Police say searching the coast at the top of the South Island for a missing sailor is like looking for a needle in a haystack.
William Kerry Blair, known as Kerry, gave no indication of his intentions before leaving the Marlborough Sounds on the nine-metre launch Erie about 4pm on Saturday.
Police say the last known possible sighting of the launch was near Cape Jackson about 5.30pm, while a signal from the 55-year-old's cellphone was last detected at the top of the the West Coast late on Sunday afternoon.
Both the Nelson and West Coast Coastguard have been searching the coast for the past two days. The harbourmaster and commercial vessels have also searched the area.
Police say the behaviour is out of character for Mr Blair, who is an experienced seaman.
The Erie has a hard top painted white and a blue stripe along the side. It has an inboard diesel engine and fuel tanks capable of taking it an extensive distance.
Marlborough area commander Inspector Simon Feltham said on Tuesday that Mr Blair is an experienced skipper and his disappearance is out of character.
Mr Feltham said the weather has been good and the only thing that would stop him travelling extended distances is fuel.