Toward a New Procedure for the Quantitative Risk Assessment of Double Hull Oil Tankers in Collisions

Abstract

In recent decades, the number of ships increased substantially and it is still expected to continue to increase. Collision risk is one of the most serious accidents that can lead to severe consequences, such as casualty, property damage and environmental pollution. According to the statistics, it is found that the developments in collision avoidance systems and the related regulations have not contributed much to prevent the collision accidents. The aim of the present study is to develop a new methodology for the quantitative risk assessment of double–hull oil tankers. Within the framework of the methodology, a probabilistic approach is introduced to define a relevant set of ship–ship collision scenarios by treating the accidental influencing parameters as random variables. The collision frequency is calculated for each of the selected collision scenarios by considering a double–hull oil tanker collided with different types of striking ships. To predict the resulting collision damage to the struck ship, numerical simulations are conducted for each scenario by performing nonlinear finite element analyses. Based on the calculated risks, exceedance curves are established that can be used to define the collision design loads in association with various design criteria. In addition, to give a more complete picture of the risk assessment, a new method is proposed for assessing the risk of ship’s hull collapse following a collision. The results are formulated in terms of the residual strength index (RSI) and the loading ratio to produce the relationship between residual strength (R) and loading ratio of horizontal bending moment to vertical bending moment (L) and design formulations for predicting the RSI of damaged ship hulls are derived in an empirical manner. As an applied example, a hypothetical Suezmax–class double hull tanker is considered as a struck ship. Collision risks to asset and the environment are assessed. It is considered that the developed methodology can be useful in the early design stage of oil tankers.