This paper presents a simplified hull girder model to quickly and accurately predict the overall whipping response of a vessel subjected to an underwater explosion. The effects of structural damping and fluid damping on the vessel dynamic response to an explosion directly below the midspan of a hull girder of uniform cross-section were analyzed. The load profile of an underwater explosion was first divided into five phases, and a theoretical model of fully elastic response and elastic-plastic response of the hull girder under the combined effects of an explosion shock wave and pulsating bubble was established and verified using experimental data. Finally, the effects of damping on the overall mode, period, and amplitude of the deformation, as well as the plastic hinge of the girder were investigated. When the damping effect is considered, the proposed model can capture the repetitive loading and unloading processes leading to plastic deformation of the girder and accurately forecast the period and amplitude of the overall periodic deformation of the hull girder with an error of less than 10%. Damping suppresses the whipping response, and the suppression effects were found to increase as the distance from the explosion decreases. Moreover, damping is an important factor affecting the plastic hinge rotation angle of the girder, and therefore, cannot be ignored.
