Objectives  Probabilistic damaged stability is one of the most important factors to ensure the safety of ships. With the release of SOLAS 2020, the passenger ship subdivision index R requirement has been greatly increased. Therefore, attention should be paid to the probabilistic damaged stability of cruise ships.

  Methods  The R of SOLAS 2020 and SOLAS 2009 were compared and analyzed for medium cruise ships. The initial scheme was analyzed by using Maxsurf software. The difference between the R of SOLAS 2020 and the attained subdivision index A was large. Through analysis of the influencing factors of A, three kinds of improvement measures, including increasing the longitudinal subdivision, setting up cross-flooding fitting, and reducing the height of the center of gravity, were put forward. Also, the improvement schemes were analyzed.

  Results  Compared with SOLAS 2009, SOLAS 2020 has increased R of medium cruise ships carrying about 1 250 passengers by about 13.6%. The improvement of A is more than 10% by setting up cross-flooding fitting, 8.7% by increasing longitudinal subdivision, and the improvement of A is weaker by reducing the height of the center of gravity because of the larger initial GM. By adopting the combination scheme of improvement measures, the medium cruise ship meets the requirement of subdivision index R of SOLAS 2020.

  Conclusions  Through comparison, aiming at the medium-sized cruise ship with large GM, the improvement effect of setting up cross-flooding fitting is seen to be the best, followed by increasing the longitudinal subdivision, and the effect of reducing the height of the center of gravity is weak.