Windmill sail

Windmills are powered by their sails. Sails are found in different designs, from primitive common sails to the advanced patent sails. The jib sail is found in Mediterranean countries and consists of a simple triangle of cloth wound round a spar. The mill must be stopped in order to adjust the reefing of the sail. Though rare in the UK, at least two windmills are known to have had jib sails (St Mary's, Isle of Scilly and Cann Mills, Melbury Abbas). Image:Windmill Antimahia Kos.jpg|Jib sails Image:Sobreiro.jpg|More fully spread Image:Spanish Mill, St Mary's.jpg|St Mary's, Isles of Scilly File:Cann Mill, Melbury Abbas.jpg|Cann Mills, Melbury Abbas The common sail is the simplest form of sail. In medieval mills, the sailcloth was wound in and out of a ladder-type arrangement of sails. Medieval sails could be constructed with or without outer sailbars. Post-medieval mill sails have a lattice framework over which the sailcloth is spread. There are various "reefs" for the different spread of sails; these are full sail, dagger point, sword point and first reef. The mill must be stopped in order to adjust the reefing of the sail. Image:Ellezelles JPG02.jpg|Furled Image:Jard moulin a vent.JPG|First reef (Medieval style sail) Image:Windmuehle.JPG|Sword point Image:Wissel.jpg|Dagger point Image:Cassel Nord (moulin).jpg|Full sail Image:Moulin-montfuron-2.JPG|Full sail (Medieval style sail) Spring sails were invented by Scottish millwright Andrew Meikle in 1772. The sail is divided into a number of bays, each having a number of shutters. All the shutters are joined together by a shutter bar, and the force required for the wind to open the shutters is adjusted by a separate spring on each sail. Although automatic in operation, the mill must be stopped in order to adjust the reefing of the sail. Image:Outwood Windmill.jpg|Open Roller reefing sails were invented by Stephen Hooper in 1789. As with spring sails, the sail is divided into a number of bays, each with a number of spars with cloth wound around them.