Foil

A foil works like an aircraft wing, but in water, 800 times denser than air: at speed, a small surface is enough to lift several tonnes. By lifting the hull partly or fully out of the water, it reduces drag and allows speeds that used to be out of reach.

On IMOCA monohulls, the foils come out on each side of the hull and relieve the boat; on Ultim trimarans they make it fly entirely. Their shape (C, J, L, U) sets lift, stability and how easy the boat is to control. They retract and their angle can be adjusted.