Mystery continues to swirl around the extraordinary tale of Alan Langdon, an experienced sailor nicknamed "Paddles", and his six-year-old daughter, Que, who were the subject of a massive air and sea search in New Zealand after they vanished there on December 17.

The pair had set off from Kawhia Harbour, in Waikato on New Zealand's North Island, and were originally planning to head north to the Bay of Islands, where Mr Langdon planned to live on the boat with his daughter.

Instead, Mr Langdon sailed across the Tasman Sea to Australia on the 6.4-metre catamaran, which a friend said he had built at home, despite one of the vessel's rudders being damaged just four days into their voyage.

He told the Milton Ulladulla Times that the broken rudder, and a prevailing wind, was the reason he changed course.

"We were heading north and once the rudder broke we were heading back to New Zealand, but the wind blew us here," he said. "I first decided [to come here] when I knew what the prevailing wind was.

"Australia was the best target, the biggest target and the best option. I didn't really care what part I got to."

Mr Langdon said he sailed into Ulladulla Harbour on Wednesday, however a child recovery expert hired by his former wife says the pair may have been in the country for several days, until a member of the public recognised them from missing person's posters.

The Australian citizen and his former wife, Que's mother Ariane Wyler, were due to appear in the Family Court in Auckland in March this year.

However, Mr Langdon denied there was a custody battle and said he had been Que's primary carer since birth.

"It's not a custody battle, it's an access thing," he said. "I've always been looking after [Que]."

He said he did not know where he was on the journey, had no way of contacting anyone, and did not have a radio, satellite phone or emergency position radio indicating beacon (EPIRB) on board.

It was only when he got to shore that he realised his case had attracted attention, which he described as "mass hysteria".

"I thought people might have been worried but I didn't think they'd call out planes," Mr Langdon said.

"She [Que] did a 56-day trip before she was one, so 27 days isn't particularly big. She's lived on boats her whole life."

When her daughter vanished, Ms Wyler hired Col Chapman, a contractor with the Australian-based firm Child Recovery, to track down her former partner and daughter.

She had previously hired Mr Chapman in 2015 to locate Mr Langdon and their daughter when they disappeared in Australia before a scheduled Family Court case here, Mr Chapman said.

Mr Chapman said that, in his latest quest to find the pair, he had consulted experienced sailors and search-and-rescue professionals to plot Mr Langdon's possible route to Australia.

"We were adamant that he was transiting to Australia," Mr Chapman told Fairfax Media.

"We came up with a projected sail pattern of what were the most likely areas that he would land in Australia and when, and Ulladulla was one of the target areas."

Mr Chapman and his team then distributed missing person's posters around the NSW South Coast - including at yacht clubs, marinas, even small general stores catering to the sailing industry - containing images of the pair and urging anyone who saw them to contact the authorities. A social media campaign was also launched.

Someone who saw those images is believed to have spotted the father and daughter in Ulladulla, possibly as early as Monday, Mr Chapman said. That is despite Mr Langdon saying he arrived in Ulladulla on Wednesday.

"We are told that ... a member of the public did notice these [posters] and did approach the authorities," Mr Chapman said.

"We want to buy whoever it was a bottle of wine, champagne, chocolates or flowers, and of course the mum wants to just give them a great big hug

"I've heard that they hit Australian shores on Monday afternoon. Alan is saying that they only just arrived. I don't know what the truth is. The authorities are saying that he has been there for some time."

Yachts arriving in Australia from other countries must first call at a specified port of entry where Department of Immigration and Border Protection and Department of Agriculture formalities can be completed. Ulladulla is not one of those specified ports.

All people on board an incoming yacht must also produce a valid passport and incoming passenger card before they can go ashore.

Mr Chapman said a New Zealand court had seized Que's passport to prevent the child from travelling internationally before her parents' scheduled court appearance.

Mr Chapman said he had called Ms Wyler, who is caring for her sick mother in Switzerland, to tell her the news that her daughter had been found.

"She's thrilled, over the moon. I got her out of bed at one o'clock in the morning to tell her, woke her up, and she thought she was dreaming," he said, adding that Ms Wyler was now returning to New Zealand.

New Zealand Police said in a statement that Australian authorities had alerted them on Wednesday that the pair had been found in Ulladulla.

"Police understand that Mr Landon and his daughter are both well, and he [Mr Langdon] is currently talking to Australian officials," the statement said.

"New Zealand Police are currently liaising with its counterparts in Australia and awaiting further information about Mr Langdon's journey.

"Police will take time to assess all the information about today's development, and the background to this matter before any further steps required from a police perspective are considered and agreed."

An Australian Federal Police spokeswoman said it was now "a matter for New Zealand authorities", and the AFP would assist them if required.

Mr Chapman said the New Zealand search for the pair had cost upwards of $100,000.

"A court of some sort needs to make a determination in the best interests of Que," he said.

with Jessica McInerney, Milton Ulladulla Times