The review of research on the hydroelasticity shows that understanding of the subject has been increased but discussions of practical implications of hydroelasticity to ship design are rare. The authors aimed to change this and investigated how allowance for the hydroelasticity affects assessment of ship performance. This has been illustrated by analyzing a modern cruiseship in the aftship slamming condition with and without hydroelastic interaction. The scope of work included analysis of a simplified hydroelastic model, which reproduces important structural ship properties such as whipping and local aftship vibration modes. The hydroelastic interaction has been modeled at the slamming position only. The following ship design criteria have been considered: passengers discomfort, overall hull girder strength and local strength. The analysis has been described to facilitate the reader with a possibility to carry out a similar analysis of his design.