## 2 Materials and Methods
### Data Collection
#### 2.1.2 Experiment Protocol  
In the ship maneuvering simulations, 100 senior cadets at Mokpo National Maritime University participated in the study; their characteristics are shown in Table 2. These participants had taken maritime training courses for three and a half years at IMO-accredited maritime educational institutions, and have been in a merchant's vessel for more than a year. Also, all participants used the Kongsberg's simulator for at least 80 h. To determine the appropriate sample size, the minimum sample size for the appropriate learning ability must be determined [21]. The dichotomous endpoint is a binary code: collision or not. The result was a minimum sample size of 122 persons (\(\alpha\leq 0.05\), power = 0.8). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Classification**} & \multirow{2}{*}{**Factor**} & \multicolumn{2}{c}{**Ship Type**} \\ \cline{3-4}  & & **Tanker** & **Cruise** \\  & & **(Own Ship)** & **(Target Ship)** \\ \hline \multirow{4}{*}{Specifications} & Length overall (m) & 226.0 & 260.8 \\  & Breadth (m) & 36.6 & 31.5 \\  & Maximum rudder angle (\({}^{\circ}\)) & \(\pm\)45.0 & \(\pm\)45.0 \\  & Maximum engine power & 13.507 & 8.441 \\  & (MW) & & \\  & Maximum speed (m/sec) & 8.7 & 11.8 \\ \hline \multirow{4}{*}{Initial conditions} & Position (\(x,y\)) & (0, 0) & (3446.57, 2168.69) \\  & Heading (\({}^{\circ}\)) & 90.0 & 180.0 \\ \cline{1-1}  & Speed (m/sec) & 6.7 & 11.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Specifications and initial conditions of ships used in the simulations. Figure 4: Simulation scenarios where collision avoidance action is required. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{1}{c}{**Characteristic**} & \multicolumn{1}{c}{**Mean (SD)**} \\ \hline \(n\) & 100 \\ Female/male & 8/92 \\ Age (year) & 22.6 (1.2) \\ Onboard experience (year) & 0.9 (0.2) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Participant characteristics. Table 3 shows the simulation procedure with the following three steps: 3 min of scenario explanation in step 1, 10 min of familiarity with the simulator in step 2, and about 5 min of simulation (ends when a collision occurs) in step 3. From the ship maneuvering simulation, the logged history data for the 100 participants were obtained; then the navigator's actions to avoid a collision were detected. To detect behavior actions, two types of behaviors, device and route control, were introduced. Device control refers to the use of rudder or engine. On the other hand, route control refers to the control of deviation or distance of the closest point of approaches (dCPA). The navigator's behavior was detected with four behavior features, i.e., rudder use, engine use, controlled deviation, and controlled dCPA. The types of behavior and their features are summarized in Table 4. Each behavior and its features assume that the navigator maneuvers the ship in accordance with international regulations for the prevention of collisions (COLREG) [22], as illustrated in Figure 5. Normally, ship maneuvering is implemented through the ship's heading and course, controlled by a rudder, as well as the ship's speed, controlled by an engine. When the navigator uses control devices (i.e., rudder and engine), there is a significant time delay between the ordered value and the response value of the devices. This time delay is a key characteristic caused by fluid pressure on the rudder and the hull [23]. Thus, ship maneuvering requires manipulative techniques of control devices. In order to avoid collisions along the designed route, the deviation between the vessel and the designed ship's route should be small, and the dCPA must be secured enough for collision avoidance. The closest point of approaches (CPA) represents an estimated point at which the distance between two objects (i.e., the OS and TS), where at least one is moving, reaches a minimum value. Thus, ship maneuvering for collision avoidance requires a technique to control the ship's route in addition to the device control technology.