Rigging, Hoisting and Lifting
Know the load, then the hardware
Every lift starts with weight and centre of gravity. An off-centre CG makes legs share load unequally even when the sling looks symmetrical. Capacity comes from a load chart or a tag, never from appearance.
Sling angles
Leg tension is T = (W/n) × (L/H), where L is sling length, H is hook height above the load and n is the number of legs. Equivalently, T = W / (n sin θ) with θ measured from horizontal. Steep slings are strong slings: for two legs at 60° from horizontal each carries 0.577W; at 45° each carries 0.707W; at 30° each carries a full W. The included angle between legs generally stays at or below 90° unless the sling rating and your jurisdiction allow more.
Hardware and inspection
Vertical, choker and basket hitches each derate a sling differently, so use the tag values. Wire rope is rejected for broken wires, kinks, bird-caging, core protrusion or diameter loss. Hooks fail on throat opening, wear and missing latches; shackles fail on damaged threads or substituted pins. Protect slings from sharp edges and use tag lines to control rotation.
Cranes and hoists
Capacity depends on radius, boom angle, quadrant and outrigger setup, and is reduced when lifting on rubber. Agree on hand signals or radio communication before the lift begins, and never stand under a suspended load.
Traps
Measuring the sling angle from vertical instead of horizontal; forgetting hitch derating; lifting off-centre; reading a load chart at the wrong radius; using a damaged or unmarked sling because it looks fine.