The man, who had been out fishing, was taken to the club's First Aid Room and assessed for any injuries.
"He was wet and cold. We called an ambulance because we were concerned he had mild hypothermia but he was okay," Costello said.
An ambulance en route was stood down.
A video, captured from some distance, shows the moment the boat flipped in the surf.
Lifeguards towed the boat back to the boat ramp after the incident so the owner could eventually collect it.
Tony Baker, from the Mangawhai Heads Surf Lifesaving Club, said boats flipping on the bar was a common occurrence, but this was the first time it had happened this year.
"Usually our major rescues around the bar entrance or exit that we get are boats flipping ... we can have three or four or five a year.
"Quite often what happens is boats come in and they sort of ride in on waves and sometimes the engine will cut out or get swamped."
Conditions did not appear to be dangerous for fishing, Baker said, although there was "definitely a bit of wind" and swells.
"The guy had a lifejacket on, so he did the right thing, obviously lifejackets save lives. And it was lucky that we've got our callout squad that can respond and did respond."
There were also two bystanders who were able to assist, Baker said, and a number of people around who saw the boat in trouble and were able to alert lifeguards.
It was fortunate the incident happened during the day, he added, with so many people around who saw it.
