Sometimes several people come with the same question. Some readers noticed that when viewed from the front, the blades of old mills always turn left, while those of their modern brothers turn the other way. How is this exactly?
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The best known explanation for why old windmills turn left is because of the material they are made of. The rods (the two wooden beams on which the blades are attached and which together form a cross) are made from a tree trunk. That trunk took a right turn when the tree was still growing. The sun rotates from the east along the south to the west every day, and the tree rotates with it.
By turning the blades of a mill in the opposite direction, so to the left (counterclockwise), you turn against the cracks in the wood, thereby closing these cracks. This way the wood will not tear quickly.
But that’s not the whole story.
Wood without fault
It doesn’t seem like this is the reason. Wood researcher René Klaassen of the Wood Research Foundation says: “The rods have to withstand considerable forces. The strength depends not only on the type of wood, but also on the wood quality. The rods will be made of fault-free wood.”
Flawless wood is straight grain, as it is called, and therefore has no direction of rotation. Such wood comes from trees that grow in dense forests.
Miller is on the right
Fortunately, there are other candidate answers. Like this: most people are right-handed, so are most mill builders. Before there were windmills, people ground by hand. Then you generally turn the top stone counterclockwise. If you want the same effect in the mill, you get left-turning blades.
Is there anything in that? You can question that. NRC Handelsblad already addressed this issue in 1993. Spokespersons for the De Hollandsche Molen association told the newspaper that the millstone was often driven indirectly. There was another stone spindle in between, an axis that reversed the direction again. So you can easily grind the top stone to the left without having to turn the blades to the left.
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A mill on Texel. (Photo: NU.nl/Peter Gooijer)
Slats break
A third statement again points to the right-handed miller as guilty. If you want to run the mill in a weak wind, you span a sail over the blades. That sail is rolled up against the rod. If you want to release that as a right-handed person, it is useful if the rod is on the right side of the wick.
A right-handed miller can, according to a fourth statement, also more easily hammer left-turning blades (because the shape determines the direction of rotation). To do this, you punch thin slats through holes in the rod. For right-handed carpenters it is easier to hit the battens from right to left.
This way you end up with mills where the rod is in a downward position on the right side of the blades. And those blades turn to the left. Thus, the right-handed miller may explain why old wooden mills rotate counterclockwise.
The question remains why no left-handed miller ever put things together the other way around. Wood expert Klaassen: “In other countries there are both left and right turning mills.”
Brothers’ competition leads to different directions of rotation of blades
So why do modern mills turn clockwise? And not, like their predecessors, counterclockwise? It is the result of an old competition between the Danish brothers Erik and Johannes Grove-Nielsen.
Both brothers were involved in the development of wind turbines from an early age. In the eighties Erik focused on the design of the blades. Erik’s old mills, like the Dutch ones, all turned counterclockwise. The windmill company where his brother worked also followed in that tradition.
Erik’s wife then suggested turning the mill exactly the other way. And so it happened. Erik’s company, Økær Vind Energi, became successful. His turbines with right-hand blades conquered the windmill market not only in Denmark, but worldwide.
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Thanks for the explanation. But still: in the picture the mill turns clockwise, against its natural built….