Loading a Container Properly: Here Is How It Works

Incorrectly Loading a Container – What’s the Worst That Can Happen?

Shipping containers are stacked high on deck — towers of eight boxes on top of each other are not uncommon. The containers are locked together using twist-lock connectors, while the entire stack is secured to the ship with special lashing systems. These securing mechanisms are exposed to extreme stress when a container ship rolls sideways in rough seas and then suddenly rights itself again.

Important: The strength of these lashing systems is designed for properly loaded containers with standard weights. If containers are overloaded or their unsecured contents get tossed around inside due to the motion of the waves, the securing systems can fail – in the worst case, causing containers to fall overboard.

This is exactly what happened with the MSC ZOE, which lost 342 shipping containers in the North Sea in 2019. Such a loss not only causes significant financial damage but also endangers maritime traffic and harms the environment

How Much Cargo Fits in a Container?

There are clear standards for this:

• A 20-foot standard container weighs approximately 2.3 tonnes (tare weight) and allows for a maximum payload of 30.2 tonnes.
• A 40-foot container has a tare weight of about 3.7 tonnes and can carry up to 28.8 tonnes of cargo.

In both cases, the maximum gross weight is limited to 32.5 tonnes. The issue: While shipping lines strictly enforce these weight limits to ensure vessel stability, some shippers – driven by economic interests – try to cram as much cargo as possible into a single box while cutting corners on securing the load. Sometimes with disastrous consequences:

When the container ship MSC Napoli ran aground off the English coast in 2007, an investigation revealed that many of the containers had been significantly overloaded – one container by as much as 20 tonnes.

Loading a Container – What to Watch Out For

Precise guidelines for loading shipping containers are provided, for example, by the Australian Maritime Safety Authority (AMSA). Their handbook outlines loading regulations and risk factors for various types of cargo. For the most common types of packages, the following rules apply:

Boxes and Crates

• If the packages do not fill the entire container space, they should be evenly distributed across the floor to achieve a uniform loading height. This approach ensures an even weight distribution within the container.
• Whenever possible, boxes and crates should be interlocked like bricks to create a tightly packed load and minimize the risk of shifting during transport.
• As a general rule, containers are loaded starting from the back wall, beginning at the sides and working toward the center and front. If gaps appear, they must be filled with suitable materials — for example, airbags, pallets, or wooden bracing.
• If a large and heavy crate is being shipped on its own, it should be placed in the center of the container and supported against the container’s corner posts.
  Important: If bracing against the side walls, large contact surfaces are required — for example, using wooden structures.
• Caution: Anyone shipping cardboard boxes should be aware that moisture (e.g., from condensation inside the container) can reduce their stability. If boxes are loaded too loosely, they can shift during transit, rub against each other, and result in cargo damage or loss.

Pallets

• Euro pallets (1200 × 800 mm) are placed in two rows along the floor of the container — one along each long side. One row typically consists of pallets oriented lengthwise, and the other crosswise, or the orientations alternate in both rows. The space in the center of the container is filled with suitable packing material.
• A 20-foot container can hold 11 Euro pallets, while a 40-foot container can accommodate 23 pallets. This results in a space utilization of 78% and 80%, respectively.
• The most efficient use of container floor space is achieved with pallets measuring 1100 × 1100 mm. With 10 of these pallets in a 20-foot container, 99.7% of the floor area is utilized.
• The cargo on the pallets must be firmly secured to the pallet using straps, bands, or shrink wrap.
• Two to four wooden blocks beneath each pallet help to secure the load in place.

Drums and Barrels

• Ideally, drums should be positioned in the container according to the “full stow” pattern — that is, in multiple rows running parallel to the back wall. The drums should fit the container’s width in such a way that no empty space remains between the end of a row and the side wall. To achieve this exact fit, all drums must have one of the following diameters: 25.4 cm, 38.1 cm, 45.7 cm, 55.8 cm, 57.1 cm, 73.7 cm, or 76.2 cm.
• The bung openings must always face upward, and none of the containers may leak.
• Wooden barrels with a bulging shape must not be exposed to pressure on their curved sides. If they are loaded lying down, their sides must be supported in a way that prevents the bulge from resting directly on the container floor. Additional wedges should be used to prevent the barrels from rolling.

Bags

• Bags can be stowed in a cross-tie pattern, but this does not prevent plastic bags from slipping. It is better to place the bags on pallets and secure them with shrink wrap.
• When loading a container with bags, there is a significant risk that the side walls may bulge due to shifting cargo, which can cause the container to become jammed in its slot on the ship.

Bales

• Bales usually cause few issues during transport but can be easily damaged during unloading. It’s important to ensure a strong outer wrapping and to arrange the load in a way that allows forklift-friendly unloading.
• This can be achieved by placing wooden slats parallel to the container’s long walls — both on the floor and between the layers of bales.

Paper or Steel Rolls

• Rolls can generally be loaded into the container either lying flat or standing upright (“eye to sky”).
• For horizontal paper rolls, plastic mats should be placed between the layers to increase friction and prevent rolling. Any side gaps must be filled with padding materials, and the rolls should be blocked with wedges on the container floor.
• Horizontal steel coils require a wooden support structure underneath to increase the contact surface with the floor. At the height of the coil centers, the end walls of the container must also be reinforced with wood. Heavy rolls must be secured with straps threaded through the center hole of each coil to keep them safely in place during transport.

Tips for Securing Cargo

There are various ways to secure cargo inside a container:

1. Lashing Rings: These steel loops are located on the corner posts and along the top edges of the container. They can be used to secure cargo with ropes, tension straps, plastic bands, or metal clamps.
2. Corrugations: These refer to the ridges in the container’s side walls. Wooden beams can be wedged across them to separate cargo layers and prevent shifting.
3. Corner Posts: Heavy cargo items placed in the center of the container should be braced with beams against the container’s corner posts.

Special Cases: How Are Large and Bulky Goods Shipped in Containers?

Vehicles, machinery, and aircraft parts are also traded worldwide and shipped by container. In such cases, a standard container is sometimes not sufficient:

• Passenger Cars: Most standard cars can be driven into a standard container for transport. Once centered inside the container, they are secured using special quick-release tie-downs.
  Important: For air circulation, car windows should be left slightly open during transport. If the vehicle contains fuel (petrol or diesel), airbags, fire extinguishers, or a starter battery, it may fall under the shipping regulations for hazardous goods.
• Trucks, Agricultural, and Road Construction Vehicles: Large vehicles no longer fit into standard containers and are instead loaded into open-top containers (no roof), flat racks (no roof or long sides), or platforms (no roof or walls), depending on their dimensions. Securing is done with steel cables, and wheel chocks are placed under the tires to prevent rolling.
• Machinery and Heavy Cargo: These items are also typically shipped using open-top containers, flat racks, or platforms.
  Key point: The center of gravity of the cargo should lie below the container’s geometric center of gravity. In many cases, a custom base structure is required to distribute the weight evenly across the container floor, to prevent damage from high point loads.

Container Loading – Is It Automated Today?

In the age of AI and digitalization, the image of dockworkers stacking coffee sacks by hand seems almost outdated. But are there already fully automated systems for loading or unloading ISO containers?

• Loading Platforms: These are steel frame platforms that can be raised to the height of the container (when mounted on a truck) using adjustable supports. A movable attachment on the platform pushes a pre-packed wooden pallet into the container and then retracts. Since the pallet matches the base dimensions of an ISO container, the entire load can be pre-assembled and loaded efficiently. Hydraulic and electric loading platforms are ideal for businesses that load containers regularly as part of their daily operations.
• Robots: While robots are not yet widely used for loading, they may soon assist with unloading. The Bremen Institute for Production and Logistics is developing an interactive robotics system called IRiS (Interaktives Robotiksystem zur Entleerung von Seecontainern) to automate the unloading of sea containers.

Here’s how it works: once the container doors are opened, the robotic unit uses suction cups to pull out each box individually and places it onto a ramp for further processing. IRiS uses 2D/3D image recognition and machine learning to determine whether the cargo can be handled by the robot or if human assistance is needed.