VESSEL REVIEW | SeaML:SeaLion – German-designed USV to operate as carrier platform for smaller mobile assets

The Fraunhofer Center for Maritime Logistics and Services (Fraunhofer CML), a research organisation based in Hamburg, has introduced a new type of unmanned surface vehicle (USV) with the objective of streamlining its research activities conducted in the field in an effort to reduce both costs and time.

"The autonomous research platform was developed to provide an easier way to conduct research," Fraunhofer CML told Baird Maritime. "The catamaran is characterised by its modular design and the sensor technologies to advance research in the field of autonomous systems."

The technologies are intended to support research in the areas of obstacle avoidance, target tracking, autonomous docking, and controlling the craft with the aid of augmented reality.

The USV was also designed to function as a carrier vehicle for smaller unmanned aerial vehicles (UAV) or underwater remotely operated vehicles (ROV). This fleet of vehicles will be used in research to provide services that are still carried out by a human operator today. Examples of duties in which such craft will be employed are ship and bridge inspections.

SeaML:SeaLion is a further development of Fraunhofer CML's earlier Seagoing Maritime Laboratory (SeaML), a 1.5-metre-long catamaran USV that was designed to serve as a test and demonstration platform for various technologies related to the maritime sector.

"During the tests within the project, we have already come close to the performance limits of the earlier SeaML, both in terms of propulsion and the available computing power. That is why we have decided to build an improved version of the vessel."

Like its smaller predecessor, the 2.2- by 1.5-metre SeaML:SeaLion runs entirely on electrical power. It was also built to sail at a minimum speed of six knots and to have high computing power that also utilises artificial intelligence. Also, the payload is set at 90 kilograms while the craft itself enjoys improved stability. Lastly, space is allocated for sensors necessary for autonomous waypoint navigation and the perception and detection of obstacles.

"One challenge in the design of the research vessel was the limited time available to us," added Fraunhofer CML. "The platform had to be designed, built, and tested within 10 months. We overcame this challenge by working closely with experts in specific fields within the Fraunhofer Society."

The owner said another challenge lay in ensuring the vessel could be adapted to serve other projects in the future. This requirement necessitated the use of a modular design characterised by small interchangeable compartments within the catamaran's twin hulls. Each compartment has access to an internal board net consisting of a network and different voltage levels.

"This means that in the future, the ship can easily be equipped with additional hardware without having to install a larger battery, for example."

Fraunhofer CML added that construction of the USV was negatively impacted by the Covid-19 pandemic. The sourcing and delivery of parts, some of which were manufactured in other European countries and in the United States, took much longer than usual.

"Also, as this is an experimental vessel, there is no final version of the boat. Instead, small improvements were gradually incorporated with recurrent testing. A particular challenge was to make the craft's hardware components, which are not designed for maritime use, safe and watertight."

The work that went into SeaML:SeaLion showed the Fraunhofer CML team the importance of communication between the software and hardware departments. Efforts were therefore made to refine communication and feedback methods while ensuring the entire design process was collaborative and without interference or potential misinterpretation.

"We also learned that it was necessary to start early with deploying software on the hardware," the owner told Baird Maritime, "especially when building a boat from scratch. This approach has proven to be very valuable to define concrete tests with specific goals already at the beginning of the project. In addition, it has always been very valuable to carry out certain dry tests before conducting a trial on the water to prevent problems on the water."

SeaML:SeaLion is designed to operate for 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.

"It was designed to make maritime research easier and faster. Due to the craft's modular design, new hardware can be easily integrated into it. In addition to the hardware-side implementation, however, it was also worthwhile to focus on a simple software-side extension. This is achieved by using the Robot Operating System as an open-source robotics middleware suite."

The owner said the USV's suite of sensors means it is ready to further advance research in the field of autonomous maritime robotics while the all-electric drive ensures that it can also be used in areas where traditional internal combustion engines are prohibited. Since the USV can also function as a carrier vehicle, it allows UAVs and ROVs to be deployed in areas that are otherwise inaccessible.

SeaML:SeaLion can provide services independently or in combination with an ROV or UAV. These include the survey of depth data, the inspection of ship hulls, and the inspection of sheet piles.

The vessel is powered by two ePropulsion Spirit 1.0 Plus electric outboard motors. These were rigidly installed, and the vessel is steered by controlling the differential thrust of the two engines.

The electric outboards are also much quieter than petrol outboards with noise levels set at just around 60 dB. This is made possible by a gear-free motor design, a brushless DC motor, and the absence of a gearbox, which also significantly lowers maintenance requirements.

The engines and the onboard systems draw power from two 48V, 2.3kWh batteries that can last up to 24 hours in between rechargings. Yhe voltage of the batteries is converted to different levels (24V, 12V, 5V) for the sensors, computers, actuators, and other equipment that are installed.

The entire craft is controlled by a main computer, a small form factor PC from Intel NUC. This PC communicates with several small single-board Raspberry Pi computers via ethernet. In addition to these computers, an NVIDIA Jetson AGX Xavier AI computer for autonomous machines is also installed. This AI computer delivers the performance of a GPU workstation in an embedded module under 30 W.

"The special feature of the USV is the modularity of the deck equipment," added Fraunhofer CML. "This can be adapted depending on the research project. By default, it includes a Zed 2i Stereo Camera with advanced depth sensing, Velodyne vlp-16 LIDAR for obstacle detection, EMLID Reach M+ RTK-GNSS-Module, Emlid Navio2, and a Mikrotik Metal 52 Wifi Antenna."

Under the EU-funded Risk-aware Automated Port Inspection Drones (RAPID) project, the USV's deck will become a landing platform for an aerial drone. In addition to the pure landing platform, the deck will also be equipped with a battery hot swap system to change the batteries of the drones automatically.

The RAPID project will combine and extend drone technology to deliver a fully automated and safety-assured maintenance inspection service for bridges, ship hull surveys, and other associated applications. The aim is to reduce the time and cost of structural condition monitoring of maritime transport infrastructures such as material-handling equipment, cargo and passenger ships, and bridges. Meanwhile, in the Robotic Vessels as a Service (RoboVaas) project, an additional underwater ROV and a winch can be mounted on the deck to carry out investigations on quay walls and ship hulls.

Click here for more news stories, feature articles, and vessel reviews as part of this month's focus on unmanned craft.