The cableway

Gondels closed the remaining 900m gab after which the brouwersdam was finished.
Video: Brouwenshavense Gat closed
The southern canal, which runs from ‘Middelplaat’ to Schouwen-Duiveland was closed by a cableway. Research was carried out to determine which sort of cableway was most appropriate for this job. The cableway had to meet certain demands. The cableway had to be able to transport so much stone, that the closure would not last longer than nine or ten weeks. A potential extension to twelve or fifteen weeks was possible if needed. The dam had to be finished before the autumnal storms could start. In total, 600,000 tonnes of stone (note: one ton is a thousand kilograms) had to be plunged in the southern canal. Giving a twelve-hour working day, the cradles had to be able to plunge an average of 700 tonnes of stone per hour. One knew by the experience of the Grevelingen dam, that any delay could arise, especially at the beginning of the process. Thus in practice, a cableway needed a capacity of 1200 tonnes per hour, otherwise the time schedule would not be reached.

Cabins 14 (unloaded) and 15 (loaded) are passing each other
Passing cabins
Three kinds of cableway were considered: a circuit way, a return cableway and a cable crane. 
1. A circuit way is a long cable under which unmanned cabins are hung at fixed points. The cable turns around, driven by an engine. The cabins are fixed to the cable and turn automatically. At a filling station, the cabins could be taken from the cable temporarily to load them. However, the capacity of such a circuit way is no more than 400 to 500 tonnes per hour - only 5 tonnes of material could be transported at a time. Given the large pieces of concrete that needed to be transported, this capacity was found too small. A third disadvantage was the plunging height of the circuit way: the height of the cabins in relation to the water could not be changed. It was feared that stones plunged from such a great height would damage the dam.
2. A return cableway had been used before during the construction of the Grevelingen dam. With a return cableway, the cable is fixed to both sides of the closing gap. With a
Cabin 8 discharges first blocks of concrete during eduction of cabineers
Discharging blocks
circuit way, the cable moves, whereas with a return cableway, the cabins move. With a circuit way, there is a central engine which drives the cable; whereas with a return cableway each cabin has its own drive engine and its own driver. You can read more about this system at the page of the Grevelingen dam.
3. The cable crane is in fact not a cableway. With this method, a crab is pulled over a cable. A crab is a wagon which drives over a trail, provided with a hook to transport weights. The crab could only drive up and down between two high towers on the shore. The big advantage of the cable crane is the variable plunging height. However, this did not weigh against the restricted capacity and the high construction costs.

New cradles

The return cableway was chosen, primarily because of the experience gained

Cable installation with cabin
from the Grevelingen dam. On the sandbar Middelplaat and on the shore at Schouwen-Duiveland, a filling station and a filling blade were built. In the middle of the canal, pylons of reinforced concrete were placed to support the cable. The total length of the cableway and the filling stations was almost 1.8 kilometres! The difference with the cableway of the Grevelingen dam was the weight and the capacity of the cradles. The cabins of the Grevelingen dam had a capacity of ten tonnes, while they weighed twice as much themselves. The new cradles weighed fifteen tonnes and could carry fifteen tonnes of material. One also wanted to use other plunging material for the Brouwers dam. Large, self-made concrete blocks were used, which were hung under the cabin by means of buckets. The blocks of concrete each weighed 2.5 tonnes. Thus, six blocks of concrete could be carried each time. In total, more than 240,000 blocks of concrete were plunged into the closing gap. However, the dam was still not completely closed. Between the blocks of concrete, water could still flow. Filling the dam with sand soon put an end to this.