Editing Sailing (section)

== Hull physics ==
{{See also|High-performance sailing}}
Waterborne sailing craft rely on the design of the hull and keel to provide minimal forward drag in opposition to the sails' propulsive power and maximum resistance to the sails' lateral forces. In modern sailboats, drag is minimized by control of the hull's shape (blunt or fine), appendages, and slipperiness. The keel or other underwater foils provide the lateral resistance to forces on the sails. Heeling increases both drag and the ability of the boat to track along its desired course. Wave generation for a displacement hull is another important limitation on boat speed.<ref name=:1>{{Cite book|last=Garrett|first=Ross|url=https://books.google.com/books?id=0VLXORumEF4C&dq=hull+design&pg=PA68|title=The Symmetry of Sailing: The Physics of Sailing for Yachtsmen|date=1996|publisher=Sheridan House, Inc.|isbn=978-1-57409-000-0|language=en}}</ref>

=== Drag ===
Drag from its form is described by a [[Hull (watercraft)|prismatic coefficient]], C<sub>p</sub> = displaced volume of the vessel divided by waterline length times maximum displaced section area—the maximum value of C<sub>p</sub> = 1.0 being for a constant displace cross section area, as would be found on a barge. For modern sailboats, values of 0.53 ≤ C<sub>p</sub> ≤ 0.6 are likely because of the tapered shape of the submerged hull towards both ends. Reducing interior volume allows creating a finer hull with less drag. Because a keel or other underwater foil produces lift, it also produces drag, which increases as the boat heels. Wetted area of the hull affects total the amount of friction between the water and the hull's surface, creating another component of drag.<ref name=:1 />

=== Lateral resistance ===
Sailboats use some sort of underwater foil to generate lift that maintains the forward direction of the boat under sail. Whereas sails operate at angles of attack between 10° and 90° incident to the wind, underwater foils operate at angles of attack between 0° and 10° incident to the water passing by. Neither their angle of attack nor surface is adjustable (except for moveable foils) and they are never intentionally stalled, while making way through the water. Heeling the vessel away from perpendicular into the water significantly degrades the boat's ability to point into the wind.<ref name=:1/>

=== Hull speed and beyond ===
[[Hull speed]] is the speed at which the wavelength of a vessel's [[bow wave]] is equal to its [[waterline length]] and is proportional to the square root of the vessel's length at the waterline. Applying more power does not significantly increase the speed of a [[Displacement hull|displacement vessel]] beyond hull speed. This is because the vessel is climbing up an increasingly steep bow wave with the addition of power without the wave propagating forward faster.<ref name=:1 />

Planing and foiling vessels are not limited by hull speed, as they rise out of the water without building a bow wave with the application of power. Long narrow hulls, such as those of catamarans, surpass hull speed by [[Wave-piercing hull|piercing]] through the bow wave. Hull speed does not apply to sailing craft on ice runners or wheels because they do not displace water.<ref name=":2">{{Cite book|last=Bethwaite|first=Frank|url=https://books.google.com/books?id=WTRLAAAAQBAJ&q=faster+than+the+wind|title=Higher Performance Sailing: Faster Handling Techniques|date=4 August 2013|publisher=A&C Black|isbn=978-1-4729-0130-9|language=en}}</ref>