In practice, in the plural: so at Lucian, Navigium 4, and cf. its Latin equivalent ceruchi in Lucan and Valerius Flaccus. For more precision, on their nature and function, than is proffered in the entries in LSJ and Lewis & Short, see Lionel Casson, Ships and Seamanship in the Ancient World (Baltimore & London 1995) 230 and 257. A pair of such "lifts" -- his preferred translation -- ran from masthead to yardarm to keep the latter level.