Aha! Thanks, Shorty! That 'splains it!
Jack Aubrey is sailing on a brigantine named the
Sophie. There's an illustration at the front of the book that shows the names of the sails but this ship doesn't have royals. I see the point now--the royals would put the most torque on the mast per square foot of sail, hence the most wear on this and that.
He keeps talking about the quarterdeck as if it were a poop deck, and in one spot even says it's "like a poop deck, almost a castle." It's a relatively small ship; a 150-foot brig that previously belonged to the Spanish. I think it was taken as a prize, but the book hasn't made that clear.
I'm guessing that Jack Aubrey's brig must look like this:
