Effect of Forward Speed on Ship Rolling and Stability

Ship stability is evaluated at zero speed most of the time. Majority of the stability criteria is also based on the behavior of ships at standstill. However unlike fixed offshore platfoims, ships are on the move due to their nature of operation. Therefore a ship's hydrostatic and hydrodynamic characteristics undergo changes because of the varying underwater volume, centers of buoyancy and gravity and pressure distribution. This work deals with the effects of forward speed on ship stability and motions, particularly on rolling motion in synchronous beam waves. An equation of nonlinear roll motion is chosen to calculate roll responses of a test vessel in beam seas. The speed of advance is incremented and roll responses are determined at each speed interval. Various characteristics of GZ curve for the selected test vessel are altered systematically to observe their effects on roll responses along with the forward speed. Several computer programs are also employed to handle colossal mathematical manipulations.