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13. Octopus

Length: 414 feet
Top speed: 20 knots
Total power: 19,200 hp

Purchased by Microsoft (MSFT) co-founder Paul Allen for $121 million in 2003, the Octopus features some intriguing onboard toys, including a 63-foot tender, two submarines, a remote control submarine, a dock for Jet Skis, a pool, and two helicopters on the top deck.

It has also been used for humanitarian efforts. Allen loaned the yacht to a flotilla helping to stop the poaching of giant clams, and it helped in the unsuccessful searchfor an American pilot and two police officers from Palau after their plane disappeared in April.

The exterior was designed by Espen Oeino and was built by Lurssen and HDW in Germany. The interior was designed by Jonathan Quinn Barnettof Seattle.

Photo: SuperYachts.com