Ben Ainslie made sure of a silver in the sailing today while Britain's Yngling trio also guaranteed themselves a medal.

Ainslie, twice an Olympic champion, finished runner-up in race eight of the Finn class after the competition had been delayed for nearly four hours by shifting winds off Qingdao.

The 31-year-old took the early lead and was 30 seconds ahead at the second mark but was caught on the second windward leg and ended up eight seconds behind the winning Spanish boat.

But poor results for Zach Railey, of the United States, who was 19th and Guillaume Florent, of France, who finished 21st, saw the Briton sew up at least second place, ensuring he will surpass Rodney Pattison as Britain's most successful Olympic sailor with a fourth medal tomorrow.

Ainslie leads the standings with 21 points, 12 ahead of Railey, and would clinch a gold for the third consecutive Games if he finishes no more than six places behind the American in tomorrow's final race, in which points count double.

"I'll stick to Zach like glue," said Ainslie.

"But it's not over yet by a long way, I'm going to have to go out there and get a good race in.

"I hope we get some decent breeze. It was pretty tough today, but I'm pleased with the overall outcome."

But while Ainslie is in a comfortable position, the crew of Sarah Ayton, Sarah Webb and Pippa Wilson face a battle in their double-points medal race tomorrow after managing only fifth place in race eight of the Yngling class.

The reigning two-time world champions came home 52 seconds behind the Netherlands, trimming their lead overall to only one point.

However with the United States finishing down in 10th place, the Britons are guaranteed at least a silver medal if they complete the race tomorrow but will get a bronze even if they fail to finish.