The country's best known emergency physician "Dr Tom" has set sail on a six-month circumnavigation of New Zealand to address a health issues in his own watery backyard.

Dr Tom Mullholland will be docking at 16 different ports around the coastline of Aotearoa to offer free medical assessments and advice.

Dr Tom said he expected to encounter a litany of ailments but he hoped his greatest impact would be influencing people's behaviour towards healthy living.

"About 30 per cent will have diabetes or pre-diabetes, maybe 40 per cent have high blood pressure they don't know about and 40 per cent might have anxiety, stress or depression," Dr Tom said.

"But it's also about those other things that influence wellbeing because it's not just about blood tests or an eye test. It's up to the individual whether they want to go and do something about it. We can only present them with the numbers and say, 'here's the risk'."

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Dr Tom hopes to affect up to 1000 people on his maritime mission. Photo / Supplied
Dr Tom hopes to affect up to 1000 people on his maritime mission. Photo / Supplied

Dr Tom has labelled his voyage the HOPP tour, standing for healthy oceans, people and ports.

He departed from Tauranga on Saturday, heading south, clockwise round the country to finish in Auckland on March 31, 2019.

His 12m catamaran has been trialled on land by his medical helper team in a retro Chevy ambulance, who would also pull up at each of the 16 ports.

Dr Tom estimated he would checking the health and wellbeing of at least 1000 people on the tour.

Despite still working regular shifts at Auckland Hospital's emergency department "patching people up" he said the wellness talks would reach far more people indirectly.

"I'm specialising in preventative health," he said.

"Working in an ED, I might see 10 patients in one shift. If you worked four shifts a week, you might influence 40 people.

"But if I can talk to 1000 people and 500 change their behaviour… it's a lot more rewarding doing that.