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An experienced seaman who went missing in the calm waters of Marlborough Sounds three days ago didn't tell anybody where he was going, and the search for him is proving a "needle in a haystack", police say.
The last possible sighting of Kerry Blair, 55, was near Cape Jackson about 5.30pm on Saturday.
His vessel is equipped with navigation equipment and a radio and weather and sea conditions have been good.
Mr Blair has made no attempt to use his radio or cellphone and his family have grave fears for his welfare.
Niece Georgia Bidois says the disappearance is "extremely out of character" for the "much-loved father of three and grandfather of four".
"There are many people looking for him and want to see him get back safely, although as more time passes things are not looking good," the 23-year-old said.
"We are desperate to find him and fear for his wellbeing. If we can can get any help at all we would really appreciate it."
On Sunday, the Harbourmaster searched Queen Charlotte Sound and regular requests for other vessels to look for him have been made over marine radio.
The Nelson Coastguard has searched Tasman Bay to the top of Farewell Spit, and the Abel Tasman coastline from Awaroa back to Nelson.
The West Coast Coastguard vessel, which was in Nelson, searched on its way back to Greymouth.
Freight vessels travelling along the West Coast have also been on the lookout.
Search coordinator Sergeant Bill Talbot said there were a lot of fishing boats off the West Coast of the South Island and they had all been informed of Mr Blair's vessel's disappearance.
The 9-metre Senator brand aluminium boat, called Erie, has an inboard diesel engine and is capable of travelling long distances, depending on the amount of fuel onboard.
It has a white hard top and a blue stripe along the side.
Police say the behaviour is out of character.
Mr Talbot said without having any indication of Mr Blair's intentions the potential search area was enormous.
"We don't know if he has been motoring and if so what direction, or drifting, or whether the boat has gone down. Right now it's a needle in a haystack."
Today, police are also investigating whether Mr Blair had discussed any plans with anyone.