Chart interpretation, load geometry and rigging calculations
Match the chart to the actual configuration
A capacity value is meaningful only with the correct crane, jib, support or tie condition, hook, reeving and operating geometry. Read notes and restrictions as part of the chart rather than use the largest visible number. The relevant radius includes the actual planned path and placement, not only the pickup location. Use the manufacturer’s method between listed values; do not invent a favorable interpolation. A lower line-pull or structural limit can govern even when an overturning calculation appears acceptable.
Separate gross and net quantities
Identify what the chart includes and what must be deducted. Hook block, slings, lifting beam, bucket and other accessories can consume part of the allowable suspended load. If a supplied gross allowance is four thousand kilograms and specified deductions total five hundred fifty, the remaining object allowance is three thousand four hundred fifty. This arithmetic does not establish wind suitability, ground support, rigging condition or overall lift permission. A moment divided by radius is only a supplied ideal model when the problem explicitly states that basis.
Define sling geometry and units
For a static symmetrical two-leg model, each leg force equals total vertical force divided by twice the cosine of its angle from the vertical. If the angle is measured from horizontal, the corresponding sine relation applies. Flatter legs increase tension. A tonne is a mass unit; an answer written as a tonne-equivalent tension must state that force convention. Unequal centers of gravity, different lengths, stiffness and more support points can invalidate equal sharing. Do not divide by the number of visible sling legs without a valid basis.
Preserve the actual load path
Assess accessories for their actual hitch, load direction, geometry and condition using the relevant manufacturer ratings. A choker reduction, edge-protection arrangement or allowable angle is not universal. Sharp edges, side loading, shock and an uncertain center of gravity can create hazards beyond a simple mass comparison. Establish an appropriate competent plan for unusual loads or multiple cranes rather than apply an invented fixed percentage reduction. These written models teach capacity reasoning only; no physical rigging, test lift, personnel lifting or load movement is authorized by a calculated answer.