# Research on Decision-Making Methods for Autonomous Navigation in Inland Tribitary Waterways
## 4 Case Study
### The Verification of the Autonomous Navigation Decision-Making
#### 4.2.2 Multi-Ship Encounter Scenario 2  
A multi-ship encounter scenario involving the OS and seven target ships (TS\({}_{1}\)-TS\({}_{7}\)) in a tributary channel was designed. The initial states of the ships are provided in Table 4.  
Based on the analysis of the ships' initial data and navigation statuses, TS\({}_{6}\) is a retrograde ship, requiring the OS to act as the give-way ship. The OS and TS\({}_{4}\) form an overtaking situation, with the OS designated as the give-way ship; TS\({}_{1}\) and TS\({}_{7}\) are exiting  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Ship List** & **Position** & **Velocity (kn)** & **Course (\({}^{\circ}\))** & **Turning Rate (\({}^{\circ}\)/s)** \\ \hline OS & 119\({}^{\circ}\)28.782\({}^{\prime}\) E, 32\({}^{\circ}\)16.302\({}^{\prime}\) N & 12.5 & 275 & 0 \\ TS\({}_{1}\) & 119\({}^{\circ}\)27.906\({}^{\prime}\) E, 32\({}^{\circ}\)16.704\({}^{\prime}\) N & 6.5 & 180 & 0 \\ TS\({}_{2}\) & 119\({}^{\circ}\)27.996\({}^{\prime}\) E, 32\({}^{\circ}\)16.374\({}^{\prime}\) N & 3 & 260 & 0 \\ TS\({}_{3}\) & 119\({}^{\circ}\)28.026\({}^{\prime}\) E, 32\({}^{\circ}\)15.9\({}^{\prime}\) N & 7 & 355 & 0 \\ TS\({}_{4}\) & 119\({}^{\circ}\)27.702\({}^{\prime}\) E, 32\({}^{\circ}\)16.11\({}^{\prime}\) N & 11 & 090 & 0 \\ TS\({}_{5}\) & 119\({}^{\circ}\)28.35\({}^{\circ}\) E, 32\({}^{\circ}\)16.03.2\({}^{\prime}\) N & 10 & 330 & 0 \\ TS\({}_{6}\) & 119\({}^{\circ}\)28.17\({}^{\prime}\) E, 32\({}^{\circ}\)16.272\({}^{\prime}\) N & 7 & 090 & 0 \\ TS\({}_{7}\) & 119\({}^{\circ}\)27.906\({}^{\prime}\) E, 32\({}^{\circ}\)16.572\({}^{\prime}\) N & 6 & 160 & 0 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The initial information of scenario 2.  
Figure 16: Autonomous navigation trajectories and encounter data of scenario 1. (**a**) Collision avoidance trajectories with TS\({}_{1}\) without maneuvering (**b**) encounter data with TS\({}_{1}\) without maneuvering (**c**) Collision avoidance trajectories with TS\({}_{1}\) under maneuvering condition (**d**) encounter data with TS\({}_{1}\) under maneuvering condition.  
the tributary channel, and OS is a stand-on ship; TS\({}_{3}\) is entering the tributary channel, again making the OS the give-way ship. The autonomous navigation decision-making process and results for this scenario are illustrated in Figure 17.  
Using the collision risk identification model, the OS prioritizes avoiding TS\({}_{3}\) (entering the tributary) as the most urgent threat. To mitigate this risk, the OS implements a deceleration maneuver, passing astern of TS\({}_{6}\) at 96 s. To safely avoid TS\({}_{1}\) and TS\({}_{7}\), the OS evaluates feasible maneuvering combinations, maintains deceleration, and adheres to the recommended route. This strategy ensures safe distances of 93 m from TS\({}_{1}\) at 217 s and 149 m from TS\({}_{7}\) at 293 s. Finally, the OS executes a portside turn and completes overtaking TS\({}_{4}\) at 447 s.  
As shown in the results of Figure 18, the minimum distances between the OS and TSs during autonomous navigation are as follows: 93 m to TS\({}_{1}\), 48 m to TS\({}_{2}\), 83 m to TS\({}_{3}\), 437 m to TS\({}_{4}\), 152 m to TS\({}_{5}\), 110 m to TS\({}_{6}\), and 149 m to TS\({}_{7}\).  
Figure 17: Autonomous navigation trajectories of scenario 2.