The lifting skills of Johnson Crane Hire were put to the test on a challenging heavy lift contract for a large marine diamond miner.
As part of routine quarterly maintenance, dredging vessels are brought into Cape Town harbour where the necessary servicing and repair work is undertaken in the dry dock. In this particular instance, Johnson Crane Hire was called upon to remove three large components from the vessel, being the vessel’s 52 t gimbal head, the 42t derrick and the 20t crown.
Removal of these large components facilitated important repairs to both these critical items and the dredging vessel while it was in the dry dock. A set number of days had been allocated to the maintenance programme and this meant that all contractors needed to adhere to the work schedule.
Close interface between the crane specialist and the mining house’s own maintenance teams was critical. The mining house had allocated exactly 35 days to the maintenance programme and Johnson Crane Hire had to ensure that we were able to make their lifting deadlines.
Among the challenges that Johnson Crane Hire had to contend with on this specialised lift was the high wind speeds that occur in the area, which at times can reach 108 km per hour. This caused lifting operations to be stopped during these periods. Conditions were monitored and close communication between the operator and the team on the ground was essential as the lifts could only be done when the wind was below 38 km per hour.
Another complexity was the extremely congested working environment on the quay side, where there was just enough space in the laydown area to place equipment and lower the boom and luffing section of the crane.
Johnson Crane Hire made use of its 750 t mobile crane to undertake all three lifts. The crane was equipped with 204 t of counterweight and a 31.5m luffing jib. The first component to be lifted was the gimbal head as this was on the critical path of the project.
The gimbal is a pivoted support that allows the rotation of equipment on a single axis and more importantly keep them upright with respect to the horizon despite the rolling or pitching of the vessel when at sea.
The gimbal with its 35 metre 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.
The crane’s sophisticated guide system aided the seasoned Johnson Crane Hire operator to accurately control the deflections on the boom during all the lifts. This was particularly important during the lifting of the gimbal head.