Removal and heavy lift of container ship's damaged onboard crane
It’s not every day that you see those big lifts coming off ships. A container ship suffered damage to one of its onboard cranes while unloading cargo at the Port of Auckland. Diverse Engineering was commissioned to lift off both the jib and the turret, each weighing approximately 32 tons. Two 250-ton cranes were used to carry out the lifts. Once removed from the ship, the two parts were trucked to Diverse’s Auckland premises.
From there, they were transported to Tauranga where laser level equipment was used to determine whether the bearing surface was flat, which it was not. The slew ring was removed in Tauranga and mounted on the front of the superstructure before laser alignment could be completed. A .5mm tolerance was permitted for the slew bearing, but laser checking showed that this was not met.
The ship was around 15 years old and port technology has advanced considerably in that time. The shipboard crane had not been used for several years and had only been pressed into service on that occasion because of delays in the Ports of Auckland due to CoVid restrictions. Eventually the ship had to return to Singapore, so Diverse positioned the two parts of the damaged crane horizontally on deck for the passage. In the course of normal operations the ship uses only port cranes, which are faster and more time efficient.
Many ships carry two cranes, though they take up a lot of space because of the swing arc. Two onboard cranes can be operated simultaneously, but up to five port cranes can be used alongside at any one time, allowing for far more movements. With two onboard cranes, 30 containers per hour can be moved, whereas with four port cranes working on a ship that number increases to 160 containers an hour.
Most ships visiting NZ exchange around 1500 containers, which can easily be accomplished in a 12-hour shift using port cranes. This is essential when ships are in port for a maximum of 12 hours between high tides. However, the smaller ports throughout the Pacific Islands don’t have their own cranes, so ships on those runs will use port cranes in New Zealand and then unload in island ports using their onboard lifting equipment.
Diverse’s Auckland operation undertakes a significant amount of crane maintenance work on ships employed on the island runs. This includes changing sheaves, routine wire exchanges and greasing and general repair. Entire removal of shipboard cranes is unusual, however.