(CNN) As a child, Nic von Rupp had an abject terror of rocks. Today, his phobia of being under the water makes his career choice of a big-wave surfer all the more remarkable.

Big-wave surfing is dangerous enough -- the world's best taken into the maelstrom by jet ski -- but Von Rupp makes the thrill-seeking more dangerous still by paddling himself in.

"It's the difference between night and day," he tells CNN Sport . "It's like the difference between doing the Tour de France on a motorbike or a bicycle. In surfing, it's a big deal."

And a big danger too. The Portuguese surfer's aim to enter the big waves naturally and ride their monstrous barrels rather than the face of it, means there is little room for maneuver between him and the reef or the rocks below, where the wave breaks habitually happen.

The 27-year-old, whose big wave season starts in earnest in October and runs until April, is well aware his career choice is not the most obvious one bearing in mind his start to life in the water.

"Being scared of the waves is normal when you start but I had a big phobia of the rocks," he recalls, laughing at the recollection as he talk to CNN Sport by the swimming pool of his parents home 30 minutes from Lisbon on Portugal's Atlantic coastline. "That's not normal!

"There wasn't anything else in the world that scared me more than standing on rocks in shallow water. So the teachers gradually took me to the rocks when it was dead flat but it was a barrier that took a long time breaking."

Agent Orange🍊 photo by @manu__miguelez @carvemag #kandui #indonesia A post shared by Nic von Rupp (@nicvonrupp) on Aug 29, 2017 at 1:38pm PDT

Underwater fear

Even now, though, there is a love-hate relationship with the water. Von Rupp's hatred of being under water is understandable in one sense given the ferocity of the waves he is tackling.

"I know both things makes it crazy with what I do," he says 50 kilometers away from his main workplace and playground, Nazaré, which habitually boasts the world's biggest waves.

"Not being able to breathe is the biggest sacrifice I can make, especially in training. Training is sometimes a big nightmare."

A standard practice is to do hard exercise in the gym and then force himself -- weighted down -- to hold his breath for up to two minutes at a time.

"You're trying to recreate the worst-case scenario," he says, "when you've lost all your air and you still have to go on. I hate it but I have to do it to stay alive."

Von Rupp looks every bit the modern-surfer, tanned, in shape and his hair partly bleached by the sun and sea.

He has been a professional surfer of sorts since the age of 14, the trappings of his sport -- initially on the World Tour in smaller wave surfing -- enabling him to be independent for the past 13 years and buy the neighboring house for his parents.

But it's the big waves that have always lured him, and he was recently given the green light by main sponsors Hurley and Monster to turn his attention solely to them.

For family and friends, it is a tough career choice. His mother Isabel says she never hears about the gargantuan waves he has tackled until after the event while his father Roman admits it is a challenge to watch.

"The windows were shaking of the house on the land because of the waves crashing down and in the middle was my son," says Von Rupp's father, reminiscing about a time his offspring was surfing off Nazaré.

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Death in the waves

Von Rupp is all too aware what he does is dangerous. While he has not lost close friends, he knows those who have died doing what he does, including one surfer who perished in Hawaii in the same waters he was surfing.

"I had another friend who we pulled out of the water unconscious, his face all cut up. My first thought was he'd be a paraplegic but he recovered okay."

Despite the perils, Von Rupp says his family have always been hugely supportive of his ambition, which in short is to ride the planet's biggest and most intense waves.

In some ways, he knows what he does is wrong but simply cannot help himself: "I've never done drugs but I know this is an addiction. It's just such a unique feeling.

Surfing at 1.000frames per second thru the lense of legendary @chrisbryanfilms #thoseclips📹 A post shared by Nic von Rupp (@nicvonrupp) on Aug 28, 2017 at 1:03pm PDT

"But also it's really dangerous, it's not safe, the waves at Nazaré are all over the place and it makes it hard to catch one rather than it land on top of you."

It has turned him into something of a storm chaser -- "It's the buzz, it's what we live for," he says -- the arrival of Hercules Storm to European shores in 2014 a case in point.

While the advice was to stay inside, Von Rupp took to the water at Mullaghmore, Ireland, with five to 10 other surfers.

"Ireland's got gigantic waves and humungous tubes but that was something else," he recalls, where he sat for five hours in the water waiting for his turn to ride a monster.

"The whole thing got more scary as the scientists were warning about this century-old storm. It was different to a few surfers talking about riding big waves. Action sports are a thin line but a big reward."

Agent Orange🍊 photo by @manu__miguelez @carvemag #kandui #indonesia A post shared by Nic von Rupp (@nicvonrupp) on Aug 29, 2017 at 1:38pm PDT

The sweet and sour of surfing

The reward is not necessarily huge financially, Von Rupp pointing out that surfing won't make you rich although he is comfortable enough.

"We don't do it for the money," he explains, "but for the opportunity to do crazy things. That's different to competition surfing. I love this because it's the occasion of man versus nature. It's like you're in an arm wrestle with nature."

At 27, Von Rupp is young for the big-wave surfing genre and he's well aware that as he rides those big waves that he's perilously close to the precipice.

As he puts it: "Being in the wave is a sweet and sour moment. You want to get out of there as fast and safely as possible but, at the same time, you want to enjoy it.

"It's extremely dangerous but you want to be deep in the barrel. If you're making it, you're not deep enough. There's a fine line between being deep inside and getting out ok."