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Searchers - including those in vessels, helicopters, and a Royal New Zealand Air Force Orion - failed to find any trace of Munetra as they scoured around Muttonbird Island and the west of Stewart Island.
Last night police said the operation was now in a ''limited continuous search phase'' for the vessel, which was occupied by the captain and two female passengers.
That meant there would be no further active searching for the Munetra but any new information surrounding relevant tidal patterns, current movements and debris could result in future searches.
''Police had hoped for a better outcome at this stage and our thoughts and sympathies remain with all families involved,'' Southland area commander Inspector Lane Todd said.
The 7.5m vessel and its skipper is believed to have sailed with two foreign female tourists from Bluff in rough conditions on Wednesday, April 16.
''If they had come into some grief we would have expected to have seen some wreckage by now'', Insp Todd told the Otago Daily Times last night.
''Unfortunately, they haven't come up with anything. ''We have to keep an open mind ... but certainly it looks quite a serious situation.''
The 33-year-old skipper was a German immigrant who had been living in Southland for the past four years, he said.
The identity of two female passengers on board the vessel, reportedly German tourists, had yet to be confirmed, Insp Todd said.
''We think we know who's on it, but we want to obviously check that with the families and next of kin, which we're struggling to do at the moment.''
Bluff Marine Radio operator Meri Leask, believed to have been the last person to speak to the skipper, said he was headstrong and disregarded basic safety advice.
''It didn't matter what you said. He just had his own way of doing things and refused to listen to any other advice.''
Mrs Leask said the alarm was raised last week when a friend of one of the female crew members reported the vessel overdue. The skipper's employer was also concerned when he failed to show up for work.
Mrs Leask said the vessel was not equipped for the trip, and it was particularly concerning the skipper had only an inadequate VHF hand-held radio as his sole means of communication.
He had last made radio contact while sheltering beside Centre Island during rough weather.
''It is a serious situation. We have treated it as that all the way through,'' she said.
Searchers had covered an enormous area, and Mrs Leask said a keen eye would be needed to spot the vessel if it had overturned, because it was blue-hulled with a black bottom.