Going by the formulas worked out in
this thread, a single world with a population of 90 billion, a TL of 15, and an 'industrial' trade classification will have 2,377 trillionaires
* and up. One of them will be a 10-quintillionaire
*.
If we assume a 50,000T yacht will cost MCr50,000 and that no one will buy a yacht more expensive that 1/200th of his wealth, one such world will have 792 people who could afford it (which doesn't mean that they would all buy one).
Frankly, I hope that I've made a mistake in my calculations somewhere. But 15 trillion people do generate a lot of money.
Hans