# Fuzzy Logic in Selection of Maritime Search and Rescue Units
## 4 Case Study
### Procedure Description
Cargo vessels are the most suitable for the job, as they usually meet the SOLAS and STCW requirements concerning the navigational, communications, and rescue equipment, as well as training of the crew. Ships with a specially trained crew (e.g., military) are equally preferred. Passenger ships and some ships carrying dangerous goods (e.g., tankers) have similar characteristics to cargo ships but also have a higher risk of being used (e.g., presence of large numbers of people). They are less preferred than regular cargo ships. The least useful are fishing vessels and pleasure yachts. Most of them do not meet the STCW standards in terms of equipment and qualifications of the crew. Communications problems can be expected (they use shorter range communications equipment) as well as language problems (in some parts of the world). Compared to merchant vessels, the assessment of small vessels in terms of suitability for participation in an SAR operation is poorer. It must be noted here, however, that exceptions may apply. The criterion shall be evaluated qualitatively. The criterion is minimised. The weighting of the criterion is significant but less than the Navigational status (0.175). The AIS does not provide data on superstructure height or vessel equipment. Deductions in this regard can be drawn on the basis of general knowledge of ships, analysis of known parameters (e.g., length over all, beam, type) or direct communication with the ship. A defuzzification method was used to determine the values of the new criterion 'quality'. The method is discussed in the next section. Defuzzification Methode  
Experts have developed reasoning rules for obtaining a new criterion value. This was done based on the ability to detect objects and to provide medical assistance. The developed controller is aimed to classify the vessel into one of three qualitative categories. The input \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**No** & **Criterion** & **Mode of Assessment** & **Preference Direction** & \begin{tabular}{c} **Weight, Preference Function** \\ \end{tabular} & **Methodology of Assessment** \\ \hline C1 & Speed & quantitative & max & 27.5\%, linear & Numerical value \\ \hline C2 & Draught & quantitative & min & 12.5\%, usual & Numerical value \\ \hline C3 & \begin{tabular}{c} Navigational \\ status \\ \end{tabular} & qualitative & min & 22.5\%, usual & Level 2 & \begin{tabular}{c} At anchor, Moored, Engaged in fishing \\ \end{tabular} \\ \cline{3-6}  & \begin{tabular}{c} Navigational \\ status \\ \end{tabular} & qualitative & min & 22.5\%, usual & Level 3 & \begin{tabular}{c} Not under command, Restricted \\ manoeuvrability, Constrained by her \\ draught, Aground \\ \end{tabular} \\ \hline C4 & Type & qualitative & min & 17.5\%, usual & Level 2 & Tanker, Passenger, etc. \\ \cline{3-6}  & \
\begin{tabular}{c} Quality \\ \end{tabular} & quantitative & max & 25\%, linear &
\begin{tabular}{c} Numerical value based on results of \\ defuzzification \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Criteria evaluation methodology. linguistic variables are the observation altitude and medical equipment, while the output variable has been denoted as quality (Figure 3). The output quality is represented by three sets (Low, Average, High Quality) within a range of 0 to 100%. Observation altitude is the point above the water surface from which the lookout scans the area. The higher the eyes of the lookout are, the greater the distance from the horizon and the better the range of search. Surface vessels have a fixed observation altitude and the lookout is posted on the navigation bridge or in another spot. Observation altitude is an important coefficient determining the sweep width. An appropriately adjusted sweep width has a significant impact on the success of search. It should be noted here that the observation altitude on surface vessels may vary within a range of 2 to 55 metres.