VESSEL REVIEW | SeaML – Compact, versatile autonomous craft for German research body

The Fraunhofer Center for Maritime Logistics and Services (Fraunhofer CML), a research organisation based in Hamburg, has developed and begun operating a new autonomous surface vehicle (ASV) that is intended to serve as a test and demonstration platform for various technologies related to the maritime sector.

Named the Seagoing Maritime Laboratory (SeaML), the catamaran measures only 1.5 by 1.2 metres and is designed to be integrated with a customer-oriented web user interface developed in-house by the Fraunhofer CML. The craft itself is of modular construction, enabling various sensors and other payloads to be installed and removed quickly and easily.

In addition to aiding in scientific research, the ASV will also be used to perform missions in support of port operations such as bathymetric surveys, infrastructure inspection, and environmental data collection.

“The goal was to develop a compact unmanned research platform using reasonably priced components,” Fraunhofer CML told Baird Maritime. “The design and construction of the craft had to stay within a specific budget but still had to ensure it can accommodate a 40-kilogram payload.”

The designer added that the craft was meant to be capable of autonomous operation, necessitating the use of specific hardware and software. It also needed to possess a modular hull assembly to permit use in different types of research projects. For instance, when used as part of the Fraunhofer CML project dubbed Robotic Vessels as a Service (RoboVaaS), the ASV is fitted with a camera-equipped remotely operated vehicle (ROV) connected by a cable and winch. Among other things, the ROV will enable the ASV to perform inspections of submerged objects such as quay walls and ships’ hulls.

“The biggest challenge in the design of the craft involved the integration of all the sensors into the compact overall structure. We were able to overcome this by continuously carrying out system tests even as the craft itself was being assembled. Furthermore, only some parameters of the mathematical model can be determined a-priori, meaning that the low-level controller cannot be tuned before sea trials.”

The designer added that the high flexibility of the domain in which the ASV is designed to operate required additional interfaces and modules, which must be developed and integrated. Most of the software solutions available on the market are either developed for specific-use cases (e.g. surveys) or are solely for autonomous navigation, and so testing was carried out just prior to installation on the craft. As regards the hardware, challenges were also encountered in making these safe and watertight, since these were not originally designed for maritime use.

“We also learned not to underestimate the time needed for debugging errors in the software and hardware,” Fraunhofer CML added. “Fortunately, we refined our communication between the software and hardware development teams, and this went some way in overcoming these issues.”

The designer realised earlier on that SeaML‘s compact size will mean that there will be limits to the hardware’s expected performance. Thus, work is already underway on a considerably larger craft with a 2.5-metre length, a 48V battery for greater endurance, more powerful motors, a greater payload, and even higher processing speeds. This newer and more capable ASV will be used to test systems for obstacle avoidance, target tracking, and autonomous docking.

SeaML is designed to perform research in harbours, lakes, or rivers. In these areas, tests will be conducted to validate new software systems, new sensor concepts, and robot-as-a-service concepts. Fraunhofer CML said that one of the technologies to be tested is control of the craft using augmented reality.

“The ship offers the option to quickly test and validate new innovative approaches,” the designer told Baird Maritime. “New concepts can be tested and validated with a wide range of sensors. The modular framework enables mounting of any technology and concept, and it is possible for us to easily switch between any provided configuration or adapt our own systems and sensors to test them as soon as possible.”

The craft’s twin hulls are connected by a superstructure that can also accommodate various combinations of sensors and equipment used to perform a range of missions. The installed web-based user interface allows for proper mission planning in addition to enabling the ASV to be controlled and monitored from any location.

Power is provided by two electric motors while two BlueRobotics T200 thrusters are fitted as propulsion units in each of the two hulls. Each thruster is capable of delivering 50 N of forward thrust and 40 N of reverse thrust at 16 V. The thrusters also enable the craft to sail at a speed of three knots.

The main control unit is in the form of a Raspberry Pi board while a Navio2 board was selected for enabling direct control of the motors and various sensory elements.

“The reasons for choosing Raspberry Pi for the main control unit are its universal-use microcontroller, open-source architecture, the abundance of successful automation projects completed with it, and the wealth of multi-purpose protective layers [against system failure] that have been developed over the years.”

Interestingly, the craft draws all its power from an array of lithium-polymer (LiPo) batteries similar to those used in the radio-controlled vehicle hobby market.

SeaML has been put through its paces in various tests since it was introduced. These included port surveys, trials of a new type of hull coating being developed, and tests of an air-holding foil concept that can help reduce hull friction, and therefore minimise fuel consumption. Additional trials in the pipeline will include determining the feasibility of the ASV as a take-off and landing platform for a small unmanned aerial vehicle and use of a prototype waste-collecting assembly that can be fitted onto the hull.

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