# Estimating Critical Latency Affecting Ship's Collision in Re-Mote Maneuvering of Autonomous Ships
## 5 Discussion  
The need for discussion was previously raised about the following:  
1. Consideration of vessel scale (length, width) in estimating critical latency;
2. Consideration of turning circles that can be observed on actual vessels;
3. Application of critical latency for collision avoidance in remote maneuvering.  
The first point is about the vessel scale. The collision position of the OS-TS is theoretically the point at which the OS-TS relative distance is zero unless the vessel scale is considered; whereas, when the vessel scale is considered, the collision positions of the OS-TS are the points where the hulls of the two vessels can meet each other, which may appear complex depending on the encounter situation and vessel shape. This complexity can be an obstacle in applying vessel scale to critical latency estimation. The introduction of the ship domain concept, now widely applied in the maritime domain, can be considered as a solution. The concept defines the OS safety zone or the other ship safety zone where the two vessels can be safely separated to avoid collision [36; 37; 38; 39]. The study of  
Figure 14: Estimation results for Scenario 1 (1-degree head-on situation): (**a**) OS-TS encounter and collision points; (**b**) Estimation of the OS-TS relative distance and the time at collision Points C and M over time.  
estimating critical latency introducing the concept of ship domain is put aside as a task to be studied later.  
The second point is about the acquisition of turning circles. Turning circles are required by international regulations to be measured and posted on the bridge for a combination of certain speeds and rudder angles [10; 35]. It is observed that turning circles for a combination of various vessel speeds and rudder angles must be obtained at real sea; however, this requires a lot of cost and time. A number of studies have been reported in the past on how to obtain turning circle data from numerical analysis using the current ship's hydrodynamic model. [31; 32; 33]. In addition, it is reported that numerical simulation can be a method of evaluating remote maneuvers of autonomous vessels [3; 4]. Therefore, the second point is considered as an issue to be addressed by comparing the turning circles measured using numerical simulations with some turning circles measured on actual vessels.  
The third point is regarding the application of critical latency of collision avoidance. It was confirmed through the experiment that the critical latency estimation method proposed in this study is applicable to the estimation of the location and time at which two ships can collide. Using this result, it can be applied to the current ship domain and collision avoidance assessment. When the application of collision avoidance is considered in remote maneuvering, the method in this study needs to be concerned so that the OS-TS's safety distance can be secured. According to [PERSON] [39], it is known that the ship's domain can be safely separated from the other ship's length of 3.58 times the ship's length. In addition, various studies that can secure the safety distance of OS-TS have been reported [23; 24; 27; 28]. This will be left as a future task for this study.  
An additional point to discuss is the extent to which the speed of the vessel affects the turning trajectory. The results rendered by the simulator mean that the ship's circulation radius depends only on the angle of deflection of the rudder blade, and the otherwise obvious influence of the ship's speed on the turning trajectory is not noticed. Further research in this area is considered necessary.