Crane Lifting Plan Design: A Complete Guide

A crane lifting plan is a documented procedure that ensures every lift is carried out safely. Under BS 7121 (British Standard for crane safe use) and the Lifting Operations and Lifting Equipment Regulations 1998 (LOLER), every lifting operation must be properly planned by a competent person — the Appointed Person (AP). This guide covers the essential calculations and documentation for a compliant lifting plan.

The Role of the Appointed Person

The Appointed Person (AP) is the competent individual responsible for:

• Planning the lifting operation
• Selecting appropriate lifting equipment and accessories
• Assessing ground conditions and environmental factors
• Producing the lifting plan and risk assessment
• Briefing the lifting team

The AP does not necessarily operate the crane but holds overall responsibility for the lift's safety.

Key Lifting Plan Calculations

1. Total Gross Load

The total load the crane must lift includes not just the payload but all rigging:

Total Gross Load = Payload + Rigging Weight + Hook Block Weight + Dynamic Allowance

Dynamic allowance accounts for wind, crane movement, and sudden stops — typically 10% for standard lifts, 25% for rapid or multi-crane lifts.

Example: Lifting a 5-tonne steel beam with 0.5-tonne rigging and 0.3-tonne hook block:

Total Gross Load = 5.0 + 0.5 + 0.3 + (5.0 × 10%) = 6.3 tonnes

2. Crane Utilization (Capacity Ratio)

Crane utilization tells you how much of the crane's rated capacity you're using:

Utilization (%) = (Total Gross Load / Crane Rated Capacity at Radius) × 100

Industry best practice:

• < 75%: Green — safe, normal lift
• 75–85%: Amber — caution, requires additional controls
• > 85%: Red — critical lift, requires enhanced planning and permits

3. Working Radius

The working radius is the horizontal distance from the crane's center of rotation (slew center) to the hook:

Radius = Horizontal distance from slew center to load CG

Crane capacity charts show the rated capacity at each radius and boom length. Always verify the crane can lift the gross load at the maximum radius during the lift cycle — not just at the pick point.

4. Sling Tension Calculation

For a two-leg sling at an angle θ from vertical:

Tension per leg = (Total Load / 2) / cos(θ)

Sling Angle (from vertical)	Tension Factor	Load Multiplier
0° (vertical)	1.000	1.00×
30°	1.155	1.15×
45°	1.414	1.41×
60°	2.000	2.00×

Example: 10-tonne load on a 2-leg sling at 45°:

Tension per leg = (10 / 2) / cos(45°) = 5 / 0.707 = 7.07 tonnes per leg

Critical: Never exceed 60° sling angle (from vertical) — tension doubles and sling WLL is effectively halved. BS 7121 recommends keeping sling angles at 60° or less from horizontal (30° from vertical).

5. Outrigger Mat Sizing

Outriggers transfer the crane's load (including the lifted load) to the ground. The mat must spread the load over enough area to prevent ground failure.

Required Mat Area = Outrigger Reaction Force / Allowable Ground Bearing Pressure

Outrigger reaction force can be up to 75% of the total gross load + crane weight on the most heavily loaded outrigger during a side lift.

Example: 40-tonne outrigger reaction on firm ground (200 kN/m²):

Required Area = (40 × 9.81) / 200 = 1.96 m²

A 1.4 m × 1.4 m timber mat (1.96 m²) would be required.

Ground Condition Assessment

Ground bearing capacity is critical. Common values:

Ground Type	Bearing Capacity (kN/m²)
Soft clay	50–100
Firm clay	100–200
Loose sand	100–200
Dense sand/gravel	200–400
Weak rock	500–1,000
Concrete (C25)	5,000+

Always conduct a ground bearing assessment or geotechnical report before heavy lifts. Use steel or timber mats, crane pads, or road plates to distribute load.

Environmental Factors

Wind Speed Limits

Most crane manufacturers specify a maximum wind speed for lifting — typically 9–11 m/s (20–25 mph) for general lifts. For tower cranes and high-boom lifts, the limit may be lower.

Wind force on the load increases with the square of wind speed and with the load's exposed area. Large, flat loads (sail effect) require lower wind limits.

Temperature and Visibility

• Extreme cold affects crane hydraulics and steel toughness
• Rain/snow reduces ground bearing capacity
• Poor visibility requires additional lighting or lift postponement

Lifting Plan Documentation

A compliant lifting plan (per BS 7121) must include:

1. Project details — site, date, lift number
2. Load details — weight, dimensions, CG, lifting points
3. Crane details — type, capacity chart, configuration
4. Rigging details — sling type, WLL, angles, accessories
5. Ground conditions — bearing capacity, matting plan
6. Environmental limits — wind speed, visibility
7. Method statement — step-by-step lift sequence
8. Risk assessment — hazards and controls
9. Sign-off roster — AP, crane operator, slinger/signaller, banksman
10. Verification — QR code linking to digital verification

LOLER Examination Requirements

LOLER requires thorough examination of lifting equipment:

• Before first use (unless accompanied by valid examination certificate)
• Every 6 months for equipment used to lift persons
• Every 12 months for other lifting equipment
• After exceptional circumstances (damage, long idle periods)

Examination must be by a competent person and results recorded in the Register of Lifting Equipment.

Tools for Lifting Plan Design

The SkillJet Crane Lifting Plan Calculator automates load calculations, crane utilization, sling tension, and outrigger mat sizing. It generates a 3-page PDF engineering package with load breakdowns, 2D geometry sketches, and authorization rosters — all with QR verification.

Conclusion

A well-designed crane lifting plan protects workers, the public, and the load. By mastering gross load calculation, crane utilization, sling tension, and outrigger mat sizing — and documenting everything per BS 7121 and LOLER — the Appointed Person ensures every lift is executed safely. Never compromise on planning; a 10-minute calculation can prevent a lifetime of consequences.