Wave drag during an unsteady motion

The average wave drag in unsteady motion is studied experimentally with force measurements. Towing hulls of size at sinusoidal speed, the mean drag is measured for different amplitudes and frequencies of the fluctuating velocity, as well as different Froude numbers associated with the mean velocity . The wave drag is reported to be either increased or decreased by velocity fluctuations depending on. For small fluctuation amplitudes, this drag change is proportional to the square of the amplitude. The effect is maximized for a resonance frequency identified as the Wehausen frequency, which scales as times the inverse of the Froude number. All these results are rationalized by developing an extension to Havelock's theory.