Bernoulli equation

The Bernoulli equation states that along a streamline in steady, inviscid, incompressible flow the sum p + 0.5 rho V^2 + rho g z stays constant, trading static pressure against dynamic pressure and elevation head. In ship hydrodynamics it underlies potential-flow and panel methods, links the pressure field around a hull to local velocity, and explains why pressure drops where flow accelerates over the shoulders and at the propeller. When local pressure falls to the water vapor pressure, cavitation begins, which is the Bernoulli result behind cavitation-number analysis. The equation ignores viscosity, so it does not predict frictional resistance.