Competition of Class I and II Instabilities in Evolution of Crescent Waves

A laboratory experiment on the instability of Stokes wave trains with large steepness in finite water depths in a wave basin is performed. Two class instabilities of Stokes wave, quartet interaction and quintet interaction, were observed, and it is found that the evolution of crescent wave pattern is affected by the development of quintet interaction. The dependence of this effect on relative water depth was analyzed. The wave steepness for the occurrence of the competition is examined by applying linear instability analysis of Stokes wave.