'The magic of long sea passages has soaked deep into my bones,' writes poet and broadcaster Theo Dorgan, who embarks today on a six-week sailing trip in the South Atlantic.

The internet can be a tricky place to go dreaming. I find myself on the eve of departure, somehow committed to sailing in the South Atlantic for the next six weeks, and even now I'm not quite sure how this came about.

I'd been passing a winter evening, browsing through boats for sale, when I stumbled across a website for the legendary racing skipper Skip Novak, and discovered it was possible to sign up with him for a yacht delivery trip from Punta Arenas in Chile to Cape Town, South Africa.

That, I reflected, sounds like an interesting kind of thing to do. Then, I think, I closed down the laptop and went to make tea. I recollect sort of drifting into the credit union the next day, I recall e-mailing Novak later that week, perhaps the next, but I don't think I really understood that I was going until my partner Paula, observing all this without surprise, gently pointed out that I had signed up to sail around Cape Horn in winter. And then sail on for another 4,500 miles or so. That, I have to say, woke me up.

Less than a decade ago, without much meaning to, I started sailing, and quickly discovered a taste for long voyages. Day sails along the Irish coast led to two trips to Portugal, both out of Kinsale, Co Cork; one that took us down to Nazaré in a little over five days, a second that saw us headed by south-westerlies in Biscay for a pounding four or five days, a few days in which the learning curve became as vertical as some of the waves we ran into. I mean, literally ran into. That was, as they say, a bit of a shaker.

These trips were on Oliver Hart's Spirit of Oysterhaven, a 70-foot steel schooner that I would eventually crew, with three others, on a transatlantic trip from Antigua to Kinsale. By the time I got back from that particular journey the magic of long sea passages had soaked deep into my bones.

It's something to do with the long rhythm of it all, the world shrunk to the confines of the boat but at the same time expanding into the limitless indifference of the sea and sky; the emptiness of the world, and yet the deep sense of being alive right out to the light crackling just beneath your skin.

A long voyage is profoundly seductive, the sea and the wind get into your very bones, opening you up, making light what was heavy. The world falls away and what you are left with is unexplained experience, life in the moment-to-moment as you live it.

I remember, approaching Faial in the Azores, 21 days out of English Harbour, Antigua, feeling stricken at the thought of going ashore; I understood what the great French sailor Bernard Moitessier felt when, powering into the Atlantic on the home stretch in the first Round the World solo race he suddenly turned away for Africa again, on into the Indian Ocean, refusing home, refusing the race, choosing the limitless freedom of the sea.

OF COURSE I was glad to be sailing for home, and Moitessier was born for the sea as I am born for the particular life I cherish, but I understood him for a moment - and I understood what is meant by the call of the Sirens.

My friends have been asking, "But aren't you afraid?". Of course I am, it would be stupid not to be. The prudent sailor keeps room in his bag for fear, because fear is what keeps you from vanity and delusions, fear is what you use to remind yourself of the endless indifference, the raw brute power, of the uncaring sea. But, you have to ask yourself: what kind of life would it be if we let fear stop us from doing what we want to do?

The same friends have been tactful enough not to ask the better question, "Why are you doing this?". Tactful because I suspect they know that I don't have an answer, yet. Maybe that's why I'm going, to find out why I went?

There are seven others embarking on this trip, plus three professional crew. Like myself, each stumbled on the opportunity by chance. Each has, I'm sure, a very different explanation for why they're going, but in e-mails back and forth as we prepare for the trip I get a growing sense that part of the attraction for all of us is Cape Horn.

Pelagic Expeditions, the company organising the trip, is at pains to play down the bravado factor, and we all know that a purpose-designed 70-foot aluminium expedition sailboat (with heating, for God's sake!) is not a windjammer chasing down her easting in the cold fury of a winter passage. Fair enough. We all know, too, that a fair number of other people will make the passage this year, some of them single-handed in small boats.

But we also know that there's a better than even chance of very rough weather indeed, we all know that something inside us will be tested on this trip, something we might never otherwise encounter. We know it's no joke. We know we will be cold and battered and wet and worn out before we make Cape Town. We're looking forward to exploring the channels around Tierra del Fuego. We know that landfall in the Falklands, and in Tristan da Cunha if the ocean swell allows it, will be memorable experiences, and we suspect that the long battle across the Roaring Forties will be a test of endurance and fortitude. We know these things, we accept them, but what we all dream of is the Cape at the end of the world.

To the sailor, there are three Great Capes: the Cape of Good Hope, Cape Leeuwin in Australia, and Cape Horn. And the greatest of these, the one that calls most urgently to all who go down to the sea, is surely Cape Horn. Moitessier, a serviceable writer as well as a great sailor, had this to say about the Capes: "A sailor's geography is not always that of the cartographer, for whom a cape is a cape, with a latitude and longitude. For the sailor, a great cape is both a very simple and an extremely complicated whole of rocks, currents, breaking seas and huge waves, fair winds and gales, joys and fears, fatigue, dreams, painful hands, empty stomachs, wonderful moments, and suffering at times. A great cape, for us, can't be expressed in longitude and latitude alone. A great cape has a soul, with very soft, very violent shadows and colours. A soul as smooth as a child's, as hard as a criminal's. And that is why we go."

I want to see for myself what he meant by that. I want to test it against my own pulse. I want to know if I have become a sailor yet.

AND AFTER ALL that, I have another, more private, reason for making this journey. My grandfather on my father's side was born off Cape Horn, on the White Star liner Rimutaka; his mother died giving birth to him, and her body was given to the deep.

A long time she's been drifting there, without reck or benediction from her family. Something is owed. A gesture. News from home.

Theo Dorgan's first report from his trip will appear on this page next Friday. The Pelagic Expeditions website is www.pelagic.co.uk