## 3 Trends in Operational USVs
### Key Findings  
Although substantial progress has been made in control theory and artificial intelligence for USV control [2; 9; 79; 80; 81], the analysis of the 47 operative USV models suggest that  
Figure 10: Histogram representing the frequency distribution of the maximum sea states tolerated by the USVs. Figure 9: Bar charts illustrating the frequency of different situation awareness technologies used in USVs. the majority of market-ready USVs have only conventional control modes like waypoint navigation, station keeping, and collision avoidance, with remote control being a standard feature. Thus, differently from the significant strides in shore and aviation industries, these findings highlight the barrier that exists between the state-of-the-art research and the deployment of these new developments in the maritime sector. Despite that, USVs like the Shadow Fox are already able to operate in a swarm configuration, for instance. In terms of endurance, there is a notable variation, with some models designed for short-duration missions of a few hours (e.g., 8 h: C-Cat3, ME120, Uni-Pact, HydroCat-550, and EchoBoat-240) while others can operate autonomously for up to 12 months (e.g., Explorer, Sailbuoy, and Wave Glider). These differences arise mainly due to the source of energy used to propel the USVs. The models with short endurance (\(10^{0}\) days) are commonly equipped with battery-powered electric motors. The mid-endurance (\(10^{1}\) days) USVs are mostly equipped with diesel or gasoline engines, as for instance, the DriX H-8 equipped with a 37.5 HP diesel engine and 10 days of endurance time, and the Mariner X equipped with a Hamilton Jet HJX29 and Yanmar 4 LV230 with redundant twin electric pods and a bow thruster [82] for slow speed navigation and an endurance time of 25 days. For long endurance time (\(10^{2}\) days), only the solar-, wind-, or wave-propelled USVs are able to achieve months of activity, such as the solar-powered SP-48 equipped with a 1000 W brushless motor and months of endurance, the wind-propelled Explorer with over 12 months of endurance, and the wave-propelled Wave Glider with 12 months of endurance. All these variations emerge from the types of applications that require different levels of power. While short-endurance USVs are sufficient for surveys on lakes and rivers, defense and offshore industries tend to demand more endurance time. Concerning the propulsion systems arrangements, the distribution indicates a growing preference for electric motors, aligning with industry trends favoring efficiency and sustainability, though diesel and hybrid alternatives remain relevant for high-power applications. As previously mentioned, the choice of arrangement strongly depends on the required endurance time. However, the last advancements in battery and electric motor technologies have enabled a shift toward more sustainable systems, which allows USVs to carry out silent and emission-free operations. The solar-, wind-, or wave-propulsion systems enabling months of endurance represent valuable technology for persistent oceanographic research and climate monitoring, as it eliminates the need for frequent refueling or battery replacement. The integration of satellite, 4G LTE, and emerging 5G solutions by USV companies highlight the increasing reliance on high-bandwidth, low-latency connectivity for real-time data transmission. Also, the communication range plays a crucial role in USV operations since it influences the distance between vessels and their remote operators. The results suggest that within each manufacturer, these technologies are somehow standardized, varying in general only between the models from different companies. For instance, the models Auto-Naut 3.5 and 5.0 from AutoNaut are both equipped with satellite communication, but their setup differs from, for example, the Mariner and Mariner X from Maritime Robotics, which use LTE (4G) communication. Furthermore, as for all other features of the USVs, the communication also depends on the purpose of the vessel.