Hydrofoil - Hydrodynamics of Hydrofoil-equipped Boats ("hydrofoils")

Hydrodynamics of Hydrofoil-equipped Boats ("hydrofoils")

Since air and water are governed by similar fluid equations, albeit with vastly different levels of viscosity, density, and compressibility, the hydrofoil and airfoil create lift in identical ways (see foil (fluid mechanics)). The foil is shaped to move smoothly through the water causing the flow to be deflected downward which according to Newton's Third Law of Motion exerts an upward force on the foil. This turning of the water causes higher pressure on the bottom and reduced pressure on the top of the foil. This pressure difference is accompanied by a velocity difference, via Bernoulli's principle, so the resulting flowfield 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 is lifted clear, turbulence and drag act only on the much smaller surface area of the hydrofoil and there is a marked increase in speed.