Ketch mizzen sheet. So on a ketch, the dual purpose of the mizzen sail is to both propel and balance the vessel, while on a yawl, the smaller mizzen mainly serves the purpose of trim or balance. Yawls tend to have mainsails almost as large as those of comparable sloops. A ketch may be distinguished from a cutter or a sloop by virtue of having two masts rather than one, though a ketch with two foresails is sometimes called a "cutter-rigged ketch". Both the ketch and the yawl differ from the two-masted schooner, whose aft mainmast is taller than the foremast.
Sailing have any number of masts provided the second from the front is the tallest (called the "main mast"). In both a ketch and a yawl, the foremost mast is tallest, and thus the main mast, while the rear mast is shorter, and called the mizzen mast. The difference between a ketch and a yawl is that in a ketch, the mizzen mast is forward of the rudderpost (the axis of rotation for the rudder), while a yawl has its mizzen mast behind the rudderpost. In modern parlance, a brigantine is a vessel whose forward mast is rigged with square sails,