Slingwright Rigging Calculator

What it does

Slingwright is a rigging calculator for riggers, signal persons, crane crews, lift planners and students. It works like a hardware calculator: a safety-orange chassis, real keys and a clear LCD, with each answer labelled so you know what you are reading.

Worked examples

• Leg tension. 2000 lb on two legs at 60° -> 1154.7 lb per leg.
• Offset cg. 10000 lb, hook 8 ft up, CG 4 ft from A and 6 ft from B -> share A 6000 lb.
• Sling angle. 10 ft slings, hook 8 ft above the pick points -> sling angle 53.13°.
• Load weight. Steel plate 96 x 48 x 1 in -> estimated weight 1306.67 lb.
• Percent capacity. 2000 lb at 60° against a 2000 lb rated capacity -> load 100 % of capacity.
• Metric tension. 1000 kg, 4 m slings, hook 2 m up -> 1000 kg per leg at 30°.

How it's calculated

Every trade key and the formula behind it, as shown in the app's key guide. A second legend is the shifted function.

Load TonsLoad weight / Load weight in tons

Stores the typed load weight, pounds or kilograms by the unit setting; nothing typed recalls it. Shifted works in US tons of 2000 lb, or metric tonnes.

Angle FactorSling angle from horizontal / Sling angle factor

Stores the typed sling angle, in degrees from horizontal; nothing typed solves it, e.g. asin(height ÷ sling). The last two typed of sling, height, span and angle set the geometry. Angles under 30° are flagged LOW ANG (ASME B30.9 discourages them). Shifted shows the angle factor 1 ÷ sin(angle).

Sling HeightSling length / Height from hook to pick points

Stores the typed sling leg length, hook to pick point (plain numbers are feet or metres); nothing typed recalls or solves it. Shifted does the same for the vertical height from the hook down to the pick points.

Tens LegsSling leg tension / Number of legs

Leg tension = load ÷ legs ÷ sin(angle), then vertical and horizontal force per leg and the angle factor. For 3 or 4 legs only 2 are assumed to carry the load. Shifted stores the leg count, 1 to 4 (2 by default).$_planning

Pick SlingAPick points / Sling A length

Type the horizontal distance from the centre of gravity to pick point A, then to B, pressing Pick after each; then gives each point's share W × other distance ÷ span and, with the hook height set, each leg’s tension, angle and length for a level lift with the hook over the centre of gravity. Shifted turns a typed sling A length into the hook height.$_planning

CG NewCGCentre of gravity / Start a new centre of gravity

For each item type its weight and press CG, then its position from a datum with a length key and press CG: shows the centre of gravity Σ(W × x) ÷ ΣW and stores the total as the load. Nothing typed steps through CG, total and item count. Shifted starts over.

Dim ShapeShape dimension / Load shape

Type each dimension of the shape, pressing Dim after each (plain numbers are inches or millimetres): box L, W, H; round bar diameter, length; pipe OD, wall, length. Shifted steps through the shapes.

Wt MatEstimated weight / Material

Estimates the load weight = volume × density from the shape and material and stores it as the load; press again for the volume and density. A typed volume (cubic feet or metres) is used directly. Shifted steps through the materials. Nominal densities: use the actual weight when it is known.

%Cap ClearPercent of rated capacity / Clear rigging registers

Stores the rated capacity typed from the equipment tag or chart; nothing typed shows the load and the leg tension as a percentage of it. Shifted clears every rigging register.$_planning

Span HorizSpan between pick points / Horizontal force per leg

Stores the typed horizontal distance between two equal legs’ pick points; nothing typed recalls or solves it. Shifted shows the horizontal force per leg, tension × cos(angle): the compression in a spreader beam.$_planning

FOR LIFT PLANNING ONLY. Slingwright computes geometry and statics; it is not certified and does not replace a lift plan. Check every result against the rated capacities on the equipment tags and load charts, and have a qualified person review the lift. Weights from shapes use nominal densities: use the actual weight when it is known. The developer accepts no liability for loss, damage or injury arising from use.