Characteristics of Roll Damping of Pure Car Carrier and Liquefied Natural Gas Carrier and applicability of Ikeda’s Method

It is important for the safety of ship in waves to understand its roll characteristics at the design stage. However, it is not easy to estimate roll accurately, because the viscous effects on roll damping affect significantly roll near its resonance frequency. For that purpose, it is significant to estimate roll damping accurately. As one of prediction methods of the viscous effects, Ikeda’s method is well-known. However, it is pointed out by Tanaka et al. (1981) that the method overestimates the roll damping when the method is applied to a ship with shallow draught. On the other hand, with the recent enlargement and specialization of merchant ship, its breadth has increased compared to the hull form at the time when Ikeda's method was developed, and its height of the center of gravity has increased relative to draft. Therefore, when Ikeda's method is applied to such hull form, there is a concern that the estimation accuracy will deteriorate. In this study, the characteristics of roll damping for two hull types (PCC: Pure Car Carrier and LNGC: Liquefied Natural Gas Carrier) with shallower draft and higher center of gravity compared to the ships which existed when Ikeda's method was developed, are investigated experimentally. The measured results are compared with the results of Ikeda’s method to confirm the estimation accuracy and its characteristics, and the results of investigating the difference of them are reported.