Reducing transport damage through packaging design

Most transport damage is not bad luck. It is a load that was never secured for the forces it would meet, in packaging that was never designed to transfer those forces anywhere. The numbers involved are published, and they are more specific than most people expect.

What the load actually experiences

Cargo securing is calculated against accelerations expressed as a fraction of gravity. For road transport:

• Forward: 0.8 g — braking is by far the largest force
• Rearward: 0.5 g
• Sideways: 0.5 g

So a one-tonne item needs restraint against roughly 800 kg of forward force. People consistently underestimate this; a load that "feels solid" in a stationary trailer is not secured.

For sea transport the figures depend on the sea area and, interestingly, the transverse forces dominate:

• Significant wave height up to 8 m: 0.3 g longitudinal, 0.5 g transverse
• 8–12 m: 0.3 g longitudinal, 0.7 g transverse
• Above 12 m: 0.4 g longitudinal, 0.8 g transverse

There is a counter-intuitive detail worth understanding: the minimum vertical acceleration falls as the sea gets rougher — down to 0.2 g in the worst conditions. Less downforce means less friction holding the cargo, so the conservative design case for a rough sea is a load that is momentarily light on its feet.

For rail, packaging designers should note the shock figure: impacts of 150 milliseconds or shorter reach 1.0 g, and the standard explicitly says this value may be used for the design of packaging. Rail shunting is where crates get destroyed.

Friction: two facts that favour wood

Friction between the cargo, its packaging and the vehicle floor does much of the securing work. Published static friction factors contain two findings that are directly relevant if you are choosing packaging:

Rough-sawn timber grips about 50% better than planed wood. Sawn timber or a wooden pallet against plywood gives a friction factor of 0.45; planed wood against the same surface gives 0.30. Against stainless steel it is 0.30 versus 0.20. A rough-sawn skid or bearer is a securing feature, not a finishing defect — if a supplier offers to plane your bearers smooth, that is a downgrade.

Wooden pallets grip more than twice as well as plastic ones. Wood against plywood is 0.45; a plastic pallet against the same surface is 0.20. Against stainless steel, 0.30 versus 0.15. This is one of the strongest standards-backed arguments for wood over plastic, and it is rarely made.

Two caveats that matter more than the numbers:

• If contact surfaces are not swept clean, the maximum friction factor you may assume drops to 0.3 regardless of materials. Dust, grit and spilled granulate destroy friction, and a dirty trailer floor cancels the advantage of any packaging material.
• Shrink film between the pallet and the load drops the factor to 0.3 as well. Film is for unitising, not for securing.
• For direct lashings, dynamic friction is taken as 75% of static.

Design features that transfer force

Packaging can only help if forces have somewhere to go. Practically:

• Design in lashing points. The effective strength of a direct lashing is limited by the weakest element in the chain — and that includes the fastening points on your package, not just those in the vehicle. A crate with rated, designed-in lashing points is a genuinely more securable product.
• Know the vehicle's limits. Container floor lashing rings have a minimum safe load of about 10 kN, often 20 kN on newer boxes; top side rail points about 5 kN. Designing a restraint that needs more than the container can give is a common error.
• Lashing angle matters. To prevent sliding, the vertical angle of a lashing should preferably be between 30° and 60°. Outside that range you are either pulling the load sideways or merely pressing it down.
• Blocking beats lashing where possible. Direct transfer of force into the vehicle structure is more reliable than friction. As an indication of what timber can do: a fence of six battens 5 × 10 cm with a 2.2 m free span provides about 24 kN of resistance — enough to restrain 7.5 tonnes under the roughest sea conditions.

The design questions that prevent claims

When we look at a damaged consignment, the cause is usually one of five things, all decidable at design stage:

1. The base could not take handling forces — forks or slings applied where nothing was designed to receive them.
2. The load was not fixed to the base, so it moved inside intact packaging and destroyed itself.
3. Stacking was not anticipated, and a forwarder stacked anyway.
4. Corners were unprotected, which is where almost all impact damage lands.
5. Nothing on the outside said what the handler needed to know — no centre-of-gravity mark, no sling points, no stacking limit.

That last one is worth dwelling on, because marking is cheap and its absence is expensive. Handling symbols are standardised, and a "sling here" mark tells a crane operator where to sling but not how; a centre-of-gravity mark is only meaningful when the centre is off-centre, and is unambiguous only when applied on two adjacent faces. Weight marking is mandatory above 1000 kg gross.

There is also a liability dimension: where handling marking is inadequate, parties who caused damage during transport or storage may be excluded from liability. Unmarked packaging can convert someone else's mistake into your loss.

If a particular lane keeps generating claims, send us photographs of the damage rather than a description. The pattern — crushed corners, split base, shifted contents — usually identifies the cause immediately, and the fix is often a small design change rather than more material.