Rigging
How lifts are actually calculated: sling geometry, attachment design, the standards that govern below-the-hook work, and the ground the crane stands on. Written for the engineer who signs the lift plan.
A presumed value is a sizing aid, not a property of your ground, and it is not automatically conservative: on the worked sand the borrowed 200 kPa became a calculated 138. Three routes compared, plus the groundwater lever that halves the answer.
Updated 2 September 2026
Sling tension, load share, centre of gravity, the three plate checks at a pin hole, a weld group under a moment, ground pressure under a mat, and beam actions. Each worked through with its boundary named, then the same padeye checked by the engine.
Updated 1 September 2026
Two declarations, neither about the steel: how well the loads are known, and how often the device will be used. The category moves every check by half again; the service class doubles one check in a single step and then stops.
Updated 31 August 2026
Rotation decides it, not strength. On the worked vessel the trunnion steel sits at 21 percent while the shell it is welded to fails at 181, and a padeye at the same demand passes everything and has no shell check at all.
Updated 30 August 2026
A capacity chart and an outrigger reaction chart are different documents, and only one is any use to a foundation. What to check before using a number off either, and what an estimate costs: 10 percent low, and a different governing slew angle.
Updated 29 August 2026
The mass-weighted average, then the number almost nobody computes: how far the answer moves if one part's mass is wrong. Plus what an offset costs downstream, why the vertical position decides something different, and what to do when you genuinely cannot calculate it.
Updated 28 August 2026
It is a load, not a safety factor, and it depends on how heavy the item is and how much the crane is moving. A derived curve from 1 t to 2500 t, the two other factors that travel with it, and the same lift point passing onshore and failing in open water.
Updated 27 August 2026
One reference padeye and eight variants, each with a single field changed, so the difference in the numbers is that field alone. Edge distance trimmed 35 mm takes the governing check from 68 percent to 163, and the three weld details nobody records as a design change move it from 53 to 79.
Updated 26 August 2026
Share first, then angle, done per leg. Symmetric and asymmetric two-leg picks, the area method for three legs, why four is a different problem, and what a solver reports that a nominal drawing angle does not.
Updated 25 August 2026
Fifteen contents, the three number chains a plan has to carry, and a twenty-minute review order. With a worked ground check that fails at 126 percent and passes at 94 after two controls are added, and no extra steel.
Updated 24 August 2026
Two questions decide it and neither is about the beam. A decision tree, what each region's documents actually cover, and the same spreader beam run through three routes: 55.7 percent, 59.6 percent and 31.0 percent on identical steel.
Updated 23 August 2026
A padeye weld is a moment connection, not a shear connection. The arithmetic written out step by step on one 200 kN lug, then the three levers that move it: weld length, the pin's height above the weld, and whether the runs are returned.
Updated 22 August 2026
Four lift points on a rigid load is one equation short of determinate, so the equal-quarter split is the one distribution you cannot demonstrate. The worked lift point reads 57 percent on a quarter share and fails its weld at 114 on the share you can prove.
Updated 21 August 2026
One machine, five cases, the engine run on each: the worst leg against the average, the swept slew angle against the parked one, a mat credited with its plan area, one bearing check where there are three, and an allowable borrowed rather than established.
Updated 20 August 2026
What each number is, which direction the arithmetic runs, and the distinction the whole subject turns on: an accessory is rated with its design factor already inside, and a structure is designed with the factors in its code.
Updated 19 August 2026
One over the sine of the angle from horizontal, derived, tabulated and plotted, then run through a real padeye: the same 12 t load on the same lug passes at 60 degrees and fails the weld at 30, and the plate barely notices either way.
Updated 18 August 2026
Every check a single-plate padeye has to pass, worked through on one real geometry: net section, shear-out, bearing, pin shear and the weld group at the sling angle, with the numbers coming from the engine rather than from memory.
Updated 17 August 2026
From the outrigger load on the chart to a pad you can defend: what the pressure under a float really is, how a mat earns its area, why the pad has its own bending and punching checks, and what the ground is allowed to take.
Updated 17 August 2026
The two devices look similar and load completely differently. What each one does to the beam, what the sling angle costs you, why the same section passes as a spreader and fails as a lifting beam, and how to tell which one is wrong for your lift before you hire it.
Updated 17 August 2026
Each one produces a report that records its inputs, the check that governed, the source basis for that check, and what stayed outside the validated scope.
lifting
Track hook loads, tail reaction and attachment vectors through an upend or tailing lift.
rigging
Size a spreader or lifting beam and check its padeyes, welds and sling angles.
rigging
Check a single-plate lifting lug or padeye for plate, pin and weld at the sling angle.
rigging
Check a pair of vessel lifting trunnions for member, weld and local shell stress.
rigging
Find the ground pressure under a crane's outriggers or tracks and size the pads.
