## 6 Simulation Environment and Results
### Simulation Results: The Effects of Delays  
Initial tests with delayed AIS data transmission were carried out using the current configuration of the ship handling simulator. In this specific case, an ice-going vessel, 100 m in length, equipped with two azimuth propulsors was selected as the 'own ship' utilized in the simulations. The chosen ship represents a typical modern vessel with reasonable good maneuverability properties, that is, the responses to navigation commands are rapid and vessel can be stopped from cruising speed within a couple of ship lengths. Simulation scenarios are presented in Figure 9. The simulated 'own ship' follows the given track, with the autopilot using the defined trackpilot mode. 'Own ship' confronts three vessels in two separate encounter situations:  
1. In the first encounter, a smaller vessel 'Ship1' is approaching from the starboard side, that is, it has right of way and 'own ship' has to conduct an evasive action. 2. In the second encounter, 'Ship3' is approaching 'own ship' from the port side and 'Ship2' from the starboard side. Consequently, 'Ship3' has to give way to 'own ship' and 'own ship' has to carry out an evasive action in order to avoid collision with 'Ship2'. Figure 9: Selected simulator scenario and two locations for connectivity delay testing. Simulated vessels are presented in amplified figures. The whole area is approximately 3.5 km in width and 5 km in length, located close to Helsinki, Finland. Three delay times were applied during the simulations in order to determine by how much it is possible to delay situational awareness data, based on which the vessels are controlled, before the operation becomes too dangerous. The AIS data carries information about ships in the vicinity, such as identifying them, locating where the ships are, what their speed is and where they are heading. In case A, the AIS data are delayed by 0.1 s, case B uses a 3 s delay and case C uses a 6 s delay. The actual distance as a function of time between 'own ship' and 'Ship1' is evaluated for the first encounter condition and between 'own ship' and 'Ship2' for the second condition. The distances for all cases--A, B and C--are shown in Figures 10 and 11. Vessels 'Ship1' and 'Ship2' are the critical objects, as 'own ship' has to avoid both ships due the COLREGs. As shown in Figure 10, when the delay is only 0.1 s, the distance between the ships remains over 200 m at all times. Increasing the delay of the data to 3 s keeps the distance above 100 m and 6 s leads to dangerously close distances. The more challenging second encounter case shows similar behavior but, in this case, the distances become smaller; and in the case of the longest delay, this leads very close to a collision. A 6 s delay means approximately 50 m distance when the speed is 15 knots. Even though the situation is simplified to study the effect of delays in the situational awareness data, this shows that long delays cannot be tolerated, e.g., in the remote control scenario and the connectivity system needs to be designed accordingly with high enough capacity and redundancy in the system to ensure timely data for the decision making. Figure 10: Actual simulated distances between ’own ship’ and ’Ship1’ as a function of time for simulation scenario cases A, B, and C. The first encounter situation. As stated, the current decision-making module of the collision avoidance system in the simulator can be characterized more as a reactive than a pro-active system. Nevertheless, the simulated results reveal that delays in data transfer are crucial for the decision-making procedures. Case C, utilizing a six second delay, produces near collision situations, as the situational awareness module provides misleading information to decision-making modules. That is, the decision-making module believes that the vessels are bypassing each other with appropriate distances, which is not actually the case. Large ships are slow in changing directions according to steering and propulsion control.