Natural frequencies of the vertical vibration of bulk carriers and destroyers were calculated by means of a digital computer, with a special attention to the shear rigidity, and the results were compared with those of the measurements on their sea trials. Both results showed good agreements in the lower mode, while in the higher mode there are discrepancies which are attributed to the estimation of the physical properties of ships. The ratio of calculated frequencies are nearly equal in the same type of ship and the empirical coefficients can be made for the similar ships. Contents