Ship wakes: Kelvin or mach angle?

Abstract

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 Fr=U/√gLâ‰0.5, where L is the hull ship length. © 2013 American Physical Society.