EXERCISE 1

Lifting Calculations

Determining Safe Working Loads (SWL)

A step-by-step interactive whiteboard session.

🎯 Learning Objectives

✅ Understand tension physics in rigging.
✅ Calculate capacity based on angles.
✅ Identify the limiting component.
✅ Determine the final Max Load.

📋 The Scenario

Equipment Data

2x Wire Rope Slings
SWL: 4.0 Tonnes

2x Bow Shackles
SWL: 3.0 Tonnes

📐 The Physics

                    Rule of Thumb: As the angle gets flatter (wider), the tension in the slings increases significantly.
                

90°

Vertical Lift
100% Load

60°

Included Angle
115% Load

30°

Included Angle
200% Load!

🧮 The Load Factor

To calculate the safe load, we divide the SWL by a Load Factor based on the angle.

For a 60° Included Angle:

Load Factor

1.154

Step 1: Calculate Sling Capacity

Formula

( Sling SWL ÷ Factor ) × 2

Input Data

Sling SWL: 4.0T
Factor: 1.154

Calculation

(4.0 ÷ 1.154) × 2

= 3.466 × 2

= 6.93 Tonnes

Step 2: Calculate Shackle Capacity

Formula

( Shackle SWL ÷ Factor ) × 2

Input Data

Shackle SWL: 3.0T
Factor: 1.154

Calculation

(3.0 ÷ 1.154) × 2

= 2.60 × 2

= 5.20 Tonnes

📊 Comparison

We must always select the lowest value as the Safe Working Load.

Slings 6.93 T

Shackles (Limiting Factor) 5.20 T

MAX LIMIT

Maximum Safe Load

5.20T

RESTRICTED BY SHACKLES

Option A: Reduce Load

Option B: Upgrade Shackles

🎛️ Simulator

Angle Adjust

Drag to change angle

60°

Load Factor: 1.154

Sling Capacity

6.93 T

Shackle Capacity

5.20 T

Max Safe Load

5.20T

Restricted by: Shackles