Bart Schultz
Five types of windmills for the discharge from polders can be distinguished: hollow post mill, top porter, wind motor, tailed mill and tjasker.
For the first application of windmills for the discharge from polders, different authors give different dates and examples. For example, J.P.A. Stroop mentions that windmills for the discharge from polders already existed in Holland in 1282. G. Husslage writes that the first windmill for the discharge from a polder was built around 1326 in Oterleek in the Province of North Holland, and that this will undoubtedly have been a hollow post mill. Many authors mention as the first example of application that in 1408 two councillors from the Principal Water Authority of Delfland travelled to Alkmaar to see the windmill of Floris van Alkemade and Jan Grietenzn. that had thrown out water.
In windmills for the discharge from polders, the mill body could initially not be placed directly on the stand so that it could rotate, because the lifting device, which was then a paddle wheel, could not be driven. Hollow post mills were derived from the standard mills by replacing the stand with a tube through which the mill axle runs. In this way the upper part of the mill could freely rotate. The hollow post mill was therefore the first larger windmill type that was suitable for the discharge from polders.
A major improvement of the hollow post mill was the top-sail mill. With this type of windmill, only the cap, which houses the mill shaft with the sails, needs to be turned. There are also various versions of the first application of the top-sail mill in the discharge from polders. The most reliable reference is probably from Dirk Burger of Schoorel, who reported that the introduction took place in 1573. The well-known Jan Adriaansz. Leeghwater perfected this type of windmill and made it particularly useful for the discharge from polders.
The wooden top-sailers were originally built as so-called inner-sailers, where the winding gear is located in the cap of the windmill, to adjust the cap and the sail cross to the wind direction. In the Province of North Holland, most windmills for the discharge from polders were designed as inner-sailers. In other provinces, the windmills for the discharge from polders were later often designed with a so-called tail gear. In this case, the winding takes place outside on the ground floor. The first large windmills for the discharge from polder - octagonal inner-sailers - were probably built around 1565 for the discharge from the Egmondermeer and the Bergermeer polders. From the start, these windmills had to bridge a for that time relatively high lifting height of over 1 metre.
Simon Stevin invented placing multiple windmills with paddle wheels in a series, in order to make the discharge from deeper polders possible. Each windmill could pump up the water to a maximum of 1.5 metres. Such a setup is called a series of windmills, and has been characteristic of many projects for draining of lakes for many years, because these are precisely the polders that require deeper drainage.
The first large windmills for the discharge from polders had a span - the distance between the ends of the blades - of over 25 metres. The windmills that were used in the first half of the 17th century for the drainage of the large polders in North Holland - Beemster, Heerhugowaard, Purmer, Schermer and Wormer - were of the same size. By the middle of the 17th century, a span of 26 - 27 metres had already been used here and there, and a century later windmills with a span of 27 - 28 metres were built. Ultimately, the windmills for the discharge from polders never had a span greater than 29 - 30 metres.
A wind motor is a type of windmill that is characterized by a wind wheel, which is made up of many blades. Wind motors have been used since the beginning of the 20th century mainly for areas up to approximately 1,000 hectares, with little variable lifting heights. The wind wheel has a diameter of 3 - 12 metres. They are mainly found in the provinces of Groningen, Friesland and North Holland. The largest lifting height that has been used with wind motors is 2.5 metres. The wind motors already worked at lower wind forces than the old windmills.
The tailed mills are called this way because they direct themselves to the wind by means of a tail or wind board. When the tailed mills were first used is not actually known. A.A. Beekman mentions that they were only used in smaller polders, or dammed parts of larger polders, and at small lifting heights. In practice this is still the case.
For small areas, tjaskers were also used in the northern provinces. These windmills consist of a wooden axle, to which a wooden, cased screw is attached. The wooden axle is provided with a sail cross at the top. The tjasker was possibly invented in 1598. Also tjaskers were applied for discharge from small areas at small lifting heights. There are almost no data available on the distribution.
Over time, many improvements have been made to windmill blades. These have been described in various publications and patents. In addition to the so-called Old Dutch blade type, which has traditionally been used in windmills for the discharge from polders, J.Th. Balk and especially G.J. Pouw described the various improved blade types and their properties.
The windmills could not always be in operation, namely not at too low, and not at too high wind speeds. The range was between wind speeds of 6 and 11 metres per second, which occur approximately 25% of the time. By improving the blades, they could also be operated at lower wind speeds. A number of improved blade types also had a braking effect at high wind speeds, which allowed the range to be increased, even at high wind speeds. H.E. Boer and J.A. Kielman state that windmills with streamlined blades already pumped water at a wind speed of 4-5 metres per second.
For some polders the discharge is still done by windmills, but automatic electric discharge is now predominantly used. However, several windmills are still visible in the landscape and much is being done to preserve them.
