The best friend of a fisherman lost at sea says he is not giving up hope, three days after his mate disappeared.

Authorities are still hoping to find the Rotorua man who went missing after his 4m aluminium dingy capsized near the Bowentown bar at 11.20pm on Monday.

The 24-year-old's brother-in-law and 10-year-old nephew managed to make it to shore, where they were rescued by another fisherman.

Read more: Police dive squad and navy personnel join search for missing Rotorua fisherman

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The man was last seen by rescue helicopter personnel clinging to the boat but he has not been seen since.

At the beach yesterday, an Auckland man who said he was one of the man's best friends said the Rotorua man was a keen fisherman.

"He used to go around fishing quite often and he knew this area."

The friend, who would not be named, had joined search parties scouring the beach. He said he hoped for the best.

"We will just carry on [the search] I guess, until something happens," he said. "We are not giving up hope to find him."

Royal New Zealand Navy officers returned to shore yesterday afternoon to analyse data collected from sonar equipment, mapping the seabed between Waihi Beach and Bowentown.

They joined the Waihi Beach Coastguard and New Zealand Police dive squad searching the area where the boat was found washed ashore near the bar and Waihi Beach shoreline.

Rescue co-ordinator Sergeant Vince Ranger said there had been little progress.

"Nothing that we are looking for has been located at all," he said.

"We have been searching and will still search [today]. Then we will make the call on where do we go from there.

"At the moment we are waiting for more information on the data collected from the Navy team," he said.

The man's brother-in-law and nephew also on board were found, treated and discharged from Tauranga Hospital on Tuesday.