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Balmain Shipyard Graving Dock Caisson Replacement

Client: Transdev/Waterway Constructions
Location: Balmain, NSW
Date: 2019

The Balmain shipyard graving dock has been in operation since 1975 and is the backbone of the maintenance of the Sydney Ferries Fleet now operated by Transdev and called Transdev Sydney Ferries. The 30 tonne caisson has a unique and innovative design in that it is hinged to concrete plinths set into bedrock on the seabed and is operated entirely by dewatering a ballast tank with compressed air. Once flooded the caisson sits into a pit excavated into bedrock on the seabed. Having provided underwater servicing to this asset for 35 years as well as providing diving support for the 2 previous removal, refurbishment and reinstalment the company was requested to provide diving support for the design and installation of the new caisson. This included the removal of the old caisson and the installation of new stainless steel hinge studs 600mm into the concrete plinths. These were successfully installed having to core drill over the existing studs and plates . The new caisson was successfully installed and is fully operational allowing the vital dry docking facility to continue maintaining the ferry fleet.