Influence of water depth on roll natural period and added mass moment of inertia of large commercial ships in shallow water regions

Roll stability is the dominant factor in ship stability in order to ensure safety, comfort, and vessel and goods survivability. The popularization of seakeeping software based on strip theory resulted in high prediction accuracy of heave and pitch motion. However, some commercial software neglected the effect of change in water depth on the added mass moment of inertia which lowered the accuracy in roll motion prediction.

This study aims to investigate the effect of water depth on the added mass moment of inertia in vessel roll motion, to improve the accuracy in roll period prediction under various water depths. Roll decay tests were conducted to obtain the roll period of bulk carrier model (C_B:0.85) and container ship model (C_B0.69) at different water depths. The added mass moment of inertia increased exponentially with the decrease in water depth within the shallow water region; no significant influence was observed in the deep-water region. The ratio of added mass to the models’ displacement were found to be 125.7% and 146.8% greater at d/T of 1.166̇ than that in deep-water which has resulted in an increment of 7.6% and 16.3% in the roll natural period of the container ship and bulk carrier model respectively. The experimental results helped in understanding the effect of water depth on the roll added mass moment of inertia and the natural period, and also served as base data for validation and comparison in accuracy of numerical simulations.