Not that surprising actually, while not having sailing ship experience I was told that the helmsman would steer by
paying attention to the weather leech of the topsail or topgallant (the tallest sail set) of the mast in front of him, never letting it flap
(keeping the sails full). The responsability of cheking if there was an excessive ruder angle being used (or if they were
straying too much from the course) fell on the officer of the watch, and he would call for a sail trim or order a change of course if needed.
He was the one that reallyhad to know how things were going.