K. Somsak Chaivichit
Head of Marine & Cargo Insurance
18 years structuring marine cargo and trade insurance programs for exporters, importers, and freight forwarders across ASEAN and beyond.
Short answer
Container shipping moves standardized steel units — primarily 20ft and 40ft dry vans, plus reefers, open tops, and flat racks — through a chain of stuffing, sealing, terminal handling, ocean carriage, and delivery. Cargo integrity depends on proper stuffing and securing, ISO 17712 high-security seals, verified gross mass declarations, and supervised handoffs at each transfer point, where the majority of losses and substitutions occur.
Container Types and Selection
| Type | Characteristics | Typical Cargo |
|---|---|---|
| 20ft dry van | ~28 m³, 21,700 kg max payload | Dense cargo — machinery, metals, bagged goods |
| 40ft dry van | ~58 m³, 26,500 kg max payload | Voluminous cargo — consumer goods, furniture |
| 40ft high cube | ~68 m³, extra 30 cm height | Light, voluminous cargo, garments on hangers |
| Reefer | Temperature-controlled −35°C to +30°C | Food, pharmaceuticals, chemicals |
| Open top | Removable roof, top-loading | Over-height machinery, stone, timber |
| Flat rack | Collapsible sides, heavy-duty floor | Project cargo, vehicles, industrial equipment |
Selection errors cost in both directions: dense cargo in a 40ft container hits weight limits with half the volume unused (paying for air), while voluminous cargo in a 20ft wastes weight capacity. The density calculation — payload divided by usable volume — should drive container choice before rate comparison.
Stuffing: Where Most Damage Is Decided
Cargo damage claims trace disproportionately to stuffing decisions made in the first hour: load distribution, securing method, and moisture management. A container experiences ship roll of 20+ degrees, rail shocks, and crane accelerations — cargo that can move, will move, and will damage itself and adjacent cartons.
- Weight distributed evenly across the floor, heavy cargo below and centered
- Load secured with dunnage, airbags, lashing, or blocking — never left to friction alone
- Container inspected before loading: no holes, intact door gaskets, dry and odor-free floor
- Moisture management for susceptible cargo: desiccants, ventilation settings, dry loading conditions
- Photographic record at stuffing — empty container, loading stages, completed load
- Carton counts reconciled against the packing list during loading
Seals and Chain of Custody
The container seal is the physical expression of chain of custody between stuffing and destination stripping. ISO 17712 high-security seals are mandatory for international shipments; the seal number must match the bill of lading, and any discrepancy at destination — broken seal, mismatched number, reseal evidence — triggers investigation before cargo release.
- Seal applied immediately upon stuffing completion, witnessed where possible
- Seal number recorded on the B/L, manifest, and loading report with photographs
- Seal condition verified at each handoff — gate-in, vessel loading, discharge, gate-out
- Destination seal verification before stripping, with photographic evidence of any anomaly
Verified Gross Mass: The SOLAS Requirement
Since 2016, SOLAS regulations require every packed container's gross mass to be verified before vessel loading — either by weighing the packed container or by certified calculation from constituent weights. The shipper bears VGM responsibility; carriers refuse containers without it, and misdeclared mass carries fines plus stowage and safety consequences.
Practical compliance is simple: weigh at a certified facility after stuffing, or maintain a certified calculation method with audited component weights. The VGM declaration then flows through shipping instructions to the carrier and terminal — one more document, but one that has eliminated a historic source of container stack collapses and vessel instability.
Managing Risk at the Handoff Points
Containers change custody repeatedly — shipper to haulier, haulier to terminal, terminal to vessel, and the reverse at destination. Each handoff is a documentation event and a risk transfer point. Loss patterns concentrate at handoffs: substitution during transit legs, pilferage at storage yards, and damage attribution disputes between successive custodians.
The defense is consistent: photographic condition records at each transfer, seal verification at each gate, and cargo insurance written on a warehouse-to-warehouse basis so that no leg of the chain falls outside cover. The insurance policy is the instrument that converts multi-custodian complexity back into a single recoverable loss.
Key takeaways
- Container choice is a density calculation — weight-limited versus volume-limited cargo price differently.
- Most cargo damage is decided during stuffing: distribution, securing, and moisture management.
- ISO 17712 seals and verified seal numbers at every handoff are the chain-of-custody backbone.
- VGM declaration is the shipper's legal obligation under SOLAS — carriers refuse non-compliant containers.
- Warehouse-to-warehouse insurance converts multi-custodian risk into a single recoverable loss.
Frequently asked questions
Roughly 28 cubic meters in a 20ft (up to ~21,700 kg payload) and 58 m³ in a 40ft (up to ~26,500 kg). Practical usable volume runs 10–15% below theoretical due to packaging and loading realities.
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