Rigging, Slinging and Load Control
Rigging questions test whether you can select and inspect gear and predict how the sling angle changes the load.
Selection and inspection
- Gear must be rated for the load, marked, and in date for examination. Check for cuts, broken wires, distortion, corrosion, and illegible tags - reject if in doubt.
- Use protection at sharp edges and correct shackle pins fully engaged and moused where required.
Sling angles
- The sling angle factor increases tension as the angle to the horizontal decreases. A two-leg sling at 60° to horizontal carries about 0.58 of the load per leg; at 30° it carries the full load per leg.
- Rule of thumb: keep slings as vertical as practical; never exceed the manufacturer's minimum angle.
Load control
- Determine the centre of gravity; an off-centre lift tilts and can swing.
- Use tag lines where rotation or swinging is a risk, and plan for wind on the load - a large sail area can overload the crane or spin the load.
- Never leave a suspended load unattended; never lift people unless the crane and procedure are specifically designed for it.
Worked example
A 2,000 kg load on a two-leg sling at 45° to horizontal: each leg tension ≈ 2,000 / (2 × sin 45°) ≈ 1,414 kg. A 2-tonne rated sling per leg is only just adequate - a 3-tonne sling gives margin.
Traps
Assuming a two-leg sling halves the load regardless of angle.