Abstract This paper is part II of a two part paper. The model used in this part is a parallel flat plate-type structure in a rigid water trough or rigid rectangular tube. A narrow channel exists between any two adjacent plates of the structure. The motion equations of the plate-type structure vibrating in water are obtained by extending the method for a typical cross-section of plate-fluid-plate system presented in the first part of this paper. The computational frequencies of the structure vibrating both in air and in water are compared with those measured by a resonance test. The results show that the local frequencies of the minor plate-type beams of the structure decrease much more strongly than those of the structure vibrating in water. Moreover, the varying tendency of frequencies of the structure with two different water boundary conditions is discussed.