Loading a container of sawn timber: stowage, moisture, weight and damage in transit

A container is not storage. It is a sealed steel box that spends weeks being heated by the sun and cooled at night, tilted, vibrated and shunted, and it does all of that to whatever you put inside it. Almost every complaint that arrives after a voyage — staining, mould, splits, warped boards, a collapsed stack, a rejected weight — traces back to a decision made on the yard in Cameroon while the box was being stuffed.

This article is the depth behind the loading section of the Export Academy pillar. It is written so that an exporter can load a container that arrives in the condition it left in, and so that a buyer can write loading requirements into an order and recognise a bad job when the doors open.

One thing it will not do is give you numbers. You will not find internal dimensions, payload limits, tare weights, cubic capacities, target moisture percentages, temperatures or costs here. Those are properties of a specific container, a specific line's equipment, a specific species and a specific contract — and a figure invented on a web page is exactly the kind of detail that gets acted on and turns out to be wrong for your box. Every figure you need exists on the container's own CSC plate, in the line's specification, in the species data and in your contract. Read them there.

Before you accept the box

The container is the packaging. Accepting a bad one is accepting the damage that follows from it, and once it is on your yard and stuffed, nobody at destination will believe it arrived that way.

Inspect the empty container before a single board goes in, in daylight, with the doors closed and someone inside:

• Look for light. Standing inside a closed container, any pinhole in the roof, walls or floor shows as daylight. Every one of those is a path for rainwater onto your cargo.
• Check the roof from the inside. Roof panels take impacts from handling equipment and the damage is invisible from ground level outside.
• Run a hand along the door gaskets. Perished, torn or displaced seals are the most common water ingress point, and the easiest to reject the box for.
• Smell it. A container that carried chemicals, fish, hides or anything aromatic will pass that odour into timber over a voyage, and a taint claim on joinery stock is expensive.
• Check it is dry and clean. Residual water, mud or previous cargo residue goes into the humidity budget of a sealed box.
• Look at the floor. Delaminated, oil-soaked or broken flooring will not hold a nailed dunnage arrangement, and oil migrates into the bottom boards.
• Read the CSC plate on the door. It carries the container's identity and its weight data. This is where your payload arithmetic starts.

If the box fails any of this, refuse it and ask for another. Refusing a container costs a delay. Accepting a leaking one costs the cargo.

Photograph the empty interior, all four walls, the roof, the floor and the CSC plate, before loading starts. This is the single cheapest piece of evidence you will ever collect.

Moisture: the failure mode that does the most damage

Most arrival complaints on Cameroonian hardwood are moisture complaints, and they share one mechanism.

Wood holds water. As it dries it gives that water up to the air around it, and it keeps exchanging with that air until the two are in equilibrium. Inside a sealed container there is only a fixed volume of air, so water leaving the timber has nowhere to go. The box then travels through a daily heating and cooling cycle, and often from a hot humid origin to a cooler destination. When the steel skin drops below the dew point of the air inside, that water condenses on the roof and walls and runs or drips back down onto the cargo. This is what the trade calls container rain, and it is what produces the classic pattern of damage: worst on the top layer and down the sides, cleaner in the middle of the stack.

What condensation does to timber:

• Sticker stain and grey discolouration where free water sits on a surface.
• Mould and blue stain, particularly on sapwood and on species with a high starch and sugar content, which need only surface moisture and warmth to colonise. It is a surface defect on paper and a rejection in practice, because a buyer producing joinery or furniture cannot use stained stock and cannot always machine it away.
• Re-wetting of dried stock, which undoes the drying you paid for. Timber that arrives having reabsorbed moisture will move again in the buyer's workshop, and that shows up as cupping, twist and failed glue lines weeks after delivery — a dispute that is very hard to trace back to the container.

The other half of the moisture problem is differential drying. If timber is loaded before it has stabilised, the pieces on the outside of a bundle dry and shrink faster than the pieces at the centre, and the ends of every board dry faster than its middle because water leaves far more readily along the grain. Uneven shrinkage sets up internal stress, and stress relieves itself as end-checks, surface checks and splits. A container that is loaded hot, straight from a kiln, and then sealed, is doing this to every board in it.

The practical rules that follow:

1. Load at the contract's moisture content, and verify it with a meter. Not by assertion, not by "it's been on the yard a while". Take readings across the consignment, not one convenient board, and record them — the reading is evidence. The glossary defines moisture content, kiln dried and air dried; the contract defines which one you agreed to.
2. Let kiln-dried stock cool and stabilise before it is stuffed. Hot timber sealed in a cold-skinned box is a condensation machine.
3. Never load wet, and never load in the rain. Surface water on boards, on the dunnage, on the packaging or on the container floor is water that will be airborne inside the box within a day. If it starts raining, stop stuffing and close the doors.
4. Wrap or don't wrap, deliberately. Impermeable wrapping around a bundle that is not yet dry traps moisture against the timber and grows mould. On properly dried, stabilised stock it protects against condensation from above. The wrapping is not the decision; the moisture state underneath it is.
5. End-seal where the species and the specification justify it. Coating the end grain slows the fastest drying path and is the most direct defence against end-checks on high-value stock.

Weight: why the box fills up before it looks full

Dense tropical hardwood reaches the container's maximum payload long before it fills the space. A stow planned by volume will be rejected at a weighbridge, at the terminal gate or on the road, and a container that has to be stripped and re-stuffed at the port is one of the more expensive mistakes available in this trade.

Two numbers govern this and neither of them comes from us: the maximum payload of the specific container — on its CSC plate, and confirmed by the line for the equipment it is actually giving you — and the density of the species at the moisture content you are shipping at. The species directory records density for each species we have assessed, and the difference is not marginal: planning a stow of Azobé the way you would plan a stow of Ayous is planning two different problems with one answer. Density also changes with moisture, so a species figure is a starting point for arithmetic, not a substitute for weighing.

Weigh, don't estimate. Weigh bundles as they are made up, keep a running total against the payload limit, and stop when the arithmetic says stop rather than when the box looks full.

Alongside the payload limit sits a separate obligation: the shipper must declare a verified gross mass for a packed container before it is loaded on board. This is an international requirement, not a courtesy to the line, and a container without a valid declaration does not get shipped. Establish with your forwarder, before the box is positioned, how that mass will be determined and who submits it. Do not derive it from a calculation you would not want examined.

Road weight limits on the inland leg to Douala or Kribi are a third, independent constraint, and they can be tighter than the container's own limit. Ask.

Weight distribution and stow discipline

Getting the total right is not enough. Where the weight sits inside the box matters to the crane, the chassis, the vessel's stability calculation and to whether your cargo stays where you put it.

• Distribute the load evenly along the length of the container and across its width. Concentrating dense timber at one end produces an axle overload on the road even when the gross figure is legal, and an off-centre load twists the box.
• Spread point loads. A heavy bundle bearing on a small footprint concentrates force on the container floor. Bearers underneath spread it.
• Heavy low, light high. A high centre of gravity in a box that will be lifted, tilted and rolled is how stacks collapse.
• Build a tight stow. Timber that cannot move does not move. Every gap you leave is room for a bundle to gather momentum in a seaway, and a moving bundle destroys its neighbours, punctures the container walls and can burst the doors. Fill voids with dunnage, airbags or braced blocking rather than hoping the friction holds.
• Load in bundles, not loose boards. Bundled, strapped units behave predictably, can be weighed, can be counted against the packing list and can be handled at destination. Loose stow is slow to load, slow to discharge, and impossible to reconcile.
• Keep bundle lengths consistent within a tier. Mixed lengths in one layer leave the short bundles unsupported and the long ones bridging, and both cases end in broken stock.
• Leave the timber off the floor and off the walls where you can. Air movement around the stow, and separation from the steel skin where condensation forms, is worth more than the small volume it costs you.
• Think about discharge. Someone has to take this out, often with a forklift through one end. A stow that can only be dismantled by hand costs your buyer money and costs you goodwill.

Protection, lining and dunnage

Having understood the mechanism, the protective measures make sense rather than being a shopping list.

Floor and bearer dunnage lifts the cargo clear of any water on the floor and spreads the load. Lining the walls and roof with a protective sheet intercepts condensation before it reaches the timber, so that water runs down the lining rather than dripping onto the top layer — this is what most directly addresses container rain. Desiccants reduce the humidity of the air trapped in the box, and are useful in proportion to how much water is in that air; they are a supplement to loading dry timber, never a substitute for it, and a desiccant will not keep up with a cargo that is still drying out. Corner and edge protection under strapping stops the strap crushing the arrises of the outer boards.

Then the rule the pillar page already sets out, which this article does not soften: the wood you use as dunnage, bearers, blocking and packaging is regulated separately from the cargo, under the international standard for wood packaging material, and it is expected to carry the appropriate treatment mark. Do not assume the cargo's own plant-health position and the packaging rule are the same thing — they are not, and they vary by product form and destination. Non-compliant dunnage inside a perfectly compliant consignment is still a problem at arrival, and it is a problem discovered at the border rather than on your yard. Confirm what your destination requires, in writing, before you cut a single bearer. The Export Academy pillar covers the phytosanitary sequence this sits inside.

Securing the stow

Blocking and bracing exist to take up the space that would otherwise let cargo accelerate. The forces in a container come from ship motion at sea and from shunting, braking and cornering on road and rail — and the ones that catch people out are longitudinal, because a container's doors are its weakest structure and the whole load can end up leaning on them.

• Brace against the door end deliberately. Whatever is holding the last tier back is holding it against the moment the doors are opened at destination. Nobody should be standing in front of a stow that has shifted.
• Strap and lash to the container's own securing points, not to whatever is convenient.
• Use dunnage as blocking, not as filler. Blocking transmits force into the container structure; a loose board wedged into a gap does not.
• Check the stow before the doors close, walking the length of it and pushing on it. Anything that moves under hand pressure will move at sea.

What to photograph and record

A claim is won or lost on what was captured at loading. Photographs cost nothing and are the only account of the container's condition that exists between your yard and the buyer's warehouse.

Capture, with dates:

• The empty container: all four walls, roof, floor, door gaskets, and the CSC plate showing the container number and its weight data.
• The moisture meter readings, with the meter and the board visible in the same frame.
• Bundle marks as they are made up, tying to the packing list.
• The stages of the stow — floor dunnage down, lining in place, first tier, mid-load, final tier — not just the finished result.
• The completed stow with the doors open, showing the bracing at the door end.
• The closed doors with the seal fitted and the seal number legible, and a separate close-up of the seal.

And record, on paper: the container number, the seal number, the bundle count and marks, the piece counts and dimensions, the weights as actually weighed, and the moisture readings. Build the packing list from what was loaded, not from what was planned — the pillar page's point about documents matching the goods is never more testable than here, because the packing list is the document a physical inspection is checked against.

What goes wrong, and why

Read the right-hand column rather than the left. Every one of these is a mechanism a loading team can reason about, and none of them needs a number to understand.

If you are the buyer, write this into the order

Loading is the one part of the shipment you cannot supervise and will not see. So specify it, in the contract, in the same place you specify grade and dimension:

• The moisture content, stated as a figure with a tolerance and a measurement method, and a requirement that readings be recorded and supplied.
• Container inspection before stuffing, with photographs of the empty box.
• Lining, floor dunnage and desiccants where your route or season justifies them — say which, rather than "suitable protection".
• Bundled, strapped, marked units, with marks that tie to the packing list.
• A photographic record of the stages of loading and of the sealed doors, sent before the vessel sails, not after a complaint.
• The seal number, transmitted independently of the container itself.
• Wood packaging compliant with the destination's requirements for solid wood packaging material — named as your requirement, so it cannot be treated as an afterthought.
• Pre-shipment inspection, if the value justifies it, with loading conditional on it passing.

Then, on arrival: photograph the seal before it is cut, photograph the stow before anything is moved, and note any discrepancy on the delivery documents at the time. A defect recorded a week later is a defect that was arguably created a week later.

A written RFQ is the natural place for this to start, because it captures the specification and the destination together — and the destination is what determines the climate the box will travel through, the plant-health requirements on your packaging and, frequently, the difference between a stow that is adequate and one that is not. Sending the same brief to several exporters also tells you something useful: the ones who answer the loading questions specifically are the ones who have done it before.

Where this sits

Loading is where the care taken in grading, drying and documentation is either preserved or thrown away. It is also the last point at which a problem is cheap.

• The Export Academy covers the whole export sequence this step sits inside — documents, phytosanitary requirements, ports and Incoterms.
• The Logistics Academy covers freight, routing and insurance.
• The Processing Academy covers the drying that has to have happened correctly before any of this matters.
• The glossary defines container loading, CBM, moisture content and the drying terms.
• The species directory carries the density figures your weight planning depends on.

If you are sourcing, browse sawn timber on the marketplace, look at verified suppliers, and post an RFQ that states your moisture content and your loading requirements in writing. It is a great deal cheaper than a survey report.