Wilbur Hubbard wrote:

A 'brig' is the term used for a prison. You know like, "Throw the
******* into the brig!" Buck up there, man! Call a spade a spade. It's
a 'brigantine.'

Not so. They are brigs (square rigged on both masts). Brigantines
are square rigged only on the fore mast.

That's what it says on Wikipeia at any rate, which cannot always be
taken for gospel, but ought to be good enough for you.