In the old historic mills, the cap (top of the mill) could rotate relative to the hull with the lofts (the superstructure). This turning of the cap is called cruising and the system in these old mills we call the kruiwerk. There used to be two systems for this: sliding or rolling.

GLIDING

When sliding, the cap slid over the so-called neutes that were covered with metal. This ‘neuten crosswork’ is fairly sensitive to wear and the resistance was also considerable.

Picture of the neutencrosswork.

ROLLERS

A second system works with rollers, made of wood or metal, depending on the design. This ‘English crawling’ causes less resistance than sliding and is more maintenance friendly.

Picture of the English jug work.

Photo of the English jug work.

THEN – INFINITE ROTATION

The hood has no further fixed connection to the attics and hull; only a rotating shaft (king’s spindle) runs through it. Therefore, in theory, the canopy can rotate infinitely without anything getting tangled.

NOW – LIMITED ROTATION…

In the modern wind turbine, the nacelle (top of the mill) can also rotate relative to the tower. This is also called creeping, and depending on the brand of wind turbine this is done via gearboxes or hydraulically with oil pressure. The two parts slide over each other on the crawling plate. This may be lined with friction-reducing plastic and is lubricated with grease or oil.

…WITH A POSITION SENSOR

The nacelle can rotate up to three times without problems. One limitation is the cables through the turbine. There is a chance that these get twisted too much and break. A position sensor measures the position of the nacelle and also knows its position in relation to the 0-point. That is the point at which the nacelle has completed 0 rotations on its axis. Preferably with little wind and low production, the computer lets the nacelle crawl back to the 0-point, so that the wind turbine can continue to turn after this pause position.

Photo of a creeping nacelle.