I would guess that a little more than half of the natives with a college education know the word, and a much smaller percentage of the natives without a college education. It is not very common. If you use it, only use it in writing with a college-educated audience. (note: in the US, "college" means "college or university")

Thanks Su.Ki.

I agree that it's not in common usage. Only a relatively small proportion of the English-speaking population would know this word, and only a tiny proportion would have it in their active vocabulary. Many would confuse it with 'flounder'. There's probably an age factor as well as an education factor. A young maths graduate probably wouldn't know it, whereas an older, well-read non-graduate may well know it.

The dictionary has some examples.like Six drowned the the yacht foundered off the coast of Florida. The plan foundered on the issue of reform. But thanks for commenting, it's helpful to get a native speakers' perspective. :)

not really. Do you have any examples?