Zaandam is a town about 30 km from
Amsterdam, which
is renowned for the
Zaansche Schans, a museum of traditional, active
windmills. The windmills are impressive works of 18th century
engineering with their tall bodies, rotating top, and complex mill
gearing. Even though the mills look massive on the outside, there is
actually very little unoccupied space on the inside: every inch is taken
up by rotating gears and shafts to convert wind energy to work. As a
result, it is a
dangerous place as well.
Many years ago, you could still visit the mills to see their
operation. A guide would show you around and explain the details of the
heavy machinery in operation. Guiding a bunch of photo-happy tourists
through a windmill is a typical job for a student trying to make an
extra buck: a clean cut, a smile, and a tie easily double the tip
earnings.
But one day things went terribly wrong. One of the guides showed
around a group of Japanese tourists. They crammed around him in the
small milling space to listen to the history of the mill, and watch him
point out the workings of all the gears. The young student was so
engaged in his narrative that he did not notice his tie getting caught
into one of the gears. As soon as he felt his head being jerked aside,
it was too late: the youngster was pulled into the gearhouse and mangled
to death. Unfortunately there was nothing the horrified tourists could
do to stop the massive power of the windmill.
***
The goal of this anecdote was not just to freak you out as
it did to me when I was 10 years old: it shows the tremendous power of
the 17th and 18th century windmills. This power was utilized to keep the
vastly expanding Dutch economy moving forward during its Golden Age.
Windmills were used for milling of grain, pumping water and sawing
timber. Windmills were common throughout most parts of Europe, but
Holland was the undisputed forerunner with respect to design and usage
of windmills. Around 1850, the number of windmills in use peaked at
approximately 9000. Although no longer in use, the traditional windmill
is still an essential part of the landscape of the Netherlands.
It should come to no surprise that windmills played an important role
in the development of Holland: there is plenty of wind, water, and
it's flat as a pancake. During its Golden Age, Holland was an
important naval power. Advanced woodworking skills and an extensive
knowledge of harnessing wind power were crucial for perfecting the
windmill design. There were marshes and lakes to be pumped to reclaim
land for an expanding economy. Ships sailed the orient, returning with
raw materials to be milled. Increasing amounts of flour were necessary
to keep up with population growth.
But the windmill was not invented in Holland. The first
windmills were built in Persia around 600 A.D. to grind grain.
The first designs may have been derived from water wheels, or grinding
wheels driven by animals. They were built like a merry-go- round, with a
vertical shaft and blades. Part of the construction was
shielded from the wind to direct the rotation (see figure).
__________
\ | / <- Prevailing wind direction
| __\|/__ |
| /|\ |
| / | \ |
|_________|
(top view)
This early design had significant drawbacks: at any time, only half of
the blades were effective for propulsion, and the construction was fixed
at one wind direction. The Chinese discovered that a wheel on a
horizontal shaft with angled blades would not require the shielding walls.
The Crusaders returned to Europe with the concept of the
early windmills. Around the 11th-12th century, windmills were built all
over Europe. Colonialization spread the use of windmills all over the
world. Most of the early European windmills were still very primitive.
They consisted of a cylindrical body with a conical roof. The mills were
usually fitted with bars rigged with simple jib sails. These
windmills, as popularized by Don Quixote still exist in several
countries around the Mediterranean.
But the Dutch took the design of the windmill to another level. In
fact, they built a wide variety of types. Although there is some overlap
in the various styles, the main types are:
- Post mill (Standaardmolen)
- Hollow post mill (Wipmolen)
- Dutch drainage mill (Kloeke poldermolen)
- Tower and stage mill ((Stellingmolen, Torenmolen)
- Paltrok
The mills consisting of a rotating cap (bovenkruiers or "upper
winders"). These are further categorized as binnenkruiers
("inside winders") with a cap that can be turned by an interior winch
mechanism, or buitenkruiers ("outside winders") in which the cap
is turned by a winch on the end of an exterior tail pole. Alternatively,
windmills are categorized by their application: corn mills, mustard
mills, drainage mills, saw mills, paper mills, etc.
Windmill designs vary from model to model, and they were refined over
several ages. It is difficult to give a detailed description of the
various designs. However, a typical Post mill consists of a heavy wooden
vertical pillar, or post, which supports a large square house.
The post allows for rotation of the box in the direction of the wind
using a large tail pole on the back of the mill (considering a
buitenkruier.) The windmill house has vent holes on its sides.
These holes were used to warn the miller for changing wind directions.
The house is raised high above the ground for the
sails to have a significant length, and to catch sufficient wind. The
mill can be entered by stairs at the rear of the windmill house. During
operation, the stairs rest on the ground to support the mill against the
wind force on the sails and mill house. The heavy staircase also forms a
counterweight for the massive sail construction.
Traditional Dutch mills always have four sails. The span of the sails
is approximately 100 feet; the length of the sails was limited by the
size of the available tree trunks. The sails are attached to a wind
shaft sloping down away from the sails. On the center of the shaft is a
large gear called the brake wheel. In case of too heavy winds, the
brake wheel allows the sails to be slowed down or stopped using brake
blocks. The brake wheel also transfers rotation onto a wallower
connected to an upright shaft. The bottom end of the upright shaft is
connected to a large horizontal grinding wheel, which rests in a stone
casing.
A grinding mill usually has a sack hoist, which can be coupled to
the wind shaft inside the mill. The sack hoist allows raw materials to
be hoisted.
The Post mill was typically a small mill. Large mills, like the
Hollow post mill also served as storage facility for milling products,
and as living space for the miller and family.
The miller played an important role in the community because of his
interaction with many customers. An interesting aspect of living at a
windmill was the communication by means of the sails. The windmill was a
very visible structure in the landscape, and the miller could send codes
over great distances. Each mill always turns counterclockwise. A
rising sail position, which has one sail slightly short of
reaching its highest position would indicate a joyful occasion: birth,
marriage, a birthday or celebration. A falling sail position
would indicate mourning. There are many other signals, sometimes
combined with flags to signify other occasions.
Windmills were not only used for grinding purposes: the other major
application was to reclaim land. Holland consisted of large peat bogs
that were harvested for home heating. Since the peat was collected from
increasingly greater depths, the marshes needed to drained. Furthermore,
as a defensive strategy against the Spanish, Holland deliberately broke
its dykes. At the end of The Dutch Revolt in 1609, this land
needed to be reclaimed.
Two people played a major role in the development of drainage mills:
the engineer/mathematician Simon Stevin (1548-1620), and particularly
the inventor/engineer/constructor Jan Adriaensz Leeghwater
(1575-1650). Leeghwater (whose name coincidentally means "empty water"
in Dutch) executed several large drainage projects. Leeghwater achieved
international fame with his study on the drainage of the
Haarlemmermeer; a 13 feet deep lake that was to be drained using
160 windmills. However, the project was only started in the mid-1800s,
with the introduction of steam engines. If you ever fly
to Holland, look around you during the landing; Schiphol (Ship's Hell)
is right in the former Haarlemmermeer.
The introduction of the steam engine marked the end of the
traditional windmill as a major workhorse. The number of windmills dropped
from its peak of 9000 in 1850 to approximately 2500 in 1900. With the
founding of The Dutch Windmill Society in 1924, the interest in
preserving these historical landmarks increased, but many mills were
severely damaged during World War II. Approximately 900-1000 windmills
are remaining in the Netherlands.
But the concept of wind power isn't completely forgotten. During the
oil crisis in the 1970s, modern wind turbines were
studied to replace fossil fuel power plants. Advances in materials have
made these windmills more reliable and more efficient. Although
these windmills aren't sufficient to supply the entire electricity
demand, they may form a useful addition to Holland's power requirements
in the future. Several wind parks are set up along the coast. As an
engineer, I am happy to see these modern windmills spinning on the Dutch
horizon; a reflection of an 800 year old tradition.
Factual sources:
http://www.tem.nhl.nl/~smits/windmill.htm (amazing historical details)
http://www.garfnet.org.uk/new_mill/autumn96/jv_mill.htm
http://www.looklearnanddo.com/documents/history_windmills.html
http://www.windmillworld.com/windmills/history.htm (with many more interesting links)