Sails


The 2 main types of windmill sail that we construct are 'Common' sails and 'Patent' sails but we also undertake repair and replacement of 'Spring' sails. We are always careful to follow the local tradition to ensure historical accuracy.

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'Common Sails' have been used on windmills since medieval times. The sail consists of a wooden lattice over which the sail cloth (canvas) is spread. To adjust the sails the mill has to be stopped and the cloth rolled in or out on each sail.  Although these are the simplest sails to construct it is still important to achieve the correct 'weather', which is the slight curve the sail has, to ensure that the mill develops enough power to do the grinding. 

'Patent Sails' were invented by William Cubitt in1813. The sail consist of a number of bays each with its own shutter. The shutters are connected together by a shutter bar which is connected to the striking gear. This allows all the shutters to be opened and closed even while the mill is working. This mechanism is more complicated but does have the advantage that the 'cloth' can be adjusted while the mill is running and the adjustment is automatic.

'Spring Sails' are similar to 'patent' sails however the shutters are held closed by the tension of a spring. The tension of the spring needs to be adjusted as the cloth is applied to each sail. The mill needs to be stopped if the spring tension needs to be changed.  

In 'Patent' and 'Spring' Sails, the shutters (shades) are usually made of canvas which help reduce the weight of the sail. In the midlands the canvas is stitched to a thick wire frame attached to a wooden back whereas in the south the canvas is tacked to an entirely wooden frame. A typical 'Patent' sail can weigh in excess of 1 ton. 

For any sail the choice of timber and the method of construction are very important. Windmill sails are subject to all types of weather from winter gales to baking summers. The wood needs to remain stable in these conditions without splitting. The paint needs to keep the weather out but still allow the wood to breath. If the materials used are not of best quality then the sails might look pretty for a few years but soon begin to decay. The metal work also needs to be substantial, the striking gear does not want to bend in high winds nor do the shackles want to work loose in a gale. 

The sails are usually attached to the wind shaft in one of two ways. Either the sails are bolted directly on to a cast iron cross attached to the wind shaft or the sails are bolted to a pair of stocks which pass through the canister on the end of the wind shaft.  Where stocks are used these also need to be substantial and made of good quality timber.