update : we drove 3 hours under the rain on Saturday, visited the mausoleum of Qian Long, slept by a Lake near the Eastern Qing Tombs and built the kayak on Sunday morning.
Alas, the wind was between force 4 and 5, so I did not dare trying the sailing rig as the Klepper is notoriously easy to capsize... (my kayak partner can't even swim !)
I just tried an umbrella as a drift sail, that worked beautifully downwind until it totally collapsed as the wind was really too strong. I also tried the rudder for the first time and it's a big help for small heading corrections, especially with strong winds.
As the wind was getting even stronger (the lake was getting foamy), we packed the boat after lunch, and thanks to a road mistake drove 4 hours behind weird trucks in clouds of dust, resting occasionnally in huge traffic jams.
I don't know when will be my next attempt, as the temperature has really dropped this week...