I just listened to Kirsten Neuschäfer’s interview on the OCC news page https://www.oceancruisingclub.org/home/news/2719 in which she talks about using both forestay grooves at the same time for twin head sails. She says that such a configuration might damage the foil and, instead she had her twin sails stitched together. I’m pretty sure many of us fly twin sails simultaneously (one in each groove) and wondered if anyone has suffered foil damage as a consequence?
Simon