Intermediate Rigging (RI) cheat sheet

Working load limit (WLL) = minimum breaking strength (MBS) divided by the design factor; slings commonly use a 5:1 factor, wire rope slings often 5:1, and rigging hardware typically 4:1 to 5:1.

Sling tension for a two-leg bridle: tension per leg = (load weight x half the load) / (vertical height of the bridle), or load / (2 x cos of the angle from vertical).

Tension increases as the horizontal angle from vertical increases: at 30 degrees from vertical tension = 0.577W per leg, at 45 degrees = 0.707W, at 60 degrees = 1.0W, at 75 degrees = 1.93W.

The load angle factor (multiplier applied to share of load) is 1.000 at 90 degrees from horizontal, 1.155 at 60 degrees, 1.414 at 45 degrees, and 2.000 at 30 degrees.

Center of gravity: an object lifts level only when the hook is directly above the CG; an off-center CG shifts load between legs in proportion to horizontal distance from the CG.

Total load on a lifting beam or spreader includes the payload plus the beam's own weight plus hardware; the beam must be rated for the resultant forces at its attachment points.

Shock loading from rapid acceleration or sudden stops can multiply static tension several times; avoid jerking and keep hoist acceleration smooth.

Personnel must never stand or pass under a suspended load; the exclusion zone radius should exceed the potential swing or fall radius of the load and rigging.

Environmental limits: wind acting on large sail-area loads adds horizontal force and reduces effective capacity; stop lifts when wind exceeds the lift plan or manufacturer limit.

Chain sling grades: Grade 80 and Grade 100 are standard alloy grades; never use proof coil, transport, or other non-alloy chain for overhead lifting.

Wire rope sling inspection rejects: broken wires exceeding removal criteria, kinks, bird-caging, crushed or severely corroded sections, and damaged or cracked fittings.

Synthetic web sling capacity drops with hitch type: vertical rated capacity, choker about 80 percent, basket about 200 percent, and bridle per manufacturer; capacity also derates for wider angles.

Web sling rejection: holes, snags, burns or charring, ultraviolet degradation, red core yarn exposed (indicating damage beyond the cover), and missing or illegible tags.

Sling angle affects capacity: a multiple-leg sling's rated capacity applies only at the stated angle; steeper angles from horizontal reduce allowable load per leg.

Protect slings from sharp edges with softeners or corner protectors; protect synthetic slings from heat, chemicals, and sunlight, and wire rope from tight bend radius.

Never tie knots in a sling or use a sling with a knot; knots reduce strength drastically and are cause for removal.

Inspect slings before each use and at intervals required by the employer; remove damaged slings from service immediately and destroy or tag them out.

Shock loading, sustained tension, and repeated bending fatigue shorten sling life; keep records of periodic inspections for wire rope and chain slings.

Shackle WLL is based on the pin or bow diameter and the marked rating; screw-pin shackles must be fully seated, and the pin must not be replaced with a bolt of unknown strength.

Never side-load a shackle or hook beyond its rated design; shackle capacity applies to the centerline of the bow and pin.

Hooks must have a working safety latch; a hook with a spread or distorted throat, cracks, or excessive wear is removed from service.

Master links and master rings must be rated alloy; the assembly WLL is limited by the weakest component, not the strongest.

Eyebolts: shoulder eyebolts are rated for angular loading within limits; plain (non-shouldered) eyebolts are for vertical lifts only unless designed otherwise.

Turnbuckles, swivels, and links used in lifting must be marked with a rating and intended for overhead lifting; hardware not marked is not assumed rated.

Wire rope clips: use the correct number and spacing for the rope diameter, with the U-bolt on the dead end (never saddle a dead horse), and retorque after initial loading.

Rigging hardware must be proof-tested and marked; remove hardware with cracks, bends, deep nicks, or thread damage, and never weld or heat-treat rated hardware.

Load chart capacity is the gross load at a given radius and boom configuration; net capacity = chart capacity minus the weight of all lifting attachments below the boom tip.

Radius is measured from the center of rotation to the center of the load, not to the boom tip; swinging or booming out increases radius and reduces capacity.

Deductions typically include hook block, slings, spreader beams, and any attached rigging; the payload must fit within the remaining net capacity.

Crane configuration matters: boom length, boom angle, jib stowed or erected, outrigger extension, counterweight, and track or tire condition all change the chart.

On rubber-tired cranes, capacity depends on whether the chart is for stationary pick-and-carry, and capacities are lower when traveling with a load.

Ground bearing pressure must be checked: outrigger float load = total weight plus load, distributed to floats; use mats or cribbing to spread pressure on soft soil.

A lift plan documents load weight, rigging, crane position, radius, chart used, ground conditions, power line clearance, and the path of the load.

Critical lifts (near capacity, multiple cranes, personnel nearby, or unusual configuration) require engineered planning and often a pre-lift meeting.

Only one designated signal person directs the crane operator; anyone may give a stop signal, which must always be obeyed.

Standard hand signals: raise and lower by rotating the forearm with index finger extended; stop is an open palm held stationary; emergency stop is both arms extended palms out.

Before the lift, verify the load weight, rigging, hook latch, tag lines, exclusion zone, and communication method; test-lift slightly to confirm balance and rigging.

Tag lines control rotation and swing; they must be long enough to keep personnel clear of the load, and workers must not wrap tag lines around hands or body.

The operator must stop when signal communication is lost, when the load is out of view without a signal person, or when a safety concern arises.

Riggers keep hands and feet clear of pinch points, never place body parts under the load, and push rather than pull a swinging load.

Set-down: lower slowly, land the load, confirm stable support and blocking before releasing tension, then unhook and clear the area.

Power line safety: maintain the required minimum clearance, use a spotter, and treat any contact as energized; keep the crane and load away from overhead lines.