• Credit: Saab Group
    Credit: Saab Group
  • The Sabretooth is lowered into the water near a tunnel intake. Credit: Hibbard Inshore
    The Sabretooth is lowered into the water near a tunnel intake. Credit: Hibbard Inshore
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Snowy Hydro is faced with the difficult prospect of maintaining and inspecting its underwater assets including water conveyancing tunnels, while minimising outage times.

In recent years it has worked with Hibbard Inshore to meet this demanding requirement via the use of Remotely Operated Vehicle technology in the form of the Saab Sabretooth.

With some tunnels up to 23 kilometres in length it was not feasible to de-water them given the stresses imposed by the process and the subsequent drying and re-watering. 

In learning these requirements, Hibbard Inshore determined that the Sabertooth was definitely the best suited vehicle for this project. The vehicle can collect high density data at rates of speed that are far greater than other ROV inspection methods. Typically, long range ROVs that can travel over two kilometres in linear distance travel at approximately 0.3 metres per second.

However, the Hibbard Inshore Saab Sabertooth can travel and collect tunnel dimensional and imaging data at swimming speeds that are many times faster than that, drastically reducing outage time.  The Sabertooth is uniquely configured with very powerful thrusters that give it propulsion and allow it to orient itself in any manner so that it can swim down shafts, through angles and around bends effectively.

The Saab Sabertooth solves the issues of tunnel or shaft size since it has the unique ability to enter a shaft nose down and navigate into the tunnel.  The power of the thrusters and the length of the tether allow the vehicle to effectively inspect from fewer access points and around more bends while the narrow and short form factor of the vehicle allow it to access through smaller cross-sections increasing the variety of possible locations to access each tunnel.

The Sabretooth is lowered into the water near a tunnel intake. Credit: Hibbard InshoreThe Hibbard Inshore Sabretooth is lowered into the water at one of the tunnel intakes. Credit: Hibbard Inshore

The Hibbard Inshore Saab Sabertooth system was equipped with a long distance fiber optic umbilical cable enabling full coverage of the tunnels as outage time permitted.  The inspections have generated high density cross-sections as well as acoustic imagery.   The vehicle carried multiple types of sonar in addition to its onboard cameras and lighting. 

The vehicle employed multibeam sonar units that update multiple times per second to image the top, bottom, and both walls of the tunnel concurrently while also taking dimensional measurements to look for rock falls, missing areas of liner, open cracks, shape anomalies, holes, rock trap conditions, debris or sediment level changes.

Each of these inspections were round trip excursions meaning that for the 12 kilometre Eucumbene-Tumut run, the vehicle actually travelled a total of 24 kilometres.

“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," COO Snowy Hydro Ken Lister said.

"This multi-million dollar investment is a great outcome for the business, for the safety of our people and contractors and is part of our wider program of Scheme upgrades and on-going maintenance.”

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