It was almost three weeks after the old schooner went missing in a storm off New Zealand before Ricky Wright confessed his fears to his wife, Robin. Even after members of their Full Gospel Baptist Church in Louisiana began calling Robin to ask if the couple's 19-year-old daughter, Danielle - a crew member on the yacht - was okay, Ricky tried to bluff through.

"I was like, 'Ricky Wright! Am I supposed to be worried about Danielle?' " says Robin. "And he said, 'No, no.' "

But despite what he'd been telling himself about the schooner being likely to turn up any day, and how its captain was resourceful and experienced, Ricky was so worried he'd already unburdened himself to their pastor, who in turn had "got people praying over the situation", which led to the anxious phone calls to Robin. By the time Ricky admitted this to his wife, NZ rescue authorities were about to begin what became the biggest maritime search in the nation's history.

Yet no trace has ever been found of the Niña - a classic 21-metre racing schooner launched in 1928 - or her seven-person crew. Sailing from Opua in the Bay of Islands to Newcastle, Australia, the vessel struck a series of fierce storms in the Tasman Sea just north of NZ, and issued its last communication on June 4 last year.

The subsequent 12-day search covered 737,000 square nautical miles before being suspended on July 5. Officially, it's deemed likely that the Niña was "overwhelmed in a catastrophic event" in gale force winds and eight-metre swells soon after June 4, and sank suddenly with the loss of all hands.

For the Wrights, and others related to the Niña's crew, that conclusion wasn't the end of the story but the start of a gruelling odyssey to find the loved ones they believe survived the storms and may still be alive - either on board the crippled but still-floating schooner, or marooned on some remote reef or island far to the north of their last known location.

Even now, eight months after Danielle Wright disappeared along with five other Americans and an Englishman, her deeply religious parents - sailors themselves - look you in the eye and say they know their beloved only child has somehow survived. "This trial that we're going through, we're able to get through it because of our built-up faith in Christ," Ricky tells me at the house in Port Macquarie, on the NSW mid-north coast, where they've been based since leaving their home in Louisiana in November 2013 to begin their own aerial searches for the Niña.

"Danielle and the others know exactly where they are," ventures Robin. "They'll be charting everywhere they're going. When they're found, we'll know exactly what happened to that boat."

There are precedents for survival at sea long after official searches have been abandoned. But the odds against it after this long are astronomical, which makes the Wrights' unfailing use of the present tense in referring to Danielle difficult to cope with. Nor in all conscience could I bring myself to wear the printed wristband ("Bring home Danielle & Niña crew") Robin had dutifully handed over when we first met earlier in the day.

Yet as they sit on the verandah that night and tell their harrowing story it's impossible not to be moved by their bravery and determination, or not to recognise - like some tiny object glimpsed by chance on a vast and unforgiving sea - the possibility of a "miracle".

Robin, 54, and Ricky, 49, met at a Bible study group and have been together for 25 years. He was a Lafayette college athlete who narrowly missed selection as a pole vaulter for the 1996 Olympics in Atlanta. She grew up on a farm near Baton Rouge; later, when Danielle was young, the couple bought land adjoining Robin's childhood farm, raised animals and enjoyed the good life.

Keen sailors, the Wrights had chartered sail-yourself yachts for holidays, and in 2009 - when Danielle was 15 - they realised a long-held goal of buying their own live-aboard vessel and cruising the Caribbean. But before they set off in their 11.6-metre catamaran a "strange thing" happened that Robin and Ricky now see as a prophecy involving Danielle.

"Even as a little girl, there was something very special about her," Robin says over the screech of cicadas on the verandah in Port Macquarie. "She wrote beautiful songs, and was always very tender towards God." She tells how a friend unexpectedly brought an evangelist from Puerto Rico to their farm as they prepared to go sailing, and how, on meeting Danielle, the preacher raised his arms, declaring, "She will go all over the world, and when she speaks young people will listen."

Not sure how to react, I tell Robin that I don't share their faith. She shrugs. "It's just ... it was just such a strange thing. And now, I think it was God's way of giving me hope, like, just hang on, hang on, there's a purpose to everything."

Soon after they began their live-aboard cruise, the Wrights met members of the Dyche family, owners of the Niña (Spanish for "little girl"), at a marina in Florida and struck up a lasting friendship. Designed specifically for the 1928 Queen of Spain's Cup, a transatlantic race from New York to Santander in Spain (which it won, along with many subsequent races), the Niña was bought in 1988 by David Dyche III, a tugboat captain who overhauled the elegant schooner before setting out with his family on an open-ended world cruise.

To finance the voyage, Dyche worked two months out of three as a tug master at oilfields off Brazil, using his time off to move the Niña from one port to the next. He's wasn't on board when the Wrights met his wife, Rosemary, and their teenage son, "Little" David, on the schooner in Florida. "We only met David the once [in 2011] when we all went to dinner in New Orleans," explains Robin. "He was very friendly and outgoing, a jack of all trades who could fix anything. His son was the same."

When their cruise ended, the Wrights sold their catamaran and set up a business brokerage in Lafayette. Danielle and Little David stayed in touch via Facebook, and in February last year the Dyches (by then berthed in NZ) sent a message inviting the Wrights to join them on their upcoming voyage to Australia, which they estimated would take 14 days.

"Ricky was like, 'Yeah! Let's go!' " says Robin. "But I said, 'The Tasman Sea? Are you crazy? No, I'll be sick! I'm not doing that.' Then Danielle told us, 'I really want to have this experience without y'all.' We did have to look after the business, so we let her go. We gave her the airline ticket as an early [19th] birthday present."

An honours student studying psychology at the University of Louisiana, Danielle finished her exams the day before leaving. As a car waited to take her to the airport on May 12, she ran back to the house calling, "I almost forgot my Bible!"

To fill a silence, I ask if Danielle and Little David, 18, had a romance going, then wish I hadn't. But the Wrights just laugh. "Not that we knew of," says Robin. "But they've been on that boat together for seven months now, so who knows!"

The Dyches had spent more than a year at a marina in Whangarei, north of Auckland, then sailed further up the east coast to Opua a couple of months before leaving for Newcastle.

Their crew was an interesting and capable bunch: Danielle, a qualified scuba diver who'd been Ricky's "first mate" in the Caribbean; Kyle Jackson, 27, an adventure-loving rancher's son from Nebraska who'd worked for now-retired Democrat senator Ben Nelson; Matthew Wootton, 35, a musician and a member of the national executive of the Green Party in the UK who refused to fly and was on the final leg of a three-year "eco-friendly" world trip; and professor Evi Nemeth, 73, a veteran American sailor, mathematician and IT scientist famous as the "grandmother" of the Linux computer operating system.

Significantly, given what was to come, the Niña carried little of the high-tech equipment now common on offshore cruising yachts. It had a VHF radio (with a maximum range of about 50 kilometres) but no short-wave radio for long-distance communications. The Niña's emergency position indicating radio beacon (EPIRB) was an outmoded version that had to be manually activated (newer models send a distress signal automatically when they get wet).

The vessel carried a satellite phone, a spot tracker device (which stopped working soon after the Niña left NZ), and an eight-person life raft, but no radar and no generator, meaning it had no way of charging batteries or generating power if its diesel engine (replaced in Opua) failed. The sails on the two-masted schooner were second-hand but reconditioned.

David Dyche, 58, was a traditionalist sailor who could navigate by stars and sextant and apparently preferred his vessel's equipment to match its vintage. "There was no luxury accommodation," says Robin Wright. "It had fold-up bunks, one little main cabin, one little head [toilet], and no refrigeration. Rosemary had all their meat freeze-dried."

The Niña left Opua on May 29, a wet and blustery Wednesday, on a course that would take it north past the tip of Cape Reinga, then north-west towards Australia. "The Tasman Sea is shooting gales out like a machine gun, living up to its reputation," Dyche posted on Facebook three days before setting sail. "We are shooting at leaving after the first one this week. No doubt we will be dancing with one or two of them [en route]."

Back in Lafayette, Ricky was anxiously monitoring the low-pressure systems which came from below Australia, then crossed the Tasman and roared north off NZ's west coast. "They were coming through every seven days," he says. "[Dyche's] plan was to ride the clear winds in the wake of the low that had just passed out into the Tasman, and to be far enough west to miss the next low when it came through."

But it didn't pan out that way. On June 3, Evi Nemeth on the Niña contacted NZ meteorologist Bob McDavitt by satellite phone, saying, "The weather's turned nasty, how do we get away from it?" McDavitt asked her to call back in 30 minutes, and when she did - sounding "like everything was under control" - he told her they should steer south and prepare for a storm. McDavitt suggested they might want to heave to (reduce sail and put the boat into a holding pattern facing the oncoming storm) until it passed.

Later that day McDavitt received a text: "ANY UPDATE 4 NINA? ... EVI." He responded with a number of texts about the storm's progress, but got no reply. It was weeks later - after repeated pleas from family members of the missing crew - before the US State Department finally approved their requests for the satellite cell phone provider, Iridium, to provide confidential information about further calls from the Niña's phone. There was just one text, sent on June 4 but never received by McDavitt: "THANKS STORM SAILS SHREDDED LAST NIGHT, NOW BARE POLES GOINING [sic] 4KT 310 DEG WILL UPDATE COURSE INFO @ 6PM".

No update was sent, and the Niña's manual EPIRB was either never activated or failed to function. The schooner's last position was estimated to be about 370 nautical miles west-north-west of Cape Reinga.

In the weeks and months following the Niña's disappearance, Maritime New Zealand's Rescue Coordination Centre was criticised for searching in the wrong area, for not searching soon enough, or long enough, and for assuming - in the face of its own "errors" - that because it couldn't find the schooner it must have sunk.

Ricky Wright brought the volunteer-based search organisation Texas EquuSearch into the fray, and by late July it had a team of search-and-rescue experts, including fluid hydrologists, geophysicists and NASA scientists, involved in the hunt. A Colorado-based satellite services provider, DigitalGlobe, agreed to reposition its WorldView and QuickBird satellites to take images across huge swathes of the Tasman, and recruited thousands of online users of its Tomnod crowd-sourcing site to comb through the myriad images for anything resembling the Niña or its life raft.

"They've looked and looked ... and all they see is nothing," mourned David Dyche's mother, Caryl, from her home in Florida. Believing the Niña had gone down, Caryl Dyche revealed that her son had been carrying the ashes of his sailor father, David II, in an urn on the schooner: "If they went down, both of them went down. That's where they'd both love to be."

But others, especially the Wrights, were convinced their missing loved ones were still alive. "I had a lot of people praying with me," Ricky tells me, "and they came back to me with word from God that said Danielle was like Solomon's son when he went out to search for some missing donkeys. He was gone for many days and his dad ... sent him a message saying he was now more concerned about his son than the missing donkeys." Ricky interpreted this to mean that Danielle wanted him to stop fixating on her and concentrate on the search.

By July, NZ media outlets were running criticism of the Niña's seaworthiness. Russ Rimming-ton, a yachtsman and former mayor of Hamilton, claimed the old wooden schooner was "hogged" - meaning the fastenings of its hull planking had loosened - making it a "lead mine that would have gone straight down" because of the tonnes of metal in its keel. (Rimmington told me he'd never seen the Niña and had based his opinion on reports from an "expert" in Whangarei.)

Hopes for the missing sailors flared when a QuickBird satellite image taken on September 16 showed what appeared to be a boat of the same dimensions as the Niña floating (with no sign of a wake) in the Tasman near Norfolk Island. But the image was too fuzzy for positive identification. Texas EquuSearch sought help from the US National Geospatial-Intelligence Agency (NGA) in accessing better resolution satellite imagery unavailable to the public, but met a brick wall.

Ian and Sue Wootton, the parents of missing English crew member Matthew Wootton, spent months poring over satellite images. Ian Wootton suspects clearer versions of the September 16 image exist but are confined to military sources. "A contact high up in DigitalGlobe told me even they don't have access to this area of the company," Wootton, a retired industrial chemist, tells Good Weekend from their home in Kent. He believes NGA personnel are "probably the people behind the closed doors at DigitalGlobe".

Wootton says David Dyche's minimalist approach to technology "wouldn't have been the approach I would have taken", and that if he'd known more about "the Tasman and EPIRBs and communication devices, I would probably have had a lot more to say to Matthew at the time".

In an unsettling prelude to joining the Niña's crew, Matthew Wootton posted a piece called The Ocean on a creative writing site in 2012 in which he described a recurring nightmare about being "overwhelmed" by a tsunami: "I'm trying to work out, is my fear rational or irrational? Do I think the sea, the ocean, symbolises something, someone? Do I think something - like the tsunami - is coming to get me?"

Encouraged by the September 16 satellite image, but frustrated anew by the refusal of maritime authorities in NZ and Australia to begin searching the area, Robin and Ricky Wright flew to Australia on November 12 to conduct their own searches. So far, they've spent more than $500,000 on aerial charters.

Jack Hart, the owner of air charter company Macquarie Air, invited them to stay at his home in Port Macquarie (where Ricky is training to get his pilot's licence) and they've been there ever since. They initially spent a week searching in the vicinity of Norfolk Island, believing at first they would spot the Niña "at any minute". Their hopes faded as the scale of the immense emptiness below began to sink in.

"There's nothing out there," Robin says wonderingly on the verandah, as the cicadas build to a crescendo around us. "In seven days we saw just one sailboat and three freighters." Then they searched up and down the Great Barrier Reef, praying - as always - for the miracle they still believe may unfold. On New Year's Day, when Ricky had the flu and they were holed up in a poky apartment in Gladstone, Robin finally raised the question neither of them had wanted to face.

"I said, 'Okay, Ricky, if we don't find them, and they don't wash up, when do we quit searching?' And he said, 'After a year.' And that seemed right, because in my heart I'd already said it would be on Danielle's birthday, which is May 18th."

Robin cries a bit, then looks at Ricky, who is busy studying the table. "But first," he says defiantly, "there are some unpopulated islands around the Solomons, and we want to go there and search every one of them."