Effective horsepower (EHP)

Effective power $P_E$ (EHP) is the power needed to tow the bare hull at speed $V$ against total resistance: $P_E = R_T \cdot V$. It is the resistance side of the power chain, before any propulsive losses. Delivered power at the propeller $P_D = P_E / \eta_D$, where the quasi-propulsive coefficient $\eta_D$ folds in hull, open-water, and relative-rotative efficiencies. EHP comes from model resistance tests or methods like Holtrop-Mennen.