"The operation management team has also asked the local fishing community to report any information that they believe could be useful to the operation."
Police said they had hoped for a better outcome at this stage, and their thoughts and sympathies remained with all families involved.
"Since Friday the combined efforts of Police, SAR staff, the Airforce, Southern Lakes Helicopters, Coast guard Air-patrol have put in three full days of searching in the vicinity and wider locality of where the missing yacht was expected to be travelling.
"The local commercial fishing fleet have also been actively carrying out observations during their routine fishing operations.
Southland Police area commander Inspector Lane Todd said a Royal New Zealand Air Force P-3K2 Orion today joined the search, bolstering efforts made by a Coastguard plane on Friday and two helicopters yesterday.
Regular broadcasts were continuing on marine radio.
The 33-year-old skipper was an ex-German immigrant who had been living in Southland for the past four years.
The identity of two female passengers on board the vessel, reportedly German tourists, had yet to be confirmed, Mr 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."
The last person to speak to Munetra's skipper, Bluff Marine Radio operator Meri Leask, said the yacht was in "unsuitable waters" when it made radio contact in rough weather off Centre Island on April 16.
Prospects of finding the yacht and those on board were "grim", she said.
The veteran radio operator told the skipper to take shelter alongside bigger vessels in seas being whipped up by strong easterly winds, and told him that when he arrived at a lodge on Preservation Inlet to advise Bluff authorities that the yacht and its crew had arrived safely.
However, the skipper was headstrong and disregarded basic safety advice, Ms Leask said.
"It didn't matter what you said. He just had his own way of doing things and refused to listen to any other advice."
He had left Bluff without filing a travel plan and was using an inadequate VHF handheld radio as his only means of communication.
Ms Leask said the alarm was raised this 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.
Mr Todd yesterday said the skipper had kept poor records of his movements, and in the past hadn't been good at communicating via his marine radio.
