Lift Planning
By Timothy Klein
Below The Hook
Rigging fundamentals are central to lift safety and performance
In lifting operations, attention is often directed toward crane capacity, configuration, and reach, as these parameters define capability under controlled conditions. On site, however, the outcome of a lift is shaped by how loads are rigged, balanced, and controlled below the hook, where forces are introduced into the system and begin to develop. The crane responds to those forces, but it does not define them. This becomes critical when real conditions differ from planning assumptions.
Lifting incidents typically develop from small deviations in setup and execution that become significant once the load is applied. Sling configuration, load balance, and equipment condition may appear acceptable during preparation, yet these same factors determine how forces develop as the load leaves the ground.
On many jobsites, these decisions are made under time constraints or physical limitations, increasing the likelihood that small inaccuracies carry through into the lift. Once the load is suspended, correcting these conditions becomes more difficult, and the system must respond to forces that were introduced at the start of the operation.
Real Conditions
Rated capacity is established under defined conditions and does not account for how loads are rigged in the field. Sling configuration, hitch type, and geometry determine how load is transferred through the system. Sling angle has a direct effect on tension, and as the angle between the sling and the horizontal decreases, the force in each leg increases. Sling angles are always measured from the horizontal, and small changes in angle can have a significant impact on loading.
This relationship between angles and tension can be expressed through basic rigging calculations:
• At 60 degrees, forces remain relatively controlled.
• At 45 degrees, tension increases significantly.
• At 30 degrees, the tension in each sling leg can equal the full load, effectively doubling the expected force in a two-leg configuration.
In addition to vertical loading, shallow sling angles also introduce inward forces on connection points. These collapse forces increase as angles decrease and can place additional stress on hardware, attachment points, and the load itself. Both tension and compression must be considered when evaluating rigging configurations.
In field conditions, sling angles are often adjusted to accommodate obstructions, limited headroom, or fixed lifting points. These adjustments change how forces are distributed, even when the load weight remains constant. A configuration that appears stable may introduce significantly higher stress into the rigging system than expected based on rated capacity alone.
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November 2026 • www. cranehotline. com