More than 80 people have already ignored the possibility of sharks, container ships, strong currents and reefs to conquer the notorious Heads into Port Phillip Bay.

Entrepreneur Grant Siedle​ took six groups across last summer, and believes his Group Rip Swims could become an international tourist drawcard.

He said 46 people had booked out swims scheduled for January 23 and February 21, but there were still places available for March 11 and March 25.

Participants get a T shirt and cap saying, "I survived the rip".

Mr Siedle said many clients "want to tick it off their bucket list", or are attracted because it's "dangerous, difficult, something that you shouldn't do. They know there are sharks and ships in the water and they think it's something they can look back on and never forget."

Mr Siedle, who swam the rip unofficially with four mates in 2012, said he had been given approval from Water Police, Parks Victoria and the Port of Melbourne for the regular swims.

He sent them a 72-page risk management plan. "With the first trip [in October 2014], they were really nervous; they were watching us very carefully. But I think now they realise that it can be done safely and I guess we've built some trust with them."

Swimmers are flanked by escort boats, including a doctor, plus kayaks and a jet ski. Mr Siedle has cancelled two trips because of bad conditions, including winds of more than 20 knots and over one metre of chop.

Katrina Bromell​, 44, of Hawthorn, a life and health coach who did the swim in February, is afraid of sharks, and on the boat across to Fort Nepean, the start point, she felt scared.

But during the swim, she and her group of friends stopped to "woo-hoo" and high-five one another, and later celebrated with champagne. She felt "a sense of accomplishment".

"It's a really good feeling when you stretch yourself," she said.

Her son, Ben, 15, was watching from an escort boat and asked his father, Simon Bromell, to swim with him: they will do so on January 23.

Ben says he swims three times a week in Melbourne "so I think my fitness will hold up" but he also admitted a "fear of the unknown".

"Anything could be underneath you, like sharks," Ben said. "Also the ships; a couple of groups have to stop and tread water waiting for ship to pass by. It's just dangerous."

Simon Bromell said he felt daunted. He has grown up coming to the area for summer holidays and the rip had a kind of "mythical status".

"Everyone knows that in its day it can be an incredibly dangerous stretch of water," he said.

But he has been training every morning off Point Lonsdale since late December, so it was "not terrifying because we've prepared for it".