What causes weather helm to slow the boat down?

Weather helm occurs when a sailboat has an imbalance between the forces acting on the sails and the underwater foils, primarily the rudder and keel. When a significant amount of rudder angle is applied to counteract weather helm, it creates drag. This drag can slow the boat down because the rudder generates lift as it moves through the water, but it also creates resistance against the boat's forward motion.

When the rudder is angled too much, not only does it lose its efficiency in steering the boat, but it also increases the wetted surface area, which leads to more friction with the water. Consequently, the more the rudder is turned to counteract the weather helm, the slower the boat can go because that drag directly opposes the boat's forward motion.

In contrast, large sail area, excessive ballast, and high wind speed can also affect a boat's performance, but they do not directly relate to the concept of weather helm and its consequent drag effect as the rudder angle does. Understanding how the rudder's angle affects speed and control is crucial for sailing efficiently, particularly when managing weather helm.