By Emma Clark BBC News Online business reporter

A luxury cruise liner with 110 permanent apartments sets sail on Tuesday for Lisbon. BBC News Online visited the ship in Greenwich and talked to some of its new residents.

Anyone who has seen the film The Royal Tenenbaums will remember the ex-tennis pro, Richie Tenenbaum, who spends several years on a cruise liner.

Life on the high seas

Average occupancy of 390 residents Apartments range from 100-300 sq. meters Ship designers include Nina Campbell, J.P. Molyneux, Luciano Di Pilla and Yran & Storbraaten All apartments have a 50-year leasehold All buyers have to be vetted Itinerary includes Cannes Film Festival and Grand Prix in Monaco

Following a break-down on the tennis court, he retreats to a life of soul-searching on the high seas.

In turning to the sea, Richie is not unique - it is not uncommon for wealthy Americans to enjoy long-term trips aboard luxury liners.

But a bunch of Norwegian entrepreneurs have decided to take this concept one step further.

Home from home

In 1995 cruise-ship magnate Knut U. Kloster Jr. came up with the idea of a liner that combined permanent accommodation for the super-rich with all the trappings of a luxury holiday resort.

Seven years later on 29 March, 2002, "The World" set sail from Oslo with about 70 enthusiastic residents on board.

This apartment costs more than $2.7m

"It is definitely a new idea," says Oivind Mathisen, the editor of the trade journal Cruise Industry News.

"But it took time and effort, particularly in terms of finance, to get this idea off the ground."

Fr�dy Dellis, chief executive of ResidenSea - the company that markets the ship - admits plans for a larger ship were abandoned because of financial problems in 1998.

So far ResidenSea has sold 80% of the 110 plushly furnished apartments, ranging from $2.3m (�1.6m) to $7.5m (�5.2m) in value.

Just under half of those have gone to Americans and the rest to Europeans, including 12 UK buyers.

Life of luxury

The facilities on board are impressive even by cruise liner standards.

One of two large swimming pools on board

Alongside two swimming pools and five restaurants, there is a golf driving range which uses golf balls made out of fish food to allay any environmental concerns.

"About 70% of the residents play golf," explains Hans Henrik Sando, the ship's own golf pro and director.

The residents also enjoy a full-sized tennis court, several bars and shops, a library, a health spa and a fitness centre.

Hans Henrik Sando designed the golf facilities

And if one does not feel like mixing with one's fellow millionaires on deck, each apartment boasts a fully equipped kitchen with dishwasher, cooker and fridge - not to mention the washing machine and jacuzzi on the balcony.

Tax haven?

There is also one other benefit that isn't mentioned in the brochure. The World offers potential tax advantages.

The ResidenSea team is reluctant to promote the ship as a tax haven - "We are selling a lifestyle," says Mr Dellis - but admits that prospective buyers have asked about the tax advantages.

Golf balls dissolve into fish food once in the sea

David Rutnam, a director in Deloitte & Touche's private clients group, says that full-time residents could avoid paying the UK's capital gains and income tax.

"It is possible to avoid paying tax, if you get rid of your UK property and live on the boat for at least three years," he says.

However, he warns that the Inland Revenue would "start on the assumption that you were just off on a jolly holiday".

It is also likely that most residents who could afford an apartment on board have already addressed their tax affairs.

An elegantly dressed traveller, who reveals she is the mother of Henning �gl�nd, the chairman of ResdenSea's board, says several of the residents on board are based in the Cayman Islands.

"They have already sorted out their tax arrangements," she adds, smiling.

Retirement home

In reality, the ship seems a perfect setting for the elite world of wealthy, retired folk.

Lorna Lllewellyn: Worth every penny

Sally Tischo, an American on board with her partner, explains how nice it is to have "a home away from home... as we age".

She will be visiting the Monaco Grand Prix and the Americas Cup in New Zealand from her new mobile home.

Another resident, 80-year old Lorna Lllewellyn from Shirley in the UK, is staying in an apartment belonging to her venture capitalist son, Kevin.

"We are getting every penny's worth," she beams.

Ten days into The World's maiden voyage, both women are unable to find fault with the boat - a good sign for ResidenSea.

Clouds on the horizon

But it has not all been plain sailing for the company. An order for a second ship was shelved after 11 September amid the global economic slowdown.

"We want to focus on this ship and sell all the apartments first," says Mr Dellis.

Mr Dellis is focusing on selling all the apartments

He adds that sales of the remaining apartments have slowed down as buyers "thought twice" about making a final commitment to buy.

Cruise Industry News' Mr Mathisen is also sceptical that ResidenSea will start a trend.

"It is directed too much at the high-end of the market and it will take a while to see if it is successful," he says.

He also casts doubt on ResidenSea's plans to operate part of the ship as a hotel, with rates of $500 a night.

"It's a tough sell for a luxury cruise ship in today's market."

On Monday, troops of prospective buyers filed cheerfully through the rooms of the ship in a cloud of expensive perfume.

If they all opt for life on the ocean waves, ResidenSea could be in sight of safe harbour.

Otherwise, the company will forced to run a tight ship indeed.