Countermeasures of ships for tsunamis became a major concern for ship operators after the Great East Japan Earthquake in 2011. Evacuation from ports is generally recommended to avoid tsunami disasters. However staying in port with enhancement of mooring lines could be another option. In this study, a dedicated model experiment to tow a quay wall and a ship model together was conducted to estimate hydrodynamic forces acting on a containership alongside a quay wall under tsunami attack, to discuss the required strength of mooring against tsunami flows. Finally, a simple conversion formula was proposed based on the experimental results, to estimate the wind speed equivalent to the tsunami-induced hydrodynamic forces.