Submarine Cables

Transpower Subsea Inspection

If you ever take the ferry across Cook Strait, spare a moment for the submarine cables beneath your feet. You may not know it, but a Seaworks expert or one of our remotely operated vehicles (ROVs) could be working not too far away.

Our role in these waters (considered some of the most dangerous and unpredictable in the world) is to undertake yearly inspections of Transpower’s underwater high voltage electricity and telecommunication cables. The cables sit on the floor of the Cook Strait Cable Protection Zone, a 7-kilometre wide, 40-kilometre-long stretch between Oteranga Bay in the North Island and Fighting Bay in the South Island. It is illegal for vessels to anchor and fish there, and it’s routinely patrolled by sea and by air.

“The Seaworks team have continually proven to be innovative and professional marine operators who have been integral to the ongoing improvement of Transpower’s marine regime."


Seaworks has been undertaking ROV inspections of the cables since 1991 and dive inspections and maintenance since 1980. We annually ensure that they’re in good shape and securely in place, and that any problems or faults are addressed promptly. Divers cover shallow water areas, and ROVs up to 250 metres in this cable corridor.

However, the challenging environment inevitably brings complications and limitations: ROVs can only operate in this area twice a day around slack tides (and all tides are unpredictable), and some seabed areas are difficult to access owing to strong currents and often severe sea conditions. It all makes effective site selection and prioritisation critical, and success depends on our having the right people and the right equipment ready to go at the right times.

"The Seaworks vessels have an excellent safety record operating in the challenging and harsh environment of Cook Strait."


As of 2022 we’ve recorded more than 10,000 days of operational experience in Cook Strait, and surveyed more than 3,000 kilometres of cable and pipelines around New Zealand – more than any other New Zealand subsea operator. We also operate the country’s only hydraulic work class ROV, which enables us to maximise dive time in the strongest of currents.

We continue to develop and improve our services. For example, we’ve developed:

  • Cook-Strait-specific launch and recovery (LARS) systems that operate from DP1 vessels. Together, the systems offer world-class ROV capabilities and a sustainable and cost-effective package
  • Proprietary data eventing software
  • An extensive database of past inspections that can be used to compare condition assessments and take appropriate actions in response

The Cook Strait continues to challenge our team and our capabilities with every visit we make – but it’s a challenge we welcome, every time!

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We are always interested in new ways we can help. We have a range of equipment and skills to solve any problem you have.

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