In the course of looking up your question, I came across this.
http://cs.finescale.com/fsm/modeling_subjects/f/7/t/64162.aspx?sort=ASC&pi240=2
Apparently the nannybot is not retroactive.
Back to the question, apparently not or lost in the bilges of the internet. I would bet that Melville had in mind a double topsail bark like the Morgan, or the Acushnet if she was rigged that way.
Transom looked like this, usually.