When you open a container at the destination, the marks inside can tell you how the cargo moved during transport. Curved scuff marks may mean the load rolled or shifted sideways, while straight scrape marks toward the doors can show that the cargo moved during braking or acceleration.
Cargo usually shifts because there is empty space for it to move into. Rough seas, sudden braking, and vibration create the force, but proper blocking, bracing, and load placement are what stop that movement. Before choosing straps or lashing materials, it is important to control the gaps around the cargo and secure it in every direction.
In this article, we explain the basic logic, the gap limits that matter, and where different securing materials should be used.
Why Cargo Shifts During Shipping
Three axes, three different causes, three different fixes. Mixing them up is why loads that “were secured properly” still arrive damaged.
- Longitudinal (toward the doors or the front wall). Road braking and acceleration. Under the CTU Code that’s 0.8 g forward — the highest force in the whole journey, and it happens on a highway, not at sea.
- Transverse (side to side). Ship roll and road cornering. Up to 0.8 g transverse in heavy ocean conditions. This is the dangerous one, because container side walls are thin corrugated steel, not structure.
- Vertical. Pitching and heave lift the cargo, friction drops to nothing for a moment, and the load lands somewhere slightly different than where it started. Repeat a few thousand times and the load has walked.
The vertical one is the one people miss. Cargo doesn’t need to slide continuously to end up two feet from where you left it.
How to Fill Gaps in Cargo
Every gap is a runway. A 4-tonne skid that travels 300 mm before it hits something arrives with far more force than the same skid pressed against a wall from the start.
Working thresholds:
- Under 100 mm — acceptable in most cases; fill with void material or ignore if the load is otherwise blocked
- 100–300 mm — dunnage bags are the efficient answer
- Over 300 mm — rigid bracing. Timber or steel. An airbag that size becomes a spring, not a stop
- Anywhere at all — no void at the door end without a bulkhead or a gate. That’s where the load ends up
And keep gaps between cargo pieces under about 100 mm too. Not just to the walls — between the units.
How to Plan Your Cargo Loading
You cannot secure your way out of a bad stow. The load plan does more work than any strap.
- Heavy items on the floor, centred within the middle half of the container’s length
- No more than about 60% of total weight in either half — terminals weigh, and axle limits bite before payload limits do
- Match tier heights so the top surface is flat; a stepped top face has nothing to strap against
- Keep the centre of gravity below the halfway height of the load
- Separate incompatible freight — anything that can leak, anything that can abrade
Best Tools for Securing Cargo
Blocking
Physical barriers against movement. Timber blocks, filler pallets, purpose-cut bracing.
Blocking works well longitudinally, because the front wall and the door frame are structural. It works poorly transversely, because pushing a load against a container side wall just transfers the force into sheet metal. Brace side to side against other cargo or against a floor-anchored frame — not against the wall.
Dunnage Bags
Inflatable void fill. Excellent in the 100–300 mm range, fast to apply, cheap.
Two rules people break constantly:
- Size the bag to the gap, don’t stretch it. An undersized bag inflated hard is a burst waiting to happen
- Don’t over-inflate. Around 75% of rated capacity is the working point for most bags. Fully inflated, the bag has no reserve when the cargo settles or the temperature climbs inside a steel box in the tropics
Bags fill voids. Bags do not restrain heavy loads. Anyone who tells you otherwise is selling bags.
Anti-Slip Mats
The cheapest securing force in the container and the most ignored. A steel skid on a bare wooden floor gives you roughly 0.2–0.3 friction. A rubber mat takes it to about 0.6.
Run that through the securing calculation and it can halve your lashing requirement. Cost per container: negligible. We keep saying this because people keep not doing it.
Lashing
Straps from the cargo to the container’s rated lashing points. Two forms:
- Top-over — the strap presses the load into the floor, raising friction. Needs real pre-tension to do anything at all
- Direct — the strap runs at an angle from a fixed point on the cargo to a lashing ring, resisting the force head-on. Far more efficient per strap. Keep the floor angle under 45°
Only lash to rated points. Container lashing rings are typically rated around 1,000 kg each — the door frame, the vent grilles and the corrugations are rated at zero.
Bundling
Turn many units into one mass. This is where composite cord strapping does the most work, and it’s the step that addresses all three axes at once.
A pipe bundle strapped into a single rigid unit can’t roll, can’t spread, and can’t have individual pieces migrate. Same for drum groups, tile stacks, timber packs, coils. Once the load is one mass, the securing problem gets dramatically simpler — you’re restraining one object instead of forty.
Step by Step
- Sweep and inspect the container. Nails, oil, previous dunnage, holes in the floor. Photograph the empty box.
- Lay anti-slip mats where heavy items will sit.
- Load heavy and central first, building outward and upward.
- Bundle multi-piece loads with cord strapping before they go in, not after.
- Fill voids as you go. You cannot reach a gap at the front wall once the container is half loaded.
- Block longitudinally against the front wall and, at the door end, against a proper gate or bulkhead.
- Brace transversely between cargo units, not against the side walls.
- Lash to rated points, tensioning symmetrically from the centre out.
- Push-test the load. Firm shove by hand on each accessible face. Anything that moves, moves more at 0.8 g.
- Photograph everything before the doors close. Wide shot, then each securing point.
Common Cargo Securing Mistakes
- Void at the door end, “because we’ll be careful opening it”
- Stretch wrap treated as securing — it’s a dust cover with delusions
- Dunnage bags used to restrain instead of to fill
- Bracing timber that isn’t anchored, so it walks with the load
- Loads secured for the sea leg only, ignoring 0.8 g of road braking
- Lashing to the door hinge or the vent, which happens far more often than anyone admits
- No anti-slip mats, on a wooden floor, with a steel skid
FAQs
How big a gap is actually acceptable? Under 100 mm to walls and between units. From 100–300 mm use dunnage bags. Over 300 mm use rigid bracing — an airbag that large compresses and rebounds instead of stopping the load.
Can I use stretch wrap or shrink film to stop shifting? No. Film holds a stack together against handling, not against transit forces. It has almost no tensile capacity in the direction that matters and it relaxes over time. Use it in addition to strapping, never instead of it.
Where can I lash to inside a standard container? The rated lashing rings on the floor and along the side rails, typically around 1,000 kg each — check the container’s own markings. Never the door frame, hinges, vents, or corrugated wall panels.
Do I need to brace if the container is completely full? Usually less, but “full” and “tight” aren’t the same thing. Cargo compresses in transit and a fully packed container can develop 50–100 mm of slack within days. Fill voids and check the door face.
What single change reduces shifting the most? Bundling multi-piece loads into single masses before loading. It removes the internal movement you can’t reach once the container is packed, and it makes everything downstream easier.
Key Takeaways
Kill the voids, plan the stow, buy friction where it’s cheap, bundle the load into as few masses as possible, and lash only to rated points. Do that and there’s nowhere for the cargo to go — which is the entire objective, dressed up in three thousand words of industry vocabulary.
Tell us what you’re loading and how it’s stacked. We’ll tell you where the bundling should happen.
Amass Strapping Solutions manufactures composite cord strapping, container lashing strips and matched galvanised wire buckles from Rajkot, Gujarat. Widths from 13 mm to 32 mm, rated as a strap-and-buckle system, built for exporters who ship containers rather than pallets.
Request a sample roll and a load-securing review for your cargo → amass-strap.com