This summer Transpower will spend $5 million repairing a fibre optic cable under the Cook Strait.
The cable was damaged by a boat anchoring in a place it shouldn't have - the Cable Protection Zone.
The Sea Patroller has been tasked with patrolling the Cable Protection Zone (CPZ), all day, every day since 1996. The CPZ is seven kilometres wide and stretches from Wellington's Oteranga Bay to Fighting Bay in the Marlborough Sounds.
High voltage power cables and fibre optic telecommunication lines run along the seabed. Transpower says it's impossible to bury them.
“The Cook Strait cable is like a ravine - rocky, craggy, so the cable lies on the surface and in parts spans across gullies,” says Transpower CEO Patrick Strange.
That makes them vulnerable to damage from fishing gear and boat anchors, which is where the Sea Patroller comes in.
The ex-navy vessel has become a home-away-from-home for master Ken Bedford, who been patrolling the Strait for a decade. He says people's attitudes to the zone are slowly changing.
“In years gone by we used to get a lot of people who weren't that happy with it, possibly because they didn’t know but as we've gone on in the years more people know what we're doing,” says Mr Bedford.
Education is a key part of protecting the zone.
“We might talk to 10 people in one day, and then recreational people, nothing for the rest of the week because it's too rough but we do talk to commercial fisherman every day when we see them,” says Mr Bedford.
The zone is patrolled by sea and air at an annual cost of around $3 million. But Transpower says it's money well spent.
“Without it, without a doubt we would have been through at least one major repair in the past few years,” says Mr Strange.
Any major repair to power cables would cost upwards of $30 million and take months to fix, so deterrents are in place to prevent damage.
The zone comes under the Submarine Cables and Pipelines Protection Act. Those found in breach of the act face a maximum of $100,000 for fishing or anchoring within the zone, and up to $250,000 for damaging the cable.