# A Survey on Unmanned Surface Vehicles for Disaster Robotics: Main Challenges and Directions
## 6 Discussion
### Technological Guidelines
It may also be possible to connect multiple USVs to form an autonomous containment line to pollutants or a blockade to alien vessels [95]. _Thrusters:_ There are objects such as plastic objects, and plants, such as eelgrass, which may damage underwater propellers [102; 241]. Furthermore, propellers should not pose a hazard to humans in disaster sites (e.g., drowning victims). Therefore, USV design should consider proper propeller casing to preserve its integrity and prevent injuries to others in need e.g., the UCAP moved fromconventional propellers to water-jet ones [202; 203; 204]. [PERSON] and [PERSON] [242] argue that sailboats can be effective for both monitoring and disaster response due to the lack of propellers and the potential for power savings. However, the absence and excess of winds may limit the use of sailboats in real disaster response scenarios. On the other hand, [PERSON] et al. [70] indicate the use of airboats since usually possess a flat-bottomed hull, using an above-water fan to propel themselves forward safely and effectively through shallow or debris-filled water. Finally, thrusters should be strong enough to compensate or minimize river/sea current effects which, in case of flooding, can be stronger than in normal scenarios [90]--which may be problematic for airboats. _Bathymetry:_ Even though bathymetry instruments are essential tools to address many problems, they are prone to errors which depend on sensor limitations and the environment (e.g., up to 30 cm average error were reported in some studies [77]). Performing bathymetry surveys during high tides is a good strategy as it is possible to place the USV as close to the shore as possible to assess regions near the water with risk of collapse to improve the bathymetry results. Furthermore, calm waters are always the best scenario of choice for a survey, since environmental disturbances such as waves and wind may affect instruments. _Sensor Payload and Threat Detection:_ Appropriate sensor positioning must be considered during the design and testing of the USV, to avoid problems while in operation: as seen in [62], the sensor payload must be robust to withstand the water force, especially in the case of underwater sensors since it may damage or knock them out of alignment. Furthermore, a USV designed for DM should ideally be equipped to detect different types of threats, such as nuclear, biological, chemical and even explosive detectors: for example, the CBRNE sensor system, which integrates Chemical, Biological, Radiation, Nuclear, and Explosive sensors [243]. _Load Capacity:_ The USV must be able to carry all sensors, batteries, and extra weight, but if the vehicle is expected to work in shallow waters or ebbs, the weight must not be excessive to allow for mobility [90]. _Real Scenario Testing:_ USVs must be thoroughly stressed and tested in real-world situations before their actual deployment, risking complete mission failure. Disaster sites can be dangerous both to humans and USVs. Currently, exercises with the navy and disaster missions [167; 201] simulated in competitions [168; 169; 170] are ways to perform such evaluations and operational validation. [PERSON] et al. [244] argue that SAR scenarios can be used to validate robotic systems. However, in some cases such as those involving extreme hazards, e.g., radiation, it may be more suitable to make use of computer simulations [165] instead.