Tjasker

The tjasker (West Frisian: jasker, German: Fluttermühle) is a small type of windmill used solely for drainage purposes. It is distinctive for its simple construction, featuring only a single inclined shaft that carries the sails on one end and an Archimedes' screw on the other, in this way avoiding the need for any gearing. The tjasker is commonly known as a typical Frisian windmill though it is also found in other Dutch provinces and in north Germany.

The tjasker seems to have been developed somewhere towards the end of the 16th century, though there is no conclusive date for its invention. The total number of tjaskers at their peak is also unclear. The mills were used to drain small plots of land but also found their use at peat digging sites as they could be easily moved. Millwright R.W. Dijksma of Giethoorn was well known for his tjasker building. He constructed 400 to 500 tjaskers between 1910 and 1945, though these numbers include hand powered Archimedes' screws. In the first half of the 20th century tjaskers almost completely disappeared as they couldn't compete with the metal windpump which was more practical as it could turn itself to face the wind and didn't require any supervision. The last tjasker was erected in 1935 and by 1963 there were only three left in the Netherlands. In that year emerging views on nature preservation and cultural history resulted in the installation of a brand new tjasker in De Weerribben. Since then, several other new tjaskers have been built, to pump water into wetlands and as cultural monuments. Currently, there are 28 tjaskers in the Netherlands and six tjaskers in Germany.

The tjasker has only one wooden millshaft on which all machinery is carried. This shaft is inclined at an angle of approximately 30° and supported in a wooden frame. On the lower end it carries the Archimedean screw which is partly submerged in water. The screw doesn't rotate in a pipe but has a fixed encasing which simplifies the design further. The top end of the shaft carries the Common sails with a span of approximately 5 to 6 meters. In some cases wooden slats are used instead of sail cloth. The mill can be stopped using a band brake on the brake disk which is fitted on the shaft behind the top bearing.

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Wikipedia