Abstract: An investigation on smeared thickness method used in prediction of grounding characters for double bottom tanker over obstacles with large contact surface and trapezoidal cross-section is conducted. Paik calculates the smeared thickness by adding a parameter kto consider the property of stiffeners on the plating. In order to decide the parameter k, detailed research is conducted in this paper by using numerical simulation technique. A hold of a double bottom tanker is chosen as the object. Two finite element models are built, one with stiffeners and the other without stiffeners but with smeared plate thickness. With the comparison of simulation results, the feasibility of the smeared thickness method is verified. The suitable values of parameter kin smeared thickness method are determined for different indentation and slope angle cases. The research provides a basis for determination of the parameter k, which improves accuracy for predicting ship grounding characters by smeared thickness method.