Olympic champions Percy and Simpson had gained the medal race lead by the time they reached the first windward mark and then sailed a conservative race to win by 1:20 while others around them battled with the tough conditions.
"After breaking the rig yesterday whilst leading we obviously didn't want to make the same mistake twice – well, it wasn't a mistake, the rig failed – so we were a bit more cautious today than we maybe would be normally," Simpson explained.
"Iain did a great job and we managed to get into the lead at the top mark and sailed pretty conservatively from there, let everyone else wipe out a bit, go on their side and fill up with water! We managed to get round without too many issues, so it was great."
Percy and Simpson will race their World Championships at the same venue starting on May 5 and while they have learned lots about the venue and their equipment, they also admit that their eyes are on Weymouth rather than adding a World Championship title to the one they won in 2010.
"The Worlds is obviously very different to the Olympic format, so we're more focussing on how we're going at Weymouth and focussing there. We probably wouldn't have done the Worlds if we hadn't had the injury to Iain's back in Perth, so we're here to try and make amends for that, and we've learnt a bit this week.
"It could be a completely nice sunny, light winds regatta rather than the breezy regatta we've had here, but it will be great learning and probably a bit of speed testing mainly as part of that event."
After a promising week, there was disappointment for Alison Young in the Laser Radial event as she missed out on the podium spots by one point to the Netherlands Marit Bouwmeester with gold going to China's Xu Lijia and silver to Belgium's Evi Van Acker. Charlotte Dobson finished ninth.
Stevie Morrison and Ben Rhodes, poised in fourth but on equal points with the third-placed Danish boat, were denied the chance to improve on their position when racing for the 49er class was called off.
Lucy Macgregor, Annie Lush and Kate Macgregor finished fourth in the women's match racing event as strong wind conditions meant race officials were unable to complete a potentially decisive final round robin match for the British trio against USA's Sally Barkow, meaning the medals were decided on percentage wins.
John Robertson, Hannah Stodel and Steve Thomas took gold in the Paralympic Sonar class.
Helena Lucas in the 2.4mR event and the SKUD crew of Alexandra Rickham and Niki Birrell, added two silver medals to the haul, although no racing was possible for the Paralympic classes in Hyeres on Friday due to the breezy conditions.