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50 Insight | USVs Heavy industry The Apache 6 USV from CHC Navigation is a 40 kg vessel measuring 1.8 m in length, and is built largely from carbon composite with anodised aluminium and stainless steel. It can carry up to 60 kg of payload, and operates at speeds of between about 7.2 and 9 kph, with a maximum speed of 12.6 kph. “We’ve done a lot of survey work for the Macau bridge, which connects Hong Kong to mainland China, and the Apache is also often used to perform inspections on hydroelectric dams,” says PJ Walker, managing director at CHC Navigation UK. “We have also carried out a water volume survey at the Dorothea Lakes in North Wales, the site of a former slate mine, which ranges from 5 to 70 m deep. That was particularly tricky because the environment in the water has unusual ‘thermal climb’ properties, with sudden changes in water temperature – if you don’t select and calibrate your echo sounders correctly, the sonar will think it’s found the bottom, when really it’s just found a different density of water.” Key to its ability to conduct survey work for heavy industry infrastructure and projects was it being designed and optimised around a Norbit multi-beam echo sounder, which is integrated into the underbelly of the central hull section. Development of the Apache 6 was originally spurred by CHC Navigation customers who were familiar with the craft’s smaller predecessor, the Apache 5, but who wanted a USV that could provide a higher quality data set. The Norbit sensor was selected for meeting the specs to provide that, but its weight and power requirements – typically 9.5 kg and 60 W respectively on the standard Norbit – meant creating a larger USV than the 160 cm-long Apache 5. The standard version of that sensor operates at a frequency of 400 kHz and covers a swathe of 7-210°. It has a range of up to 275 m from the craft and a range resolution accurate to within 10 mm. An Ethernet link is used to interface with the Apache 6’s onboard processor. Its trimaran shape was chosen for stability during data gathering in turbulent waters with 2-3 m swells. However, the outboard riggers are removable in case the operator is working in reasonably calm waters or needs a narrower hull shape for navigating tight spaces or busy areas. It also typically comes with an 8 W Lidar sensor with a 360° FOV, mounted on a bracket atop the hull for gathering 3D image data above the surface (and below) in the ‘roll’ axis. “The USV has two covered bays. The front one is for installing processing computers for sensors, while the larger, rear one is for the lithium-ion batteries and the main processing computer for navigation and telemetry,” Walker adds. In order to view, analyse and dynamically react to surveyed data in real time, the USV comes with a complex comms architecture. Although mission routes can be plotted and automated beforehand through the vehicle’s CHCNAV Auto Planner software, a 1 GHz remote command link is supplied via an omnidirectional antenna over a 1 km range. Imagery is supplied to the GCS over a live 5 GHz data link with a 0.8 km range, and for surveys further away or for redundancy a 900 MHz connection with a 1.5 km transmission range is also integrated. Conclusion As in the air and on the ground, USV designs are becoming more diverse as manufacturers identify how best to cater for different users and mission profiles. As technological progress, climate change and user awareness grows, the years ahead will probably see even more configurations abandoning traditional ‘boat-like’ hulls for bodies designed around the unique dynamics and applications of maritime unmanned vehicles. June/July 2019 | Unmanned Systems Technology The Apache 6 USV was designed as a trimaran for stability while surveying in choppy waters, but the side hulls can be removed if users want to operate the craft in shallow rivers or narrow canals