Cavitation Water speeds up over the top of a hydrofoil, and where it goes fast enough the pressure falls below the point where water simply boils — at room temperature. A silvery sheet of vapour clings to the blade; bits break off, sweep downstream into slower, higher-pressure water and implode, each collapse a tiny violent flash that pits propellers and pumps. The journey: Bernoulli ties speed to a pressure drop; the suction peak is set by the lift (a bound vortex, Kutta 1902). Lower the cavitation number σ = (p∞−pᵛ)/(½ρU²) and the vapour sheet grows; each shed bubble follows Rayleigh’s 1917 collapse.