Cape Town’s breakwater recently received some much-needed attention through a maintenance project undertake by Guerrini Marine Construction (GMC).
Lifting solutions leader Johnson Crane Hire was called on to assist GMC on the project which took place on the ‘spur’ section at the southern end of the breakwater between March and November 2017.
The project involved lifting and placing 155 concrete dolosse – each weighing 25 tonnes at the breakwater. The main breakwater – the central section of the breakwater – spans a distance of 500 meters and is protected on the seaward side by dolosse. The whole breakwater structure is crucial for the safe entry of vessels into the port, as well as for berthing and operations in the port.
Rising to the occasion
“One of the most challenging aspects of the project at the spur was to create a two-meter trench underwater in the bedrock so that the first line – or toe – of dolosse would not move on the seabed,” says GMC chief executive officer Adrian Guerrini. “We used a piling crane to chisel through the rock, and our tug dredged the broken material away. These activities were highly dependent on good weather, so the variable weather conditions – including the storms of June 2017 – made it difficult to work to schedule.”
Guerrini says the choice of crane was perfect for the application, especially as certain days required the crane to cover substantial ground. It would have to move about 10 meters while carrying a 25 ton dolos and 10 meters back to a pick-up point for the next unit.
“The crane was also able to manage the placing of the dolosse at the maximum distance of 38 meters to the underwater trench,” he says. “The mobility and productivity of the crane was a key factor in completing the project on time. We were able to move one dolos from the deck and into place in just one hour.”
According to Cornelis Grotius, general manager of Johnson Crane Hire Heavy Lift Division, the company’s 400-ton crawler crane was the ideal machine to undertake the lifting duties on this contract because of its mobility and strength, enabling it to move swiftly between installation positions as the project progressed.
“This type of project requires the lifting equipment to move efficiently from one position to another, so called for a higher level of mobility than can be offered by a mobile hydraulic machine,” says Grotius. “We chose the Kobelco CKE4000 from our fleet as it packs the necessary lifting capacity, and also offered the required reach.”