Blocking and bracing inside an export crate: what actually holds the load

A crate surrounds the goods; the bracing holds them still

A crate and its blocking and bracing are usually planned together and bought separately. The crate is the enclosure. Blocking and bracing is everything inside it that stops the goods moving relative to that enclosure: the timber that carries the load down to the base, the foam or rubber that separates hard surfaces, the strapping that ties the item to the deck, and the fill that stops lateral travel.

The two are bought separately for a simple reason. The crate comes from a box supplier or from your own line, and the bracing comes from whoever loads the box. That split is also where most damage claims begin, because the person designing the bracing is working with a container they had no say in.

This article is about the interface between the two: what the bracing needs from the crate, and what the crate has to be able to give it.

The three jobs bracing does

Bracing is often described as "stopping it moving", which is too vague to design against. It is three separate jobs, and they fail in different ways.

A brace that does one of these jobs well and the other two badly is common and hard to see on a loading photo.

• Carrying the load down. The goods have mass and the crate has a floor. Something has to transfer one to the other along a path that can take it, which usually means a skid, a saddle or a bearer under the heavy points, not a flat panel.
• Stopping lateral travel. Shock loads in a container arrive sideways and lengthways during shunting, cornering and lifting. Lateral restraint is what keeps a heavy item from arriving against the far wall of its own crate.
• Separating surfaces. Metal on metal, or metal on a painted face, becomes a wear point under vibration that lasts for weeks. Every contact between the item and the crate, and between the item and its own components, needs a soft interface or a designed clearance.

Where the brace load actually goes

The single most useful question to ask about any bracing plan is: what is this timber fixed to, and what is that fixed to?

On a plywood crate the answer should end at the base, ideally at the skids or runners, because the base is the part designed to be lifted. A brace that lands on a side panel puts its load into the panel face, and a panel in bending is far weaker than the same panel in its own plane. The panel then bows outwards and the fastenings start to work loose, which shows up weeks later as a bulging side and a loose item.

The rule that follows: brace to the base and to the structural edges, never to the middle of a panel.

What the crate has to provide

If bracing is planned before the crate is built, four questions get answered while the drawing is still open.

1. Hard points. Is there a piece of structure at the height where the brace needs to land? If the answer is a panel face, the crate needs an internal cleat or a bearer there, and it is a trivial addition at build time and an awkward retrofit afterwards. 2. Deck strength. Can the floor take the load concentrated on a small footprint rather than spread over the whole base? Point loads are what crush a deck, and a crushed deck is a base that no longer sits flat on the container floor. 3. Access. Can the item be fastened down and inspected with the lid off? Assembly inside a closed box is where bracing gets improvised. 4. Internal height. Is there room for the bearer or saddle plus clearance, or has the crate been sized to the goods with nothing left over?

The fourth one is the most expensive mistake, because it is discovered after the box exists. A crate sized tightly to the item leaves no space for the thing that holds the item, and the usual fix is to brace against the lid, which is the weakest panel in the box.

Dunnage, and what each type is for

The choice of dunnage follows from the load path, not from what is in the workshop.

Mixing these is normal. Substituting one for another is where bracing plans quietly stop working.

• Timber blocking and saddles take compression and carry load down. They are the right tool when the item is heavy and has a defined footprint.
• Foam, rubber and cork isolate and spread pressure. They do not carry load down and they compress permanently under sustained load, so they belong between surfaces rather than under a heavy base unless the load is genuinely light.
• Strapping restrains movement in one direction and does nothing in the other two. Strapping to the deck is common and effective, provided the deck is where the strap is anchored and the contact points are protected against cutting.
• Air bags and void fill stop travel and absorb shock, but they lose pressure over a long voyage and they are a poor primary restraint for a heavy item on their own.

The two failures bracing cannot fix

Two problems look like bracing problems and are not.

The first is panel crush from a point load. If the load arrives through a small hard contact, no amount of surrounding dunnage stops the panel failing at that point. The fix is distributing the load, which is a crate design change.

The second is bracing to a wall that is not a load path. A side panel is a membrane, not a column. Fastening a brace to it transfers the shock into the panel rather than into the base, and the panel will eventually delaminate or pull its fastenings.

Both are decided at crate design stage. That is the whole argument for planning bracing before the box drawing is signed off.

Designing the box so that bracing is straightforward

The crates that are easiest to brace tend to share a few features: a base built as a proper skid structure rather than a flat sheet, internal cleats at the heights where restraint is needed, a load-bearing edge on the panels so the sides behave like columns rather than membranes, and access that does not require working through a lid opening.

That last point connects to how the box is made. A steel edge pressed onto the panel edge changes the panel from a membrane into a panel with a stiffened boundary, which is exactly the property that lets a side carry a share of the stack and resist bowing when something inside pushes against it. The joint matters too: where the panel joints are fastened at programmed positions rather than by eye, the box that arrives is the box that was drawn, so a bracing plan written against a drawing still applies to the crate on the dock.

What to send us

If you are specifying crates for an item that needs internal restraint, send the item's footprint, its lifting points and how it will be loaded into the container. We can tell you what the base and the internal structure need to look like for the bracing to have something to hold on to — and where the box has to change to make that possible.