## 5 Testing and Navigation
### Collision Avoidance  
There are a number of potential risks for collision during a transatlantic mission. In this section, the importance of preventing collision is discussed, and an overview of techniques that can be adopted to mitigate the risk is provided. A prime example to explain the importance of an anti-collision system is what is believed to have happened to the Breizh Tigresse during its mission. On September 7, 2015, 14:00 UTC, after having validated waypoint number five shown in Figure 4, the NYK DIANA, a 300-meter-long container ship, crossed the trajectory of the Breizh Tigresse. After that time, the Breizh Tigresse velocity made good (VMG) dropped by 66%. At the same time, the standard deviation in heading angle increased by 49%. As such, there is a strong suspicion that collision occurred with a ship. It is interesting to note that the route taken by the container ship was not clearly visible in the density map by marine traffic in 2015, as shown in Figure 5; however, it appears clearly at the north of Sable Island in the 2018 version, represented in Figure 6.  
In the 2018 version of this map, the contours of the Grand Banks of Newfoundland are clearly visible. This reveals the presence of intense fishing in these areas. Collision with fishing vessels or fishnets are unmistakably the most common reason for failure in the Microtransat's history ([[https://www.microtransat.org/history.php](https://www.microtransat.org/history.php)]([https://www.microtransat.org/history.php](https://www.microtransat.org/history.php)), accessed on 29 August 2021). As such, these zones must be avoided as much as possible. In Figure 5, yellow arrows show two ways to avoid the main fishing areas. Detouring the Grand Banks to the south  
Figure 5: Marine traffic 2015 density map (Mapbox® OpenStreetMap®). Figure 6: Marine traffic 2018 density map and routing options (Mapbox® OpenStreetMap®). seems a good option. However, this causes the drone to enter the main commercial northern route from America to Europe. Therefore, for the SeaLeon, the second option through the Grand Banks was chosen. While the path is narrower, it keeps drones away from the main traffic until Europe is reached. Given the deviations from the route observed in Figure 4, the narrowness of the path used may legitimately raise questions. Just after validating the ninth waypoint, the SeaLeon trajectory can be observed several times crossing the southern Flemish Cap limit in an intense fishing zone, as shown in Figure 6. This could be where she received damage, as it remains unclear if the next waypoint was ever validated and the trajectory soon became erratic. Participating in the Microtransat Challenge under these conditions may seem like a lottery. It is worth identifying alternatives, other than increasing the number of waypoints locally and reducing the validation radius. The first alternative to mitigate collisions is undoubtedly to build a ship capable of withstanding the shock. This is a strategy that has been adopted with limited success. The SailBuoy team actually conducted real-life collision tests ([[https://www.youtube.com/watch?v=wMbAxejIDAM](https://www.youtube.com/watch?v=wMbAxejIDAM)]([https://www.youtube.com/watch?v=wMbAxejIDAM](https://www.youtube.com/watch?v=wMbAxejIDAM)), accessed on 29 August 2021). However, as [PERSON] points out, such robustness limits the sailing abilities [24]. As such, other solutions must be considered. An efficient anti-collision system requires the design of three subsystems:  
1. A risk assessment system to avoid the anti-collision system being permanently on alert and consuming unnecessary energy [25];
2. An algorithm that defines avoidance solutions according to the situation [26];
3. A realistic simulator that can validate the complete system before expensive sea trials [27], while keeping in mind an important observation made by [PERSON] in 2011 that \"anti-collision usually works in simulation but in real world never\" [26].