1 INTRODUCTION The paper seeks for a simple formula for a rapid prediction of grounding damage of double hull tank- ers. Such simplified formulation could be used in risk analysis studies where there are no specific in- formation regarding the structural arrangement of ships and the main available parameters are the main dimensions of the ships. Several simplified models have been developed to describe a ship grounding accidents. The models either base on a simplified closed form expressions (Simonsen et al, 2009; Hong & Amdahl, 2012) or on numerical simulations (Alsos & Amdahl, 2007). Precise numerical simulations hardly suit to risk analysis studies as the simulation of a single scenario will take several hours. On the other hand, simplified models are often limited to a certain sea bottom to- pology or to ship’s structural configuration. Moreo- ver, often the methods require that to some extent the damage mechanics are prescribed: for example, the description of contact energy is based on the fracture propagation in the bottom plating. Paper aims to derive a simple formulation based on small number of parameters that describe the structural resistance of a tanker in a grounding acci- dent. The principle of the simplified approach is pre- sented in Figure 1. The approach is similar to Ehlers & Tabri (2012), where such combined approach was presented for the analysis of ship collisions. The simplified formula is derived based on a number of numerical grounding simulations. Three double- bottom tankers of different length are included in the analysis- 120, 190 and 260 m in length. Each tanker is analyzed for five different penetration depths and for four different rock sizes. First, numerical simula- tions are conducted in displacement controlled man- ner as the aim of the numerical analysis is to study structural resistance alone. Analyses provide the contact force time-history for each grounding scenar- io. As here our aim is to evaluate the extent of dam- age, we concentrate on the horizontal grounding force as a main energy absorbing mechanism. Based on these time histories the average horizontal contact force is evaluated. Evaluating the average horizontal grounding forces for all the scenarios for a certain ship gives as a result a set of curves that describe the dependency of the average grounding force as a function of penetration depths and the rock size. Other grounding simulation models such as GRACAT for example, are not included in the anal- ysis as they require rather detailed presentation of the ship structure. A simplified approach to predict the bottom damage in tanker grounding Martin Heinvee, Kristjan Tabri Dept. of Civil Engineering, Faculty of Mechanical Engineering, Tallinn University of Technology, Estonia Mihkel Kõrgesaar 2 Dept. of Applied Mechanics / Marine Technology, Aalto University, Espoo, Finland ABSTRACT: A simplified formula to evaluate the grounding force and the longitudinal extent of structural damage in tanker groundings is derived in the paper. The formula is derived based on numerical simulations. First, a set of grounding accidents are simulated numerically for tankers of different dimensions- 120, 190 and 260 m in length. The simulations are conducted for five different penetration depths and for several rock/ground topology. Thus, the numerical simulations provide a response of different structural configura- tions to different combinations of penetration depth and bottom topology. Average horizontal grounding force is analysed and presented through the pressure acting on the contact surface between the rock and the ship’s double-bottom. It is shown in the paper, that this pressure can be described as a function of rock size and a constant depending on the ship size. Simplified equations are derived for the average contact force and the longitudinal length of the penetration. Comparison to numerical simulations reveals that such a simplified equation is capable of describing the grounding force for penetration depths larger than 0.5 m i.e. for the sce- narios, where significant structural damage occurs.