A buddy of mine circumnavigated in a 27 foot boat. Took him four years. He wasn't in a big hurry. It wasn't a cheap 4 years, even though he did it on a tight budget. That's a lot of wear and tear on the boat, and of course you also have to eat, and pay all sorts of "fees" anywhere you land. He didn't have any sponsors to speak of. One factor is that once you circumnavigate, you can make money doing appearances and lectures. You can also write magazine articles. My friend is also an artist, and he painted all during the voyage. His paintings now go for much higher prices than before he circumnavigated.