Ellen MacArthur, sailor, tolerates a fond nation's veneration. Since her remarkable performance in the Vendee Globe single-handed round-the-world yacht race last March, which won her second place and international acclaim, the elevation has been swift and determined. Some would have her as a deity of derring-do, an object lesson in miraculous motivation, who famously saved her dinner money to buy her first boat, and slept beneath her yacht mid-winter because she needed to turn a heater on at 20-minute intervals to dry the resin. Others choose to see her as British pluck incarnate: the brave little girl on the great big boat who manoeuvred sails the weight of a car, and hung off a 90ft mast in a force-10 storm, pitting against the mighty ocean her mightier spirit. Others still take a psychoanalytic route, pondering the secret sadness that drives her to spend months alone on the ocean without human touch or conversation.

"To be honest," she says cheerily, "I never even thought what I was doing was odd. I did what I had to do." What did annoy her, she tells me later, were the headlines about "fastest woman around the world, Ellen has won the hearts of the nation, to us she's the winner".

"I was not the winner," she says emphatically. "I came second and the objective was to win. I'm not competing against other women, I'm competing against everyone. It's not about being the fastest woman, it's about being the fastest."

It is the morning after the night of the British Nautical Awards, at which the 25-year-old was named Yachtsman of the Year for the second time. The celebrations went on until 3.30am, but seven and a half hours later, the bloom is fresh on those rosy cheeks. What a bonny wee thing she is, snuggled into her armchair, tugging a hand through her tufty locks. Last night's award joins a fistful of other accolades: an MBE in the Queen's birthday honours list, runner-up as BBC Sports Personality of the Year, France's yachtswoman of the year. Does she allow herself time to appreciate it? "No!" she splutters, horrified, as though I have just asked her whether she enjoys oral sex. "It's not about patting yourself on the back, it's about getting on to the next project. Of course you're overwhelmed when you get the award but it's not just about you, it's about the team. When you say that, it sounds alien to me."

Across the road from her hotel, the London Boat Show is in full swing, where MacArthur performed the opening ceremonies and celebrated a five-year extension to her sponsorship partnership with the retail group Kingfisher. The two are surely not unrelated. Does she feel she has to give her sponsors value for money?

"I don't see it like that. This is not about sticking your name on the side of a boat and going out to try and win yacht races. It's about making the project work outside of the results." When she and her business partner Mark Turner first approached the company, she reminds me, she had little more to offer than her passion. "It's very easy now to say, 'Kingfisher must be happy, they've got loads of publicity', but they took a risk. They believed in this 21-year-old standing in their boardroom. Good on them - they deserve it."

Is she being ingenuous? Not exactly. There's a level of nuance that's not on MacArthur's radar - probably because nuance isn't much use in stormy weather. Her endless references to "the project" and "the team" are less jargon than jolly-hockey, coupled with a genuine concern that those working with her share the credit. And, while not without humour, her jokes probably work best when bellowed across the deck of a boat at sea. But there are worse crimes than being straight up and down at heart.

Nor does that detract from MacArthur's devastating determination, or her consuming passion. From her first trip on the water, on her Aunt Thea's boat at the age of four, she says she found a love that has never been lost.

"I've always loved the sea and the sea has always been a great inspiration to me - seeing the things that other people have done, dreaming about going out on it. That's the reason for being on the water, and I'm a very competitive person, which is the reason for racing."

It's a sport, she adds, but it's also her life. "If you are playing at the top level, it has to become your life because you give everything you have to in order to stay at the top."

Can anything ever match up to it? "It's very special what you have on the water. Racing with the guys last year, it's almost like you don't need words. It's not something you find every day on the land."

Was she scared of dying? "You only think about that afterwards. Yes, I have [come close to death], but when it's happening to you, you don't think about falling off the mast, you think about holding on to it with every brain cell you've got."

Does proximity to death provide an unimpeachable perspective on life? She has matured, she says, though fundamentally she's the same person she was 10 years ago (when she was 15). "Taking yourself well beyond your limits and coming back, that's an amazing lesson in life and it's not something that many people get to do with that intensity. Often people push themselves too hard and the result is that they can't cope. That's exactly what happens on the Vendee, but you have to cope."

Did she surprise herself? "No, it's not a moment for surprise. It's not somewhere you'd recommend other people going."

Not even in retrospect? "No," she says adamantly. "You do what you have to do."

This could be tough-girl posturing, or inarticulacy over an indescribable experience. Like appreciating awards, perhaps pride in self is another concept she just can't conjure with.

So she doesn't feel proud?

"No, I've learned a terrific amount, but I wouldn't say that going beyond your limits is something to be proud of." What does she feel proud of? "My team and all those people who helped me to get where I am. It's not always been big sponsorships and big projects. It started off kicking around a boatyard, living in a box, spending sod all on food and living off a kettle and sandwich-maker for 18 months.

"The people who just bothered to talk to me when I lived in a boatyard and had no friends there. I'm proud of those people." There's the tiniest tremor about the lips. "And I'm proud of my team, I'm proud of Kingfisher, I'm proud of my parents. I am such a small part in all this."

She acknowledges that there is something particularly compelling, and disturbing, about the notion of a person alone on the ocean.

Does she daydream?

"I think a lot."

What about?

"Over 75% is completely to do with the race, checking things, repairing things, but your mind does wander, you think about home and about those people who are supporting you."

Does she ever get depressed? "Exhausted is the right word. But it's more than exhausted and I don't know how to express that in words."

Does she miss physical contact?

"It'd be quite nice to have a hug sometimes. But it's not an issue. You know that you're going to be out there for a long time on your own. It's not a surprise to you."

The television images of MacArthur disembarking captured her in awful tears, pressing her forehead to the hull of her boat, kissing it fervently. "I do like being on my own," she says, "but I'm not a solitary person. People assume I'm a right weirdo, but I'm not that strange."

Of course MacArthur is strange. Strangely determined. The daughter of Derbyshire teachers, she hated going to the pub as a teenager because she didn't want to spend her money and, when she brought along her yachting magazine, "people would look and smile but you knew they weren't really interested".

Strangely austere, she becomes confused when I ask her to choose one luxury item for her newly bought flat on the Isle of Wight: "I'd say nice clean water - that's a luxury item on the boat. I don't like the word luxury. It's just not a word I'm accustomed to."

Strangely self-contained: "With certain people for sure you talk about things that concern you; with your parents, for example, there's not a lot you don't discuss. But sometimes I will bottle things up inside. There are some things its just best to keep to yourself."

But also strangely non-plussed about her "very happy" two-year relationship with a graphic designer. "If you want to do something, it's possible."

I tell her that when I was due to interview her, a friend said,"I'd love to know what I wanted to do like she does". "Yeah," she sighs contentedly. "I feel very lucky, at the age of 17, to have known exactly what I wanted to do. I've many friends who didn't, and it's not a problem not to, but I feel lucky to have had that passion."

What does she think of people who have a passion but never fulfil it? "If they're happy, that's the most important thing. But if it makes you unhappy not doing it, then go out and do it."

Oh Ellen, is it really as simple as that?

She laughs. "No, it's far more complicated but if you don't simplify things then it's just a chore for everyone."