An Air Force Orion is searching near Norfolk Island today for missing vintage American schooner Nina.
It is nearly a month since the last contact with the vessel, and family members of some of the seven-strong crew have spoken of their desperate need for answers.
The Air Force plane left before dawn today and is focussing its search south of Norfolk Island, Rescue Coordination Centre New Zealand spokeswoman Rosemary Neilson said.
The aircraft was expected to make a detailed search for the vessel's life raft south-east and south-west of the island until about 6pm, she said.
The search area would cover nearly 6000 square nautical miles.
"The plane will be flying low and slow in a tight zigzag," Ms Neilson said.
The seven-strong crew of the classic 21-metre racing yacht, which was sailing to Australia from Opua in the Bay of Islands, was last heard from on June 4.
"Obviously time is passing and concerns are increasing, but (searchers) remain optimistic," Ms Neilson said.
There was no deadline set for how long the search will continue, she said.
The 84-year-old wooden vessel, owned by American David Dyche, 58, was heading for Newcastle, Australia.
Mr Dyche was travelling with his 60-year-old wife, Rosemary, their son David, 17, a 35-year-old British man Matthew Wooton and well-known maritime technology expert Evi Nemeth, 73.
An 18-year-old American woman called Daniella and 28-year-old American man named Kyle were also on board.
Mr Dyche's sister Cherie Martinez said the worst possible outcome would be for the crew to be lost at sea forever and to never know what happened to them.
Mrs Martinez said she was terrified the search would be called off before they knew what had happened. The last known contact was a text message on June 4 inquiring about weather conditions.
"At the end of the day I would rather find out they made it okay, which is better, or at least debris or something so I can call closure. But for them to be lost at sea and never be heard of again, that will be very difficult."
Speaking from her home in Tennessee, Mrs Martinez said the not knowing was the hardest part.
"It's a rollercoaster. One day you think they will make a phone call, the next you're [resigned] to have lost them at sea ... Deep down I think at times they are lost but this boat has always made it to shore.
"It's lost its mast, it's gone through rogue waves through the Pacific, the Atlantic a couple of times, it's sailed even without engines - it was built to race."
But she is in no doubt her brother would have done everything possible to save his family.
"I grieve for him at times but being a pilot myself I know there is risk inherent in the job ... But he wouldn't put his family at risk."
The family of Mr Wooton, a Green Party activist from the UK, still held on to hope he might be found alive.
His sister Lara told the Daily Mail her brother was "very environmentally aware" and travelled by boat or public transport when possible.
He was writing sporadically about his travels, and the last post on his blog, written last July on board a freighter, was a piece about facing his fears of the ocean. His mother Susan said the family hoped the search for her son would continue.
MISSING AT SEA:
• In March 2010, Tafadzwa was sailing from Tauranga to Gisborne. It was found 16 days later near the Chatham Islands without its skipper, Paul Janse van Rensburg. However, his dog Juanita was still on board.
• The New Zealand yacht Manoah set sail for Rarotonga from Nelson with two crew on board in 2005 but then disappeared. Its wreckage was found on Uonuku Island, halfway between Nuku'alofa and the Vava'u islands group, in Tonga in February 2007.
• In 1989, four men spent 119 days adrift on their capsized trimaran, the Rose Noelle, before washing up on Great Barrier Island. The men had set off from Picton for Tonga but storms flipped their boat off the Wairarapa coast.
• The yacht Smackwater Jack and its four crew disappeared during a race from Hobart to Auckland in 1980. The crew reported difficult and heavy seas on January 9 but were not heard from again.