Planing

Planing is the high-speed regime in which a hull is supported chiefly by hydrodynamic pressure on its bottom rather than by buoyant displacement, so it rides up and skims the surface with sharply reduced wetted length and resistance. It sets in above the hump speed, conventionally a speed-length (Froude) regime with the volumetric Froude number above about 1.0, once dynamic lift L = 0.5 rho V^2 b^2 C_L can carry the weight. Bottom deadrise, trim, and wetted length govern the lift and spray, analyzed by Savitsky’s prismatic-planing method from deadrise, loading coefficient, and speed. Running trim is the key variable: too much raises induced drag, too little floods the bow and raises friction.