Nice theory, but I'm not buying it. Case in point. Catalina 310. Reasonably stiff boat. Anyway, it doesn't heel enough to make any appreciable difference in hull lengths in 10 knots that suddenly becomes 15 knots. The wind gusts, and there's an immediate strong weather helm as if the wind grabbed the boat by the nose and snarled, "Get over here!" The wheel was a solid stone in my hands. That's the hull being yanked around by the rig, not the hull dictating the course. This happened in a fraction of a second....far too quickly for it to be a response to differential hull waterlines. Flattening the main solved the issue. It's your idea, but it applies to air over the sail, not water over the hull. Flattening the sail reduces the differential between both sides of the sail, thus easing the weather helm forces that had been present. Try this. Get a tender boat and put everyone on one rail. The boat (sails down, engine putting along) will most likely need corrective steering to weather to compensate as it will favor the low rail. Now, raise the main and watch the boat go to weather as it fills. Trim it flat and watch it ease off. Even with all the people on the windward rail and the boat sailing flat, it'll have weather helm if overpowered. At least, that's where I am on things.
Last edited by seabreeze_97; 12-07-2009 at 11:05 PM.