## 4 Case Study
### Numerical Simulation Results
#### 4.1.1 Micro-Level Results  
For the micro-level case study, it was assumed that a drifting fishing boat incident occurred on 13 August 2024, at 33\({}^{\circ}\) 33 min 01 s N, 127\({}^{\circ}\) 39 min 13 s E, approximately 36 nautical miles from Seongsanpo Port on Jeju Island, as illustrated in Figure 14.  
The data for the five determinants influencing collision risk and the ten determinants influencing pollution risk are summarized in Tables 8 and 9, respectively.  
The collision risk was evaluated, as shown in Table 10, by applying the data from Tables 8 and 9. In this process, object size was calculated using the Pythagorean theorem, assuming a ship length of 30 m and width of 5 m. For moving ships, the maximum number of ship passages per hour within the grid at the drift point was considered.  
The collision risk index (level) and pollution risk index (level) were calculated as 6.37% (medium) and 16% (selective), respectively. By inputting these values into the fuzzy  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Input Variables** & **Input Data** & **Collision Risk** \\ \hline Number of navigational obstacles & One obstacle \\ \hline Size of navigational obstacle & Size, shape, and structure & Approximately 30.41 m \\ \hline Velocity of navigational obstacle & Tidal range, current, and weather conditions & 0.2 knot & Risk index: 6.37\% \\ \hline Moving object & Ship traffic density and frequency & \\ \hline \hline \end{tabular}
\end{table}
Table 10: Collision risk assessment in the micro-level case study.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Pollution Risk Assessment Factor** & **Collected Data** \\ \hline Navigational obstacle & Fishing boat \\ Type and size & 68.9 tonnage \\ Risk of navigational obstacles & Not applicable & \\  & Oil: Estimated to be less than 10 kL of MFO \\ Residual hazardous materials & Hazardous liquid substances: Not applicable & 4 \\  & Radiactive materials: Not applicable & Risk index 16\% \\ \hline Spill probability and risk & Age of ship before the incident: Unknown & Risk level: selective \\  & Elapsed time since the incident: less than 1 year & 1 \\ \hline Under-keel clearance & Above 30 m & 1 \\ \hline Current & 0.2 knot & 1 \\ \hline Marine environmental sensitivity & 36 nautical miles from Seongsan Port, Jeju Island & 1 \\ \hline Maritime traffic environment & General navigation routes & 4 \\ \hline \hline \end{tabular}
\end{table}
Table 11: Pollution risk assessment for micro-level case study.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Pollution Risk Assessment Factor** & **Collected Data** \\ \hline Navigational obstacle & Fishing boat \\ Type and size & 68.9 tonnage \\ Risk of navigational obstacles & Not applicable & \\  & Oil: Estimated to be less than 10 kL of MFO \\ Residual hazardous materials & Hazardous liquid substances: Not applicable & 4 \\  & Radiactive materials: Not applicable & Risk index 16\% \\  & Age of ship before the incident: Unknown & Risk level: selective \\  & Elapsed time since the incident: less than 1 year & 1 \\ \hline Under-keel clearance & Above 30 m & 1 \\ \hline Current & 0.2 knot & 1 \\ \hline Marine environmental sensitivity & 36 nautical miles from Seongsan Port, Jeju Island & 1 \\ \hline Maritime traffic environment & General navigation routes & 4 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Pollution risk assessment factors for micro-level case study.  
set theory-based navigational obstacle risk assessment system, the comprehensive risk index (level) was inferred and evaluated as 48.74% (low), as illustrated in Figure 15.