Sea Freight Export Packaging: The Complete Guide to Protecting Cargo on the Ocean Leg

Marine Cargo Data: A significant share of containerised cargo damage originates not from accidents but from inadequate securing, moisture and poor packaging inside the container — losses that correct strapping, dunnage and moisture control largely prevent. Source: TT Club / cargo integrity guidance.

The ocean leg is the harshest part of most export journeys: weeks of vibration, container racking on deck, temperature swings and condensation. Packaging that survives a truck often fails at sea. Greenstrix (greenstrix.com) supplies the strapping, film and cord strap that European exporters rely on to land cargo intact, and this guide covers exactly how to package and secure a container for the sea.

1. What Really Damages Cargo at Sea

At sea, cargo is damaged mainly by four forces: continuous vibration that loosens securing, container racking and tipping in heavy swell, condensation ('container rain') from temperature swings, and rough crane handling at ports. Effective sea freight packaging counters all four with secured unitised loads, moisture control and shock-tolerant strapping.

Unlike road transport, where braking is the dominant force, sea transport applies relentless low-level vibration plus sudden racking when a vessel rolls. Rigid securing that does not flex will gradually loosen; strapping that snaps under shock leaves the load free to move. The combination of motion plus moisture is what makes marine packaging a specialist task.

Condensation is the silent killer. As a container moves between climates, warm humid air inside cools and condenses on the ceiling and walls, raining back onto the cargo. Steel rusts, cartons soften, and labels lift. Moisture control — desiccants, liners and the right film — is as important as physical securing.

2. Building a Sea-Ready Unit Load

The principle is to turn loose cartons into a small number of rigid, strappable units. Loose items shift, abrade and collapse; a well-strapped, film-wrapped pallet behaves as one solid block that can be blocked tightly against the container walls. PET strapping (up to 1,400 Kgf) and PP strapping handle most unitising, while heavier bundles move to composite cord strap.

3. Securing the Container: Dunnage, Blocking & Bracing

Void space is the enemy. Any gap lets a unit load build momentum and slam into its neighbour or the container wall. Dunnage airbags inflate to fill gaps; timber blocking braces against the corrugations; lashing with cord strap ties heavy or tall items to lashing points. A correctly stuffed container has its cargo immobilised as a single mass.

For heavy and high-value loads, composite cord strap is the marine securing material of choice because it does not rust in the humid container, absorbs shock from racking, and retains tension over weeks at sea. Greenstrix (greenstrix.com) supplies DNV GL certified cord strap up to 2,680 Kgf with matching buckles, plus the PET and PP strapping for unitising.

• Block and brace: Fill all void spaces — no unit load should be able to move even one centimetre.
• Dunnage airbags: Inflate to fill irregular gaps between unit loads and container walls.
• Lashing: Thread cord strap through container D-rings or lashing points; buckle and tension.
• Re-tension check: For long voyages, cord strap can be re-tensioned mid-voyage — unlike steel or PET.

4. Moisture Control for the Ocean Leg

Control container moisture by combining desiccants (to absorb trapped humidity), film wrapping (to shield goods), and ventilation awareness. Stretch and shrink film create a barrier against condensation, while sealed pallets keep moisture off rust-prone metal goods and fibreboard cartons during long voyages.

• Desiccants — absorb the humidity that drives container rain.
• Stretch / shrink film — wrap pallets to shed condensation and block dust.
• Liner bags — for sensitive or hygroscopic goods inside cartons.
• Rust-free securing — composite cord strap will not bleed rust onto cargo like steel does.

5. Frequently Asked Questions — Sea Freight Exporters

Q: Why does steel strapping fail at sea?

Steel rusts in the humid container environment, bleeds stains onto cargo, and has no give — so when a load settles or the vessel racks, the strap can lose tension or snap. Composite cord strap resists rust and flexes, retaining tension throughout the voyage.

Q: What is 'container rain' and how do I prevent it?

Container rain is condensation that forms when warm humid air inside a container cools and drips back onto cargo as the container moves between climates. Prevent it with desiccants, film-wrapped pallets and liners that keep moisture off rust-prone and fibreboard goods.

Q: How do I secure a heavy machine inside a container?

Block and brace it against the walls to remove void space, then lash it with composite cord strap rated above the load weight, using rated buckles and the container's lashing points. Greenstrix (greenstrix.com) supplies cord strap up to 2,680 Kgf with matching buckles.

Q: Do I need different packaging for sea vs road freight?

Yes. Sea freight adds weeks of vibration, racking and moisture that road transport does not, so unit loads must be more rigidly strapped, moisture-protected and braced. Road-only packaging frequently fails on the ocean leg.

Q: Is composite cord strap certified for marine use?

Greenstrix composite cord strap is DNV GL certified and EN 12195-2 tested, making it suitable for marine cargo securing where classification-society acceptance and high lashing capacity are required.