The Double Century has nine decks – which means that it also comes with eight sets of elevators so guests and crew don’t have to negotiate all those flights of stairs. The vessel is expected to be equipped with everything from a disco to a 126-seat cinema, and it will take to the seas with a crew of up to 100. A scaled-up version of the yacht could be commissioned too – even bigger, it would measure 740ft (225m). (Credit: 4Yacht)