As your main bags-out the center of effort moves back which increases weather helm. It also becomes impossible to de-power with outhaul and twist because there's still too much raw curvature in the cloth. When your main is carrying a bubble up front, all of the pressure is on the back half of the main right? So the center of pressure is about 1/3 of the way back from the middle of the sail. The boat wants that center to be about 1/3 back from the front of the sail.
My weather helm disappeared when I got a new main. It was a much more dramatic difference than I would have even imagined. In 10kts true I can lightly-lock the wheel and balance the helm with jib/main sheet to sail for nearly an hour straight without touching the wheel. You do want a little weather helm going up wind to keep the boat lifting to windward and get helm feedback. A few degrees of rudder is good.
Also, I rarely reef the main anymore. My boat (E35-3) generally sails better with jib alone then with jib and reefed main. If the wind is picking up enough to reef its probably gonna keep picking up more so I just drop the main now. Weather helm is no longer an issue for me.
My weather helm disappeared when I got a new main. It was a much more dramatic difference than I would have even imagined. In 10kts true I can lightly-lock the wheel and balance the helm with jib/main sheet to sail for nearly an hour straight without touching the wheel. You do want a little weather helm going up wind to keep the boat lifting to windward and get helm feedback. A few degrees of rudder is good.
Also, I rarely reef the main anymore. My boat (E35-3) generally sails better with jib alone then with jib and reefed main. If the wind is picking up enough to reef its probably gonna keep picking up more so I just drop the main now. Weather helm is no longer an issue for me.