3D Model — Orbit & Inspect the Rigging
Scenario Description
This 3D model shows a real lift scenario — pipes rigged with reeved yellow slings ready for crane lift. Orbit the model to inspect the rigging arrangement from all angles.
As a dogger, you need to be able to look at a rigging configuration like this and determine whether the slings, angles, and hardware are adequate for the load.
What to Observe
- Sling configuration: reeved (basket) hitch around the pipes
- Sling angles: the included angle between legs at the hook
- Number of legs: how many sling legs share the load
- Attachment points: where the slings contact the load
- Centre of gravity position: is the load balanced between the pick points?
- Tag line position: for controlling load rotation and swing
Calculation Walkthrough
Follow these steps to verify the rigging is adequate for the load:
Estimate Load Weight
Use pipe dimensions (OD, wall thickness, length) and material density to calculate the total weight of the load.
Count Legs & Measure Angle
Count the number of sling legs sharing the load. Measure or estimate the included angle between legs at the hook.
Apply Angle Factor
Use the angle factor table to determine the effective WLL per leg. As angle increases, effective capacity decreases.
Verify Total WLL
Total WLL of all legs must exceed the load weight. Include any required safety factor for the application.
Pipe Weight Formula
Hollow Pipe Cross-Section Area
OD = outside diameter (m) • ID = inside diameter (m) • L = length (m) • ρ = density (kg/m³)
Where ID = OD − 2 × wall thickness
| Material | Density (kg/m³) |
|---|---|
| Mild Steel | 7,850 |
| Stainless Steel | 8,000 |
| Aluminium | 2,700 |
| Copper | 8,940 |
| Concrete (reinforced) | 2,400 |
Sling Angle Factors
| Included Angle | Factor (2-leg) | Effect on Capacity |
|---|---|---|
| 0° (vertical) | 2.00 | Maximum — both legs share equally |
| 30° | 1.93 | Minimal reduction |
| 60° | 1.73 | Standard angle |
| 90° | 1.41 | Significant reduction |
| 120° | 1.00 | Each leg carries FULL load |
Never Exceed 120° Included Angle
- At 120° each leg carries the entire load weight — zero mechanical advantage
- Above 120° sling tension exceeds the load weight — catastrophic failure risk
- If the load requires a wider spread, use a spreader bar
Common Exam Question
Typical Assessment Question
Working:
1. ID = 150mm − (2 × 10mm) = 130mm
2. Area = π × (0.15² − 0.13²) / 4 = π × (0.0225 − 0.0169) / 4 = 0.004398 m²
3. Volume per pipe = 0.004398 × 3 = 0.01319 m³
4. Weight per pipe = 0.01319 × 7,850 = 103.6 kg
5. Total load = 4 × 103.6 = 414.3 kg
6. At 60° angle factor = 1.73, so minimum sling WLL = 414.3 / 1.73 = 239.5 kg per leg
7. Select slings with WLL ≥ 240 kg per leg (always round UP)
Key Principle
The Golden Rule of Load Weight
- Always use the ACTUAL weight, not an estimate
- If you can’t weigh it, calculate it from dimensions and density
- If you can’t calculate it, DON’T LIFT IT
- Never guess a load weight — guessing kills people
Best Practice
- Check the delivery docket or manufacturer’s data for certified weights
- Use a load cell or dynamometer for unknown loads
- Cross-check your calculation against known reference weights
- Account for any extras: water, mud, fittings, packaging
- When in doubt, use the next size up sling
Standards & References
- AS 4991 — Lifting equipment (general requirements for design, manufacture, testing)
- NSW Dogging & Rigging Guide — load calculation methods, sling angle factors, safe working procedures
- AS 1353.1 — Flat synthetic webbing slings
- AS 1666.1 — Wire rope slings
- AS 3775.1 — Chain slings
- Always check sling manufacturer’s WLL tables — they are specific to construction and grade
- WLL tables in the NSW D&R Guide are the exam reference — memorise the common angle factors