A man missing in the Far North is believed to have drowned, but experts say he could have survived if he had been wearing a lifejacket.

Bernard Kuczera has not been seen since Friday afternoon when the crew of a fishing boat saw him in a 3.5m dinghy 11km off Nine Pin Rock in the Bay of Islands.

The 63-year-old didn't appear to be in difficulty but wasn't wearing a lifejacket. The alarm was raised when the same crew saw the dinghy empty five hours later.

Senior Sergeant Cliff Metcalfe, of Northland Search and Rescue, said it was a mystery why the experienced deep water sailor had taken such a small craft so far out.

It did not appear that he had been fishing, and two lifejackets were found aboard the dinghy. Mr Kuczera was not known for wearing a lifejacket.

The official search was scaled down on Sunday night after searchers concluded that the missing man had fallen from the dinghy and drowned.

"If he had been wearing a lifejacket we'd have found him, probably alive," Senior Sergeant Metcalfe said.

Mr Kuczera's family hired a helicopter and searched the coastline. They also took an advertisement in the Herald appealing for anyone who has seen him to come forward.

Family member Lisa Sargison said the family were as good as they could be but declined to comment further.

An extensive sea and air search over two days failed to find any sign of Mr Kuczera, who lives aboard a boat at Paihia.

Northland police spokeswoman Sarah Kennett said police had examined the boat Mr Kuczera lived on but were yet to examine the dinghy.

"Nothing of note has been found. Police are still doing inquiries but at this stage it looks as if the man has possibly fallen out of the dinghy and drowned."