SHIP ROLL RESPONSE AND CAPSIZE BEHAVIOUR IN BEAM SEAS

Abstract

The Authors (or, respectively, the University of Bristol and the AMTE, Haslar) present a simple mathematical model for ships' rolling motions in beam seas, and test its predictive capability by comparisons with the results of some model experiments carried out in regular beam-sea conditions. The response of this roll equation to a periodic input is described and the stability of the response is analysed. Computer programs used for predicting the roll responses are briefly discussed, and comparisons are drawn between the predicted and measured responses of some actual model forms. One of the programs is then used to produce the roll responses of several hypothetical ships whose GZ curves are near the limits given by the present IMCO stability criteria for ships under 100 m in length. The results illustrate the importance of the ship's range of stability and the roll damping upon safety from capsizing, and it is concluded inter alia that new stability criteria should stipulate minimum roll-damping for ships with a small range of stability. The paper includes a consideration of a more comprehensive roll equation embracing the effects of heave, pitch, and sway, and also discusses the extension of the roll excitation to represent a continuous random perturbation of physical origin. Order from BSRA as No. 51,193.