Well, I can quote an impeccable reference for it being the winds! If you read Richard Dana's Two years before the mast you'll find he says 'She was going at a prodigious rate [...] The captain walked the deck at a rapid stride, looked aloft at the sails, and then to windward; the mate stood in the gangway, rubbing his hands, and talking aloud to the ship- "Hurrah, old bucket! the Boston girls have got hold of the tow-rope!"'

I rest my case.

Steve