Second Blue Nodules field trial succesfully accomplised
On 26 August 2019 a team of Blue Nodules engineers and scientists onboard the Spanish research vessel Sarmiento de Gamboa returned to port at Málaga, southern Spain, after a successful two-week trial at sea with Apollo II, the scaled polymetallic nodule mining vehicle built by Royal IHC. The trial represents an important milestone in the Blue Nodules project, proving that important components of a yet to be built full-scale seabed mining system fulfill their required performance under conditions approximating those of the eastern equatorial Pacific Ocean where future polymetallic nodule mining is likely to take place.
The field trial of the scaled test vehicle Apollo II was the crown on several years of work by engineers of Royal IHC, who in 2016 started with its design and construction. After extensive lab testing of the propulsion and collector systems in 2017, all components were assembled into the integrated test vehicle Apollo II, which was first tested dry and wet in the Netherlands and then subjected to a first field trial offshore Málaga in 2018. After a round of technical revisions, Apollo II was deemed ready for its second field trial in the summer of 2019. In a convoy of four trucks with trailer, Apollo II and a whole load of other equipment required for the trial was driven from the Netherlands to Vigo in northwestern Spain, and there loaded onboard the Spanish research vessel Sarmiento de Gamboa. This ship, operated by the Marine Technology Unit of the Spanish National Research Council (CSIC-UTM) was chartered for the field trial because of its favourable overall size and deck space, DP navigation, hoisting capacity of A-frame, cranes and winches, and state of the art scientific facilities.
After four days of preparations including a test dip of Apollo II in the port of Vigo, RV Sarmiento de Gamboa departed from port on 9 August 2019 and set course to the test area in the Spanish Mediterranean offshore Málaga. The 300 m deep test area had been chosen, in consultation with Spanish marine scientists, because of its gently sloping muddy seabed and relatively weak bottom currents, comparable to operational conditions in the deep ocean for which the mining vehicle is designed. In addition and not unimportant, the area has excellent weather and sea-state statistics especially in summer.
On 12 August 2019, with the city of Málaga and its mountainous hinterland in full view from the ship, Apollo II was hoisted overboard and lowered to the seabed 300 m below the ship and there subjected to a sequence of technical tests. The performance of the vehicle was closely monitored by the IHC members of the team, who received a continuous stream of sensor data and live video images from the vehicle via the umbilical cable by which it remained connected with the ship. In parallel with the technical testing of Apollo II, team members from NIOZ and Aarhus University, assisted by the ROV team of the Flanders Marine Institute (VLIZ) and technicians of CSIC-UTM, made surveys of the local current regime, hydrography of the water column, seabed topography and sediment characteristics.
In the second week at sea, an array of moored sensors was set out on the seabed, including turbidity sensors, current profilers, sediment traps, an in-situ particle sizer and a recorder for underwater sound contributed by partner UPC. The sensors would record the plume of sediment stirred up by Apollo II and underwater noise produced by the vehicle as it was driving in parallel lines at various distances along the array. Given the variable direction of tidal currents in the area, the passage of the vehicle along the array needed to be carefully timed in order to ensure that the sediment plume produced by the vehicle would be carried towards the array and not away from it. To this end, bottom currents were continuously monitored with the ship’s current profiler.
Results of the first week of technical performance tests were very satisfying. Apollo II drove several kilometers of straight and curving trajectory over soft muddy seabed, proving functionality of propulsion, steering, underwater navigation and the hydraulic collector, whilst critical issues which need attention in the further development of the system were brought to light. Technical issues with the track propulsion and hydraulic collector limited the number of environmental tests that could be carried out during the second week. Even so, analysis of the collected sensor data showed out that the plume and sound produced by the vehicle had been clearly recorded, despite notable interference from nearby trawling. Inspection of the trail of Apollo II by ROV yielded video images and high-resolution scanning sonar images of the imprint produced by the tracks and the hydraulic collector in the seabed. Also, boxcore samples of seabed disturbed by the vehicle as well as reference samples from undisturbed seabed could be collected. The trial provided an excellent opportunity to test and improve methods for evaluating environmental performance of gear used for harvesting metalliferous nodules from the seabed.
Greatly contributing to the success of the trial were the excellent technical and scientific facilities of RV Sarmiento de Gamboa and the professionality of its captain and crew, as well as the support provided by personnel of CSIC-UTM both on board and on land.