Narrow ship wakes and wave drag for planing hulls

The angle formed by ship wakes is usually found close to the value predicted by Kelvin, α=19.47°. However we recently showed that the angle of maximum wave amplitude can be significantly smaller at large Froude number. We show how the finite range of wavenumbers excited by the ship explains the observed decrease of the wake angle as 1/Fr for Fr>0.5, where Fr=U/gL is the Froude number based on the hull length L. At such large Froude numbers, sailing boats are in the planing regime, and a decrease of the wave drag is observed. We discuss in this paper the possible connection between the decrease of the wake angle and the decrease of the wave drag at large Froude number. •Simulation of narrow wakes at large hull Froude number.•Observation of a decrease of the wave drag when the wake is narrow.•Comparison of the wave drag evolution to the case of planing hull.