AUSTRALIA’S Snowy Mountain Hydro scheme has played host to what underwater service provider Hibbard Inshore says is the longest ever tunnel inspection by a tethered remotely operated vehicle.

Travelling a 24 kilometre round trip using a customised Saab Seaeye Sabertooth, Hibbard Inshore collected real time visual data for the scheme.

This involved scanning the tunnel with multiple types of multibeam sonar to take high density dimensional data, identifying rockfalls and detecting open cracks or holes, areas of debris buildup and lining failures.

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

With the information acquired, Hibbard Inshore was able to create 3D models for analysis for maintenance and comparison to future inspection data to identify trends in the condition of the tunnel.

Snowy Hydro chief operating officer Ken Lister said the investment was a great outcome for the business.

“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,” he said.

Previously the tunnels had to be drained for examination, risking collapse of the tunnel, endangering inspection personnel and meaning power stations had to be temporarily closed down.

Hibbard Inshore has so far inspected six trans-mountain tunnels across the Snowy Hydro Scheme using this method and will return later this year for further inspections, the company said.

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.