The center of lateral resistance is the
center of pressure of the
hydrodynamic
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including '' aerodynamics'' (the study of air and other gases in motion) a ...
forces on the
hull of a
boat
A boat is a watercraft of a large range of types and sizes, but generally smaller than a ship, which is distinguished by its larger size, shape, cargo or passenger capacity, or its ability to carry boats.
Small boats are typically found on inl ...
. The center of pressure is the point on a body where the total sum of a pressure field acts, causing a force and no moment about that point. The total force vector acting at the center of pressure is the value of the integrated vectorial pressure field. The resultant force and center of pressure location produce equivalent force and moment on the body as the original pressure field. Pressure fields occur in both static and dynamic fluid mechanics. Specification of the center of pressure, the reference point from which the center of pressure is referenced, and the associated force vector allows the moment generated about any point to be computed by a translation from the reference point to the desired new point.
The relationship of the
aerodynamic center
In aerodynamics, the torques or moments acting on an airfoil moving through a fluid can be accounted for by the net lift and net drag applied at some point on the airfoil, and a separate net pitching moment about that point whose magnit ...
of pressure on the sails of a sailboat to the hydrodynamic center of lateral resistance on the hull determines the behavior of the sailboat in the wind. This behavior is known as the "helm" and is either a
Weather helm 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 le ...
or
lee helm. 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 and pointing into oncoming waves. Other sailors disagree and prefer a neutral helm.
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, the result is a weather helm, the tendency of the vessel to want to turn into the wind.
If the situation is reversed, with the center of pressure forward of the center of lateral 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.
Other boats
Other boats, including
kayak
A kayak is a small, narrow watercraft which is typically propelled by means of a double-bladed paddle. The word kayak originates from the Greenlandic word ''qajaq'' ().
The traditional kayak has a covered deck and one or more cockpits, each se ...
s, are subject to the same phenomena. To counter this, they use a
rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...
or
skeg
A skeg (or skegg or skag) is a sternward extension of the keel of boats and ships which have a rudder mounted on the centre line. The term also applies to the lowest point on an outboard motor or the outdrive of an inboard/outboard."A small fin f ...
.
See also
*
Centerboard
*
Keel
The keel is the bottom-most longitudinal structural element on a vessel. On some sailboats, it may have a hydrodynamic and counterbalancing purpose, as well. As the laying down of the keel is the initial step in the construction of a ship, in Br ...
*
Leeboard
A leeboard is a form of pivoting keel used by a sailboat largely and very often in lieu of a fixed keel. Typically mounted in pairs on each side of a hull, leeboards function much like a centreboard, allowing shallow-draft craft to ply waters f ...
*
Rudder
A rudder is a primary control surface used to steer a ship, boat, submarine, hovercraft, aircraft, or other vehicle that moves through a fluid medium (generally aircraft, air or watercraft, water). On an aircraft the rudder is used primarily to ...
*
Skeg
A skeg (or skegg or skag) is a sternward extension of the keel of boats and ships which have a rudder mounted on the centre line. The term also applies to the lowest point on an outboard motor or the outdrive of an inboard/outboard."A small fin f ...
References
Further reading
*{{cite web , url=http://www.paddling.net/guidelines/showArticle.html?show=779 , title=Rudders & Skegs: Maneuvering Aids , first1=Tom , last1=Watson , publisher=paddling.net , date=February 12, 2014 , accessdate=February 12, 2014 , archive-date=February 23, 2014 , archive-url=https://web.archive.org/web/20140223103456/http://www.paddling.net/guidelines/showArticle.html?show=779 , url-status=dead
Boating