Types and Jobs

Vertical Axis Windmills

Grinding/Irrigation/Pumping/Electrical

The very first windmills originated in Persia over one thousand years ago.  Similar to a revolving door, an opening within a stone enclosure allowed air to flow into the chamber to turn the canvas sails, which were stretched over rectangular frames.  The Persians used this design for hundreds of years for both irrigation and grinding purposes; a few still stand today.  The Persians introduced these windmills to China in the 1200s. 
 
Vertical-axis windmills were used periodically as wind engines both by individuals and manufacturers.  Though not as popular as the “standard” horizontal-axis models, these “turbine-style” engines were sometimes enclosed by a wooden box to capture the wind.  In the 20th century, several kinds of vertical mills were introduced as electricity-producing wind turbines.

Photo from the Deutsches Museum

Torenmolen: Tower Mill

Industrial Grinding/Sawing/Pumping/Irrigation/Draining/Pressing/Electrical

European windmills first developed around 1000 A.D. along the coasts of Greece, Crete, Italy, and Spain.  They were all grinding mills built facing into winds from the Mediterranean Sea, and they typically cannot be turned if the wind changes direction.  The sails are constructed in the literal sense; they are jib sails like those of a ship, with what appear to be several masts fixed to a rotating shaft.
 
Tower mills became larger over time so that their sails could reach the wind over the height of buildings, trees, and other obstructions in populated areas.  In the Netherlands and elsewhere, tower mills come in different styles: grondzeilers, where the sails rotate and can be accessed from the ground (rather than a stage—see Stellingmolen below for stage mills); beltmolen, a windmill built atop a hill or dike; binnenkruier, a smock mill with a cap that is turned internally (or by a windrose, a tail fan); or buitenkruier, with a cap that is turned externally (by the tail pole).

Photo by Steven Fruitsmaak, Wikimedia

Standaardmolen: Post Mill

Light-Duty Grinding

The need to turn a mill into changing wind directions led to the development of the post mill.  The post mill gets its name from its construction: the body, which contains all of the gears and milling equipment, is balanced on a large post.  This crude design meant the entire windmill had to be turned into the wind.  On early post mills, this design was particularly cumbersome because the mill had to be turned manually.
 
Many early post mills were also built without a brake system.  The miller would have to turn the body of the mill away from the wind in order to slow its rotation. Because of their design, post mills could not be built very large and often only had enough room for one run-of-stone.  Post mills were constructed until about the mid-nineteenth century.  By then, post mill design had evolved to include a Flemish brake and a tail fan to luff the mill automatically. 
 
There are two varieties of post mill: the open post mill, in which the bottom timbers are exposed to the elements; and the closed post mill, as pictured to the right, where the bottom is enclosed and may be used for storage.  Although small, their inexpensive and revolutionary design was adapted by countries all over the world.

Photo by Quistnix, Wikimedia

Wipmolen: Hollow Post or "Wip" Mill

Industrial Draining/Grinding

Wipmolens are the Dutch version of the post mill.  Although similar in design, the Dutch built wipmolens almost exclusively for draining; in fact, the Dutch once employed hundreds of them to reclaim land from flooded low-lying areas of the country.
 
Similar to the mills mentioned above, the machinery and sails of wipmolens are contained in a box which must manually be turned into the wind.  But unlike post mills, wipmolens are larger in general, and the bottom portion is large enough for a small dwelling.  These mills were first used for drainage, but a few were also used for grinding.

Photo by Quistnix, Wikimedia

Spinnekopmolen: "Spider" Mill

Medium-Duty Irrigation

Spider mills (or meadow mills) are modeled after the wipmolen but are designed for medium-duty irrigation applications.  Some are luffed by hand at the tail pole, but another variation includes a large vane attached to the upper body.  Although wipmolens are traditionally built with a pyramidal base, spinnekops are sometimes built with six or eight sides.  These windmills are small, with just a ten to twenty foot sail span.

Photo by Groucho NL, Wikimedia

Tjasker: Simple Mill

Light-Duty Irrigation

Although this is not the earliest form of Dutch mill, it is certainly the simplest.  This small mill consists of nothing more than sails fixed to an inclined Archimedean screw to lift water into irrigation canals.  These mills are almost exclusively found in the Friesland province of the Netherlands.  Because they operate near ground level, they are not as powerful as spinnekops, but are very easy to operate and maintain.

Photo by Udo Ockema, Wikimedia

Paltrok: Dutch Saw Mill

Industrial Sawing

There are only five paltroks in the entire world, all unique to the Netherlands.  This four-sided stage mill is designed only for sawing logs; but unlike stage mills, the windmill and its connecting buildings rotate as a unit into the wind on a giant turntable, which operates on a live curb.
 
Paltroks are always built near a river or canal.  Because Holland does not have any large forests for lumber, logs are delivered by boat.  The logs are left in the water for days at a time, allowing them to absorb moisture so they will be less likely to catch fire during the sawing process.  Using a wind-driven hoist, the logs are lifted out of the water and onto the sawing floor of the mill.

Photo by Hand de Kroon, Wikimedia

Stellingmolen: Stage Mill

Industrial Grinding/Sawing/Pumping/Irrigation/Draining/Pressing/Electrical

The success of the wipmolen design led to the development of the iconic Dutch stage mills.  These towering structures allowed the sails to catch the wind over the height of crops, buildings, and other obstructions; because they catch the wind better than ground-sailing (grondzeiler) windmills, they are employed in a variety of heavy industrial applications.
 
The miller is able to access the sails, brake rope, and tail pole from the stage, a raised platform.  The bottom floors can be used for storage, bagging, sawing, or as a dwelling.  Stage mills can be made of stone, brick, or wood, and the materials used vary between countries. 
 
The tallest and most powerful stage mills ever created still stand in Golden Gate Park: the Dutch Windmill to the north, and the Murphy Windmill (currently being restored) to the south.  Together, these windmills once pumped 70,000 gallons of water daily to transform sand dunes into the lush park we see today.

Photo by Tom Haskell