hoped to go ahead with early racing, but with winds gusting in excess of 30mph we could not risk the safety of the crews and public, and their welfare is paramount.
"Due to high winds, the Waterfront Festival Arena and Fanzone Arena closed and we asked the public to leave the event site.
"For everyone who booked tickets in the Fanzone Arena and Grandstand today, refunds will be issued through Ticketmaster."
Waterlogged
The royal couple were hoping to cheer on Olympic champion Sir Ben Ainslie in his bid to be the first British challenger to win the trophy
The royal couple were due to watch the first of two races from a boat and tour the festival site, but the ground had become waterlogged.
Sir Ben, who has won four Olympic golds and a silver, was joined by the Duchess as he launched Britain's bid to win the 35th America's Cup in June last year.
The Duchess, a keen sailor herself, is also royal patron of the 1851 Trust which provides training for young people who want to learn about sailing and the marine industry.
"The English summer, you just can't count on it," Sir Ben said, after the race was called off.
"Yesterday was the most amazing day of my sailing career. There were so many people out, everyone had a fantastic time.
"Today was a shame, but we will get that sorted out and book the weather in for next year."
'Deeply disappointing'
Donna Jones, leader of Portsmouth City Council, called the cancellation "deeply disappointing".
She added: "While this is incredibly sad news for the thousands who were due to experience another spectacular event, the safety of the crews and spectators is paramount.
"The race village will remain closed for the rest of the day.
"While this has been a tough difficult announcement for the organisers, who don't want to let anyone down, it was the right choice given the circumstances."
The first America's Cup race took place off the Isle of Wight in 1851 but a British team has never won it.
The four-day World Series event in Portsmouth opened on Thursday with a sailing parade.
The weekend's racing was the start of a lengthy qualification process that will count towards the 2017 America's Cup Challenger Series, the winner of which will take on holders Oracle Team USA in the 2017 America's Cup.
The abandonment meant Sir Ben Ainslie and his Land Rover BAR Racing team secured the overall victory across the weekend.
America's Cup racing cancelled: William and Kate's day out dashed - BBC News