The mast of a sailing vessel is a tall spar, or arrangement of spars, erected vertically or near-vertically on the median line of a ship or boat. A mast may carry sails, spars, and derricks. It may also give necessary height to a navigation light, look-out position, signal yard, control position, radio aerial, or signal lamp. Large ships have several masts, with the size and configuration depending on the style of ship. Nearly all sailing masts are guyed.