Alte Weser (lighthouse) - Construction

Construction

The “Roter Sand“ lighthouse (German transl. “red sand“) is located in the "Outer-Weser" waterway in the German Bight, southern North Sea. At the end of the 1950s the lighthouse had been badly damaged by corrosion, corrasion, and leaching of its concrete. To replace the old lighthouse, the “Alte Weser” was built in the years 1961-1964 not far from the former location. Simultaneously, the conditions for the ships' traffic in the "Outer-Weser" waterway were intended to be improved and the new lighthouse was planned to be established as an offshore part of the radar chain on the Weser between Bremen and the North Sea (Fig. 1).

The novel form of the tower (Fig. 2), i.e. its downward tapering tower-shaft together with its cantilevered upper storeys was based on a design by engineer Andreas Carstens, Bremerhaven. The conical design of the tower was intended to minimize exposure to waves and drift ice. The German Waterway Administration, the Wasser- und Schifffahrtsamt (WSA) Bremerhaven as the responsible governmental agency, assigned the task of workmanship to a cooperative of companies: Philipp Holzmann, Strabag Bau AG, Hermann Moeller. This cooperative instructed the Howaldtswerke in Kiel to carry out the steelworks.

The steelwork's for the tower-shaft, the upper storeys and the equipment were carried out in a dry dock of the Howaldts-factory in Kiel (Fig. 3). The tower-shaft was towed through the Kiel Canal towards its destination site in the Outer-Weser waterway (Fig. 6). For this purpose a floating offshore-lift platform which had been supplied with a central cut-out for the tower was used. At the site the shaft was lowered and subsequently jetted into the sand to the intended depth. After feeding in a layer of underwater concrete, the shaft was evacuated and the additional layers of ferroconcrete were installed (Fig. 5).

Frequently, adequate supply of building materials was hampered and delayed, because relatively small coasters had been contracted for transport, which were quite sensitive to the state of the sea and weather conditions. Timing was especially important in order to ensure joints were constructed correctly. To this end, all building materials needed for the underwater concrete had to arrive on time and without delay. Therefore, an optimal weather period was required.

A further interruption happened due to two accidents. The first was fatal when a sudden leak killed two workers. However, the exact reason for the accident was never fully revealed. The tower-shaft which had been lowered and jetted into the sand had to be abandoned. The upper storeys were detached and transported back to Kiel on the offshore-lift-platform for later use. One year later the upper storeys were re-used on a second tower-shaft nearby. The old stump of the tower-shaft remains underground today. The storm surge of 1962 which cost many human lives in Hamburg and other places on the German coast had no impact on the construction of the lighthouse. The first accident did however force a new start to the works in Kiel, causing a delay of one year. The second accident happened because of a malfunction of the gripper at the front legs of the offshore-lift-platform. A second platform had to be used in order to repair and replace the first one. In the third year, after the lift-platform had been repaired, the construction works resumed at the tower-shaft and were subsequently completed.

Next, the offshore-lift-platform could pick up the upper storeys which were still stored at Kiel (Fig. 6) to join them with the tower-shaft in the North Sea. Under favourable weather conditions the upper storeys were placed on top of the tower without complications (Fig. 7). Now, the completing works such as installation of the optics including the corresponding blinds and the installation of the standby sets were implemented. The power supply of the lighthouse demanded special attention. A 6 kV cable was run from the “Robbenplate” lighthouse (Fig. 1) towards “Alte Weser”, jetted in using a special device (“Einspuelstiefel”, Fig. 8) and threaded into the tower through a protective cable conduit. In addition, measures had to be taken to adopt the same cable for the planned “Tegeler Plate” lighthouse (see below). The foundation of the building was safeguarded with stone ballast poured down on bush mats against rinsing and water erosion. In 1964 the light of “Alte Weser” lighthouse went into service (Fig. 9). In 1972 the four keepers were displaced when the lighthouse became automated.

• Fig. 1 Radar chain, River Weser

• Fig. 2 "Alte Weser": original technical drawing, 1961

• Fig. 3 Tower-shaft with foundation at the dry-dock of Howaldtswerke in Kiel

• Fig. 4 Tower-shaft on offshore-lift platform passing the Kiel Canal

• Fig. 5 Surface of concrete and flanking concrete reinforcement.

• Fig. 6 Upper storeys loaded onto offshore-lift-platform at Kiel.

• Fig. 7 Upper storeys are lifted onto the tower-shaft from the offshore-lift-platform

• Fig. 8 Jetting boot (Einspuelstiefel)

• Fig. 9 "Alte Weser", original photo, 1964