Ketch ketch and the yawl have two masts, with the main mast foremost; the distinction usually being that a ketch has the mizzen mast forward of the rudder post, whereas on a yawl, it is aft of the rudder post. But the balance of sail area can be an overriding characteristic. If 20% or more of the sail area is in the mizzen sail the rig would be termed a ketch. This is particularly true on center cockpit yachts. Compared to a ketch, a similar size yawl's mizzen sail is much smaller than the main, because of the limitations of the
Radio masts and towers sometimes also constructed out of steel tubes. This construction type has the advantage that cables and other components can be protected from weather inside the tube and consequently the structure may look cleaner. These masts are mainly used for FM-/TV-broadcasting, but sometimes also as mast radiator. The big mast of Mühlacker transmitting station is a good example of this. A disadvantage of this mast type is that it is much more affected by winds than masts with open bodies. Several tubular guyed masts have collapsed. In the UK, the Emley Moor and Waltham TV stations masts collapsed in the 1960s.