Peter Bethune, whom I am allowed to call mad but "don't set me up as a nutcase", is (among other, madder things) going to circumnavigate the globe on a boat called Earthrace which will run on vege oil.

He will spend 65 days on Earthrace. Well, that is the hope and what it will take to break the record by 10 days for going round the world by powerboat.

We are on the boat, tied up at Viaduct, for 15 minutes, during which time a large chunk of interior wall (or whatever such things are called on boats) crashes down. Then the photographer bashes himself on a doorway, which results in rather a lot of blood gushing from the top of his head. In the startled moment after the crashing sound I say, wimpily, "I'm getting off."

"Safe as houses," says Bethune. Actually, he probably says "safe as houses, mate", but I wasn't really listening just at that moment. Bethune, who says we'll recognise him because he's wearing a sort of camo Swanndri, calls you mate within two minutes of an introductory phone call. This is infectious. I find myself saying, as we leave: "Good luck, mate."

There is much that is infectious about Bethune. You arrive thinking that he must be a nutcase and depart thinking that he's a sort of visionary. I even calmed down after the crashing wall thing to believe that, oh, that was nothing, just a bit of wall that hadn't been put up properly yet. And that it is really quite sane to get yourself almost $1 million in debt to go round the world on a boat that will have a minuscule amount of Bethune's body fat in the fuel mix.

Of all the mad things he's done - there have been a few and more to come - having liposuction as a publicity stunt is possibly the maddest. Even he might agree now, but his plan seemed quite reasonable at the time. He had planned a tour of the country in a car with a mobile bio-diesel plant on the back collecting olive oil from Nelson, butter from Hamilton, and "in Southland we were gonna shoot possums ... And for the final bit: what can you do in Auckland? F***, I'll go to a liposuction clinic and get some fat out of a couple of fat bastards and use that." The trip was canned for lack of time but he thought the lipo idea was still good. "I had a couple of really fat mates and one of them said, 'Look, if you're so keen on it, you undergo the surgery'."

So he did, and he tells about it in gruesome detail. "It's brutal, mate. It doesn't really hurt ... it's more the noise, this sort of squelching and grinding and ... " That's quite enough, really. He thinks so too. He convinced a clinic to do the op free. He thought it would be a bit of a joke "until you front up and the doctor's slipping his gloves on and he's got this damn big needle and ... shit, where's that going?"

Now, whenever anyone asks what it's like because they're considering it, he says, "Don't eat shit and keep fit, mate. That's a much easier way. I don't recommend that surgery to anyone. Too much hard work."

I hadn't meant to go on about the lipo because it does make him sound a bit loopy, as he well knows: "I did get set up. A German TV network came over specifically to film us and just turned me into a crackpot and that's the risk you run."

But his main role in the Earthrace project, aside from having dreamed it up in the first place, being skipper and project CEO, is raising sponsorship deals, and here he is telling people that having liposuction is a bad idea.

I've been reading his Captain's Blog on the project's website and there's an entry where he talks about meeting Jim Anderton in the hope of getting the Government to provide some sort of assistance.

I ask him about this and he shakes his head and says, "They've been useless, mate, they've been useless."

"No wonder, mate," I say, "when you write on your blog that Anderton looks like he's eaten a few pies lately." He looks not at all abashed but says, "Yeah, fair enough." Diplomacy is not his greatest skill. "No, and it's probably one of the reasons we haven't got a title sponsor. I'm an advantage for the project and a disadvantage, and one of the disadvantages, I'm sure, is that a few big companies look at that [the blog] and think: 'Whoa. Jeez.' And yeah, [think] that I'm a liability or a loose cannon. I call it like I see it. We've got BP as a sponsor ... but I'm not going to go around and say that the oil majors are great for bio-fuel because they're not. They should be doing a lot more."

What he does have are the skills to "get people enthused about this and bring them in." He's pretty sure he's got Goldie Hawn to come on board for a five-day leg. "She's a cool chick, mate! She's tall!"

He's excited about this, but just as enthusiastic telling me about the first time he saw a video of the wave-piercing technology used on Earthrace - and which really started all of this.

"I saw this video and it was the most amazing video I've ever seen. This boat quite literally smacking through these waves. So I started off thinking, 'It's very cool.' And then, 'I'm going to figure out what makes these things tick'."

He has an engineer's mind and gives me such a good demonstration - using a teaspoon and three packets of sugar - of how to extract fuel from vegetable oils that I almost understand it.

What he's useless at is "brown-nosing". Tourism NZ would tell you that. He's embroiled in a row with them over his use of a 100 per cent Pure Biodiesel logo which Tourism NZ says is too close to its 100 per cent Pure New Zealand campaign. He says he'll give in despite it being "bananas" because "we're just a small puppy and they've got lawyers coming out their arse".

I've been with Bethune about 20 minutes and most of that time I've been wondering how to say this: "Have many people expressed the idea that you might be a bit nuts?" He's not offended. "No, I don't mind. It's all part of the package. If there wasn't an element of risk and madness in it, it makes it less appealing. It's not as good a story if it's just ordinary stuff."

He doesn't do ordinary stuff. After university he worked as an oil exploration engineer in the Middle East and the North Sea. Everyone thought he was taking career risks then, he says. The risk, and the dreaming, he gets in good part, he guesses, from his father, who was the president of Social Credit "back in the days of Bruce Beetham". Which some might say involved just as big a leap of faith as Earthrace.

His dad is "a clever bastard", his mother "a gutsy lady" who worked full-time with five kids and studied to become a lawyer. He grew up in Hamilton East, where he and his brothers "ran amok in the neighbourhood, mate. Dad showed us at a young age how to make a shanghai, so we spent the next five years intimidating the neighbourhood".

He says I'm not to put in that the Bethune boys were expelled from Sunday school for using standover tactics on the other kids to relieve them of their collection money. But, as I tell him, it's irresistible and I bet he's told a fair few people before me. Anyway, he says, "I like to think I've moved on from those days." I don't know that he has, quite. It's just that now he uses his not inconsiderable charm to relieve people of their cash, or engines, or a $10,000 toilet - the only luxury item on the boat.

He enjoys the irony of using the money he made from his oil field days on an alternative fuel project. He's so broke now his phone bill is weeks overdue. He has an understanding wife and loyal mates he worries about paying back.

He's an odd sort of Greenie. "I've come from a very unusual background to be a conservationist. Hunting, fishing and diving and, you know, I'm a raper and pillager of the seabed and if it's out there to hunt or shoot, I'm into it."

Whatever he's into, he's into with everything he's got. I think he is, in truth, a bit mad, but he's so engaging and so engaged in his great dream, that after an hour with him you end up thinking: "We could do with a few more madmen like you, mate."