The prediction of large amplitude roll motions and capsize events has proven to be difficult and includes large uncertainty. One of the reasons for this is a lack of knowledge of hydrodynamic forces and moments for large roll angles. Currently, the equations used by numerical models to predict forces and moments due to roll motion are based on small roll amplitude experimental data. In 2005, the Carderock Division, Naval Surface Warfare Center (NSWC/CD) tested Model 5613 (Figure 1), a tumble-home hull form, with the primary objective of obtaining model-scale forced motion seakeeping data to provide information necessary to perform validation of surge, sway, heave, roll, pitch, and yaw forces and moments acting on a combatant hull during large amplitude motions and capsize events. The model was forced in roll with amplitudes ranging from 5 to 50 and roll periods from 1 s to 3 s, at 4 forward speeds. During the test, the model was forced in roll both with and without bilge keels, with freedom to pitch and heave. The model had the ability to be fixed in yaw or free to yaw (only the fixed in yaw data are discussed in this paper). By performing a least squares fit of the measured data to a linear one-degree-of-freedom roll equation, the added inertia and roll damping coefficients can be determined. The added inertia and roll damping coefficients are greatest in magnitude for the higher speeds. Also, the added inertia coefficient reaches a maximum value for roll amplitudes of 20-30, while the roll damping coefficient reaches a minimum value for amplitudes of 20-30. This paper further examines the trends of the forces and moments, as well as the roll damping and added inertia coefficients as they relate to the roll characteristics and model speed.
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