## 4 Results and Discussion
### Excessive Acceleration Level One Operational Limitation  
To this end, it is clear that WST varies significantly over the season for the considered sea area, hence the probability of wave occurrence. Therefore, this variation could negatively affect the estimation of simplified OM, given that the modification of environmental factors is possible in achieving OM using VC1 and VC2. In this study, [PERSON] methodology, as discussed in Section 2.3, is used to introduce operational limitations for evaluating excessive acceleration level one for C11 container ships. In the following discussion, only mean sea AHD data are considered, and a similar comparison could be made with AHD wind data. Tables 8 and 9 show the estimated wave height and wind speed for developed WST based on [PERSON]'s method. The standard WST's wave height and wind speeds are 8.9 m and 26 m/s (green font) [26]. The values of the same parameters for the AHD estimate, which are higher than the standard WST, are highlighted in red. Based on the developed table (Tables 8 and 9), the wave steepness table was developed for each WST to introduce seasonal and regional operational limitations. The wave steepness factor for the standard WST recommended by IMO (Figure 11), mean AHD data sea area S full year (Table 10) and mean AHD data sea area S season 4 (Table 11) are given. It is clear that the wave steepness factor has changed significantly. With the modified WST and wave steepness factor, the excessive acceleration of C11 was estimated using the VC1 equation outlined in Section 2.3.1 of IMO SGISC guidelines [1]. \begin{table}
\begin{tabular}{c c} \hline \hline
**Natural Roll Period, \(T_{r}\), (s)** & **Wave Steepness Factor, s** \\ \hline \(\leq\)5.9 & 0.100 \\ 6.9 & 0.098 \\ 7.9 & 0.093 \\ 11.8 & 0.065 \\ 13.8 & 0.053 \\ 15.7 & 0.044 \\ 17.7 & 0.038 \\ 19.7 & 0.032 \\ 21.7 & 0.028 \\ 23.6 & 0.025 \\ 25.6 & 0.023 \\ 27.6 & 0.021 \\ \(\geq\)29.5 & 0.020 \\ \hline \hline \end{tabular}
\end{table} 
Table 10: Wave steepness table (full year). Figure 11: Standard wave steepness table. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Data** & **BGW** & \multicolumn{5}{c}{**AHD**} \\ \hline
**WST** & **Annual** & **Annual** & **Season 1** & **Season 2** & **Season 3** & **Season 4** \\ \hline Sea area S & 25.9902 & 25.5994 & 24.2071 & 17.2204 & 24.2071 & 28.6489 \\ Sea area 8 & 25.795 & 25.5994 & 24.4084 & 17.4588 & 24.8086 & 28.0899 \\ Sea area 9 & 25.9902 & 27.7141 & 25.2055 & 18.3964 & 25.4028 & 31.3669 \\ Sea area 15 & 24.6089 & 22.7736 & 22.7736 & 15.5026 & 21.508 & 25.0074 \\ Sea area 16 & 25.5994 & 25.2055 & 23.5981 & 16.9804 & 23.5981 & 27.9023 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Mean wind speed (m/s) corresponding to significant wave height estimated in Table 8.  
To quantify the difference in using individual WSTs, the estimated excessive acceleration is compared to the example provided in [2]. Table 12 shows the estimated acceleration for the C11 container ship. It is apparent that the acceleration estimated by the standard WST is less compared to season 4 results. The excessive acceleration provided in [2] is highlighted in green. In all the WST cases considered in Table 12, the ship is vulnerable to excessive acceleration, since the estimated value is above the maximum limit of 4.64 m/s\({}^{2}\). Let us assume that 8.1 m/s\({}^{2}\) is the cut-off for excessive acceleration for the following discussion. The ship assessed using the standard WST will successfully pass the level one assessment and be allowed to operate unrestricted. However, the same ship which is allowed to operate in all sea areas and seasons failed the season 4 for sea area 9 assessment, which contradicts the stability results estimated with the standard WST. This demonstrates the necessity of using local and regional WSTs rather than a universal WST for the SGISC stability assessment to avoid misinterpretation of stability estimations while improving safety.