Navy sonar team on Hertz search

Navy personnel load their sonar equipment before leaving the wharf at Raglan. Photo / Alan Gibson

The underwater search for plane wreckage believed to contain the bodies of 2degrees boss Eric Hertz and his wife has turned high-tech, with the operation drawing upon the same sonar equipment that rediscovered the Pink and White Terraces.

A navy squad specialising in mine sweeping yesterday joined efforts to retrieve the bodies of Mr Hertz, 58, and Kathy Hertz, 64, whose light plane ditched at high speed off Kawhia on Saturday.

The navy team deployed the Remote Environmental Measuring Unit (Remus) 100 - an autonomous underwater vehicle which travels along the contours of the ocean floor at speeds of up to 5 knots.

Grid-searching a 1sq km area 60m below the surface using a technique called "lawnmowing", the device was deployed for around five hours yesterday. It would have taken about the same time last night to analyse the data it captured.

Warrant Officer James Harper, officer in charge of the navy's Mine Countermeasures team, said the torpedo-like device was capable of gauging ocean depths as far as 100m below the surface.

"More importantly for this operation, it has side-scan sonar fitted on it and we can get imagery of the ocean floor and everything on it."

The Remus 100 unearthed part of the buried Pink and White Terraces at Lake Rotomahana in May 2011. The same team recently assisted police in searching for the bodies of Russian swimmer Alexy Ivanov in Northland and 73-year-old boatie Donald Ravenscroft on the Mahurangi River.

The Remus 100 was also used to find the wreckage of the Princess Ashika after it sank off the Tongan coast in 2009. This week was the first time it had been used to look for downed planes, but it had been previously deployed to detect a crashed microlight.

A 20-strong team of police, Coastguard, navy and volunteers were involved in the search off Kawhia, and Mr Harper said he was pleased with progress of the sonar scan.

"Everything is based on the best information you get at the time," he said.

"Can I put a confidence factor on it? Not necessarily now, but I have a reasonable confidence level in what we are achieving today."

It was only when the aircraft was pinpointed that police would consider putting divers in the water.

A major challenge was that the aircraft had potentially broken up - and there was the chance that surface currents could have carried some objects up to 5km a day.

Aerial flights were scanning the shoreline for debris, which could indicate drift patterns.

If the wreckage wasn't found, the search area would be widened today.

Asked if the bodies of Mr and Mrs Hertz might never be found, Mr Harper said: "That is always a possibility - but my team and the police are doing our utmost to find these people.

"We will continue giving our best effort up until someone higher up in the food chain tells us to stop."