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Dutch Windmills left Behind

Inspired by the landscape images of windmills by painters of the Dutch golden age and the Impressionists, I take a trip out to the Zaanse Schans area about an hour’s drive north of Amsterdam to get up close to them.  Zaanse Schans was the first industrial area of Western Europe.  In the 18th and 19th centuries there were 700 active windmills in the region.  As pretty and picturesque as the windmills are that dot the Dutch landscape, darling scenery of painters as they may be, a windmill is actually a business, not an objet d’art.  They are little miniature factories which convert wind power into manufacturing output through the marvel of engineering.  Wind power is transmitted through gears, levers, cams and crankshafts to the business end of the windmill, be it grinding, sawing, pounding, turning, water pumping etc.

Why windmills?  Wind energy is clean and cheap, but inconsistent.  However, the power of the windmill was greater than most forms of energy available at the time.  Before the industrial revolution, apart from wind, you essentially had water, tide and muscle, the latter being the most flexible but weakest of the lot.

How much more power could you get out of a wind-driven sawmill compared to having two men sawing a log, or from horses connected to log-sawing machine?  James Watt, the great Scottish engineer, calculated that a horse could work for long periods at what he defined as one horsepower (HP).1  The typical Dutch windmill of the time could generate between 14 and 18 HP of working power, i.e. the sawing power of roughly 150 men or 15 horses.  Which is why the typical Dutch sawmill operatives, around six or seven per sawmill, did maintenance and other work when the wind was low, never any sawing themselves.  It was simply too inefficient compared to wind power.  The traditional Dutch windmill’s power is in turn insignificant compared to that of modern wind turbines.2

It’s a fine autumn morning in Zaanse Schans.  Tourists of the world flock here to see the remnants of what once was an industry built on a latticework of canals.  It’s very picturesque and the Dutch have the tourist thing down to a tee.3  Colourful sheds manned by workers in traditional garb sell handicrafts which are paired with demonstrations such as the making of clogs, etc.  I wend my way towards a series of windmills along a canal and enter the first one, Molen De Kat.4  The smiling owner-manager takes my 4.50 euros and addresses me in Dutch.  I answer in Afrikaans and we get along famously.  He asks me how it’s going with the Cape Colony and with racism.  Very well on both fronts, I reply.

He tells me that the Molen De Kat was established in 1642 and that its business is to grind pigment ores for paint and dyes.  I should note that Rembrandt himself was a client of the mill back in the day.  The mill is in operation as we speak, and quite impressive.  A crank drives two huge wheel-shaped grindstones, each weighing three tons, over a millstone containing stony clumps which are gradually being reduced to powder.  The same wind energy lifts giant pestles up and down in adjacent mortars, pounding coarser ore to dust.  It is noisy, it wobbles, creaks and rumbles.  The fine powder eventually gets sifted, put into vials and sold to the art market.  Such is the reach of this industry that Molen De Kat has been importing raw ores from all over the world for centuries.

I climb the staircase to the first floor to inspect the transmission system.  It’s basically an assemblage of wood.  There is a constant rumbling and a periodic creak as the teeth of the turning gears drive the crankshaft relentlessly.  The noise and speed of operation are not constant but ebb and flow with the wind speed.  Wind millers have a maintenance headache.  They not only have to harness, but must also control the power of the wind.  Too much wind can wreck the gearing mechanism.  Being made of wood, it can even go up in flames if the friction gets too high.  Wind millers must therefore adjust the sails that cover the latticed blades of the windmill to different extents. They can change the direction of the blades and can even disengage the gears altogether if the wind gets too strong.  What they need is a stiff but steady breeze, not a gale.  Dutch mills are around seven storeys high and are a continual challenge for a milling crew.

The adjacent windmill is the sawmill Het Jonge Schaap.5  Logs arrive by boat on the water and are pulled up onto the mill’s ramp by wind power, and further onto a sliding platform.  By crankshaft motion, wind power advances the platform containing the logs in jerks towards a set of saws, the spacing of which can be adjusted to lumber specification.  The mill existing today was built between 2005 and 2007 and is an exact replica of the original built in 1680 and demolished in 1942.  The manager/tour guide explains that for all its clever engineering, the mill’s workflow can only proceed in a one-way direction.  Once the log is sawn into large planks, human power has to move the planks back to the beginning of the sliding platform for further sawing.  A more efficient configuration would be possible I’m sure, but they wanted to replicate the mill in exactly the way it was originally built.6  He explains that they aim to produce around fifty tons of lumber for commercial sale to the building trade per year.  This alone does not render the mill commercially viable.  For that, they have to get 25000 paying visitors a year.  They luckily got 50000 visitors over the past year, so business isn’t that bad.

I mill around marvelling at the ingenuity of 18th century Dutch engineering.  The workflow is neat, logical and accessible.  Here and there electrical equipment is subtly in evidence, so the 21st century does encroach.  Yet, in 1750 there were 700 mills in operation in the Zaanse Schans, today only a handful still operate, and for good reason.  For all their ingenuity, steam, electricity and technology have superseded these little factories.7  Like the circles that you find in the windmills of your mind, they are today of curious interest at most, resurrected relics of past achievement.  I am nonetheless thrilled at the efforts going into preserving these cogs of Dutch cultural heritage.8

Happy for that, I lugged myself off to a stall next to a polder, ordered a coffee and an Edam cheese sandwich and checked the timetable for my bus back to Amsterdam.

Notes: (to Windmills Left Behind)

  1. In a series of experiments, the Scottish engineer James Watt (1736-1819) calculated that a horse could do work amounting to lifting a weight of 75kg against gravity by one metre per second for sustained periods of time. On this measure, a man can generate 0.1 horsepower.  James Watt conducted the experiment because he was trying to sell his new steam engines to people using horses.  His potential clients would ask him how many draft horses his engines could replace, so he set about determining it.  Watt’s original steam engine had ten-horsepower (HP), so it could do the same work (e.g. lift the same amount of water out of a well at the same rate) as a team of ten horses could.  In honour of Watt, the SI unit for power was named the Watt, making Watt’s name probably the most uttered name of any scientist’s, including the greats like Einstein and Newton.  In our energy-hungry world, Watt’s name appears on every electrical appliance or machine in the form of watts, kilowatts, megawatts etc.  Note: 1 HP = 746 Watts.On a technical note, James Watt’s calculations were made before the units of physics were standardised.  The modern scientific concept of power is defined as work done (energy) per unit time.  On this measure, horses can achieve a power output as high as 15HP in bursts, but they cannot sustain it for long.  Watt’s experiments worked the horses for four hours, and over that length of time, the sustainable power output of the average horse, subsequently confirmed by numerous researchers over time, is indeed around 1HP.  Bravo Mr. Watt!
  2. Today the standard wind turbine is around 8mW, roughly 250 times more powerful than a traditional Dutch windmill assuming a power efficiency of 50%. General Electric Renewable Energy last year announced the construction of a 12mW turbine which will stand 260m high and is due for commercial operation in 2021.  See  https://www.fastcompany.com/40538304/heres-the-worlds-most-powerful-wind-turbine.
  3. For a general impression of the Zaanse Schans area, Zaandam, see https://www.youtube.com/watch?v=1aHeuuR6n7E
  4. For a short clip on the operation of De Molen Kat see https://www.youtube.com/watch?v=_wfBVKUAqb0
  5. For a short clip on the operation of Het Jonge Schaap see https://www.youtube.com/watch?v=ipD8RoioEEc&t=6s
  6. Het Jonge Schaap was rebuilt between 2005 and 2007. The construction of the replica was based on detailed drawings that Anton Sipman made before the original mill was demolished.
  7. The technology of a windmill like Het Jonge Schaap is nearly four centuries removed from the comparatively super-efficient technology of today. For a ‘Logs-to-Lumber’ journey through a modern saw mill, see https://www.youtube.com/watch?v=NvbgwdTGoyo and compare it to the clip of Het Jonge Schaap in Note 5 above.
  8. To run a traditional mill today, Dutch millers serve an apprenticeship and write a wind millers’ exam. They work with a miller for a few years and learn to operate it in all sorts of weather conditions, then go to work other types of mills.  These people consider it as part of their heritage; some windmills are even family homes.  For a clip (in English) on the maintenance of a Dutch windmill see:  https://www.youtube.com/watch?v=3STOY9DEi2s