Many surgical procedures taken for granted in the West are not available to the world's poorest people. But a dedicated crew of shipmates is determined to bring hope to those in need

In Monrovia, Liberia, this February, there were a few things to be excited about. Peace was holding, for a start, after 14 years of civil war. Thousands of peacekeepers were on the streets. New bars and restaurants were cautiously opening; refugees were going home. And a ship was coming to town.

Liberia knows about ships, of course. Its history is founded on the ship which brought 40 or so freed slaves from America to their new home, a small country in West Africa between Sierra Leone and Cote d'Ivoire. Today, the Liberian Shipping Registry, which sells flags of convenience, is still the country's largest source of income, though this isn't much when the place is so poor it's fallen off the United Nations' Human Development Index (HDI).

Still, Liberia's port is functional, and ships are no big deal. But this one was different. For a start, everyone knew about it before it had even arrived, because all around Monrovia, on noticeboards in schools, hospitals, NGOs, a strange flyer had been tacked up. A4 size, cheaply printed, it showed pictures of facial deformities, some subtle, some appalling: enormous tumours growing out of the jaw, demolishing the nose and pushing the teeth into the nostrils. Scars and disfigurements. Cleft lips and palates, which most westerners have never seen in their untreated form, because our medicine is so developed that surgeons can already repair cleft lip and palate in 8 week-old babies, and they're talking about doing it in the womb. Alongside each disfigured face was a healed and smiling one. It was an irresistible before and after. The flyer invited anyone who looked like this, or anyone who knew someone with any of these conditions, to turn up for a screening day. Anastasis, a 12,000-ton hospital ship run by the global charity Mercy Ships, might be able to help them.

After I'd left Monrovia, Anastasis docked in Monrovia's Freeport and stayed there for three months. As usual, she carried a 350-strong crew of volunteers: surgeons, nurses and assorted medical personnel; carpenters, plumbers and latrine-builders along with several operating theatres, wards, hundreds of berths and five cargo holds. As usual, the Mercy Ships volunteers organised screening days, where thousands of people with facial or skeletal deformities, orthopaedic problems; cataracts, for example, or club feet were assessed. The ones who could be helped were scheduled for surgery. Everything was free, from the cataract operation that can restore sight in 20 minutes, to the longest most complicated maxillofacial reconstruction. And everything was photographed and recorded by Scott Harrison, Mercy Ships' resident photojournalist.

During his eight months on Anastasis, Harrison took 51,000 photographs. After four months in Benin and three months in Liberia, he decided to turn 108 of them into an exhibit, in his home town of New York, to raise money and awareness. The show opened the day after Hurricane Katrina - the worst possible timing - but a gala still raised $90,000, probably because Harrison is an expert: for years, the 29-year-old was one of New York's foremost event organisers. His clients included MTV, VH1, Cosmopolitan, Universal Records and Nike. His life was spent at parties. He had a loft, a grand piano, a supermodel girlfriend and a drug habit. And then he cracked. "I didn't overdose, I just hit bottom." He went travelling up to New England for a while. He rediscovered the Christian faith of his youth. He found God, then he found Mercy Ships. "I had a chance to see my life for what it was. I decided to do the exact opposite. I think a year of foreign service where you're paying $500 a month to volunteer is probably the exact opposite."

He had a degree in journalism but, beyond some amateur stuff, had never picked up a camera with professional intent. Within months, though, he had swapped 1,500sq ft of luxury loft for a tiny cabin shared with two others, and signed up for 12 months as the official photojournalist on one of the world's only two nongovernmental hospital ships.

There wasn't much time for culture shock. Within a couple of days, the first screening was underway, and Harrison was faced with 5,000 prospective patients, standing patiently in a line some of them had joined three days earlier to be sure of a place. He set up a photo station, and asked each patient to have his/her portrait taken. No matter how deformed. You'd think that they'd want to hide, not pose. But no patient has yet refused.

This could of course be attributed to their desperate need for surgery. They're not going to refuse anything, when a big white ship full of doctors arrives and offers to revolutionise their lives. Mercy Ships chooses to visit countries in the bottom third of the HDI, where healthcare f is usually desperate. (In Liberia, for example, there are two dentists for two million people.) But many of the patients who arrive at Mercy Ships have been dealing with more than medical problems. Facial deformities are considered the result of black magic in much of west Africa. Benin still has a National Voodoo Day. Most of the people in these pictures were shunned, isolated, spat at all their lives. In that context, says Harrison, it's not difficult to win their trust. "I treat them like there's nothing wrong with them. These are people who have rocks thrown at them. Just by treating them with kindness, they relax."

Like Alfred Sossou, a 14-year-old fisherman's son from Togo, whose benign facial tumour started growing when he was 10. Villagers, confronted with obvious witchcraft, cut his face with knives. His parents bought potions and consulted witchdoctors. And the tumour, being a tumour, kept growing. By the time a priest told them about a visiting ship that could help, he weighed 45 pounds, and his tumour weighed six of them. He could only eat by shoveling food up over his tumour, and he was almost suffocating. Like Beatrice and Deborah (see page 32), he only ever went out with a cloth over his mouth. "When the tumour came," said Beatrice, "I was ashamed to go among people." Deborah, a Togolese towel-seller, had lost all hope of a cure, until she dreamt of "a place like a hospital [where] I meet a white lady and we walk together towards the sea". By the time she found the hospital by the sea, her tumour was so life-threatening she was admitted late at night and operated on immediately.

Deborah was lucky. So were Allasan and Alasu (left), blind twins living in an internally displaced persons (IDP) camp outside Monrovia. Cataract removal is a simple surgery in a developed country. After an hour or so, the twins could see. Removing Alfred's benign tumour was more complicated, but to the highly skilled surgeons who volunteer on the Anastasis, it had become routine. A month after his first operation, Peter McDermott took some hips and ribs and grafted them to the titanium plate that now serves as Alfred's jaw.

It was one of McDermott's first operations as a volunteer. He'd signed up, like most, to redress the balance: "I live in a wealthy country, and I can give something back. The something is 12-hour days, five days a week, for two weeks, doing operations that western medicine stopped requiring decades ago. People don't realise that one in seven Americans is born with a cleft lip palate because you don't see them." Benign tumours are common enough, too, but in a developed country with enough doctors, they are treated early. McDermott rarely operated on anything like Alfred's tumour. "I have to confess that there is some selfishness involved," he says. "Surgically, some of these cases are very challenging."

Statistically, though Alfred's tumour is rare, his operation is commonplace. Since 1978, when Mercy Ships began, 18,000 operations have been performed. Last year 31,466 medical treatments were delivered. Soon, writes Mercy Ships founder Don Stephens in his new book Ships of Mercy, the charity hopes to treat a million people a year.

It's a big ambition, but so was the original one. In the early 1970s, Don Stephens was volunteering in the Bahamas when a hurricane hit. "I thought," says Stephens over the satellite link from the Anastasis, "wouldn't it be wonderful if there was a hospital ship that could come and help?" It wasn't a crazy idea: there are military hospital ships, and the non-governmental hospital ship Hope had operated until the 1960s. Stephens had no maritime experience and no money, but he had common sense and good friends with banking connections. And his arguments were persuasive: 90 of the world's biggest cities are port cities, offering easy access to people who were probably lacking good healthcare. If the crew were volunteers and paid their own board, it would be cheap to run. A feasibilty study passed muster. The Victoria, an Italian luxury cruise liner, was bought for scrap value, thanks to a kindly Italian shipping minister, and transformed into the Anastasis. With the sister ship Caribbean Mercy, Mercy Ships has now performed two million services since 1978.

But its success has not come without problems, technical and diplomatic. Anastasis's first visit to Africa was supposed to be to Ghana. Three weeks before departure, the invitation (Mercy Ships only visit with state permission) was withdrawn with no explanation. Maybe it was the spectre of slave ships, Stephens thought. (Later, he heard that the ship was rumoured to be a Trojan horse stuffed with terrorists who would mount a coup.) Anastasis diverted instead to Togo, where the government happily received them, and where, months later, the Ghanaian President Jerry Rawlings came to visit the wards. He saw before and after pictures of a little boy with a repaired cleft lip and palate, who was in the ward for postoperative care. "Is that you?" asked the President. The boy happily confirmed it, and the President called the crew together to apologise. "I cancelled your invitation," he announced, "because I didn't believe people like you existed today. It was too good to be true."

Is it? It is hard to find criticism of Mercy Ships, even in the happily vicious environment of online newsgroups. The respected site, which rates NGOs for efficiency, gives Mercy Ships its maximum of four stars. Mercy Ships has persuaded plenty of powerful names to support it, including various heads of state. "They come on board and watch the bandages being taken off children who've had their cataracts removed," says Stephens. "You see a child seeing for the first time, searching round the room for its mother, and not even the most hardened cynic would be unmoved."

Other supporters include Lord McColl, formerly head of surgery at Guy's Hospital in London and personal doctor to two prime ministers, and Ann Gloag, one of the richest f women in Britain, and boss of Stagecoach. In 1999, Gloag gave £4m to convert a Danish rail ferry into the Africa Mercy, currently being refitted in Newcastle, but not before doing her homework. "As a businesswoman," she wrote in an e-mail, "I realised this was a very cost-efficient charity whose donations go straight to those in need. That was very appealing."

Some still object that money spent on a hospital ship could be put into improving land-based healthcare. "But that's not the problem," says McDermott. "We visited a hospital in The Gambia, a fairly wealthy, stable country." He found a sparkling day clinic, but no patients. "There were CT scanners but no one to operate them. If the machines broke down, there was no one to repair them. You get over that by taking it all by ship. It really works."

In fact, the worst anyone seems to say about the charity is that "it's a bit happy clappy". There's no doubt of Mercy Ships' Christian ethos, which consists of doing like Jesus: heal the sick, make the blind see, make the lame walk. But that, apparently, is that. "There's no proselytising," says Harrison. Volunteers are not required to be Christian, and patients of all faiths - or lack of - are treated, regardless. "They might have a problem with an atheist," says Peter McDermott, who admits to being a Christian "at a distance". He doesn't mind the Christian tone of the ship, because the attractions are so compelling. "Bureaucracy in the NHS is an endless source of frustration. It absorbs money like a sponge. Two-thirds of our trusts are broke. The facilities on Anastasis are much better." In the NHS, it can take a month for overwhelmed pathologists to give results of biopsies. On the Anastasis, a Nikon Coolscope digital scanner now enables a surgeon in Bristol to see and manipulate a histology slide on a ship in Benin, and give a result within 24 hours.

Machinery, though, isn't everything. The people featured in Harrison's exhibit moved several visitors to tears - but they are the lucky ones. Plenty have to be turned away, because their tumour is cancerous or inoperable. "It's very difficult," says McDermott. "In the NHS, you're cushioned by a whole team of people. You can share the helplessness." On a ship off Cotonou, Benin, McDermott has no backup to help him tell an 18-year-old riddled with lymphoma that he will die. "He burst into tears," says McDermott, "and so did I."

But he's still going back, though perhaps not to the Anastasis. When Harrison joins her next month in Monrovia, it'll be the old ship's last voyage before she's replaced by the Africa Mercy. Fifty-two years at sea - much of it spent healing the sick and giving people back their lives - would be enough satisfaction to retire on, even without the ecstatic commendation of a man called Friday. Disfigured for 15 years with a facial tumour, Friday departed two months after his operation, his face beaming, saying, "Look at me now. I am beautiful!"

Scott Harrison's images can be viewed online at 'Ships of Mercy' by Don Stephens, published by Hodder & Stoughton, £7.99