## 3 Fuzzy Set Theory-Based Risk Assessment System for Navigational Obstacles
### Risk Factors for Navigational Obstacles  
In our study, \"navigational obstacle\" refers to any object or phenomenon that poses a threat to the safe navigation of vessels. This includes, but is not limited to, sunken ships, shipw debris, floating structures, and other objects that impede safe navigation. The risk assessment factors reflected in the navigational obstacle risk assessment model were determined based on the previously mentioned twelve factors that define the risks related to navigational obstacles. Relevant laws, regulations, expert interviews, and ship traffic data were used to derive the collision and pollution risk assessment factors. These laws and regulations include the Maritime Traffic Safety Act, Enforcement Rules of the Maritime Traffic Safety Act, and Enforcement Rules of the Maritime Recovery Management Act [1; 30; 31]. Additionally, expert interviews were conducted by visiting organizations that monitor navigational obstacles, such as the Korea Marine Environment Management Corporation (KOEM) (Seoul, Republic of Korea) and Korea Fisheries Infrastructure Public Agency (FIPA) (Seoul, Republic of Korea). Vessel traffic data over a specific period and region are required to assess the risk of navigational obstacles. Accordingly, we researched  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Number** & **Assessment Factor** & **Assessment Index** \\ \hline
1 & Ship type & 5 \\
2 & Ship size & 5 \\
3 & Residual hazardous materials & 40 \\
4 & Clearance over mast & 5 \\
5 & Marine environmental sensitivity & 15 \\
6 & Spill probability & 10 \\
7 & Maritime Traffic Environment & 10 \\
8 & Hull Risk & 5 \\
9 & Currents & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Assessment factors for sunken ships.  
and collected data containing dynamic and static information on vessels by using systems such as the Automatic Identification System (AIS) and the vessel position reporting system for small ships (V-Pass). The following information was gathered through expert interviews.  
* Types of major floating debris and whether they can be detected by radar or the naked eye.
* Maximum, minimum, and average sizes of the major floating debris.
* Types of floating debris collected at the study site.
* Mobility of debris influenced by current and weather conditions.
* Major collection sites, debris generation sites, and vessel traffic in and around these areas.
* Disposal procedures and recording methods after debris collection.  
Based on the aforementioned information, the collision and pollution risk assessment factors were extracted and defined from the twelve determinants for the navigational obstacle risk, as listed in Table 2. The collision risk assessment factors include five items:  
Figure 2: Development framework for fuzzy set theory-based risk assessment system for navigational obstacles.  
(1) size, shape, and structure of the obstacle; (2) tidal range, currents, and weather conditions; (3) proximity to navigational zones and routes; (4) ship traffic density and frequency; (5) ship navigation methods. The pollution risk assessment factors are (1) size, shape, and structure of the obstacle; (2) condition and type of damage; (3) type and quantity of oil; (4) state of submersion (for sunken ships); (5) water depth and seafloor topography; (6) tidal range, currents, and weather conditions; (7) proximity to nearby marine facilities; (8) proximity to navigational zones and routes; (9) safety of port facilities; (10) PSSAs.