During Robert Hewitt's 75-hour ordeal at sea he survived severe dehydration, sunburn and an encounter with a shark, but it was microscopic marine bacteria that inflicted the most damage on the Navy diver.

Robert Hewitt was readmitted to hospital 12 days ago and underwent surgery on the back of both legs to remove flesh that had become infected with the marine bacteria.

Yesterday, Mr Hewitt's brother, Norm Hewitt, told the Herald that 75 hours in the water made Mr Hewitt's body swell, causing the straps of his flippers to bite into flesh and wound his Achilles tendons.

Norm Hewitt said that during his brother's surgery the wounds were cleaned, infected tissue removed and skin grafts taken from his thigh to cover the wounds.

Mr Hewitt, now back home in Palmerston North, is recovering well, Norm Hewitt said.

"As every day moves on, he is progressing with what those 75 hours were for him," Norm Hewitt said. "He is catching up with a lot of friends and family, and also spending some quality time with himself, contemplating the enormity of the whole event really."

Norm Hewitt said the extended Hewitt family, who had to contend with intense media interest before and after his brother was found, are also doing well.

"The family have become extremely close and have come together. If you could think of a silver lining coming out of such an ordeal, then it is the closeness of what the family have become."

Mr Hewitt had been reported as being a former Navy diver, but Norm Hewitt said his brother was still in the Navy and celebrated his 20th anniversary four days after his Navy colleagues found him floating off Mana Island, north of Wellington.

Norm Hewitt said his brother would finish with the Navy on April 20 and was on a Navy programme to help him make the change to civilian life.

Norm Hewitt said there continued to be interest in Mr Hewitt's story and the brothers were contemplating writing a book about it.

"It's a story worth telling. It's a story that is going to be inspirational and will provide insights for search and rescue teams all over the world. So, it is definitely a story that will have a number of benefits for people all across."