A new method for assessing the safety of ships damaged by collisions

The longitudinal strength of a ship decreases with the reduction in its bending moment capacity following a collision accident. Therefore, the damaged ship should be able to reach the closest harbour safely without any catastrophic hull girder collapse. This paper aims to develop a method to predict the hull girder residual strength of double-hull oil tankers by considering probabilistic collision damage scenarios. The collision damage index is defined as the reduction ratio of the vertical hull girder moment of inertia, and the residual strength index is (RSI) characterised as the reduction ratio of the hull girder ultimate bending moment. Four different as-built double-hull oil tankers were studied to demonstrate the proposed method and to formulate the collision damage index. The relationships between the residual strength index and the collision damage index are identified in the form of diagrams. The produced diagrams and regressions represent a first-cut assessment of a ship's safety immediately after taking collision damage.