On a day which saw fortunes turning inside out on many courses, Percy was not the only one to be ruing the way the fates had dealt with him.
The 22-year old from Winchester had gone out for the final race in third and needing to score anything better than 19th to hold on to a podium place. But a weak northerly wind being opposed by a weakly developing sea breeze caused a tactical minefield. Twice Percy chose to work the right-hand side of the track and twice he was let down. "I went on the theory and today it was wrong," he said.
Still in medal contention is Shirley Robinson after she finished fourth in the only race completed yesterday in the Europe class, putting her level on points with the leader, Margriet Matthijsse of the Netherlands.
A bright future looks in store for Percy, an economics graduate from Bristol who is now sailing full-time. "I am pleased with the way the championship has gone," he said. "It was just a shame about today. I have been inconsistent this week, but in a way that is encouraging as it shows I have got a lot of pace."
Looking forward he hopes to continue to improve for the Finn Gold Cup, which is the class world championship, in Weymouth next year. After that come the Olympics, where he hopes to be one of the favourites.
As he retired he was in good company, joined by the current Olympic gold medallist, Mateusz Kusnierewicz. That failure cost the Pole the world championship by one point as Sweden's Frederik Loof won the race and snatched his third world title. And a sixth in the final race secured bronze for Canada's Richard Clarke.
The topsy-turvy weather was nowhere in greater evidence on the Soling course. A difficult situation was made worse as the race officer stuck to class rules and laid a five-leg course of 2.2 miles each. Even when shortening that to a still over-long 1.8 miles for the final two legs time nearly ran out and there were just 2min and 40sec of the three-hour limit left when 1996 silver medallist crossed the line
Britain's Lawrie Smith did not know whether to be pleased with his sixth or angry that he had at one time been second and then been robbed. No such dilemma for Andy Beadsworth and crew, who ended 22nd after pulling back to 11th at one stage, and were feeling out of sorts with the rules of race management.
But Beadsworth is still 10th overall, whereas Smith is 15th, and today's final race is crucial not just for honour's sake but because Beadsworth's elite funding package relies on finishing in the top 10.
Even a 16th for the series leader, Stig Westergaard, of Denmark, and a 30th for the triple gold medallist, Jochen Schumann, did not dislodge them from the top two places. The Norwegian, Herman Horn, who had been 27th at the third mark, ended up second on the day and third overall.
With two races to go in the 49er, Australia's defending champion, Chris Nicholson, and crew Ed Smyth have a single- point lead over the American pair, Morgan Larson and Kevin Hall. They are three points clear of another Australian duo, Adam Beashel and Teague Czislowski.
Britain has two in the top 10, Paul Brotherton and Neal McDonald sixth with three single figure results yesterday, and the Budgen brothers, Andy and Ian, eighth.
Results, Digest, page 25