In September a plastics processor in southern Vietnam loaded 20 tonnes of polypropylene pellets into a 40HQ in 25 kg sacks. Loading took eight hours, three percent of the sacks split at the door, and the buyer deducted for the spillage. The same volume, filled loose into a liner bag, would have taken ninety minutes and produced no split sacks at all — but a liner bag is not something you order on the morning of loading.
Bulk in a dry container is not a cheaper version of bagged cargo. It is a different structure: the goods themselves become part of the load-bearing system, and the equipment around them does the rest.
The rule: a liner is a container inside the container
A disposable liner bag hangs from the container's lashing points, is sealed around the filling spout and the vent, and is held at the door by a bulkhead — a plywood or steel wall that takes the pressure of 20 tonnes leaning forward under braking. Without the bulkhead the bag bursts the doors open at the first roundabout. Without a dry, undamaged floor the bag chafes and leaks.
Three booking windows, counted backwards
- Liner and bulkhead: 3 to 5 days. The bag has to match the container size and the filling method, and the bulkhead is cut to the door aperture. Neither is in stock at every depot.
- Filling equipment and labour: 1 to 2 days. Gravity filling needs a silo or a big bag above the container; pneumatic filling needs a blower. Book the equipment, not just the people.
- Container inspection: 1 to 2 days. No holes, no rust scale, dry plywood floor, and clean lashing rings. A leaking floor writes off the whole load.
Filling and securing
- Hang the bag from every ring, not from four, and check that the bag does not twist as it fills.
- Fill to the marked weight, not to the top. A 20-foot box takes about 18 to 20 tonnes of pellets depending on bulk density; the carrier's limit decides the rest.
- Fit the bulkhead behind the doors, then brace it with horizontal bars against the side walls. The bag presses; the bars resist.
- Leave the vent open during filling and close it before the doors shut, or the bag inflates in transit.
- Weigh the container after filling — the VGM comes from a weighbridge, not from a silo gauge.
The loading checklist, eight steps
- Confirm the product, bulk density and the receiver's unloading method: tipping, vacuum or a pit.
- Book the liner, the bulkhead and the filling equipment, and confirm the container size.
- Inspect the container: floor, walls, roof, rings, door seals.
- Hang and align the liner; check the spout and vent positions against the filling plan.
- Fill in stages, checking for bag twist and for dust escaping at the seams.
- Close the spout, fit and brace the bulkhead, and photograph the bracing.
- Weigh the box on a bridge and record it as the VGM.
- Seal, photograph the seal and the door, and send the documents with the shipping instructions.
The file that has to travel with it
| Document | Why it matters |
|---|---|
| Product data sheet and non-hazardous statement | Granules can be class 4.1 or 9 depending on the additive; the statement settles it |
| Packing declaration as bulk | The bill of lading and the entry must not read like bagged cargo |
| Weight and VGM | Loose cargo is easy to overload and impossible to re-weigh at sea |
| Liner and bulkhead specification | Shows the equipment matched the container and the product |
| Loading photographs | Bag, spout, bracing and seal — the only record if a claim arrives |
Six places this goes wrong
- A forklift punctures the bag while positioning the filling hose.
- The bulkhead is too thin, and the doors bow under braking.
- The container is filled to the roof, and there is no room for the bulkhead.
- The floor was damp, and the product cakes at the far end.
- The entry declares 800 packages because the booking did — and the cargo is loose.
- The receiver has no way to unload bulk: no tipper, no vacuum, no pit.
A plain note from the desk: a liner does not make bulk cargo simple, it makes it possible. The bag, the bulkhead and the weighing are the three things that decide whether the shipment arrives as product or as a claim.
Before the next bulk booking, send us the product, its bulk density and the receiver's unloading method on WhatsApp. We will confirm the liner size, the equipment window and the document list before the container is ordered, not after it is filled.