Bulk commodities are usually discharged using grabs attached to a crane. High capacity clamshell grabs offer high unloading rates and high efficiency. The bulk handling cranes can be positioned along the quay (quay crane), on a platform/pontoon (floating crane), or on the ship (deck crane):
- Common quay crane types include portal cranes (mounted on rails), jib cranes, and balanced hydraulic cranes. Lifting capacities can range from a few tons up to 85 tons. Slewing cranes are built with single jib and double jib designs. The main advantage of the double jib crane is the horizontal path of the load. During the luffing of the crane, the grab stays at practically the same height.
Luffing is the vertical motion of a crane. Slewing is when a crane rotates around its vertical axis.
- Floating cranes can be used for cargo handling when few quays or no quays are available or the water depth alongside the quays is too shallow. Large bulk terminals might use floating cranes for direct ship-to-ship or ship-to-barge operations. Floating cranes can also be deployed for ‘topping off’ or ‘lightening’ operations on large bulk carriers (Panamax or Capesize) using ship-to-barge transfers (river) or ship-to-ship transfers (coast or river). In this manner, the vessel draft decreases to a level that allows entry in a port with restricted nautical access.
- Deck cranes or derricks are cranes installed on the vessel itself. They are particularly used in regions where ports lack the necessary cargo handling devices.
In some cases continuous unloaders and loaders are used:
- Continuous ship unloaders are equipped with an L-shaped, bucket-elevator-type unloading device that is suspended from the boom. The material to be unloaded is scooped up by the bucket elevator and transferred to a belt conveyor.
- Ship loaders are mounted on rails that are parallel to the ship and are fed by a conveyor belt. A belt conveyor is utilized on the boom and usually, a shuttle head provides complete coverage of the ship’s hold. The discharge spout incorporates a rotating spoon, which allows the operator greater flexibility when placing the material.