Search teams are today continuing scouring uninhabited islands in Auckland's Hauraki Gulf in the faint hope a missing fisherman managed to swim ashore.
Anthony Murray Preston, 41, of Warkworth, north of Auckland, has not been seen since becoming separated from his four companions, including a 13-year-old boy, after their fishing boat sunk off Kawau Island about 6pm on Tuesday.
The others swam about 2km to Motuketekete, near Kawau Island, from where they were rescued the following morning and flown to hospital.
Two of them were still being treated for hypothermia.
Senior Sergeant Martin Paget, of the Auckland police maritime unit, said search teams would today continue to looking for Mr Preston on the gulf's numerous islands in case he had somehow managed to swim ashore and survive three bitterly cold nights.
"Based on the information we have we think it's a very slim possibility, but it's one that we want to cover."
They were particularly focusing their attention on the shorelines, he said.
It was not entirely clear why the boat had sunk, but it appeared the engine had stopped and waves began crashing over the small dingy.
Once boats had even a small amount of water in them their centre of gravity could change, tilting them to one side and making it easier for more water to get in.
"If it's rough it goes from bad to worse in a matter of seconds," Mr Paget said.
Sergeant John Saunders, from the police maritime unit, said people needed to be aware of the dangers of boating, particularly in winter.
"They need to have a disaster plan if things go wrong. You need to be prepared."
Boats should not go to sea without two means of communication -- a marine radio and a cellphone, and the cellphone had to be in a waterproof plastic bag.
People should also tell someone on shore where they were going and when they would be back.
By law boats needed enough lifejackets for everyone on board, Mr Saunders said.
Mr Preston was not wearing his lifejacket when the boat sank and it was thought he could not properly get it on in the water. The lifejacket was found but there had been no sign of Mr Preston.
"It is a very tragic way to learn a lesson," Mr Saunders said.
Police were concentrating on finding Mr Preston but would also consider a search for the boat, now believed to be sitting on the bottom near Kawau Island.
- NZPA