Lost-at-sea survivor Rob Hewitt launched boat safety classes today - and spoke of his dismay at a spate of recent drownings.

The former navy diver stared death in the face when he tread water for four days miles off the coast of Wellington in 2006 before being rescued. Hewitt headed free awareness classes at the Mangere Rugby League club as part of Safer Boating Week.

He said he felt for friends and family of recent victim Malcolm Blake, aged 57, who died on Thursday at Mahia when a small boat overturned at a remote beach on the peninsula. It came after two fishermen went missing after setting off in a dinghy near Warkworth on Tuesday.

"These kinds of incidents are so sad because usually they can be prevented," Hewitt said.

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"I know what it is like to be lost as sea and survive but I also know of the anguish experienced by loved ones waiting for news.

"I will never forget what my own family went through and it saddens me when the same thing happens to others.

"When I hear about these tragedies it is those left behind or waiting anxiously that I focus on.

"By the looks of it, in some of the recent incidents, life jackets were available but were not used."

Otara swimming pool lifeguard Teapanga Varu also spoke about boat safety at the Mangere classes. He has never got over the death of a close friend and his cousin who both drowned at Auckland's Muriwai Beach in 2008 while fishing.

"My best friend was only 20 when he was caught in a rip tide after he went to clean his hands in the water," he said. "He was wearing cut off jeans and the weight of them is what is believed to have contributed to his drowning. His cousin tried to save him but he too got into trouble and died.

"After that I took a big interest in water and boat safety and started passing it on to my community. It is tragic that so many people in New Zealand are still dying of ignorance."