Floating caisson of navigation pass C-1 is designed for shutdown in case of threat of flooding the main ship canal in St.-Petersburg flood protection barrier. Conditions, in which the floating caisson must work, resulted in creation of a special design. Research results of floating caisson damping system of С-1 navigation pass are presented in the study. Substantial vibrations of floating dams in the process of putting it on the threshold caused by wave disturbance and flow determined the necessity of the development of special devices, providing damping these oscillations in the final phase of the dam immersion. Soft-landing system of each floating dam involved the groups of hydraulic dampers and supporting structures, equipped with damping elements. The data received by mathematical modeling and by means of physical experiment are stated. The investigation became the basis for the developing and perfecting the floating caisson damping system elements during the ship canal С-1 shutdown. Commissioning tests confirmed the validity of the research results and calculations.