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Longitudinal bisection of a floating dock


Longitudinal bisection of a floating dock

The 7,500 tdw floating dock at the Schichau Seebeck shipyard in Bremerhaven was built in 1964; due to the gradual closure of shipyards it had not been used for many years. In 1986 the dock was lengthened by 30 metres and widened by 6.6 metres, meaning that it no longer fitted through the Fishing Port lock.

The dock was put up for sale and a buyer was found. The challenge faced by the engineering firm contracted to arrange the handover was to establish the exact cutting procedure for the longitudinal bisection to enable the dock to be moved. Nordseetaucher was contracted to carry out all cutting work above and below water.

Floating dock:

  • Built in: 1964
  • Length: 144 metres
  • Width: 34.8 metres
  • Weight: 7500 tdw
  • Crane: 2x75 mt

The cut along the longitudinal axis was positioned 750 mm to the left of the central girder. The cut also bisected the five central buoyancy tanks, making it necessary to stabilize the two halves of the dock by creating new buoyancy tanks. This was done by welding up all the flood holes in the tanks. The entire project required meticulous planning and all cutting had to be carried out in a specific order.

The working stages:

In each of the five central tanks a 1.0 x 1.3 m hole was cut in the deck to provide a safe entry/exit point; all fresh air/exhaust air pipes and supply lines were fed down these entry points.

The remaining water and mud in the central tanks was pumped out.

The holes in the bracket plates were enlarged with the aid of a cutting template.

Any coating on the areas which were to be cut or welded was removed with a burner and scraper. The exhaust air pipe was held directly above the burn spot to extract the smoke.

The flood holes in the new buoyancy tanks were closed with metal sheets and welded watertight all the way round.

All deck girders, holland profiles and bracket plates were cut with the aid of special templates. As with all other cutting work, it was essential that the work here followed a precisely defined sequence.

The transverse flood pipes were removed along a width of approximately 1.0 metre and the starboard side was sealed by welding covers on.

To absorb the shearing force, holders for the I-beams were welded on to the deck, the beams were inserted and wedged in.

Once the underwater cutting had been completed, we moved up on deck and proceeded to cut through the deck. After the dock was bisected it was towed to the Bremer Vulcan shipyard and welded back together again. Nordseetaucher's project manager on this project was Peter Eymann.