Inside Australia’s Snowy Mountain hydro scheme, leading underwater service provider, Hibbard Inshore, say they have broken the record for the longest tunnel inspection by a tethered vehicle using their newest long-range vehicle, the Saab Seaeye Sabertooth.

Importantly, this meant there was no need to drain the tunnel system, which saved closing down several power stations. During a round-trip of over 24km, Hibbard Inshore’s customised Sabertooth AUV/ROV collected real-time visual data whilst scanning the tunnel with multiple types of multibeam sonar.

The mission set out to gather high density dimensional data, discover open cracks or holes, find debris buildup, detect lining failures, and identify any rock falls. From the data collected Hibbard created 3D models ready for maintenance planning and comparable inspection data to identify future trends in tunnel condition.

Hibbard Inshore has so far inspected six trans-mountain tunnels across the Snowy Hydro Scheme using this method and will return in 2014 for further inspections. Previously the tunnels had to be drained for examination, risking collapse of the tunnel and endangering inspection personnel.

Chief Operating Officer of Snowy Hydro, Ken Lister said: "The use of the unmanned sub for tunnel inspections now means that it can be done more frequently, more safely and without the need to shut down power stations or drain the tunnel. This multi-million dollar investment is a great outcome for the tunnel sonar cross-section, the business, the safety of our people and contractors and is part of our wider programme of scheme upgrades and on-going maintenance".

The challenges for Hibbard Inshore included entering narrow shafts, navigating tight bends, working in limited visibility and managing within a strict schedule.

The Sabertooth can operate as either a remotely operated vehicle (ROV) with a tether to allow for real-time data and pilot control, or as an autonomous underwater vehicle (AUV) to give flexibility in various tunnel inspection scenarios.