The simplest boats use a single sail attached behind the mast. This is called the mainsail. Most boats have a mainsail plus another sail, the jib, which is in front of the mast. Both sails are controlled by ropes called sheets. The mainsail has a mainsheet attached to the boom which is used to adjust the angle of the boom to the boat. The jib has two jib sheets – one for each side of the boat.