From the analysis of a set of airborne images of ship wakes, we show that the wake angles decrease as $U^{-1}$ at large velocities, in a way similar to the Mach cone for supersonic airplanes. This previously unnoticed Mach-like regime is in contradiction with the celebrated Kelvin prediction of a constant angle of 19.47° independent of the ship’s speed. We propose here a model, confirmed by numerical simulations, in which the finite size of the disturbance explains this transition between the Kelvin and Mach regimes at a Froude number $\mathrm{Fr}=U/\sqrt{gL}\simeq 0.5$, where $L$ is the hull ship length.

• Received 2 January 2013

DOI:https://doi.org/10.1103/PhysRevLett.110.214503