Closure of the Deep Wake Hollow of High-Speed Ships

Abstract

Interest has developed in recent years in the length of the "wake hollow" downstream of high-speed vessels with blunt transom sterns. Past work has shown that this wake cavity appears to increase the effective length of a vessel, and thereby reduce its effective Froude number, with the result of a reduction in wave resistance. The research presented here is development and demonstration of a simple mathematical theory for the downstream wake closure characteristics of fully ventilated wakes of fast ships with transom sterns. The theory uses the linear thin body approximations with gravity in a formulation consistent with the thin body theory of wave resistance, although wave resistance is not dealt with here. The length of the wake hollow, or "trench," predicted is compared with recent experiments. Calculations of variation of the hollow length with transom shape and Froude number are presented.