Rig boat, hoist mainsail, apply average sailing tension to luff downhaul and leech mainsheet. Sight along mainbeam, should not dip down at all. Apply extreme tensions and check again. If there is a dip, release all tension and tighten the striker system to increase beam prebend. I use 5mm for sloop and 4 mm for cat rig, sailing in rough waters though. CU at Nats.