A procedure for strength assessment of a ship structure partially grounded in mud is developed. The paper deals with a practical engineering problem of evaluating the structural integrity of a single bottom tanker which, after its regular service, was grounded in mud and continued to be used as oil storage in order to increase the storage capacity of the port. A mathematical model of the ship static equilibrium is formulated, consistently taking into account the ship, the cargo and ballast weights, the supporting mud reaction, and the surrounding water buoyancy. For simplicity, the global strength assessment is done using the beam model, where the calculation of ship sectional properties is performed by the specialized in-house software. Subsequently, the developed model is used as a basis for a detailed 3D FEM analysis. The thickness measurements of the complete ship structure were performed in order to directly account for the corrosion effect.