Estimation of ship roll damping for the investigation of extreme roll events

Importance of ship roll motion investigation Extreme roll motions can occur for different reasons. A ship can suffer a static as well as a dynamic loss of stability. Broaching of ships, a course keeping loss, can also lead to large roll amplitudes. In irregular seaway, a combination of one phenomenon with additional external factors such as wind or green water on deck are reasons why ships develop large roll angles or accelerations, see also de Kat and Randolph Paulling (2001) [20]. Large roll angles and accelerations can cause crew accidents and cargo losses or lead to capsizing1. A sufficient roll damping moment prevents dynamic loss of stability due to parametric as well as resonant excitation induced by waves. A Sub-Committee on Ship Design and Construction (SDC)2 of the International Maritime Organization (IMO) is working on regulations to prevent stability failures which are unsafe for crew and ship3. At this time a multi-tiered approach to check the intact stability of ships is being discussed under the name Second Generation Intact Stability Criteria, see e. g. Belenky et al. (2011) [7]. To investigate dynamic stability events, three levels are introduced: Level 1, Level 2 and the Direct Assessment. Whereas Level 1 should be a simple test criteron, the more complex Level 2 and the time and cost-intensive Direct Assessment of extreme roll phenomena based on simulations have to be applied if one of the previous criteria fails.