The stability of incompressible, inviscid shear flow in sea straits of arbitrary cross section known as extended Taylor-Goldstein problem is considered in this paper. For this problem we derive the stability characteristics of shear flow at the neutral curve. A method is presented in this paper which makes it possible to study the rate of change physical quantities on the stability boundary for a class of flows.

hydrodynamic stability, shear flows, variable cross section, sea strait.