Experimental Analysis of Forced Oscillations for a Double-Stepped Planing Hull

Planing-hull dynamics differ markedly from those of displacement vessels because, at high speeds, hydrodynamic lift dominates and pressure forces depend strongly on the instantaneous wetted surface—even small heave and pitch motions can introduce non-linearities that invalidate conventional linear seakeeping methods. Moreover, modern hull forms compound this complexity through geometric features such as transverse steps, spray rails, and variable deadrise, whose unsteady hydrodynamic behavior remains largely unquantified in the experimental literature. This paper presents results of a Vertical Planar Motion Mechanism (VPMM) experimental campaign for a double-stepped hard chine hull in the high-speed planing regime corresponding to a volumetric Froude number of Fr∇=4.0. Forced heave, forced pitch, and novel combined heave–pitch harmonic motions were imposed to the model towed in calm water across four frequencies and two amplitudes. Time-histories of heave force and pitching moment reveal clear non-linearities with respect to the imposed regular harmonic motion. Linear added mass, damping, and restoring coefficients are identified via first-order Fourier decomposition. The identified coefficients provide first-order estimates for stability and porpoising-onset prediction, and the shared time-series data support development of higher-fidelity, data-driven force models. Time series of heave force and pitch moment are also provided as a benchmark for CFD validation and data-driven modeling.