Ensuring that items remain stable and secure during transport is just as critical as maximizing space utilization. A perfectly optimized load means nothing if the cargo shifts during transit, causing damage or safety hazards.
Real-World Impact: Improper stacking causes billions in cargo damage annually. Proper stacking and securing can prevent collapses, reduce insurance claims, and save lives.
Vertical Load-Bearing Capacity
Every item has a maximum stackable weight it can support from above. Tracking cumulative weight on each item is essential to prevent crushing.
┌──────────┐
│ 5 kg │ ← Top item
├──────────┤
│ 10 kg │ ← Bears 5 kg from above
├──────────┤
│ 15 kg │ ← Bears 15 kg (5+10)
└──────────┘
Key principle: Weight on any item =
sum of ALL items stacked above it
Golden Rule: The weight pressing down on an item equals the sum of all items stacked directly or indirectly above it. Always verify that each item's load-bearing capacity exceeds the cumulative weight above.
Center of Gravity & Support
An item is stable only when its center of gravity (CoG) has adequate support underneath. The support polygon is the area where the item contacts the surface below.
Support Percentage Rule
Industry standard requires 70-80% minimum of the bottom surface area to be supported.
TOP VIEW:
┌──────────────┐
│ Item Above │ ← Well-centered
└──────┬───────┘
│ 85% supported
┌────┴─────┐
│ Item │
│ Below │
└──────────┘
STABLE
vs.
┌─────────────────┐
│ Item Above │ ← Overhangs too much!
│ │
└────────┬────────┘
│ Only 40% supported
┌────┴────┐
│ Item │
│ Below │
└─────────┘
UNSTABLE
Stability Requirement: Minimum 75-80% of the top item's bottom surface must overlap with the item below. Less than this creates tipping risk during transport.
Fragility Constraints & Stacking Order
Fragility levels determine stacking priorities:
| Level | Description | Stacking Rule | Examples |
|---|---|---|---|
| 1 (Very Fragile) | Extremely delicate | Nothing on top | Glass, electronics |
| 2 (Fragile) | Moderately delicate | Only level 1 items on top | Packaged food, ceramics |
| 3 (Sturdy) | Normal durability | Levels 1-3 on top | Books, textiles |
| 4 (Very Sturdy) | Heavy-duty | Can support everything | Machinery, tools |
Optimal Stacking Order (Bottom to Top):
- Heaviest and sturdiest items (Level 4)
- Heavy sturdy items (Level 3)
- Medium fragile items (Level 2)
- Lightest and most fragile items (Level 1)
Orientation Constraints
Many items have restricted orientations that must be respected:
- "This Side Up" arrows: Only one valid orientation
- "Keep Horizontal": No rotation around certain axes
- Stacking height limits: Maximum items in a vertical stack
ORIENTATION EXAMPLES
┌─────┐ ┌─────┐ ┌─────┐
│ TOP │ OK │ TOP │ BAD │SIDE │
├─────┤ └─────┘ ├─────┤
│ │ │ TOP │
│ │ └─────┘
└─────┘
Valid Rotated OK Invalid!
upright (still OK) (wrong side up)
Common Mistake: Rotating items to optimize space while ignoring "This Side Up" labels. Always validate orientation constraints AFTER any rotation.
Dynamic Load Securing
Physical securing mechanisms prevent shifting during transport. Understanding the forces involved is critical.
Transport Forces to Consider
| Direction | Force (g) | Scenario |
|---|---|---|
| Forward | 0.8g | Emergency braking |
| Backward | 0.5g | Rapid acceleration |
| Lateral | 0.5g | Sharp turns |
| Vertical | 1.0g + bumps | Road irregularities |
The 0.8g Rule: During emergency braking, cargo experiences forward force equal to 80% of its weight. A 1,000kg load pushes forward with approximately 8,000 Newtons of force. Securing must handle this.
Securing Methods
| Method | Best For | Key Considerations |
|---|---|---|
| Straps/Lashing | Tension-based restraint | Typical capacity: 5kN per strap |
| Blocking | Preventing forward/backward movement | Wooden bracing, cargo bars |
| Bracing | Filling gaps, preventing sideways movement | Dunnage, inflatable bags |
| Friction Mats | Preventing sliding | Increases friction coefficient to 0.5+ |
SIDE VIEW OF SECURED LOAD
╔═══════════════════════════════════╗
║ ┌───┐ ┌───┐ ┌───┐ ║
║ │ A │ │ B │ │ C │ ║
───╫──┴───┴──┴───┴──┴───┴─────────────╫───
║ STRAP ←──────────→ STRAP ║
║ ┌───┐ ┌───┐ ┌───┐ ┌───┐ ║
║ │ D │ │ E │ │ F │ │ G │ ║
╚═┴───┴═┴───┴═┴───┴═┴───┴══════════╝
│ │
BLOCKING BLOCKING
Strap Requirements Calculator
Use this guide to estimate strap requirements for securing cargo:
| Cargo Weight | Friction Sufficient? | Straps Needed | Notes |
|---|---|---|---|
| Under 200 kg | Often yes | 0-1 | Friction mat recommended |
| 200-500 kg | Usually no | 1 | Single strap adequate |
| 500-1,200 kg | No | 2 | Cross-pattern recommended |
| 1,200-2,500 kg | No | 4 | Full securing required |
| Over 2,500 kg | No | 4+ | Plus blocking/bracing |
Safety Factor: Always apply a 1.5x safety factor to restraint calculations. If calculations show 2 straps needed, use 3 straps minimum.
Interlocking & Nested Packing
Interlocking improves stability by preventing horizontal movement:
TOP VIEW - INTERLOCKED PATTERN
┌───┬───┬───┐ ┌───────────┐
│ A │ B │ C │ │ X │
├───┼───┼───┤ VS ├───────────┤
│ D │ E │ F │ │ Y │
├───┼───┼───┤ ├───────────┤
│ G │ H │ I │ │ Z │
└───┴───┴───┘ └───────────┘
Interlocked Unstable
(brick pattern) (aligned)
The brick pattern prevents sliding in all directions
Best Practice: Alternate the offset on each layer (like laying bricks). Each layer offset by half an item width creates maximum stability.
Optimize Your Load Security
LoadPlanner automatically calculates optimal stacking patterns and identifies securing requirements for your cargo.
Try LoadPlanner FreeMulti-Level Stacking Checklist
For complex loads, validate each level before proceeding:
- Space availability: Is there room for the item at this level?
- Support from below: Is at least 75% of the base supported?
- Load-bearing capacity: Can items below support the cumulative weight?
- Fragility rules: Is fragility ordering respected?
- Container height limit: Does the stack exceed container ceiling?
- Orientation constraints: Are "This Side Up" requirements met?
Common Stacking Mistakes
| Mistake | Problem | Solution |
|---|---|---|
| Ignoring cumulative load | Bottom items crushed | Check total weight on each level |
| Checking centers only | Items can tip despite centered | Calculate actual overlap area |
| Rotating without checking | Orientation requirements violated | Validate after every rotation |
| Weight-only sorting | Fragile items crushed | Sort by fragility first, then weight |
| Static stability only | Load shifts during transport | Account for 0.8g braking forces |
| Vertical forces only | Horizontal shift during braking | Calculate lateral restraint needs |
Stacking & Security Quick Reference
| Support Percentage | Minimum 75-80% overlap |
| Load Capacity Margin | 20-30% safety buffer |
| Braking Force | 0.8g (~8 m/s2 deceleration) |
| Friction Coefficient | 0.3-0.4 typical (0.5+ with mats) |
| Strap Capacity | 5 kN (1,100 lbf) typical |
| Safety Factor | 1.5x minimum on all restraints |
| Fragility Rule | Lower fragility cannot support higher |
| Stacking Order | Heavy/sturdy at bottom, light/fragile on top |
Key Takeaways
- Always stack heavy on bottom, fragile on top - never the reverse
- Check cumulative load - not just immediate weight above
- Maintain 75-80% support - calculate actual overlap area
- Account for transport forces - 0.8g braking, 0.5g lateral
- Use 1.5x safety factor - on all restraint calculations
- Fragility overrides weight - a light fragile item always goes on top
- Interlock layers - brick pattern prevents horizontal shifting
- Validate orientations - after every rotation operation
- Fill gaps - prevent shifting with bracing and void fill
Ship Safely, Every Time
LoadPlanner considers weight distribution, stacking limits, fragility rules, and stability in every load plan.
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