A flat rack is a special container type with no side walls or roof, consisting of a reinforced base and two end walls. Models with collapsible end walls can be stacked on top of each other when empty. It is used to carry OOG cargo by sea whose width or height does not fit a standard container, such as machinery, pipes, cable drums, vehicles and steel structures.
What sets a flat rack apart from other containers?
The load-bearing part of a flat rack is a base reinforced with heavy steel beams and usually covered with timber. Thanks to the standard corner castings, it is handled like any other container on the vessel, at the terminal and on a truck chassis. There are numerous lashing rings along the sides and on the base. Because the cargo is free on the sides and on top, it is not limited by the container's external dimensions; loading can be done from above by crane or from the side by forklift.
There are two main types. In fixed-end models the end walls are welded. In collapsible models the end walls fold down onto the base; empty units can be stacked several high to take up a single container slot, which lowers the cost of repositioning empties. Flat platforms without end walls are classified as separate equipment.
| Feature (approximate) | 20' flat rack | 40' flat rack |
|---|---|---|
| Internal length between end walls | 5.6–5.9 m | 11.6–12.1 m |
| Tare | 2.5–3 tonnes | 4.5–6 tonnes |
| Maximum payload | About 30 tonnes | About 40 tonnes |
Values vary by shipping line and container series; the equipment's technical data sheet should be requested before booking.
What cargo is it used for?
A flat rack is for cargo whose dimensions exceed a container but which must be shipped as a single piece. Typical examples are construction machinery, generators and transformers, pipe bundles, large cable drums, boats, steel structural elements and industrial boilers. Such cargo is generally called OOG (out of gauge) cargo.
| Cargo situation | Usually suitable equipment |
|---|---|
| Only over-height, the width is fine | Open top container |
| Over-width, or both over-width and over-height | Flat rack |
| Weight exceeds the capacity of a single flat rack | Platform arrangement on several flat racks side by side, or breakbulk |
| Can move on its own wheels | Usually RoRo |
How is the cargo placed and secured?
- Load distribution: The cargo's centre of gravity is placed in the middle of the base. A heavy load resting on a small surface is spread over a larger area with timber beams sitting on the main girders.
- Lashing: Chains or ratchet straps are chosen according to the capacity of the lashing rings; the cargo is secured separately against fore-and-aft and sideways movement. The calculation method is explained in the lashing force calculation entry.
- Protection: Exposed cargo is covered with a tarpaulin or stretch film against sea water and wind; the tarpaulin itself is also lashed.
- Record: Once lashing is complete, the cargo is photographed from four sides and the dimensions are measured again from the outermost points of the cargo.
The international rules are set out in IMO's CSS Code (cargo stowage and securing) and the IMO/ILO/UNECE CTU Code (packing of cargo transport units).
Stowage restrictions on board and additional freight
Overhanging cargo prevents containers from being placed in adjacent slots. That is why OOG flat racks are usually carried on deck or on top of the stack and require the line's prior approval. For approval, the cargo drawing, net dimensions, weight, centre of gravity and lashing plan are provided. Even cargo overhanging by 30 cm on one side can mean that the adjacent slot cannot be sold; the line invoices these lost slots as additional freight. Over-height cargo cannot be lifted with a standard spreader, so it requires special lifting gear at the terminal and an additional handling charge.
Common mistakes
- Declaring the dimensions of the crate or chassis rather than measuring from the outermost points of the cargo.
- Forgetting the road leg to the port: cargo wider than 2.55 m also needs a road permit on a chassis.
- Assuming that empty flat racks are available at every port; equipment is limited and early booking is required.
Planning a flat rack from the port to the site requires container transport and road permits to be handled together.