Grabs and Bulk Handling Attachments
Mechanical, hydraulic and four-rope grabs for solid bulk discharge, how tare weight and stowage factor size the grab, and the clamshell and orange peel types.
A grab is the attachment that turns a crane into a bulk discharge machine, closing on cargo by rope, hydraulic ram or scissor linkage and releasing it over a hopper or a barge. Grab discharge is how a geared bulk carrier works cargo in a port with no shore unloader, and the grab and the crane are sized together rather than separately.
The full article will work through the sizing logic. Grab volume follows from the crane’s safe working load less the grab’s own tare weight, divided by the cargo’s stowage factor, so the same grab is correct for coal and oversized for iron ore. Tare weight counts against the certified load and must be permanently marked on the grab under the IMO lifting appliance guidelines, which is what makes the calculation auditable rather than a matter of practice.
It will cover the main types and their duties: the rope-operated clamshell on a four-rope crane, the hydraulic grab drawing power through the boom, the orange peel grab for scrap and rock, and the specialized attachments for logs, magnetic cargoes and containers. It will also treat the damage grabs do to tank top and hopper plating, which is a recurring source of hold survey findings.