Editing Hydrofoil (section)

==Hydrodynamic mechanics==
{{unreferenced section|date=March 2016}}
[[File:Hydrofoil types.svg|450px|thumb|The two types of hydrofoils: surface-piercing and fully submerged]]

Since air and water are governed by similar [[fluid dynamics|fluid equations]]—albeit with different levels of [[viscosity]], [[density]], and [[compressible flow|compressibility]]—the hydrofoil and [[airfoil]] (both types of [[foil (fluid mechanics)|foil]]) create [[lift (force)|lift]] in identical ways. The foil shape moves smoothly through the water, deflecting the flow downward, which, following the [[Euler equations (fluid dynamics)|Euler equations]], exerts an upward force on the foil.  This turning of the water creates higher pressure on the bottom of the foil and reduced pressure on the top. This pressure difference is accompanied by a velocity difference, via [[Bernoulli's principle]], so the resulting flow field about the foil has a higher average velocity on one side than the other.

When used as a lifting element on a hydrofoil boat, this upward force lifts the body of the vessel, decreasing drag and increasing speed. The lifting force eventually balances with the weight of the craft, reaching a point where the hydrofoil no longer lifts out of the water but remains in equilibrium. Since wave resistance and other impeding forces such as various types of [[drag (physics)]] on the hull are eliminated as the hull lifts clear, turbulence and drag act increasingly on the much smaller surface area of the hydrofoil, and decreasingly on the hull, creating a marked increase in speed.<ref>{{cite web
 | url =http://web.mit.edu/2.972/www/reports/hydrofoil/hydrofoil.html
 | title =Hydrofoils
 | last =Rosado
 | first =Tina
 | date =1999
 | website =Reports on How Things Work
 | publisher =Massachusetts Institute of Technology
 | access-date =11 December 2016
 }}</ref>

===Foil configurations===
Early hydrofoils used V-shaped foils. Hydrofoils of this type are known as "surface-piercing" since portions of the V-shape hydrofoils rise above the water surface when foilborne. Some modern hydrofoils use fully submerged inverted T-shape foils. Fully submerged hydrofoils are less subject to the effects of wave action, and, therefore, more stable at sea and more comfortable for crew and passengers. This type of configuration, however, is not self-stabilizing. The [[angle of attack]] on the hydrofoils must be adjusted continuously to changing conditions, a control process performed by sensors, a computer, and active surfaces.