Blurry satellite images of what appears to be a ship drifting in the Pacific Ocean have raised faint hopes that seven crew members, missing since their yacht disappeared off New Zealand four months ago, may be alive.

Mystery has shrouded the fate of the Nina, a mahogany schooner which vanished after sailing into a severe storm in June. No trace of it was found during a search of more than half a million square nautical miles of the Pacific. The last word from the boat was an undelivered text message reporting: “Sails shredded last night.”

Relatives of the crew – six Americans, including David Dyche, the Nina’s owner and skipper, and 35-year-old Matt Wootton, from Orpington, Kent – say the object in the satellite images is the same size and shape as the 21-metre Nina. A private search and rescue company recruited by the families, Texas EquuSearch, is trying to plot its probable course before conducting an aerial search.

Download the new Independent Premium app Sharing the full story, not just the headlines

“We have never lost hope that the crew of Nina is alive and well, and that they will be rescued,” Robin Wright, whose 18-year-old daughter, Danielle, was on board, told The New Zealand Herald. However, the images gathered by EquuSearch are a month old, and some are sceptical as to whether they really depict the schooner. According to an Auckland-based meteorologist, Bob McDavitt, the area – about 200 kilometres west of Norfolk Island – is traversed by a vessel at least every other day. Even if the pictures do show the Nina, it may be a wreck – or a ghost ship, with no one left aboard.

The yacht – once the flagship of the New York Yacht Club – left Opua, in New Zealand’s Bay of Islands, on 29 May, headed for Newcastle, north of Sydney. It apparently weathered a storm on 4 June, with Evi Nemeth, a 73-year-old crew member, subsequently reporting the shredded sails.

Ms Nemeth said she would update the Nina’s position six hours later. But no further message was sent. Her undelivered text was released by the satellite phone company Iridium a month later. The boat’s emergency beacon was never activated.

On the day of the storm, Ms Nemeth – in the crew’s last direct contact with the outside world – had sought Mr McDavitt’s advice. The pair spoke by phone, after which she texted him, asking: “ANY UPDATE 4 NINA? … EVI.” That was the last he heard.

Nigel Clifford, the general manager of safety and response services for Maritime New Zealand, has said that while the Nina survived the storm, “very poor weather continued in the area for many hours and… [was] followed by other storms”.

New Zealand authorities have rejected calls by the crew’s families to resume their search. “We feel they are not going to be convinced by a satellite photo until they can see seven people holding their passports up, with their date of birth clearly visible,” said Mr Wootton’s father, Ian. He told the Herald that he and his wife, Sue, had mixed feelings when they first saw the photos. “You get the elation of ‘Yep, this looks like a really good image’. But also the downside of ‘How are you going to find it [the boat] again?’”

One expert, Ralph Baird, told the NY Daily News that the Nina was “a needle in a haystack, and that needle is moving”.

After the Nina disappeared, Russ Rimmington, a New Zealand skipper, claimed that the Nina was unseaworthy, with a warped hull, and that Mr Dyche – whose wife, Rosemary, and son, David, were also on board – refused to carry modern gadgetry.

Mr Rimmington also told Fairfax New Zealand that the Nina would have sunk if it had capsized, because of the lead on its keel.