The Coastguard is warning boaties to check conditions after gusting winds caused a spate of accidents on the Hauraki Gulf yesterday.
By 4pm yesterday the Coastguard had responded to 16 calls for help around the northern region, in particular the gulf.
The spike in callouts meant volunteers had to be called on.
Many of the incidents - which included five capsized vessels - involved smaller boats which were unable to handle high winds and rough seas.
Coastguard spokeswoman Georgie Smith said it was fortunate that the boaties involved had life jackets and called for help.
"We can't stress enough the importance of checking your local marine weather forecast ... and of course have life jackets for everyone on board."
In one incident off Island Bay on the North Shore an Optimist yacht capsized, breaking its mast.
Owen Blackburn photographed the yacht from the MV Hogwash, a Red Boats vessel which stopped by the capsized yacht until the Coastguard arrived.
Rescue vessel skipper Paul Field said yesterday's weather conditions were exactly as predicted by the MetService.
He said winds of 25 knots gusting to 35 knots made the Hauraki Gulf's waters "short, sharp and unpredictable".
Rough waves also caused havoc yesterday at Mt Maunganui, where hundreds of people turned up to watch Thundercat national surfcross boat racing.
A spokeswoman for the event said boats had not been able to get in and out of the water safely because of the conditions.
The waves forced a cancellation after just two races.
The day will not count towards the national competition, which resumes at Matarangi tomorrow.
"The boys had a bit of a runaround afterwards to keep the crowd entertained - a lot of people had come down. It was definitely one of our biggest crowds," the spokeswoman said.
With fine weather around much of the rest of the country, surf lifesavers were kept busy patrolling beaches.
At Ruakaka beach in Northland, a 9-year-old boy and his father were pulled from a rip after going for a swim about 5km from a surf patrol.
Lifeguard Kyle Taylor said the pair were helped to the beach by an off-duty lifesaver.
The boy was slipping in and out of consciousness, and was given oxygen before being taken to hospital in an ambulance.
"There are no lifeguards up that end of the beach ... They were very lucky that the off-duty lifeguard was there to help them, Mr Taylor said.
"People need to be more aware of the dangers when they are swimming away from patrolled areas.
"If they're not comfortable with the water, don't go in it."
- Additional reporting: Michael Dickison