Two-masters is a term used to describe three types of sailing vessels: ketches, yawls, and brigs. A ketch is a two-masted sailing vessel with the mainmast taller than the mizzenmast. A yawl is a two-masted sailing vessel with the mizzenmast taller than the mainmast. A brig is a two-masted sailing vessel with square sails on both masts. All three types of vessels are considered two-masters because they have two masts.