Several companies have fleets of charter yachts and the expertise to manage them; several other companies have the same for private jets. No single company has both types of fleets, and none has shown an interest in making the investment to expand into a second area of primary business. "From the infrastructure, they are very different," said Heinz Aebi, vice president of marketing for Jet Aviation, which offers its corporate motoryacht, the 160-foot Blue Shadow, for charter at $115,000 per week, plus expenses. "They have similarities in the audience, but only when it comes to the high, high, high end." Partnerships are the next logical thought, particularly in today's marketplace, where a yacht management agency could partner for fractional jet ownership. Such ownership shares have increased in the United States from fewer than 1,000 in the early 1990s to about 5,000 in 2001. The number was projected to climb to 10,000 by 2003 even before September 11.