Boy sits on a buoy?

Don’t rely on your spell checker. Even if there are no language differences, it won’t always catch your errors.

Both “the buoy is floating” and “the boy is floating” are correct, but they mean different things. Of course, if you live in the USA you pronounce buoy as boo-ey so this pair of words doesn’t seem quite so similar as it does to those of us who prounce it the same way as boy.

boy: a male child
The boy was excited about his birthday.

buoy: a floating device that marks significant spots in water
The boats kept outside of the circle of buoys during the race.