Floating fortress: Chelsea owner Abramovich builds £200m super-yacht half the size of the Bismarck

By Liz Hull

When you have a personal fortune of £11.7billion, you can perhaps be forgiven for feeling the need for protection.

In Roman Abramovich's case, the solution is to order an armour-plated mega-yacht with missile detection system to offer early warning of attack by pirates or terrorists.

At 550ft long, the vessel, costing more than £200million, will be the largest private yacht ever constructed.

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A £200m floating fortress: An artist's impression of the new yacht displays its impressive size and defence capabilities

It is being built secretly at the shipyard in Germany which produced the World War II battleship the Bismarck.

The yacht will include radar equipment designed to warn the crew of incoming rockets, together with bullet-proof windows and armour plating on the bridge and around the 41-year-old Russian tycoon's cabin.

There will be twin helicopter pads and anti-bugging equipment, while the crew of 70 will include former SAS and Special Boat Service personnel.

If intruders make it on board the Eclipse, named because it is intended to overshadow all other private boats, Abramovich and his girlfriend Daria Zhukova, 26, could escape in a yellow submarine which can dive to 160ft.

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Roman Abramovich and Daria Zhukova: The tycoon is not taking any chances against pirates and other potential attackers at sea

The tycoon's other yachts - the 377ft Pelorus, 282ft Ecstasea and 160ft Sussurro - are not believed to have missile defence systems or submarines.

And with a growing number of pirates operating in the world's oceans, the Chelsea Football Club owner does not want to take any chances.

Should he decide to sail to the 2010 World Cup in South Africa, he will be prepared for an attack by gangs such as the Somali pirates who seized a Ukrainian cargo ship loaded with Russian tanks before demanding a large ransom less than a fortnight ago.

According to the International Maritime Bureau, pirates attacked 269 vessels last year, took nearly 300 hostages and killed five people.

Even the Mediterranean, where Abramovich usually keeps his yachts, is becoming less safe.

The 377ft Pelorus will soon be playing second fiddle to Abramovich's newest ship - the 550ft Eclipse

In August, a gang boarded a £20million yacht off Corsica and robbed guests and crew of £100,000.

Under maritime law, non-naval ships are banned from carrying firearms. Some yacht owners are adopting high-powered water cannon, earsplitting klaxons and lubricant foam intended to make boarders slip.

Diane Byrne, editor of Power and Motoryacht News, said pirates and terrorists were an increasing worry for private yacht owners.

'Piracy isn't a problem limited to Somalia,' she said. 'It can and unfortunately does happen around the world.'

Abramovich's yacht will also have cabins for 24 guests as well as a cinema, aquarium, disco and hospital.