An investigation into false-negative cases for low-freeboard ships in the vulnerability criteria of dead ship stability

False-negative inconsistency has been a problem in the vulnerability criteria of stability under dead ship conditions for low-freeboard ships. In this paper, model experiments of a chemical tanker and a cement carrier in beam waves were conducted to solve this problem. As a result, the primary reason for the inconsistency was identified, that is, the deck immersion, which decreases the effective wave slope coefficient and increases the roll damping. However, the deck immersion is not properly modelled in the level 2 vulnerability criterion. For this problem, these elements should be estimated with the model experiments. As alternative measures, it is confirmed that a nonlinear strip theory can evaluate the effect of deck immersion on the effective wave slope coefficient: an empirical method could be used to estimate the effect of the deck immersion on the roll damping.