By Luis Lopez, AI transportation consultant, CEO of Go Hub.io Holdings Corp and subsidiaries, and host of the Freight Guru Podcast
A container that looks neatly packed at the warehouse door can arrive overseas with crushed cartons, broken crates and freight piled against the doors. The packing looked fine on a flat, still floor. It was never tested against the movement a container goes through on a ship, a train and a chassis.
Blocking and bracing is the work that keeps cargo in place for that journey.
Why Ocean Cargo Needs More Than Road Cargo
On a truck, cargo mostly deals with forward and backward forces from braking and accelerating, plus some side force in turns. At sea, the forces are stronger and come from more directions. A vessel rolls from side to side, pitches bow to stern, and heaves up and down, often for days at a time. Cargo that is free to move will shift a little with every motion, and small shifts add up.
The container also travels by truck and often by rail before and after the voyage. Rail moves add their own longitudinal shocks from coupling and slack action, and the container is lifted, set down and stacked at terminals along the way. Packing has to hold through all of it, not just the ocean leg.
The international reference for this work is the IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units, usually called the CTU Code. It is guidance rather than a single statute, but it is the standard most carriers, insurers and surveyors look to when they ask whether a container was packed properly.
The Three Basic Ideas: Block, Brace, Lash
- Blocking means placing cargo tight against the container walls or against other cargo so it has nowhere to slide.
- Bracing means using timber or other structures to hold cargo in place, usually by transferring the force to the container’s frame, floor or walls.
- Lashing means tying cargo down with straps, chains, wire or similar materials attached to the container’s lashing points.
Most loads use a combination, and heavy crates or machinery usually need all three.
Weight Distribution and Center of Gravity
Before thinking about bracing, get the weight in the right place. The general rules:
- Spread the weight evenly along the length and width of the floor.
- Keep the center of gravity near the middle of the container, both lengthwise and side to side.
- Put heavy items low and light items on top. Heavy freight stacked high raises the center of gravity and loads the cargo underneath.
- Avoid concentrating a heavy item on a small floor area without spreading the load, for example with timber beneath it.
An off-center container is harder to lift and puts uneven stress on chassis axles. For a refresher on box dimensions and options, see our guide to ocean container types.
Filling Voids
Empty space is the enemy. Any gap between cargo and the walls, or between rows of cargo, gives freight room to build up speed before it hits something. Common ways to fill voids:
- Dunnage bags (inflatable air bags) placed in gaps between cargo rows or between cargo and the doors. They should be sized for the gap and protected from sharp edges.
- Timber bracing built into the gap, often as a frame that pushes against the cargo and the container structure.
- Load-securing panels or fillers such as corrugated or honeycomb material for lighter freight.
- Re-arranging the load so the cargo itself fills the space more tightly.
Pay particular attention to the door end. A load that shifts backward will press against the doors, which can make them hard to open at destination. A barrier or bracing at the door end keeps freight off the doors.
Timber Bracing and ISPM 15
Wood is still the most common bracing material because it is strong, easy to cut on site and can be built to fit almost any load. For international shipments, solid wood used for bracing, blocking or pallets falls under ISPM 15. That standard requires the wood to be treated, by heat treatment (HT) or methyl bromide fumigation (MB), and marked with the IPPC mark.
Processed wood products such as plywood and OSB are generally exempt. Untreated or unmarked solid wood can cause a container to be held, treated or sent back, so packers should use marked material and keep it visible where possible.
Using Lashing Points Correctly
Containers have lashing points built into the floor rails, corner posts and sometimes the roof rails. They are designed for securing cargo, but each has a limit. Good practice:
- Lash to the container’s designated lashing points, not to side panels or other parts that were not designed to take the load.
- Spread the load across several points rather than relying on one.
- Use lashing material suited to the cargo and protect it from sharp edges.
- Check that lashings are tight and will stay tight as the cargo settles.
For heavy machinery, the rating of the lashing points and lashing gear should be checked against the cargo, and the plan should come from someone qualified to make it.
Common Blocking and Bracing Failures
- Gaps left at the door end because the load ran short.
- Heavy items on top of light ones, crushing the cartons underneath.
- Weight concentrated at one end of the container.
- Bracing that pushes against thin side walls instead of the frame.
- Dunnage bags that are the wrong size, under-inflated, or placed against sharp edges.
- Untreated or unmarked wood used for bracing on an international move.
- Lashings tied to the wrong points or left slack.
- Packing that relied on friction alone to hold heavy freight in place.
Photos and Records
Photograph the container at each stage: empty and clean before loading, partway through, fully loaded before bracing at the door end, after the final bracing, and with the doors closed and sealed. Record the seal number. If there is a damage claim later, those photos are often the clearest evidence of how the cargo left. Before loading starts, the container itself should be checked for holes, damaged floor and weak lashing points; our article on export container inspection before loading walks through that.
Verified Gross Mass
Under SOLAS, a packed export container needs a verified gross mass (VGM) before it can be loaded on the vessel. Method 1 is weighing the packed container. Method 2 is weighing all the contents, including packing and securing material, and adding the container’s tare weight. Bracing timber, dunnage bags and lashing gear count toward that weight. More detail is in our VGM explainer.
Who Is Responsible
The CTU Code sets out specific responsibilities for the packer, the party that actually loads and secures the container. That might be the shipper’s own warehouse, a third-party packing station, or a forwarder’s facility. Whoever packs it should know the cargo, use suitable materials and secure it for the full journey. The shipper, as the party offering the cargo, should make sure whoever packs it knows what they are doing.
As an AI transportation consultant, the first thing I look for in a packing plan is what will stop each piece of cargo from moving forward, backward, sideways and up. If the answer for any direction is friction alone, the plan is not finished.
For more conversations on freight and AI, subscribe to the Freight Guru Podcast.
About the author: Luis Lopez is a Miami-based AI transportation consultant and logistics entrepreneur, the CEO of Go Hub.io Holdings Corp and subsidiaries, and host of the Freight Guru Podcast.
