Foils, like rudders and sails, work off pressure differentials. They are curved, so when air and water flow past them, lift is generated on one side. More suction than direct pressure. But there has to be a laminar flow past the foil, meaning the media....air or water.......has to maintain contact. When the angle of attack gets too steep, it separates and the flow is lost. It stalls and the lift is lost. Not only that, but when its severe, it creates a tremendous amount of drag, so it acts more like a brake than a foil, so too much weather helm not only makes it difficult to steer, but it also slows you down. A fat foil (full sails or fat, rounded rudder) means more curve, so it generates more lift and the flow holds together longer than say a flat plate would. But it's also speed dependent, which is why you flatten your sails when the wind gets up (and why airplanes raise the flaps once they get off the ground and gain speed and altitude). At speed, those will also generate drag and will stall. We don't get going that fast in sailboats, and our rudders are fixed, so we use a "best in most conditions design" and we live with it. If you have that much weather helm, best to start reducing or trimming sails as it will only slow you down. I don't know about anyone else, but I have more fun going fast than standing on the side of the cockpit, rail under the water, fighting with a boat that wants to round up. (And with the M17 anyway, that is also dependent on the degree of mast rake, which affects center of effort and all that jazz). On Jul 19, 2010, at 12:38 AM, Daniel Rich wrote:
OK, so I am in my Vagabond and close hauled. Blowing hard. So, under that situation the boat will try to round up as it is overpowered. So, I then have to pull the tiller to windward to compensate, but if the angle of attack becomes too high, then the rudder loses "lift", and no longer is able to overcome the tendency to round up. Is that it? So, a slender rudder will be more likely to do this. OK, I think I get it.
Daniel On Jul 18, 2010, at 10:30 PM, Stan Susman wrote: