Damping coefficient (roll)

The roll damping coefficient quantifies the energy dissipated per unit roll velocity in the roll equation of motion, appearing as b_44 in (I_44 + a_44) phi-double-dot + b_44 phi-dot + c_44 phi = M(t). Roll is lightly damped and strongly nonlinear, so b_44 is split into wave-radiation, eddy-making, hull-friction, lift, and bilge-keel components, the Ikeda prediction method being the standard breakdown. It is usually reported as a nondimensional ratio of critical damping or as linear-plus-quadratic terms B_1 phi-dot and B_2 phi-dot times the modulus of phi-dot, identified from free-decay tests. Because radiation damping near resonance is small, viscous and bilge-keel terms govern peak roll.