A day earlier than expected, three sails have been removed from the windmill. Paul Sellwood of Owlsworth, the millwrights, says that they had allowed two days for the removal – today and tomorrow – but that progress was so good that they managed to remove both the common sails and one of the patent sails today.
I arrived just as the third sail, one of the patent sails, was being removed. It was fascinating watching two men in a hydraulic lift chipping and filing away at the stock (the wooden support that holds the sail frame and that passes through the central metal shaft) to try to remove the final sail. Every now and then the lift would move away and there was an ominous creaking as the crane attempted to pull the stock, with the remaining fourth sail, out of the shaft. At one point, when the wedges fell out, I thought we were home and dry. Unfortunately, the stock continued to resist, and fading light meant that they had to call it a day at around 5.45pm – work will resume at 8am tomorrow.
Paul Sellwood says that his initial assessment of the sails’ condition is not too bad. One or two of the sail bars will need replacing, and the bolts that held the sails on weren’t galvanised, so they have gone rusty and expanded. However, he will only know for sure how much work needs doing once he has examined the sails more closely in his workshop.
Brixton Windmill has two types of sail – two common sails and two patent sails.
Common sails have a lattice framework over which a sailcloth is tied to catch the wind. Paul likened them to a kind of ladder, which the miller would climb with the sailcloth over his shoulder. At the end is a removable pole, which passes through rings on the end of the sailcloth rather like a curtain. Depending on the strength and direction of the wind, the miller could then adjust the length of the sailcloth to various rungs of the ‘ladder’.
Patent sails have wooden shutters that can be opened or closed like venetian blinds and are adjusted by a system of rods and chains, so the miller doesn’t have to climb the sails and adjust each one individually.
Owlsworth will be restoring the shutters on the patent sails (but not the cloth on the common sails), so it will be possible to close the shutters so that the sails turn (but the sails will not be linked to the millstones).
Obviously, the sails are in pairs, on opposite ends of the same stock. So the common sails are 1 and 3, the patent sails 2 and 4. However, the stocks and the sail frames are not necessarily made from the same type of wood, so the weight and density can differ. Hence there are weights attached to parts of the sail frames to ensure that the sails remain balanced.
The pair of common sails were mounted behind the patent sails, but Owlsworth removed the common sails first because the stock had slipped by about a foot. “The only things holding it in position were the wedges and the lightning conductor!” says Paul.
For more photos by Owen of the sails being removed, visit the Ashby Mill Flickr group page.
If you’d like to know more about sail structure, here are a couple of links to more detailed, rather academic discussions about sails and how they work.
Dutch site with diagrams
An engineer’s thoughts on why sails go round