Satellite data shows the doomed HMNZS Manawanui’s departure from Auckland last month was delayed a day in what appears to be last-minute testing on vital propulsion equipment.
The revelations have raised fresh questions about the state of the ship before its final voyage and whether all its systems were fully functional.
The New Zealand Defence Force is refusing to be drawn on any speculation about the state of the ship before it struck a reef and sank off Samoa.
Nor would the military discuss the exact nature of tests performed, citing the Court of Inquiry into the disaster.
After departing New Zealand waters, the ship twice paused to conduct slow, precise manoeuvres over several hours.
Because it was about to navigate busy shipping channels, its Automatic Identification System transponder had been switched on. The system broadcasts a ship’s location to other ships, but is often turned off on military vessels.
The data was logged by marine trackers and allowed the Herald to view its movements.
The HMNZS Manawanui started to pull out from its berth at Devonport Naval Base about 10am on September 28, following what the Navy has said was a period of maintenance.
The survey and dive ship can be seen heading east out of the Waitematā Harbour, then north through the Rangitoto Channel.
But instead of continuing deeper into the Hauraki Gulf towards the Pacific, the Manawanui slows and turns back on itself while off Murrays Bay on the North Shore, turns north again, then reverses direction once more shortly after 12pm.
Over the rest of the afternoon it conducts a series of precise and intricate manoeuvres off Browns Bay at differing speeds, changing direction often and generally moving slowly.
Captain Peter McGuiness, from Vancouver, Washington state, in the United States, has served as shipmaster in command of more than 100 new-build pre-delivery sea trials of various ships. He now runs the American Maritime Information Service LLC, a maritime consultancy.
His credentials and experience include graduating from the US Merchant Marine Academy and extensive experience aboard oil industry ships across the world.
McGuiness said the Manawanui’s movements while near the North Shore on the afternoon of September 28 suggest a propulsion or manoeuvring test.
“The time and location of the test is consistent with the prudent need to determine the condition of key propulsion or manoeuvring equipment before proceeding far from home base,” he said.
“Note that this need may reflect a specific concern about the success of recent repairs, or it may reflect a more general concern about equipment conditions following a prolonged stay in port, despite the absence of specific recent repairs or other specific changes that might have affected propulsion or manoeuvring equipment.
“Such a test is certainly justifiable as a matter of prudent seamanship in either case, especially given the sensitive and remote areas to be visited by [the] Manawanui.”
Manawanui’s transponder turns off at about 5pm on September 28 before it heads further north into the Hauraki Gulf. Location tracking resumes shortly before midnight.
At this point, the ship is about 40km off Waipu in Northland, between the Hen and Chicken and Mokohinau Islands.
Over the next hour and a half, it conducts a few slow loops back and forth before disappearing off the Automatic Identification System again and resuming its voyage north.
McGuiness said the time of these movements and the location, close to two remote islands with no light, makes a propulsion test less likely.
“For a propulsion or manoeuvring test, a wide, deep, remote area is ideal. It appears such an area is on offer along the intended track of the ship, nearby to the north. Such an area would be a more logical and prudent choice for a propulsion or manoeuvring test [with the attendant possibility of breakdown as a result of the test].”
However, a New Zealand source with knowledge of naval ship movements said the midnight testing is consistent with someone onboard wanting to conduct a few more tests on vital systems, possibly including propulsion equipment, or verify that all issues were resolved.
The ship disappeared off the tracker again at about 1.30am on September 29.
No system data is available until 6.47pm on October 5, a minute after the ship hit the reef about 1800m south of the Samoan Island of Upolu.
The 75 people aboard, including several civilians from GNS Science and MetService alongside its crew of Navy ratings and officers, began abandoning ship in liferafts and rigid hull inflatable boats about an hour later.
Three of the rafts went out to sea, where they were met by local boats and a Malaysian cable ship that came to their rescue.
One lifeboat and one inflatable went back on to the reef and were damaged and overturned amid worsening weather conditions. Some who were aboard walked for hours across a reef towards shore, while others spent long hours in the water before they swam ashore or were rescued.
The Herald understands Commander Yvonne Gray was with the lifeboat and inflatable that went back towards the reef.
The hydrographic and dive support vessel, bought by the Navy in 2018 after 15 years as a survey ship in the Norwegian oil and gas industry, had most recently been in a maintenance period after a busy stint of work finishing earlier this year.
The Manawanui had been the Navy’s designated duty vessel for the high-risk weather season in the Pacific from November to March.
The HMNZS Canterbury, the Defence Force’s preferred ship for duty during cyclone season because it can sail with helicopters stored aboard, was unavailable due to the Navy’s workforce shortages and unavoidable maintenance, according to briefings released under the Official Information Act.
After cyclone duty, the Manawanui undertook another mission in the Pacific where Navy divers disposed of five 453kg bombs found in Port Vila Harbour in Vanuatu.
Its crew also carried out a survey of the seafloor in Tonga to improve navigation safety after the eruption of the Hunga Tonga-Hunga Ha’apai volcano in 2022.
The Manawanui arrived back at the Devonport Naval Base on July 10.
Two days after it struck a reef and sank, Chief of Navy Rear Admiral Garin Golding said it was in a “maintenance period” after which it undertook some trials and was deemed safe to sail.
The Defence Force has not answered questions from the Herald regarding the state of the ship, including whether there were concerns about its diesel-electric generators or its propulsion systems, including the various thrusters it uses to navigate. The Defence Force also won’t comment on the reason for Manawanui’s delayed departure or the nature of the tests.
A Defence spokesman said “we have nothing further to add to questions which will fall within the scope of the Court of Inquiry”.
Minister of Defence Judith Collins said in a breakfast television interview soon after the sinking that the Manawanui “apparently lost power”. No further information has been provided.
A fire broke out aboard the ship before it sank, starting in the engine room, according to Samoan authorities.
It remains unclear and unconfirmed if the ship lost propulsion and drifted on to the reef, or whether it could have retained propulsion but lost the ability to control its movements using its thrusters.
The Manawanui, formerly the civilian oil and gas survey vessel Edda Fonn, was driven by two main azimuth thrusters at the aft (rear) of the vessel. Azimuth thrusters are propellers in pods that can rotate at any angle, making a rudder redundant.
The ship also has tunnel thrusters in the bow, providing lateral force for manoeuvring. Shortly after it was delivered, the Navy described it as the most manoeuvrable ship in the fleet.
It manoeuvred with the aid of a Kongsberg K-POS Dynamic Positioning 2 (DP2) System, akin to a marine autopilot.
DP2 refers to its level of redundancy, and means it should be able to keep station – stay on course or in one place – even if one component on board fails.
The Herald understands the crew had undertaken renewed dynamic positional training before the final voyage.
George Block is an Auckland-based reporter with a focus on police, the courts, prisons and defence. He joined the Herald in 2022 and has previously worked at Stuff in Auckland and the Otago Daily Times in Dunedin.
Reporter Martha and friends are in Minginui introducing us to their favourite four-legged neighbours, wild but friendly horses that have had free reign of the place since 1870.