At this years Grafham Cat Open there were 8 F16's, two were sailing with Stealth 'R' mainsails which are just over a meter smaller than the F16. On Saturday it was fairly windy 18-22mph I would imagine and the smaller mains weren't going that well (No offense Pepin/Jeff).
So if I was you Patrick I wouldn't cut down your old main but would consider altering the fullness to make it flatter, check the current luff curve if at it's max it's over 100mm then consider a re-cut to 90mm for instance. I was very surprised what a difference this can make to the overall sail shape/power. My Landy Luff curve had 15mm taken out last Winter (now 85mm. I'm approx 160lbs).
A good few years ago after my crew had fallen through the main I used a Dart 18 mainsail on a Stealth 'R' for a race. Never again. It was like an old potato bag, way to full and nothing I could do to flatten it. But it was a pretty colour!!
The early stealth had a 10 sq m mainsail singlehanded option and proved very competitive to windward in a blow. If you make a sail too flat you not only limit the ability to power up the sail but you also lose the tolerance to trim/sheeting angle and the sail becomes more like an off/on switch. Given that it is usually gusty when the wind gets up a lack of tolerance to trim is the last thing you want. If the sailcut allows, try to blade off the top of the sail whilst keeping the lower sections drawing. I would experiment with using stiffer/reinforcing the upper battens before looking to recut a sail.
Cheshirecatman
