## 4 Analysis of the Loading Status of an Example Container Ship (Results and Discussion)  
Figure 2 shows a simulation of the loading of containers into the examined ship. In the simulation, 2500 20-foot containers weighing 10 t were loaded, with the ballast tanks filled so that as many containers as possible could be loaded, while meeting the stability criteria. For the purpose of the simulation, the fuel, lubricating oil, and freshwater tanks were assumed to be filled at 70%. The program was used to verify whether the stability requirements for this vessel were met (Table 3). \begin{table}
\begin{tabular}{l c c c} \hline \hline \multicolumn{4}{c}{**Stability Results/without d. Cont.–SeeBG**} \\ \hline \hline \multicolumn{2}{c}{**Lever Balance—OK! Actual**} & \multicolumn{2}{c}{**Limit**} & \\ \hline GM’ (corrected) & 0.421 & 0.421 & m \\ \hline Angle due to transverse Moment & 0.016 & 3.000 & degr. \\ \hline Angle due to Wind + transverse Moment & 0.016 & 18.000 & degr. \\ \hline GZ Lever at 30 Degrees & 0.463 & 0.455 & m \\ \hline Statistical Stability Range & 53.962 & 50.000 & degr. \\ \hline Area up to 30 Degrees & 0.100 & 0.055 & mrad \\ \hline Area up to 40 Degrees & 0.191 & 0.090 & mrad \\ \hline Area between 30 and 40 Degrees & 0.091 & 0.030 & mrad \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Stability criteria for a ship loaded with 10 t containers. Authors’ work. Figure 2: Loading plan for containers of 10 t (red) and 10.5 t (green), created with the MACS3 program. The visible numbers correspond to the subsequent bays of the container ship. Authors’ work. In the examined situation, the ballasting may cause exceeding of sheer forces or bending moments, as they are close to the limits (e.g., at frame 222, Table 6). Also, the deadweight reserve in this situation is 770 t, which doesn't allow the ballasting of a great amount of water. The deadweight reserve in this situation is 770 t, which means that only 770 t of ballast can be taken so the ship is still alfloat. In this situation, only three ballast tanks can still be ballasted, and this will cause exceeding of allowable bending moments. Such a situation may contribute to the weakening of the hull structure through reducing the safety margin between the total experienced bending moment and the strength of the hull. This is considered one of the favourable circumstances of the MSC Napoli accident in the Dover Strait in 2008, which resulted in the ship breaking in two parts [48]. In the report, the following possible causes were mentioned: the ship's speed was not sufficiently reduced in bad weather conditions, no sufficient bucking strength in the way of the engine room, buckling strength calculations were not compulsory in the amidship area, load on the hull was probably increased by the whipping effect, and an insufficient safety margin between the hull's design loading and its ultimate strength [48]. Based on the mentioned report, an Ishikawa cause and effect diagram was created (Figure 3). The probable main causes of these accidents include improper storming, discrepancy between the actual weight of the containers and the declared weight, frequent loading of the ship at its limits, and exceeding the maximum bending forces. These causes depended on human actions. It can be seen that two of the three mentioned accidents were related to the loading status of the ship. One of the main problems related to cargo on a container ship is indicated here--incorrect declaration of cargo weight. The position of 700 containers loaded on the deck of MSC Napoli was checked. Of these units, 53 (7%) were in either the wrong position or declared as the wrong container. The general agreement in the container industry allows 10% of loaded containers not to be in the planned position. Moreover, the post-accident audit indicated that the weights of many containers onboard were inaccurate. About 660 dry, remaining containers were weighed. The weight of 20% of them was more than 3 tonnes different from the declared weights.