maybe not as big as Roman Abramovich's though:
The Russian billionaire owns a fleet of yachts, nicknamed "Abramovich's navy". His super-yacht, the 377ft Pelorus, has a staff of 40, a helicopter, helipad and a cinema. Worth £100m, it is usually moored in Malta – Abramovich prefers to keep his boats in the Mediterranean, although he can sometimes be spotted in the Caribbean. His other yachts include the Sussurro and Ecstasea, while in 2006 he gave Le Grand Bleu to a business associate. According to reports, he will soon add the world's largest private yacht to his fleet, the 550ft, £200m Eclipse, which is said to have two helipads, six guest suites, five VIP suites and a 5,000 sq ft owner's cabin, as well as an aquarium, a disco, a spa and a half-indoor, half-outdoor pool.
Abramovich is also reported to own not one but two submarines. His first, a 118ft Seattle 1000, commissioned from the leading manufacturer US Submarines, cost £13m to buy and a further £1m a year to run. With two deck levels, separate living areas for guests and crew, dining rooms and staterooms, the boat is capable of diving to a depth of 1,000ft and can remain submerged for two weeks. He is said to have a second sub on order from US Submarines, a smaller 65ft Nomad 1000, which cost £3m and will dock on the Eclipse.
http://www.independe...ons-830582.html
I think that's what people buy when they have more money than they know what to do with.