Weather helm
Encyclopedia
Weather helm is the tendency of sailing vessels
to turn towards the source of wind, creating an unbalanced helm that requires pulling the tiller
to windward (i.e. 'to weather') in order to counteract the effect. Weather helm is the opposite of Lee Helm
.
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.
the total sail area will have the same effect and, counter-intuitively, many boats will sail faster with less sail in a stiff breeze once heel and weather helm have been reduced, due to the reduction in underwater drag (see Over-canvassed sailing
). Easing the sheets on aft-most sails, such as the mainsail in a sloop
or cutter can have an immediate effect, especially to help with manoeuvering. Moving or increasing sail area forward can also help, for example by raising the jib
(and maybe lowering the staysail
) on a cutter.
Sailing off the wind, weather helm may be caused by the imbalance due to fore-and-aft sails all being sheeted out on the same (leeward) side of the boat. Raising a spinnaker
or poling out a headsail to windward with a whisker pole can help. Yachts making ocean trade wind
crossings have rigged 'twins' - double headsails poled out to opposite sides from the same forestay for extended downwind passages without a mainsail. Square rig
ged sails also provide relatively symmetric drive off the wind.
If the situation is reversed, with the center of pressure forward of the center of resistance of the hull, a "lee" helm will result, which is generally considered undesirable, if not dangerous. Too much of either helm is not good, since it forces the helmsman to hold the rudder deflected to counter it, thus inducing extra drag beyond what a vessel with neutral or minimal helm would experience.
See Sailing Theory and Practice by C.A. Marchaj for a mathematical analysis of the dynamics of weather helm.
Sailboat
A sailboat or sailing boat is a boat propelled partly or entirely by sails. The term covers a variety of boats, larger than small vessels such as sailboards and smaller than sailing ships, but distinctions in the size are not strictly defined and what constitutes a sailing ship, sailboat, or a...
to turn towards the source of wind, creating an unbalanced helm that requires pulling the tiller
Tiller
A tiller or till is a lever attached to a rudder post or rudder stock of a boat that provides leverage for the helmsman to turn the rudder...
to windward (i.e. 'to weather') in order to counteract the effect. Weather helm is the opposite of Lee Helm
Lee Helm
Lee Helm is the tendency of a sailboat to turn away from the wind while under sail. It is the opposite of Weather helm which is the tendency of a sailboat to "round up" into the wind. A boat with lee helm will be difficult to sail Close Hauled and tacking may be difficult.-Description:Lee helm is...
.
Overview
When a vessel is heeling, the lee side of the hullHull (watercraft)
A hull is the watertight body of a ship or boat. Above the hull is the superstructure and/or deckhouse, where present. The line where the hull meets the water surface is called the waterline.The structure of the hull varies depending on the vessel type...
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
Bow (ship)
The bow is a nautical term that refers to the forward part of the hull of a ship or boat, the point that is most forward when the vessel is underway. Both of the adjectives fore and forward mean towards 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
Drag (physics)
In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
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
Dead man's switch
A dead man's switch is a switch that is automatically operated in case the human operator becomes incapacitated, such as through death or loss of consciousness....
—the boat stops safely in irons if the helm is released for a length of time.
Mitigation
Any action that reduces the angle of heel of a boat that is reaching or beating to windward will help reduce weather helm. Racing sailors use their body weight to bring the boat to a more upright position. Reducing or reefingReefing
Reefing is a sailing manoeuvre intended to reduce the area of a sail on a sailboat or sailing ship, which can improve the ship's stability and reduce the risk of capsizing, broaching, or damaging sails or boat hardware in a strong wind...
the total sail area will have the same effect and, counter-intuitively, many boats will sail faster with less sail in a stiff breeze once heel and weather helm have been reduced, due to the reduction in underwater drag (see Over-canvassed sailing
Over-canvassed sailing
A sailing boat that is carrying too much sail for the current wind conditions is said to be over-canvassed. An over-canvassed boat, whether a dinghy, a yacht or a sailing ship, is difficult to steer and control and tends to heel or roll too much...
). Easing the sheets on aft-most sails, such as the mainsail in a sloop
Sloop
A sloop is a sail boat with a fore-and-aft rig and a single mast farther forward than the mast of a cutter....
or cutter can have an immediate effect, especially to help with manoeuvering. Moving or increasing sail area forward can also help, for example by raising the jib
Jib
A jib is a triangular staysail set ahead of the foremast of a sailing vessel. Its tack is fixed to the bowsprit, to the bow, or to the deck between the bowsprit and the foremost mast...
(and maybe lowering the staysail
Staysail
A staysail is a fore-and-aft rigged sail whose luff can be affixed to a stay running forward from a mast to the deck, the bowsprit or to another mast....
) on a cutter.
Sailing off the wind, weather helm may be caused by the imbalance due to fore-and-aft sails all being sheeted out on the same (leeward) side of the boat. Raising a spinnaker
Spinnaker
A spinnaker is a special type of sail that is designed specifically for sailing off the wind from a reaching course to a downwind, i.e. with the wind 90°–180° off the bow. The spinnaker fills with wind and balloons out in front of the boat when it is deployed, called flying. It is constructed of...
or poling out a headsail to windward with a whisker pole can help. Yachts making ocean trade wind
Trade wind
The trade winds are the prevailing pattern of easterly surface winds found in the tropics, within the lower portion of the Earth's atmosphere, in the lower section of the troposphere near the Earth's equator...
crossings have rigged 'twins' - double headsails poled out to opposite sides from the same forestay for extended downwind passages without a mainsail. Square rig
Square rig
Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or square, to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the last stay, are called the yardarms...
ged sails also provide relatively symmetric drive off the wind.
Discussion
The fundamental cause of "helm", be it weather or lee, is the relationship of the center of pressure of the sail plan to the center of lateral resistance of the hull. If the center of pressure is astern of the center of lateral resistance, a weather helm, the tendency of the vessel to want to turn into the wind, or to weather-vane, will result.If the situation is reversed, with the center of pressure forward of the center of resistance of the hull, a "lee" helm will result, which is generally considered undesirable, if not dangerous. Too much of either helm is not good, since it forces the helmsman to hold the rudder deflected to counter it, thus inducing extra drag beyond what a vessel with neutral or minimal helm would experience.
See Sailing Theory and Practice by C.A. Marchaj for a mathematical analysis of the dynamics of weather helm.