Regarding the design of anchorage depth under the influence of long-period waves,a study was conducted on the vertical motion of ships under wave action and the probability of bottoming out.The design conditions are determined through a detailed analysis of hydrological conditions,taking into account both wind-induced wave and long-period surges during monsoon periods.The probability design of anchorage depth is carried out using the UNDERKEEL software,and the model calculations are based on standard linear wave theory and potential flow theory.The model calculation includes the motion of the ship in 6 different directions and considers the wave forces in each direction.Under the specified acceptable probability of bottoming out,the safe anchorage depth of 200,000-ton class container ships under different wave heights and periods is calculated.Based on the calculation results,it is concluded that long-period wave with an average period of more than 13.0 s have an increasingly significant impact on the vertical motion of the anchored 200,000-ton class container ships.The analysis results of the impact of long-period wave with an average period of 16.0 s on the vertical motion of the 200,000-ton class container ships,which are not provided in relevant specifications,are also supplemented.The relevant research methods can be used as a reference for other projects.