On the heading stability of a ship in waves

A procedure is presented for analysing the sway-yaw-heading stability of a ship in regular waves. A linear stability analysis of the motion equations of the ship, using a mathematical model for approximating the hydrodynamic forces acting on the ship including mean forces and moments due to waves, shows if the equilibrium state for a given wave, i.e. the corresponding combination of rudder and drift angle, represents a stable condition. RANS computations for the container ship DTC in calm water and in regular waves of diverse lengths coming from several directions have been used to determine all coefficients of the mathematical model in the showed sample application. Selected situations proven to be stable in theory have successfully been directly simulated afterwards with the RANS code, confirming the validity of the proposed procedure. Some preliminary experiments at the Hamburg Ship Model Basin HSVA support our approach.