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Haigh Windmill

A tower mill is a type of vertical windmill consisting of a brick or stone tower, on which sits a wooden 'cap' or roof, which can rotate to bring the sails into the wind.[1][2][3][4][5]

This rotating cap on a firm masonry base gave tower mills great advantages over earlier post mills, as they could stand much higher, bear larger sails, and thus afford greater reach into the wind. Windmills in general had been known to civilization for centuries, but the tower mill represented an improvement on traditional western-style windmills. The tower mill was an important source of power for Europe for nearly 600 years from 1300 to 1900, contributing to 25 percent of the industrial power of all wind machines before the advent of the steam engine and coal power.[6]

It represented a modification or a demonstration of improving and adapting technology that had been known by humans for ages. Although these types of mills were effective, some argue that, owing to their complexity, they would have initially been built mainly by the most wealthy individuals.[7]

History

[edit]

The tower mill originated in written history in the late 13th century in Western Europe; the earliest record of its existence is from 1295, from Stephen de Pencastor of Dover, but the earliest illustrations date from 1390.[8] Other early examples come from Yorkshire and Buckinghamshire.[9] Other sources pin its earliest inception back in 1180 in the form of an illustration on a Norman deed, showing this new western-style windmill.[10] The Netherlands has six mills recorded before the year 1407. One of the earliest tower mills in Britain was Chesterton Windmill, Warwickshire, which has a hollowed conical base with arches. The large part of its development continued through the Late Middle Ages. Towards the end of the 15th century, tower mills began appearing across Europe in greater numbers.

Alford Windmill

The origins of the tower mill can be found in a growing economy of Europe, which needed a more reliable and efficient form of power, especially one that could be used away from a river bank. Post mills dominated the scene in Europe until the 19th century when tower mills began to replace them in such places as Billingford Mill in Norfolk, Upper Hellesdon Mill in Norwich, and Stretham Mill in Cambridgeshire.[11]

The tower mill also was seen as a cultural object, being painted and designed with aesthetic appeal in mind. Styles of the mills reflected on local tradition and weather conditions, for example mills built on the western coast of Britain were mainly built of stone to withstand the stronger winds, and those built in the east were mainly of brick.[12]

Foulsham tower mill, five stories of brick, early 1800s. Burned 1912 and converted to private residence.

In England around 12 eight-sailers, more than 50 six- and 50 five-sailers were built in the late 18th century and 19th century, half of them in Lincolnshire. Of the eight sailed mills only Pocklington's Mill in Heckington survived in fully functional state. A few of the other ones exist as four-sailed mills (Old Buckenham), as residences (Diss Button's Mill), as ruins (Leach's Windmill, Wisbech), or have been dismantled (Holbeach Mill; Skirbeck Mill, Boston). In Lincolnshire some of the six-sailed (Sibsey Trader Mill, Waltham Windmill) and five-sailed (Dobson's Mill in Burgh le Marsh, Maud Foster Windmill in Boston, Hoyle's Mill in Alford) slender (mostly tarred) tower mills with their white onion-shaped cap and a huge fantail are still there and working today. Other former five- and six-sailed Lincolnshire and Yorkshire tower mills now without sails and partly without cap are LeTall's Mill in Lincoln, Holgate Windmill in Holgate, York (currently being restored), Black, Cliff, or Whiting's Mill (a seven-storeyed chalk mill) in Hessle and (with originally six sails) Barton-upon-Humber Tower mill, Brunswick Mill in Long Sutton, Lincolnshire, Metheringham Windmill, Penny Hill Windmill in Holbeach, Wragby Mill (built by E. Ingledew in 1831, millwright of Heckington Mill in 1830), and Wellingore Tower Mill. Another fine six-sailer can be found in Derbyshire – England's only sandstone towered windmill at Heage of 1791.

Design

[edit]
Dutch windmill Dutch: De Noord, Schiedam

The advantage of the tower mill over the earlier post mill is that it is not necessary to turn the whole mill ("body", "buck") with all its machinery into the wind; this allows more space for the machinery as well as for storage. However, select tower mills found around Holland were constructed on a wooden frame so as to rotate the entire foundation of the mill along with the cap. These towers were often constructed out of wood rather than masonry as well.[13][14] A movable head which could pivot to react to the changing wind patterns was the most important aspect of the tower mill. This ability gave the advantage of a larger and more stable frame that could deal with harsh weather. Also, only moving a cap was much easier than moving an entire structure.

In the earliest tower mills the cap was turned into the wind with a long tail-pole which stretched down to the ground at the back of the mill. Later an endless chain was used which drove the cap through gearing. In 1745 an English engineer, Edmund Lee, invented the windmill fantail – a little windmill mounted at right angles to the sails, at the rear of the mill, and which turned the cap automatically to bring it into the wind.[15]

Like other windmills tower mills have normally four blades. To increase windmill efficiency millwrights experimented with different methods:

  • automated patent-sails instead of cloth spread type sails didn't need the sail cross to be stopped to spread or remove the cloth sails because they altered the surface from inside the mill by means of a controlling gear.
  • more than four blades to increase the sail surface.

Therefore, engineer John Smeaton invented the cast-iron Lincolnshire cross to make sail-crosses with five, six, and even eight blades possible. The cross was named after Lincolnshire where it was most widely used.

There are several components to the tower mill as it was in the 19th century in Europe in its most developed stage, some elements such as the gallery are not present in all tower mills:[16]

  • Stock – the arm that protrudes from the top of windmill holding the frame of the sail in place, this is the main support of the sail and is usually made of wood.
  • Sail – the turning frame that catches the wind, attached and held by the stock. The traditional style found on most tower mills is a four-sail frame, however in the Mediterranean model there is usually an eight-sail frame. An example of this in St. Mary's Mill on the Isle of Sicilly constructed in 1820.
  • Windshaft – A particularly important part of the sail frame, the windshaft is the cylindrical piece that translates the movement of the sail into the machinery within the windmill.
  • Cap – The top of the tower that holds the sail and stock, this piece is able to rotate on top of the tower.
  • Tower – Supports the cap, the main structure of the tower mill.
  • Floor – Base level of the tower inside, usually where grain or other products are stored.
  • Gallery – Deck surrounding the floor outside the tower to provide access around the tower mill if it is raised, not present in all tower mills. The gallery allowed access to the sails for making repairs because they could not be easily reached from the ground in larger mills.[17]
  • Frame – Sail design that forms the outline of the sail, usually a meshed wood design that then is covered in cloth. The Mediterranean design is different in that there are several sails on the sail-frame and each supports a draped cloth and there is no wooden frame behind it.
  • Fantail – Orientation device that is attached to the cap, allowing it to rotate to keep the sails in the direction of the wind.
  • Hemlath – Thick wooden sailbar on the side of the frame that keeps the narrower sailbars inside the sail.
  • Sailbar – Elongated piece of wood that forms a sail.
  • Sail cloth – Cloth attached to a sail that collects wind energy; a large sail cloth is used for weak winds and a small sail cloth for strong winds.

Application

[edit]
Jack (foreground), a tower mill, and Jill (background), a post mill, photographed in 1908 in Clayton, West Sussex. Immediately in front of Jack is the roundhouse of Duncton Mill, an older defunct post mill. All three have survived to the present day, and are maintained together as the Clayton Windmills.

The tower mill was more powerful than the water mill, able to generate roughly 14.7 to 22.1 kilowatt (20 to 30 horsepower).[18] There were many uses that the tower mill had aside from grinding corn. It is sometimes said that tower mills fuelled a society that was steadily growing in its need for power by providing a service to other industries as well:[19]

  • The production of pepper and other spices
  • Lumber companies used them for powering sawmills
  • Paper companies used to change wood pulp into paper

Other sources argue against this claiming there is no real evidence, specifically, of tower mills doing these things.[3]

Interesting facts

[edit]
Maltese: Ta' Buleben Windmill, in Zabbar, served as the Windmill Redoubt during the French occupation of Malta.[20]

The world's tallest tower mills can be found in Schiedam, Netherlands. Dutch: De Noord, meaning 'the North', is a corn mill dating to 1803 that is 33.3 metres (109 ft) to the cap. In 2006 an imitation, De Nolet (named after the local Nolet distilling family who owns the mill), was built as a generator mill producing electricity that is 42.5 metres (139 ft) to the cap.

England's tallest tower mill is the nine-storeyed Moulton Windmill in Moulton, Lincolnshire, with a cap height of 30 metres (98 ft). Since 2005 the mill has a new white rotatable cap with windshaft and fantail in place. The stage was erected during 2008 and new sails were fitted on 21 November 2011 to complete the restoration of the mill.[21] Larger mills have been lost, such as the Great Yarmouth Southtown mill that was 37 metres (120 ft) to the top of the lantern that functioned as a lighthouse,[22] and Bixley tower mill that was 42 metres (137 ft) to the cap top,[23] both in Norfolk.

In the Netherlands windmills named tower mills (torenmolens) have a compact, cylindrical or only slightly conical tower. In the southern Netherlands four mills of that type (Dutch definition) survive, the oldest one dating from before 1441. The cap of three of those mills is turned by a luffing gear built in the cap. Older types of tower mill with a fixed cap were found in castles, fortresses or inside city walls from the 14th century, and are still be found around the Mediterranean Sea. They were built with the sails facing the prevailing wind direction.

Tower mills were very expensive to build, with cost estimates suggesting almost twice that of post mills; this is in part why they were not very prevalent until centuries after their invention. Sometimes these mills were even built on the sides of castles and towers in fortified towns to make them resistant to attacks. Some tower mills were still in operation well into the 20th century in southern parts of the United Kingdom.[24]

Citations

[edit]
  1. ^ Righter, Wind energy in America: A History, (1996) 14
  2. ^ A short history of technology: from the earliest times to A.D. 1900 (1993), 255
  3. ^ a b Medieval science, technology, and medicine: an encyclopedia (2005), 520
  4. ^ Watts, Water and wind power (2000), 125
  5. ^ Ball, Natural sources of power (1908), 243
  6. ^ Righter, Wind energy in America: A History, (1996) 15
  7. ^ Langdon, Mills in the medieval economy: England, 1300–1540 (2004), 115
  8. ^ Hills, Power from wind: a history of windmill technology, (1996) 51–60
  9. ^ Langdon, Mills in the medieval economy: England, 1300–1540 (2004), 114
  10. ^ A short history of technology: from the earliest times to A.D. 1900 (1993), 254
  11. ^ Hills, Power from wind: a history of windmill technology, (1996), 65
  12. ^ Hills, Power from wind: a history of windmill technology, (1996), 63
  13. ^ Journal of the Franklin Institute, Volume 187 (1919), 177
  14. ^ Miller in Eighteenth Century Virginia (1958), 7
  15. ^ Cipolla Before the industrial revolution: European society and economy, 1000–1700 (1994), 144
  16. ^ http://visual.merriam-webster.com/energy/wind-energy/windmill/tower-mill.php visited 23 November 2009
  17. ^ Ball, Natural sources of power (1908), 248
  18. ^ Cipolla, Before the industrial revolution: European society and economy, 1000–1700 (1994), 144
  19. ^ Wind energy in America: A History (1996), 15
  20. ^ Spiteri, Stephen C. (May 2008). "Maltese 'siege' batteries of the blockade 1798-1800" (PDF). Arx - Online Journal of Military Architecture and Fortification (6): 30–31. Archived from the original (PDF) on 26 November 2016. Retrieved 30 March 2015.
  21. ^ "Lincolnshire mill gets new sails". BBC News. 22 November 2011 – via BBC.
  22. ^ "Norfolk Mills - Gt Yarmouth Southtown High Mill tower windmill". www.norfolkmills.co.uk. Retrieved 26 July 2022.
  23. ^ "Norfolk Mills - Bixley towermill". www.norfolkmills.co.uk. Retrieved 26 July 2022.
  24. ^ Wind, water, work: ancient and medieval milling technology (2006), 122

References

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Tower mill

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A tower mill is a type of windmill featuring a fixed, vertical tower typically constructed from stone or brick, topped by a rotatable wooden cap that houses the sails, windshaft, and grinding machinery, enabling the mill to be oriented toward the prevailing wind without pivoting the entire structure. This design provided greater stability and capacity compared to earlier post mills, where the full body rotated around a central post. Tower mills emerged in in the late , with the earliest known record dating to 1295 in Dover, , representations from 1390, and sketches from 1420 depicting them in the Byzantine town of Gallipoli. They evolved as an improvement over post mills by the late medieval period, allowing for taller constructions—up to 37 meters in height and 12 meters in base diameter, as seen in an 1812 East Anglian example that was later demolished in 1905. By the , tower mills proliferated across regions like and the , where they were essential for grain milling, through drainage, and industrial tasks such as sawing timber or processing dyes. Architecturally, the tower formed a multi-story housing internal gears, millstones, and sometimes living quarters, often accessed via an external gallery or staging deck for . The , turned manually via a tailpole or later a fantail mechanism, minimized through a curb track, sometimes fitted with iron rollers for smoother operation. Sails numbered four to eight, evolving from common to more efficient spring sails in the . Their significance extended beyond utility, as tower mills represented prowess and economic investment, often built by nobles or communities on repurposed towers due to high construction costs. In the , thousands operated until the , when steam power began supplanting them, though many survive today as cultural icons, such as the 30-meter Moulton Windmill in or the 33-meter De Noord in .

History

Origins in Medieval Europe

The tower mill emerged in late 13th-century as an advancement over earlier designs, with the earliest recorded example dating to 1295 at in , where it served as a replacement for less stable post mills by allowing taller structures without requiring the entire body to rotate. While the Dover example is the earliest documented in , similar designs may have emerged in around the late . This addressed limitations in post mills, which had appeared in by the late and involved a fully pivoting timber body supported on a central post, making them prone to wear and unsuitable for larger scales. By fixing a sturdy tower in place and mounting only a rotatable cap with sails, tower mills achieved greater stability and capacity for grain grinding, reflecting a key step in medieval . The invention occurred amid the ' population expansion, as Europe's inhabitants grew from approximately 30 million around 1000 CE to over 100 million by 1300, driving increased agricultural output and demand for efficient milling to process surplus into for burgeoning urban centers. In regions like and , where wind resources were abundant but water sources sometimes limited, tower mills offered a reliable alternative to watermills, supporting in feudal societies reliant on manual labor for food production. Early adoption was concentrated in these areas, with documentary evidence from monastic and royal records indicating their use for both practical grinding and symbolic prestige among landowners. Initial tower mills were constructed predominantly from stone or brick for the fixed cylindrical body, providing durability against harsh weather and enabling heights that captured stronger winds aloft, unlike the timber-framed post mills that dominated prior centuries. These materials, drawn from local quarries and kilns, underscored the technology's ties to medieval building traditions, where masons collaborated with carpenters to integrate the rotating wooden cap and sail assembly. Despite higher construction costs compared to post mills, the design's advantages in output and longevity facilitated gradual integration into the European landscape over the subsequent decades.

Expansion and Regional Variations

Following their emergence in medieval Europe, tower mills experienced widespread adoption across the continent from the 15th to the 18th centuries, adapting to diverse landscapes and economic demands while evolving in form and function to meet regional needs. In the , particularly the and , tower mills underwent rapid expansion beginning in the 15th century, fueled by the area's predominantly flat terrain and pressing requirements for water management to combat flooding and reclaim from marshes and the sea. These mills, often repurposed for pumping water from polders, became essential to agricultural and infrastructural development, with adaptations like arched bases elevating them above flood levels. By 1850, the alone operated over 9,000 windmills, the majority tower or derivative designs, underscoring their pivotal role in sustaining a densely populated, low-lying region. England witnessed a notable proliferation of tower mills in East Anglia during the 16th century, where the region's expansive, windy fens and marshlands necessitated efficient drainage to convert wetlands into farmland. These mills frequently incorporated variations such as combined drainage and grain-grinding capabilities, with sails driving Archimedes' screws to lift water from lowlands, thereby supporting the growth of arable agriculture in areas prone to seasonal inundation. In and , 16th-century tower mills exemplified integration into fortified landscapes amid ongoing conflicts and border insecurities, blending utilitarian milling with defensive architecture. Iberian examples, such as the cluster at Consuegra in Castilla-La Mancha, featured cylindrical stone towers positioned adjacent to medieval castles on elevated ridges, offering both grain processing for local sustenance and elevated lookouts for surveillance against invasions. Similar adaptations appeared in French regions like , where mills were constructed near fortified abbeys and coastal defenses to harness winds for milling while contributing to perimeter security. Material choices reflected environmental challenges, with dominating in the flood-vulnerable for its durability and water-repellent properties when properly fired and mortared, allowing towers to endure repeated submersion without structural compromise. In contrast, Mediterranean areas like southern and favored local stone for construction, prized for its and ability to absorb seismic shocks common to tectonically active zones, often reinforced with timber lacing to enhance flexibility during earthquakes.

Decline with Industrialization

The advent of steam engines in the post-1760s era marked a pivotal shift in power sources, as their reliable, fixed output outcompeted the variable nature of for industrial applications like milling. James Watt's improvements to the around enabled widespread adoption in factories and mills, providing consistent energy independent of weather conditions, which windmills could not match. This technological transition accelerated the decline of tower mills across , with steam-powered alternatives proving more efficient for large-scale processing and other tasks. In the , the rise of contributed to a dramatic reduction in usage, with estimates indicating an approximately 80% decline in operating mills by 1900 compared to early 19th-century peaks of 5,000 to 10,000 units. Economic pressures further exacerbated this trend; tower mills incurred significantly higher construction costs—often twice or more than those of simpler post mills—due to their or stone structures, alongside ongoing maintenance demands that became unsustainable against centralized factories. These factors rendered tower mills economically unviable in an industrializing landscape favoring scalable, coal-fired operations. Key events in the , including widespread enclosures and land reforms across , hastened the replacement of tower mills by consolidating fragmented common lands into larger private holdings optimized for mechanized . In Britain, parliamentary enclosure acts from the 1760s to 1820s privatized over 20% of , disrupting traditional milling sites and favoring steam-equipped estates that integrated processing directly into farming operations. Similar reforms in , such as Prussian land consolidations, accelerated the shift away from dispersed wind-powered . Commercial use of tower mills persisted longest in the , where hybrid wind-steam systems delayed full replacement, but the last operational mills for industrial purposes ceased around 1920 as took hold. Today, thousands of traditional windmills are preserved across , with hundreds still operational, primarily as heritage sites rather than productive assets, reflecting their obsolescence in modern energy systems.

Design and Construction

Tower Structure

The tower structure of a tower mill forms a fixed, vertical base that supports the rotating cap and provides housing for the internal machinery, distinguishing it from earlier post mills where the entire body pivoted. Typically, these towers range from 6 to 25 meters in height, with larger examples reaching over 30 meters in total structure height. The base is cylindrical or slightly octagonal, measuring 5 to 12 meters in diameter at the ground level, tapering upward to reduce wind loads and enhance stability. Walls are constructed 0.5 to 1 meter thick at the base, gradually thinning toward the top to optimize structural integrity while minimizing material use. Larger examples, such as an 1812 East Anglian mill with a 37-meter height and 12-meter base diameter, demonstrate scalability for increased power. For instance, Thelnetham Windmill in , , exemplifies this design with a tower 9.5 meters tall, a base diameter of 6.1 meters tapering to 3.7 meters at the top, and walls 0.6 meters thick. Materials for tower construction were selected for durability and local availability, with stone prevalent in coastal regions of England for its resistance to harsh weather and erosion. Local stone, such as limestone varieties quarried in southeast England, was used in such areas to ensure longevity against saline winds and storms. In contrast, fired clay bricks dominated in the Netherlands due to the abundance of suitable clay deposits, offering a cost-effective alternative that was easier to produce in large quantities for the flat, flood-prone landscapes. These brick or stone towers could endure for centuries, with well-maintained examples lasting up to 500 years or more, far outpacing wooden alternatives. Engineering features emphasize wind resistance and practical access, including a tapered profile that narrows the to lessen aerodynamic drag, often with an octagonal base in some designs for better load distribution. Entry occurs via a sturdy door at the base, accompanied by an internal or leading to multiple floors for staging machinery and storage, such as the for loading and upper levels for bins. While stone and remained dominant for their permanence, rare variations included wooden towers in forested inland regions, where timber was more accessible, though these were less common due to shorter lifespan and vulnerability to rot.

Cap and Sail Assembly

The cap of a tower mill consists of a conical wooden hood, typically measuring 4 to 6 meters in , designed to enclose and support the horizontal windshaft while enabling full rotation to face . Constructed from timber ribs, tie beams, and bracing for structural integrity, the cap rests atop the tower on a circular track fitted with wooden or metal rollers for smooth pivoting movement. This assembly allows the entire upper section to turn 360 degrees independently of the fixed stone or tower below, which serves as a stable base. Prior to the , rotation was achieved manually by millers using a long tailpole attached to the rear of the cap, often winched by chains to adjust orientation. Attached to the forward-protruding end of the windshaft through an opening in the cap's front are the sails, the primary wind-capturing elements. Traditional common sails feature a four-bladed framework of wooden spars covered in , with spans ranging from 20 to 30 meters to maximize power in moderate winds; these primitive designs required manual adjustment of the canvas for optimal performance and storm protection. In 1772, Scottish engineer Andrew Meikle introduced spring sails, an advancement using hinged wooden shutters along the framework that automatically feather—opening or closing like venetian blinds—to regulate speed and reduce storm damage without stopping the mill. These sails, secured to 9 to 10-meter-long pitch-pine stocks via U-bolts and wedges, marked a significant improvement in efficiency and were widely adopted on later tower mills. A key innovation in cap orientation came in 1745 with the invention of the fantail by English Edmund Lee, who patented a small auxiliary mounted at the cap's rear at right angles to the main sails. Comprising six to eight blades on a vertical shaft, the fantail captures crosswinds to drive internal gearing linked to the curb track's rack, automatically rotating the cap and sails into the wind and eliminating the need for constant manual intervention. This labor-saving device, first implemented on English tower mills near , revolutionized operation by ensuring consistent alignment and boosting productivity in variable conditions.

Internal Machinery

The internal machinery of a tower mill primarily consists of a series of wooden and iron components designed to transfer rotational power from the windshaft to the millstones for grinding . The windshaft, a robust horizontal beam typically made of in traditional designs or in later examples, extends from the cap assembly into the tower and supports the sails at one end while connecting to the primary gearing at the other. Representative examples feature windshafts composed of four wooden beams, each approximately 12 inches (0.3 meters) in diameter, bound together for strength. Central to the power transfer is the gearing system, which steps down the high-speed, low-torque input from the sails to a suitable speed for the millstones. Mounted on the inner end of the windshaft is the great wheel, a large horizontal gear that can reach up to 13 feet (4 meters) in diameter in powerful mills, meshing with the wallower—a at the top of the central upright shaft. This upright shaft, often a wooden or iron pole running vertically through the tower's floors, conveys the motion downward to the great wheel at the stone floor level, which in turn drives one or more stone nuts connected to the millstones via quants (levers). The system typically includes 100 or more cogs on the wheels for precise engagement, with the wallower converting the horizontal rotation to vertical. For control, the brake wheel—a wooden cogged gear enclosing the windshaft—allows operators to regulate speed or halt the mill by applying friction to its rim via wooden or iron shoes. This wheel, often (3 meters) in and fitted with an iron rim for enhanced durability against wear from the brake, directly drives the wallower and exemplifies the blend of wood for flexibility and iron for longevity in 19th-century designs. The milling equipment focuses on pairs of millstones housed in wooden tuns (bins) on the stone floor, where the power culminates in grinding. Each pair consists of a stationary bedstone and a rotating runner stone, typically 4 to 5 feet (1.2 to 1.5 meters) in diameter, made from quartz-based French burr stone for fine wheat flour or Derbyshire peak stone for coarser grinds. A single pair could process up to several tons of grain per day under optimal wind conditions, depending on the mill's scale and stone configuration.

Operation

Wind Capture and Direction

Tower mill sails function as airfoils, with flowing over their surfaces to generate lift perpendicular to the and drag parallel to it, both contributing to on the horizontal windshaft that drives the mill's machinery. This aerodynamic interaction is most effective at wind speeds of 5-10 m/s, where the sails achieve optimal rotational efficiency without stalling or excessive stress. Primitive sails, consisting of simple stretched over wooden frames, relied primarily on drag for power but were less stable in gusts, while common sails—featuring open lattice frameworks—balanced lift and drag better, allowing adjustable cloth inserts for low winds and inherent braking in high gusts. To harness varying wind directions, the rotatable of a tower mill is manually adjusted using a tailpole extending from the cap down the rear of the tower, connected to a ground-level that pulls along a or track for precise 360-degree . This alignment positions the sails perpendicular to the prevailing , a process repeated as needed when wind direction changes to maintain performance. The tailpole system, common in early designs, required the miller to monitor wind shifts closely and physically intervene, limiting operation during rapid changes or unattended periods. An important advancement was the introduction of the fantail in 1745 by English engineer Edmund Lee, an auxiliary set of vanes mounted at right angles to the main sails on the cap's rear. When wind direction shifts, the fantail rotates independently, engaging gears and a to automatically yaw the entire cap into alignment within seconds, significantly reducing manual labor and downtime. This mechanism ensured consistent wind capture, transmitting steady torque to the internal machinery for reliable operation. Misalignment, or yaw error, substantially impacts due to reduced effective exposure on the sails. Common sails mitigate this better than primitive types by maintaining structural integrity and adjustable airflow in fluctuating winds, though both underscore the need for precise orientation to maximize transfer.

Power Generation Mechanics

The power generated by a tower mill arises from the conversion of kinetic energy in the wind to mechanical rotational energy via the sails, which drive the windshaft. The theoretical power available from the wind is described by the equation P=12ρAv3CpP = \frac{1}{2} \rho A v^3 C_p where PP is the power output, ρ\rho is the air density (typically 1.225 kg/m³ at sea level), AA is the swept area of the sails (up to approximately 600 m² for large historical examples), vv is the wind speed, and CpC_p is the power coefficient representing the efficiency of energy extraction (0.2–0.4 for traditional tower mill sails). At optimal conditions with full sails, tower mills typically produced 14.7–22.1 kW (20–30 horsepower), sufficient to grind approximately 0.5 tons of per hour depending on strength and grain type. This is transmitted from the horizontal windshaft, turning at low speeds (typically 10–20 RPM), through a series of wooden or iron gears including the brake wheel, wallower, and great spur wheel, achieving a reduction ratio of 1:20 to 1:50 to drive the vertical millstones at 100–150 RPM for effective grinding. Tower mills faced inherent limitations in power generation; in winds exceeding 20 m/s, operators reefed or partially furled the sails to induce aerodynamic and avoid structural damage or excessive speed. Speed was further regulated using on the brake wheel or, in later designs, centrifugal governors to prevent overloading the machinery. Overall rarely approached the theoretical Betz limit of 59%, constrained by the fixed-pitch sails and mechanical losses in the gearing system.

Maintenance Practices

Tower mills required consistent maintenance to ensure reliable operation amid constant exposure to wind, weather, and mechanical stress. Daily tasks focused on and basic inspections to prevent immediate failures in the . Bearings and cogs were greased regularly, often using animal fats such as , which provided effective for wooden and early metal components in historical machinery. Sail cloth was checked for tears or wear, as damage could reduce capture efficiency and lead to structural failure if unaddressed. The fantail, responsible for aligning the to the , was inspected and adjusted to maintain proper orientation, preventing uneven stress on the sails and . Annual overhauls addressed longer-term , particularly in the internal machinery, which experienced the most and degradation. Wooden cogs, typically made from applewood or similar hardwoods, were replaced every 10-20 years due to gradual from grinding and wind-driven , allowing for straightforward repairs without full disassembly. towers underwent to combat mortar from and , restoring weather resistance and structural integrity to prevent water ingress. These overhauls extended the mill's lifespan, with protective coatings applied to wooden elements to mitigate further deterioration. Common issues arose from environmental factors and material limitations. Rot frequently affected shafts, exacerbated by humidity that penetrated despite ventilation efforts, leading to weakening and potential breakage in the windshaft or great spur wheel. After Industrial Revolution modifications introduced iron components, corrosion became prevalent in gears and fittings, accelerated by moisture and salt in coastal areas, requiring removal and re-greasing to avoid seizing. Operation typically involved 1-2 per tower mill, handling daily duties and basic repairs, supplemented by specialized or millwrights for and work. costs historically accounted for 5-10% of the mill's annual output in or , reflecting labor and expenses in a pre-industrial .

Applications

Grain and Food Processing

Tower mills primarily served as grain mills, processing cereals such as wheat and barley into flour and meal essential for bread and other foodstuffs in pre-industrial Europe. The milling process began with cleaned grain being fed into a hopper positioned above the millstones, where it trickled steadily into the central eye of the upper runner stone. As the wind-driven sails rotated the horizontal shaft and gears, the runner stone turned against the stationary bed stone, grinding the grain through shear and compression into a fine powder or coarser meal depending on the stone gap adjustment. This mechanical action, powered by the tower mill's cap and sail assembly, efficiently converted wind energy into the rotational force needed for grinding, producing outputs suitable for human consumption. In the , advancements in stone dressing and bolting techniques allowed tower mills to produce whiter alongside traditional wholemeal, though they continued to rely on burr stones rather than emerging roller systems. A typical tower mill could process approximately 2 tons of per week under favorable , yielding fine for or coarse meal for , with production varying based on consistency and mill size. The ground product was then elevated for further processing, where bolting cloths sifted out impurities to refine the . Byproducts from the milling process included , separated via bolting reels covered in fine or cloth, which removed the outer husks from the . This was commonly used as , with fine portions fed to pigs and , while coarser was mixed into mashes for and , providing a valuable secondary resource for rural . The economic significance of tower mills was profound, as they supplied the majority of in rural before 1800, often operating as communal hubs where collected tolls equivalent to approximately a one-tenth share of the or as payment for services. This system not only sustained mill operations but also underscored the mills' central role in security and agrarian economies.

Industrial and Drainage Uses

Tower mills played a pivotal role in non-agricultural industries during the 17th and 18th centuries, particularly in the , where they powered manufacturing processes essential to the economy. Unlike their primary application in grain milling, these mills adapted wind energy through sophisticated internal mechanisms to drive saws, stamps, and pumps, enabling efficient production of timber, , and textiles while facilitating . Over 1,000 windmills were built in the Zaan district between 1600 and 1750 dedicated to such industrial tasks, with several hundred operating simultaneously by the mid-17th century, demonstrating the versatility of tower mill designs with their stationary stone or brick towers and rotating caps. In sawmilling, tower mills revolutionized timber processing, with the first wind-powered patented in 1593 by Cornelis Corneliszoon van Uitgeest near . This innovation employed a with three bends at 120-degree angles to convert the rotary motion of the sails into reciprocating action for up to two saw frames, dramatically reducing the time to cut 60 beams from 120 man-days to just 4-5 days. These mills, often built as paltrok or ground-sailing variants of tower mills, produced planks vital for Dutch shipbuilding, supporting the maritime empire; by 1731, approximately 450 such operated across the , with 256 concentrated in the Zaan region. Tower mills also powered paper production and textile processing, using modified gear systems to operate stamps or edge runners for pounding rags into pulp or fulling cloth. The earliest wind-powered , "De Gans," began operations in 1605 in the Zaan district, followed by 40 such mills by 1740, which processed rags via heavy rotating stones driven by the mill's brake wheel and pinion gears, yielding whiter and faster-produced compared to manual methods. For textiles, similar crank mechanisms replaced grinding stones to full en cloth or prepare and fibers, softening materials through repetitive pounding; these adaptations allowed mills to handle varied loads without altering the core wind-capture assembly. Drainage applications harnessed tower mills to reclaim low-lying land, employing screws or scoop wheels connected via multiple gear trains to lift water from polders into higher channels. In the , where much of the terrain lies below , these mills drove screws—helical devices invented by the but refined here—to pump up to 60,000 liters per minute, as exemplified by 19th-century reconstructions of 17th-century designs like those in the Oostpolder near . Between 1564 and 1632, hundreds of such mills drained approximately 27,000 hectares of lakes and wetlands, contributing to the reclamation of about 20% of Dutch land by 1800 through systematic dike and canal integration. Power adaptations in tower mills featured complex gear trains, including brake wheels, wallowers, and spur wheels made of with inserted hardwood teeth, enabling multifunctionality for diverse loads. By 1700, up to 50% of Dutch mills incorporated multiple gear sets to switch between tasks like sawing, pumping, or stamping via adjustable couplings, boosting overall to around 50% with the introduction of cast-iron components in the mid-18th century. This flexibility underscored the tower mill's role as a pre-industrial powerhouse, often outpacing watermills in windy, water-scarce regions.

Specialized Adaptations

Tower mills underwent various specialized adaptations to meet unique regional needs, particularly in defensive, hydraulic, and industrial contexts during the . In 16th- and 17th-century , particularly in , some tower mills were fortified with defensive features to serve dual purposes as wind-powered structures and protective outposts amid ongoing border conflicts and pirate threats. For instance, the Tower Windmill in Llançà, authorized for construction in 1643, functioned not only for grinding grain but also as a defense tower positioned outside the town's walled , exemplifying how mills were integrated into broader strategies to monitor and deter invasions. These designs often featured robust stone towers that could withstand sieges, though specific gun ports were less commonly documented in surviving examples. Pumping variants of tower mills emerged in to address drainage challenges in low-lying, tidal-influenced areas, combining with tidal flows for enhanced efficiency in regions. In the 18th and 19th centuries, tower mills in the Norfolk Broads and Fenlands were adapted with Archimedes' screws or scoop wheels to pump water from reclaimed marshes near tidal estuaries, preventing flooding while leveraging periodic tidal assistance to refill reservoirs. This hybrid approach allowed mills to operate semi-autonomously, with wind providing primary lift during ebb tides and tidal ponding aiding during high water, as seen in historical drainage systems engineered by Dutch-influenced reclamation efforts. Experimental sail designs in 19th-century Dutch tower mills focused on increasing rotational speed and efficiency for demanding tasks like oilseed pressing, moving beyond traditional common sails to more aerodynamic configurations. The introduction of patent sails around 1807, featuring adjustable shutters that automatically feathered to optimize torque in varying winds, enabled higher operational speeds—up to 20-30 —ideal for the heavy loads of crushing linseeds or rapeseeds in oil mills. These innovations, refined by Dutch millwrights, were fitted to tower mills in industrial regions like the Zaanstreek, where they boosted productivity for non-grain processing without requiring full sail adjustments. Rare hybrid adaptations appeared in 18th-century Dutch colonial trade networks, where tower mills were modified for grinding imported cocoa beans from outposts like Surinam, adapting traditional grain stones to handle the beans' oily texture. By the early 1700s, the first dedicated cocoa-processing opened in the Zaanstreek region, roasting and grinding beans into paste using wind-driven edge runners, a process scaled up to around 27 such mills by the early to meet European demand for precursors. This specialization required reinforced machinery to manage the beans' moisture and fats, marking a shift from agrarian to proto-industrial applications in colonial supply chains.

Notable Examples and Legacy

Iconic Historical Mills

One of the most iconic surviving tower mills is the Chesterton Windmill in , , constructed in 1632 and recognized as the earliest tower mill in Britain with intact working machinery. The mill features a cylindrical stone tower built from local with accents and an arched base, topped by four common sails spanning 60 feet that rotate counter-clockwise when covered with canvas. It served primarily for grinding corn until operations ceased around 1910, after which it underwent major restoration from 1969 to 1971, including reconstruction of the cap and sails, earning a Civic Trust Heritage Award in 1975. In 2025, new sails were installed as part of ongoing restoration efforts. In the , De Noord in stands as a prime example of Dutch engineering prowess, built in 1803 on the site of earlier mills dating back to the and reaching a height of 33.3 meters, making it the tallest traditional tower mill in the world. The structure, originally a stone tower, was equipped with four sails and used for grinding grain to supply local distilleries until 1916, after which it shifted to processing cattle fodder and wheatmeal before wind operations ended in the 1930s. Restored in 1962 and again in the 1970s with volunteer efforts, it exemplifies the role of tower mills in supporting the industry. The Heckington Windmill in , , built in the 1830s, is renowned for its unique eight-sail configuration, the only such operational tower mill remaining in the . Initially constructed with five sails in 1830 by local millwrights, it suffered storm damage in 1890 and was rebuilt with eight sails—each 34 feet long with 24 shutters—along with a fantail for automatic orientation, using components from a dismantled nearby mill. Now a Grade I listed structure and operational museum managed by volunteers under , it demonstrates advanced 19th-century adaptations in sail design and power transmission for grain milling.

Preservation Efforts

Preservation efforts for tower mills in the 20th and 21st centuries have focused on restoring these structures as vital elements of , emphasizing technical conservation and community involvement. In the , the Society for the Protection of Ancient Buildings (SPAB), founded in 1877, has played a central role through its Mills Section, which serves as the national organization dedicated to protecting and promoting traditional windmills, including tower mills, via advice, surveys, and advocacy for authentic repairs. Similarly, in the , De Hollandsche Molen, established in 1923, provides expert guidance on the restoration, maintenance, and preservation of windmills, helping to safeguard over 1,200 surviving examples nationwide, many of which are tower mills adapted for drainage and milling. Restoration techniques have evolved to blend traditional craftsmanship with modern materials and to ensure without compromising historical . For instance, composites are sometimes used for to replace deteriorated wooden elements, offering enhanced against while maintaining aerodynamic . Digital monitoring systems, such as IoT-based platforms like smartmolen.com, enable real-time assessment of structural components, including windshaft stress, to prevent failures and guide proactive maintenance in heritage windmills. Globally, these initiatives gained international prominence with UNESCO's 1997 designation of the complex in the as a , recognizing the ensemble of 19 tower and other mills as exemplars of 18th-century water management engineering. Across , collaborative efforts have restored hundreds of tower mills, supported by volunteer training programs that build skills in milling and conservation; notable examples include the Gilde van Vrijwillige Molenaars in the , which trains volunteers to operate and maintain mills, and broader UNESCO-backed capacity-building for the intangible craft of mill operation. Iconic historical mills, such as those at , have been primary targets for these programs to ensure operational demonstration alongside preservation. Challenges persist, particularly in securing funding and addressing environmental threats. Post-2000, grants through programs like the European Heritage Hub's Small Grants Scheme have supported projects for heritage restoration in neighboring countries, though broader EU cultural funds often prioritize larger over individual mills. exacerbates risks for coastal tower mills, with rising sea levels threatening low-lying sites in the , where increased flooding and erosion could undermine foundations despite adaptive measures like reinforced dikes.

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