The HydroNet ASV, a Small-Sized Autonomous Catamaran for Real-Time Monitoring of Water Quality: From Design to Missions at Sea

In this paper, we describe the design, the development, and the sea trials of a novel small-sized autonomous surface vehicle (ASV) designed for monitoring the coastal water quality. The vehicle is characterized by the capability of measuring hydrocarbon and heavy metal concentrations directly onboard by means of custom-made miniaturized sensors. This capability, novel for an ASV, is combined with a winch-based sampling system specifically designed for small-sized vehicles. The sampling system can collect water samples up to 50 m in depth and measure the physical/water quality parameters of the water column. With these two features, the HydroNet ASV provides an autonomous, practical, real-time monitoring system, conceived to complement the current water monitoring practices in which samples are collected by a dedicated boat and analyzed in specialized laboratories at a later stage. The design process had the aim of realizing a vehicle capable of hosting the sampling system and the custom-made sensors that represent a unique payload in the world of small-sized ASVs. A twofold objective was pursued: realizing an ASV suited for monitoring missions in realistic scenarios (e.g., attention was paid to avoid water sample contamination), at the same time limiting the size for the ease of transportability and deployment. Severe constraints rose from these considerations and were addressed during the realization of the robot such as reduced length/weight (that limit the available space for the sensor payload) and low draft and protected propellers to allow the ASV to navigate in shallow waters with likely floating obstacles such as plastic bags. We report the design process aiming at a tradeoff between ease of transportability (small vehicle), available payload, and navigation performance in terms of achievable speed, endurance, and resistance to environmental disturbances (favored by larger ASV dimensions). We present sea trials of the realized vehicle validating the design choices. In particular, a long-range mission is discussed in which the robot executed a monitoring survey covering autonomously 12.5 km in front of Livorno, Italy, coast.