A yawl is a type of boat. The term has several meanings. It can apply to the rig, to the hull type or to the use which the vessel is put.
A yawl setting a genoa, main, and mizzen
The Drascombe Lugger is rigged as a yawl with a gunter mainsail and a leg o'mutton mizzen, sheeted to an outrigger.
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 sails, spars, and derricks, 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.
Three-masted training ship Mersey
Main topgallant mast
This photo of the full-rigged ship Balclutha, shows the fore-mast, main-mast and mizzen-mast, as well as all the ship's standing and running rigging. The Balclutha is berthed in San Francisco, and is open to the public.
Roman two-masted ship, its foremast showing a typically strong forward rake