201244 Reduction of crane's SWL in grab mode

The Safe Working Load (SWL) of an item of ship’s lifting gear is the safe maximum weight that can be lifted with the load suspended directly from the hook in the standard configuration or in other specified rigging variation(s). Ship’s crews must reduce this figure appropriately when using supplementary equipment (i.e. beam, spreader, slings, grab etc.).

In the case of beams, spreaders or slings, whose weight may be known or can be estimated with reasonable accuracy, this is a simple reduction. However, for bucket grabs connected to the crane for handling bulk cargoes, in the absence of specific data from the makers, it is prudent to make a subtantial reduction in the SWL. This de-rating or downgrading is due to the fact that when a grab digs deep into the bulk cargo, which is often of high density, and is hoisted from within the bulk material, frictional resistance and the weight of added entrained cargo may impose unknown and excessive loads on the system and components.

Grabs are often provided with removable spill or kick plates to adjust the maximum cargo volume lifted depending on the density of the cargo so that the lowered SWL is not exceeded. Shore management and the ship’s command must ensure that all
crew members assigned cargo work responsibilities are fully aware of grab design, limitations, operations and maintenance procedures.