On the F16's you can't really unhook the mainsail clew from the boom, you can however unhook the mainsheet from the boom/clew loop. So in effect the boom stays fully attached the foot of the mainsail. If the outhaul on the boom is not too loose then this setup will not allow the mainsail to flap about. That is unless the winds are strong. In most cases the boom and mainsail will just weathervane with the wind. I often pop halve the battens to the other side, getting a nice S curve in my sail from top to bottom, This seems to really calm the mainsail down as well. And the downhaul must not be tight so slacken that as well. If you have done all these tricks then the mainsail should be really calm and just hang there all the way up to 15 knots. No damage or rubbing against the sidestays. Of course you must put the boat head to winds and move it when the wind directions changes significantly

Wouter