Increasingly, terminals are considering tandem 40 cranes. This article provides owners with information on the status of dual hoist, tandem 40 (DHT40) cranes and how they operate.
Conventional single-hoist, twin lift cranes
Conventional dockside container cranes have a single hoist with a single spreader and a rated load of up to 65 LT. The single-hoist crane picks up a single 20’, 40’, or 45’ container, or two end-toend 20’ containers (twin 20s), under a single spreader.
Two styles of tandem lift cranes
‘Tandem’ means side by side, as opposed to end-to-end ‘twin’ lifts. Tandem lift cranes are designed to lift two containers in tandem, a single container in tandem with a twin-20’ lift, or four 20’ containers (tandem twin-20 lift).
Single-hoist, tandem lift cranes
Single-hoist, tandem lift cranes have one set of falls, a specialised single headblock, and spreader system (see Figures 1 and 2). These can be used for new cranes and also for converting existing conventional cranes into tandem lift cranes.
Dual-hoist, tandem lift cranes – DHT40 cranes
To our knowledge, ZPMC is the only crane manufacturer to have built DHT40 cranes, currently being used in several Asian terminals. Approximately 1125 tandem lift cranes are expected to be operating before 2008.
DHT40 cranes have two main hoists in a fixed machinery house on the trolley girders (see Figure 3). Each of two sets of main falls is independent. Ropes for each system run in parallel. Each system is the same as a conventional single-hoist system. When comparing DHT40 cranes to conventional single-hoist cranes, the most significant differences for the DHT40 crane are:
• Heavier crane and wheel loads
• Complex operator controls
• Larger trolley, twice as many sheaves, and headblock stowage accommodations
• Two main hoist systems and sets of falls
• Two headblocks and conventional spreaders
• Specialised headblock devices
• Ancillary devices to help the operator ‘see’
• Increased energy consumption