Real Dictionary

differential windlass in American English
a windlass with two drums of different diameters providing a mechanical advantage
noun: a pair of hoisting drums of different diameter turning at the same rate, such that a pulley suspended below them on a line wound on the larger drum and unwound from the smaller drum is raised with mechanical advantage

differential windlass in British English
noun: a windlass employing the velocity ratio incurred in unwinding from a small drum while winding onto a larger drum rotating at a common speed