Biggest Dry Dock Doubles Productivity

A new R98 million floating caisson is to be fabricated for the Sturrock Dry Dock operated by Transnet National Ports Authority (TNPA) in the Port of Cape Town which will enable one of the biggest dry dock facilities in the Southern Hemisphere to double its productivity.

The new caisson forms part of a multimillionrand overhaul taking place at the port’s ship repair facilities under South Africa’s Operation Phakisa programme, through which ship building and ship repair have been identified as a strategic competence for the port.

Subdividing the dock
The caisson is a large steel gate structure that acts as a secondary seal and subdivides the dock, allowing for the simultaneous docking of multiple commercial vessels within the facility. The old,
defective caisson had been out of commission since December 2016. The 74-year old dry dock was first commissioned in 1945 to repair American and
British war vessels.

Refurbishment of the old caisson cost TNPA R2.7 million and covered a condition assessment and finite element analysis, as well as stabilisation of the old caisson prior to the new one being introduced.

Phase 1, completed by Southey Co between July and August 2018, entailed the installation of special greenheart timber to seal water leaks around the old caisson. Phase 2 was completed in November 2018 and entailed the replacement of shut off doors and three sinking tank valves, as well as the addition of ballast weights to make up for lost weight due to corrosion and blanking off valves that would not be used going forward.

During the initial commissioning of the new caisson, there were challenges as the floating caisson was not sinking sufficiently at high tide. This compelled the naval architect to go back to the drawing board.

There were also minor leaks between the floating caisson steel structure and the sealing timber due to uneven steel structure surfaces. This was resolved by inserting a special sealant that is compatible with sea water.

Other work
Civil infrastructure at the Sturrock dock has also received attention including concrete repairs and replacement of corroded tunnel piping.
Twenty-nine capstans or rotating machines that assist in pulling the vessels into position inside the dock are being replaced in Cape Town at various
locations which include the Sturrock Dry Dock, the Robinson Dry Dock and the Synchrolift. In line with Operation Phakisa’s intention to fast track delivery while being respectful of governance, TNPA took a decision to execute the replacement of capstans at its dry docks as a national project for the benefit of standardising the ship repair equipment and achieving economies of scale by procuring these capstans in large numbers.

Under Operation Phakisa, the port’s Robinson Dry Dock is also undergoing a major upgrade. While this Dry Dock’s floating caisson (main gate) was
recently refurbished, it is the ultimate intention to replace this structure with a modern, fit-for-purpose caisson structure. The design process will be undertaken in the near future including replacement of the floating caisson that seals off the dry dock from the basin.

Port of Cape Town
Kevin Cavernelis