One of the world's biggest private yachts, belonging to Microsoft co-founder Paul Allen, has moored off Sheung Wan. Mr Allen bought the 127-metre Octopus for US$200 million. It carries two helicopters, seven boats and a submarine that sleeps eight for up to two weeks under water. The crew of 60 includes former US Navy Seals and the vessel costs US$20 million per year to run. It is not known whether Mr Allen is aboard on this mystery voyage, which took in Shanghai last month. Forbes magazine ranks Mr Allen the 19th richest person in the world, with a US$18 billion fortune.