Robert Hewitt could see search boats looking for him on Sunday afternoon and thought it would be only a short time until they found him.

That night, as he floated in the sea off the Wellington coast contemplating how he had become separated from the dive boat hours earlier, he watched as a search plane flew off without spotting him.

"When I saw the searchers finish up for the day, and I realised I was going to be alone for the night, I sent up a little karakia, a prayer."

By Tuesday the 38-year-old was convinced the search for him had been called off. It would be another 27 hours before Mr Hewitt, a former Navy diver, was found by his Navy mates, dehydrated, hypothermic and with severe sunburn, but alive.

He says he does not think he would have lasted another night.

Yesterday, Mr Hewitt - sitting in a wheelchair at Wellington Hospital, his face and lips swollen and blistered from the sun - described how he survived for 75 hours in the sea.

The 38-year-old said he became separated from the dive boat on Sunday after resurfacing and finding himself 300m from the boat: "Then within a matter of about five minutes I just shot straight across to the other side, around by Plimmerton."

Mr Hewitt said he was not alarmed and from his Navy training knew not to fight the currents.

"I saw the rescuers then, and I thought, oh well, just be patient."

That night, as it became dark, the loneliness of the situation struck him.

"On the first night - I was looking for some sort of spiritual guidance I guess - I said a little prayer to God and thanked him for the day. Then asked him to look after me during the night, and I felt a real warm air come through - so I knew someone was there."

During the three days he spent in the water, Mr Hewitt was swept by currents 27km up the west coast to Waikanae, before being drawn back down to Mana Island where he had started.

As he drifted he said he could see Mana and Kapiti Islands and, alarmingly, a shark.

"It came in pretty close. I've been in the Navy, I've seen a shark before, so if it's going to get you, it's going to get you."

Mr Hewitt had been diving for seafood when he became lost and had kept hold of his catch-bag containing one crayfish and four kina (sea eggs).

"Not the best dive I've had, but it certainly came in handy. I guess the biggest thing was thirst. I just dabbed my finger in the sea and touched my lips and that.

"There are people over in Ethiopia who don't have as much to drink as they should have, so I thought if they can do it, I can do it."

When it rained Mr Hewitt tried to open his mouth as wide as possible to catch the precious drops.

He passed the hours by thinking about the good times he had had with his partner Rangi Ngatai.

"Every now and again, I'd just yell out 'Love you, Rang', and 'I love you Kiriana, Meripi, Casey', 'Love you Norm'. And I was waiting for someone to yell back."

Mr Hewitt credited the philosophies he had learned in the Navy - commitment, courage and comradeship - and his love for Rangi and his family for giving him the determination to survive the ordeal.

He also said he drew strength from his brother, former All Black Norm Hewitt.

"He has survived a lot of things and he has come through it, through the other side."

By Wednesday, Mr Hewitt said, he had begun to hallucinate and thought he was at home with Rangi and his three children.

He believes it was in this state that he began to discard parts of his wetsuit and diving gear.

"I'd sort of duck my head under water and hold my breath for as long as I could, made out like it was a dream.

"I said to myself, 'Come on mate, don't do this'."

Mr Hewitt said he was hallucinating when the Navy divers - two of his friends, Lyle Cairns and Buzz Tomoana - found him.

"First of all, I was like 'What the heck are you fellas doing here?' because I thought I was already at home with Rangi and the kids.

"Then I realised I had been saved. It was unbelievable, I was overjoyed with emotion."

The first thing he wanted when he was pulled into the inflatable rescue boat was, understandably, water.

"I felt like a gallon of water. And the guys were going, 'Slow down, slow down', and I was sort of thinking to myself, 'Mate, I haven't had a drink for four days, let me appetise it, let me wet my throat'."

He then phoned Ms Ngatai to let her know he was alive.

Ms Ngatai had been asleep and said she started hyperventilating when she heard her partner's voice.

"He rings up and says, 'Hey babe, where are you?' Don't worry about where I am, where are you?"

Ms Ngatai said she had known Mr Hewitt would come back to her.

The experience has not put Mr Hewitt off diving - he plans to try for more crayfish and kina in about six weeks.

- Additional reporting: NZPA

Rescuers' care saved diver's life a second time

Keeping Robert Hewitt horizontal after pulling him out of the water saved his life, said a specialist in diving and hyperbaric medicine.

"One of the most dangerous times is actually when you're being rescued - and the way to rescue someone is horizontally," said Professor Des Gorman, head of Auckland University's School of Medicine.

If not done correctly, cardiac arrest is a certainty, he said.

On land, gravity causes blood to pool in the abdomen, pelvis and legs.

"But when you jump into the water, that gravity's lost and the blood redistributes back into your chest. And your body thinks it's overloaded in fluid, so it starts getting rid of it."

Blood volume is heavily lowered because its chief component, water, is lost through urination and the skin. With the fluid in red blood cells largely depleted, blood becomes hard to pump.

"After a few days the body still thinks it's okay, but only because there's no gravity."

When someone is hoisted out after being immersed for days, the sudden reintroduction of gravity causes blood to drop from the chest area into the lower body. Cardiac arrest happens because there is simply not enough blood to pump to keep the brain and heart working.

During World War II the Germans wrongly assumed that this was because of hypothermia, said Professor Gorman. Pilots would suddenly die after being rescued from the water, and the Germans poured resources - including experimenting on Jews - into trying to prevent it. But it was not until the 1970s that Britain's Royal Navy worked out the solution.

Professor Gorman said there had been extremely rare cases of people surviving up to 10 days in water.

"Three days is getting to the point where most people would be expected to die."

He said Mr Hewitt's wetsuit would have given him flotation, kept him warmer for longer and reduced the loss of blood volume. The raw crayfish and kina would have provided him with much-needed fresh water.

Mr Hewitt's naval background might have also played a part, he said.

"To survive this sort of ordeal you also need to be mentally robust. Those of us who did our diving training with the Australian Navy look at New Zealand divers with a touch of awe, because the bastards are just hard."

Dr Jim Cotter, from Otago University's School of Physical Education, said even water at 18 degrees is cold enough to kill most people if exposed for prolonged periods.

Dr Cotter said some people don't survive very long because their body temperature drops dramatically, while others - typically lean body types - develop a strong shivering response and can last "quite a while".

The lucky ones are those who have an insulative response. Their bodies don't lose as much heat as quickly, said Dr Cotter, and that is aided if they have a layer of fat.

- Errol Kiong