Load estimation, slinging, rigging and lifting gear selection
Know the load
Estimate mass from drawings, markings or calculation - never guess. Add the mass of the rigging: slings, shackles, spreader beams and hook block. The gross load is what the load chart uses. Traps: forgetting rigging mass; assuming a marked mass is correct without checking; and using volume-to-mass estimates for unknown materials.
Sling angles and tension
Sling tension rises sharply as the angle from horizontal decreases. Two-leg slings at 60° to horizontal each carry about 0.58 of the load; at 30° each carries the full load. The rule of thumb: keep sling angles at 60° or steeper from horizontal, and never exceed the sling's rated angle. A basket hitch doubles capacity only if the legs are vertical; choke hitches derate capacity.
Selecting gear
Match gear to the load: correct WLL, certified and tagged, inspected before use, no damaged shackle pins, no distorted hooks, no worn slings. Protect slings from sharp edges with packing. Ensure the hook latch works and the load is balanced and controlled with tag lines.
Worked example
A 4 t load with two legs at 45° to horizontal: each leg carries about 2.83 t. If the slings are rated 2.5 t each, the lift is unsafe - use a spreader beam or more legs.
Centre of gravity
Identify the centre of gravity before lifting; an off-centre load tilts and can slip.