If you ever wondered how hydrofoils work many explanations are floating around and one of the most popular ones goes something like this. Hydrofoils are like airplane wings are curved surfaces where one side is shorter than the other because fluid particles must travel from the leading edge (Front side of the wing) to the trailing edge (Backside of the wing) in the same amount of time, so fluid over the top surface must be going faster than the lower side of the wing (the longer distance on the top of the wing) and because of Bernoulli’s principle the pressure on the slower side (Bottom side) is higher than the pressure on the top side, in turn, creates an upward force called lift that explanation sounds pretty good right but the problem it’s actually wrong!

Fluid particles that split off the leading edge of the foil don’t have to reach the trailing edge at the same time! Scientists have proven it through experiments like the ones at the University of Cambridge. The second problem is how Bernoulli’s principle is used to explain the pressure gradient created by the foil, Bernoulli’s famous equation applies to fluid along the same streamline but does not apply across the top and bottom of the foil! So how do hydrofoils actually work, the answer is foils flow through the water at an angle and accelerate water downward and from Newton’s second and third law or force equals mass times acceleration, and for every action, there is an equal and opposite reaction if fluid is accelerated downward it is balanced by an upward force like a boat is held up by the downward acceleration of water.