Weather helm is the tendency of boating vessels to move towards the source of wind, creating an unbalanced helm that requires pulling the tiller windward to counteract the effect. Weather helm is the opposite of lee helm.
When a vessel is close hauled and sailing, the lee side of the hull is more under water than the weather side. Passing water pressing on the lee side of the hull creates a force (a turning moment) that pushes the bow to weather and it is necessary to pull the tiller to weather to equilibrate this force. Since a weather helm requires pulling the rudder through the water at an angle to the intended course, it produces drag and retards the boat's progress through the water. One of several ways racing sailboaters neutralize weather helm is to use bodyweight as ballast to bring the boat to a more upright position. In his book "Sailing Illustrated" Patrick M. Royce defines weather helm as simply a "heeling sailboat wanting to come head to wind." The principle is the same whether the vessel is steered by tiller or wheel; one would turn the wheel leeward to get the same rudder effect as pulling a tiller windward.