August 30 - Johnson Crane Hire has helped remove three large components from a dredging vessel at drydock in Cape Town harbour, South Africa.

As part of the ship's routine maintenance, Johnson Crane was called upon to remove a 52-tonne gimbal head, 42-tonne derrick and 20-tonne crown from the vessel, which is operated by a marine diamond mining company.

Richard Simmons, heavy lift hydraulic cranes manager at Johnson Crane, explained that careful planning was crucial before undertaking the lifts, as well as close coordination between the crane specialist and the mining company's own maintenance teams.

"The mining house had allocated exactly 35 days to the maintenance programme and we therefore had to ensure that we were able to make their lifting deadlines," he said.

Among the challenges involved in the project was the region's high wind speeds, which were sometimes as high as 108 km/h, meaning that lifting operations had to be stopped. Since the lifts could only be undertaken when the wind was below 38 km/h, Johnson Crane explained that conditions were monitored closely throughout.

In addition, stated the heavy lift operator, the working environment on the quayside was very congested, with just enough space in the laydown area to place the equipment and lower the boom and luffing section of the crane.

To complete the lifts, Johnson Crane employed a 750-tonne capacity mobile crane, equipped with 204 tonnes of counterweight and a 31.5 m luffing jib.

"This gimbal with its 35 m lifting radius was the most complicated component to lift, and required accurate movements to extract it from the vessel in the dry dock and raise it safely out of the ship," Simmons added.