Center of effort vs. Center of resistance on the sails of the Omega
When the sails are properly trimmed on a beat the center of effort of the wind will be a little behind
the center of resistance. If you think about it you will realize that this will cause a slight weather helm. If you let out the jib the CE moves back causing more weather helm. If you ease the main you
naturally get more lee helm because the wind exerts more force on front of the boat and the boat pivots around the centerboard.