By Jane Elliott
BBC News Health Reporter
They carry out operations each weekday
Each year Lord Ian McColl gives up months of his time to operate in war-torn and impoverished areas of the globe, mainly in Africa.
Ask him why at the age of 72 and after such a long career in the NHS, latterly as the former head surgeon at Guy's Hospital, London, that he feels the need to carry on working and he will reply that there is still so much to do.
He is one of the many volunteers from all over the globe who give up their time to do voluntary work on the fleet of 'Mercy Ships', operated by a Christian charity.
The ships dock, usually for up to half a year at a time, in the harbours of countries like Benin, Togo, Sierra Leone and the Gambia and open their doors to the sick.
Ship staff book a local football pitch and, on the first day, there can be as many as 5,000 people waiting to be assessed and to get operation dates.
Professor Ian McColl, chairman of Mercy Ships UK, said he had been deeply moved by the cases he had seen and the difference they could make to their lives.
"There was a little girl of about 12 who was kidnapped by the rebels in Sierra Leone and raped and tortured.
She was doubly incontinent, but made her way to our ship and we were able to give her an operation to help her.
"The operation was a success, but that was only part of it. She was quite a difficult girl, understandably, but the nurses won her over."
Without the operation the girl would probably have faced a very difficult life in her community, where incontinence is viewed as dirty and the victims are often shunned without any prospect of work or marriage.
"We also had a case of a man whose relatives had all been killed by rebels, also in Sierra Leone," said Lord McColl.
"They had taken an axe to the side of his head and we did extensive reconstructive surgery and he lived.
"But he had lost the will to live because of what had happened.
"The five-year-old daughter of the captain of the ship went to see him and gave him a Christmas card and then read to him every night because he had no visitors. She gave him back the will to live."
The ships dock in the local harbour
He says the simple gratitude of the patients makes up for the long hours of surgery on board ship. Medics work from early morning to late at night each weekday.
"While we were waiting to see one group this woman came up to me and flung her arms around me.
"She had been cured in an operation for a fistula [this often occurs following protracted and difficult childbirth and leaves women unable to control their urine and faeces] the previous year and she had just come to thank me.
"That certainly did not happen in the waiting room at Guys."
He said the atmosphere on-board was great.
"I have now retired from the NHS and the only operating work that I do is in Africa.
"There is a high morale on the ships and the atmosphere in the theatre is hilarious. You get withdrawal symptoms when you leave.
"It is like the NHS was 40 years ago with a matron and things running smoothly."
One of the ships the Anastasis, is 522 feet long and has three operating theatres, a dental clinic and an X-ray unit and it has a ward with 38 beds.
The Caribbean Mercy is smaller and has two operating theatres which deal mainly with eye surgery (mostly cataracts). Space is seriously limited and much work is done at shore-based facilities near to the port .
Africa Mercy is currently being converted in the UK from a rail ferry into a hospital ship, complete with six operating rooms and an 80-bed ward.
Lord McColl said that typical cases included eye surgery, huge goitres, an enlargement of the thyroid gland, and general surgery. Benign tumours that would be dealt with at an early stage in the UK have sometimes grown as large as ten inches because no one has the ability to operate on them.
But he said tthey were not able to handle cases which needed extensive follow up treatment and drugs, because they could not offer continuity of care.
"It is terrible having to turn them away. That is the difficult bit. But we do have nurses who run hospices and they go to the homes of these patients and offer them palliative care."
Another problem for the ship doctors are the local witch doctors.
Locals come in their thousands for treatment
"When people have cataracts they try to cure them by hitting the patient on the head repeatedly with a stick.
"That does give them clear vision for a short period, but then their eye clouds up again and it makes my life more difficult for us to operate.
"They also stick knives in the goitres in a bid to get rid of them."
Graham Reardon, a spokesman for the Mercy Ships, said the aim is to bring health to nations where there the facilities are very poor.
"Our highly skilled surgeons perform thousands of operations to remove tumours, correct cleft lips and palates, align cross eyes, repair fistulas, give sight to the blind, as well as provide a wide range of orthopaedic operations. In the countries where Mercy Ships visits these operations are unavailable for most of the population.
"In addition to the onboard hospitals, medical and dental teams establish land-based field clinics.
"These teams carry out free vaccination programmes, dental care, minor operations and medical screening, as well as supporting the training of local doctors and nurses. Mercy Ships runs education programmes in hygiene, nutrition, and basic health care."