The mast of a sailing vessel is a tall spar, or arrangement of spars, erected more or less vertically on the centre-line of a ship or boat. Its purposes include carrying sail, spars, and derricks, and giving 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 masts.