The term yacht applies to two rather different classes of sea vessel, sailing yachts and power yachts. Traditionally, yachts were differentiated from working ships mainly by purpose, yachts were swift and comfortable conveyances of the wealthy and powerful. It was not until the ascendancy of the steamboat and other types of powerboat that sailing vessels came to be seen as luxury items. Modern use of the term applies to nearly all sailing vessels, other than sailing dinghies, that are used for yacht racing or for pleasure cruising. Motor yachts, on the other hand, retain more of the original sense of power and luxury. Much larger and generally far more expensive than the average sailing yacht, the motor yacht contains sufficient living space for at least several days at sea. Lengths generally start at 11–12 m and go up to well 30 m. Mega yachts, luxury yachts such as the ones owned by Larry Ellison, Paul Allen and other billionaires, can reach over 160 m in length.