Overview
When a vessel is heeling, the lee side of the hull is more under water than the weather side. The resulting shape of the submerged part of the hull in this condition usually creates a force (a turning moment) that pushes the bow to weather so that it is necessary to pull the tiller to weather to counteract 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. In the 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; turning the wheel leeward gives the same rudder effect as pulling a tiller windward.
A slight amount of weather helm is thought by some sailors to be a desirable situation, both from the standpoint of the "feel" of the helm, and the tendency of the boat to head slightly to windward in stronger gusts, to some extent self-feathering the sails. Other sailors disagree and prefer a neutral helm. Weather helm also provides a form of dead man's switch—the boat stops safely in irons if the helm is released for a length of time.
Read more about this topic: Weather Helm