A cargo unit that shall be lifted by a crane for changing the transport mode, e.g. for loading to or unloading from a ship, must be reliably connected to the crane hook. This trivial procedure is usually called slinging and carried out according to a pre-planned suspension arrangement only, if the cargo unit in question is of particular weight, shape or value.
A suspension arrangement must be designed for accommodating the specified weight and the geometrical needs of the cargo unit, i.e. considering the location of the lift points on that unit and the position of its centre of gravity. Furthermore, sensible surfaces must be observed where contact with slings is undesirable. Uncertainties about the weight and the position of the centre of gravity should be taken into account.
Quite often the lift points on the cargo unit are positioned below its centre of gravity. This creates a potentially unstable suspension which needs particular consideration by the planner as well as the operator.
Complex suspension arrangements of cargo units may consist of the primary suspension of lifting beams or spreaders connected to the cargo hook, and the secondary suspension of the cargo unit connected to the beams or spreaders. Such arrangements are more sensitive against small transverse deviations of the cargo centre of gravity than purely primary sus-pensions. They react with a greater tilting angle due to the sideway slewing of the secondary suspension. And they can really capsize.
Certainly more the 99% of all world wide lifting operations are conducted without the need to intricately examine the lifting stability. Yet, it is the small remaining minority which may create headache if the correct mechanics of the issue are unknown and „the proof of the pudding has to be left to the eating“. For this reason this paper presents some key points, case studies and solutions for the safe lifting of delicate cargo units.
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