Rescue crews searching for a classic American schooner carrying seven people now believe the vessel sank between New Zealand and Australia, although they have not given up hope of finding survivors.
A third day of aerial searches turned up no sign of the 85-year-old wooden yacht or its crew.
The boat, named Nina, left New Zealand on May 29 bound for Australia. The last known contact with the crew was on June 4. Rescuers were alerted on June 14, but were not unduly worried at first because the emergency locator beacon had not been activated.
The six Americans on board include captain David Dyche, 58, his wife Rosemary, 60, and their son David, 17. Also on board was their friend Evi Nemeth, 73, a man aged 28, a woman of 18, and a 35-year-old British man.
Search leader Neville Blakemore, from New Zealand's Rescue Co-ordination Centre, said it is now logical to assume that the 21m boat sank in a storm but added that it is possible some crew members survived either in the life raft or by making land.
On the day the vessel went missing, a storm hit the area with winds gusting up to 110kph and waves of up to 8m.
Mr Blakemore said the Southern Hemisphere winter months tend to produce the year's worst storms, although he added that he would not normally expect a sturdy and well-maintained craft like the Nina to sink in a storm like the one in early June.
The search is focusing on the coastline around northern New Zealand, including the small Three Kings islands. Rescuers are looking for wreckage or the life raft.
Mr Blakemore said plane searches earlier this week covered a wide band of ocean between New Zealand and Australia.
He said the logical conclusion is that the boat sank rapidly, preventing the crew from activating the locator beacon or using other devices on board including a satellite phone and a spot beacon. He said that, unlike many locator beacons, the one on the Nina is not activated by water pressure and would not start automatically if the boat sank.
Mr Dyche is a qualified captain and he and his family are experienced sailors. Mr Blakemore said the family had been sailing around the world for several years and were often joined on different legs by friends and sailors they met along the way.
Susan Payne, harbour master of the St Andrews Marina near Panama City, Florida, said the couple left Panama City in the Nina a couple of years ago and sailed to Mystic Seaport in Connecticut where they prepared for the trip.
New Zealand meteorologist Bob McDavitt was the last person known to have been in contact with the schooner.
He said Ms Nemeth called him by satellite phone on June 3 and said: "The weather's turned nasty, how do we get away from it?"
He advised them to head south and brace for the storm.
The next day he got a text, the last known communication: "Any update 4 Nina? ... Evi"
Mr McDavitt said he advised the crew to stay put and ride out the storm for another day. He continued sending messages over the next few days but did not hear back. Friends of the crew got in touch with Mr McDavitt soon after that, and then alerted authorities.