Chapter 46 - Synchronous Rolling and Parametric Rolling of Ships

Abstract

This chapter discusses synchronous rolling and parametric rolling of ships. Synchronous rolling is caused by the ship's rolling period becoming synchronous or resonant with the wave period. When this occurs, the ship heels over and, in exceptional circumstances, is rolled further over by the action of the wave. Consequently, there is a serious danger that the vessel will heel beyond a point or angle of heel from which it cannot return to an upright condition. The chapter describes different methods to reduce synchronous rolling. It further deals with parametric rolling, which is produced by pitching motions on vessels which have very fine bowlines together with very wide and full stern contours. As the stern dips into the waves, it produces a rolling action. This remains unchecked as the bow next dips into the waves due to pitching forces. In effect, the rolling characteristics are different at the stern to those at the bow. It causes a twisting along the ship, leading to extra rolling motions.