The paper presents a comparative analysis of the pressures and accelerations of the ship's motions, obtained by direct hydrodynamic analysis of the ship's linear motions, with the values from the DNV normativeregulatory documents. To carry out direct hydrodynamic calculations of pressures and amplitudes of the ship's roll, the panel method has been used to solve the problem of potential fluid flow around a body. For comparison, an approach has been used based on the determination of equivalent waves that produce the most realistic dangerous states of the ship's hull and the corresponding external loads, taking into account the phase of their action relative to the passage of the wave crest of the position of the ship's midsection. A comparison of long-term responses of parameters of external wave loads based on the approach based on equivalent waves has been given. Comparison of the resulting cross-sectional pressure diagrams demonstrates a qualitative convergence with the pressure patterns presented in the rules for dynamic cases. In the course of the research, a comparison of the obtained pressures and motion parameters from direct hydrodynamic calculations with the corresponding values from the regulatory documents of classification societies has been considered.