Transport crates for bulky loads – what should you bear in mind when designing and securing the load?
A machine frame weighing 4 tonnes and measuring 3.5 metres in length. A power transformer with an offset centre of gravity. A wind turbine blade with a diameter exceeding 2 metres. Each of these loads requires a custom-designed transport crate – because no standard design can ensure safety with such weights, dimensions and values. In this article, we show how we approach the design of crates for oversized loads, what we pay attention to when securing the load inside the crate, and what mistakes to avoid so that the goods reach their destination intact.
What is bulky cargo in the context of transport packaging?
In the packaging industry, a bulky load is defined as a component whose dimensions or weight exceed the capacity of standard pallets and standard crates. In practice, this refers to loads exceeding 2400 mm in any dimension (the internal width of a 20’ container is approx. 2350 mm), weighing over 1500 kg (the dynamic load limit of a standard EPAL pallet) or with an uneven weight distribution requiring a customised base design.
Typical examples of oversized loads we handle include: frames and bodies of production machinery (hydraulic presses, CNC machine tools, packaging lines), power transformers and MV/HV switchgear, gas and wind turbine segments, pressure vessels and heat exchangers, steel structures and prefabricated components, complete control cabinets in sets of up to a dozen units. Each of these categories has different requirements regarding crate design, securing methods and transport protection.
Designing a container for bulky cargo – from specifications to drawings
Cargo specification analysis – the starting point for every project
We always begin the design of a large-scale crate with a detailed analysis of the load. We require: technical drawings of the component, including dimensions and tolerances, the total weight and the position of the centre of gravity (CoG – Centre of Gravity), information on materials (sensitivity to corrosion, moisture, shocks, ESD), transport requirements (sea, road, air, multimodal), end-user requirements (packaging specifications, industry standards) and the planned route and climatic conditions.
The more accurate the input data, the better the enclosure design. For loads valued at over €100,000, please provide a technical drawing of the component – this allows us to precisely design the securing system and verify that the load will fit within the crate with the required clearance for protective materials (VCI film, foam, shock absorbers). For simpler loads, dimensions, weight and photographs are sufficient.
The base structure – the foundation of the entire box
The base of a transport container for bulky cargo is the most important structural element – it must support the entire weight of the cargo plus the dynamic loads resulting from transport and handling. We design it on a case-by-case basis, taking several key parameters into account.
The layout of the longitudinal and cross members is determined based on the load weight and the position of the centre of gravity. For loads with a symmetrical weight distribution, the longitudinal members are spaced evenly. For loads with an offset centre of gravity, they are arranged asymmetrically, with a denser spacing under the heavier section. The thickness of the stringers depends on the weight: for loads up to 2 tonnes, we use 100 × 100 mm sections; for loads over 2 tonnes, 120 × 120 mm or larger, depending on the span.
The skids must be adapted to the method of handling. When using a forklift truck, the width and height of the skids must be suitable for forks with the appropriate load capacity. When lifting with a crane, the base must have designated and calculated lifting points.
Walls, lid and reinforcements
The design of the walls and lid depends on the type of cargo and transport requirements. For cargo sensitive to dust and weather conditions, we use solid wood box crates with wall thicknesses of 22–30 mm. For mechanically robust loads, where ventilation or weight reduction is key, we design openwork boxes made from planks spaced apart. For the heaviest loads, we use boxes with steel fittings – corner fittings, hinges, screw closures and flat bar reinforcements.
The lid of a large-size crate must be easy to remove – both by the recipient and by a customs inspector, who may request that the crate be opened for inspection. We secure the lid using machine screws or self-tapping screws instead of nails – this allows the crate to be opened and closed repeatedly without damaging the structure. For crates intended for offshore platforms or for lifting by crane, the lid must be secured against accidental opening during transport.
Structural calculations – when are they necessary?
For loads weighing up to 1,500 kg and of standard dimensions, we design flatbed trailers based on our many years of experience and proven structural solutions. For oversized loads – over 2 tonnes or with an atypical weight distribution – we perform strength calculations for the base. These calculations include: the load-bearing capacity of the side members for bending and shear, the load-bearing capacity of the skids for point loading (during forklift handling), structural stability under dynamic loads (maritime transport: accelerations up to 2 g vertically, 1 g horizontally) and the load-bearing capacity of crane lifting points (with a required safety factor of at least 2.0).
For clients in the energy and offshore sectors – where platform operators require technical documentation – we prepare technical drawings of the container, specifying its dimensions, gross weight and the load-bearing capacity of the attachment points. This documentation is required before the cargo is permitted on board an installation vessel or onto an offshore platform.
Timber for large-size crates – raw material quality and ISPM 15 certification
A large-scale crate uses significantly more timber than a standard one – for loads weighing 3–5 tonnes, the base alone may require several hundred kilograms of structural timber. The quality of this timber directly affects the strength of the crate and the safety of the load.
At Danpol, we use timber from controlled sources – every batch is recorded and traceable. We subject the timber to heat treatment in our kiln in Delów – we apply parameters that are more stringent than the minimum requirements of ISPM 15, resulting in timber with lower residual moisture content and better mechanical properties. Lower moisture content means a reduced risk of the crate warping under load and less moisture being released inside the packaging – which is crucial for corrosion-sensitive cargo packed under vacuum in VCI film.
Every crate leaving our facility bears a permanently and legibly printed IPPC stamp, including the codes HT (Heat Treatment) and DB (Debarked). When exporting to Australia, the USA or Asian markets, the legibility of the stamp is crucial – which is why we use printed stamps that are resistant to the conditions of sea transport. We operate under the ISO 9001:2015 quality management system, which ensures the repeatability of the production process and the identification of each batch.
Securing the load inside the body – a key safety feature
Designing a sturdy box is only half the job. The other half – just as important – is securing the load properly inside. Inadequate securing is the most common cause of damage during the transport of bulky cargo. Cargo that shifts inside the container by even a few centimetres can damage both itself and the container structure – and during sea transport, dynamic forces act in all directions simultaneously.
Rule: the load must be secured in all six directions
Professional securing of bulky cargo must counteract forces acting in six directions: forwards, backwards, left, right, downwards and upwards. Each of these directions requires a separate securing element. In maritime transport, we apply the following dynamic load factors: 0.8 g longitudinally (braking/acceleration), 0.7 g transversely (ship’s roll), 1.0 g vertically downwards (crane handling) and 2.0 g vertically upwards during offshore operations. This means that a lashing system for a 3-tonne load must withstand a force equivalent to at least 2.4 tonnes in the longitudinal direction and 6 tonnes vertically during crane operations.
Fastening methods used at Danpol
Wooden wedges and blocks. The basic method for securing heavy loads. Position the wedges around the load to prevent it from shifting horizontally. Secure the wedges to the base of the crate using screws or spiral nails – never leave them loose. For loads weighing over 2 tonnes, use solid wood wedges with a minimum cross-section of 80 × 80 mm, certified to ISPM 15.
Lashing straps with tensioners. These are used to secure the load to the base and counteract lifting forces. We use woven straps with a load capacity matched to the weight of the load – from 2,500 daN for loads up to 2 tonnes to 5,000 daN for heavier loads. The straps are threaded through steel hooks welded to the base of the box or through holes in the side panels. For loads sensitive to scratches, we use straps with edge protectors.
Welded steel brackets and hooks. For the heaviest loads – over 3 tonnes – we use steel fastening brackets welded to the base of the box or to a dedicated steel frame built into the structure. We design the brackets individually, calculating their load-bearing capacity for dynamic forces. We use this type of fastening particularly for offshore loads, where platform operators’ requirements are the most stringent.
Engineering foams and shock-absorbing materials. PE polyethylene foams (with a density of 30–45 kg/m³) and anti-vibration pads are used to absorb shocks and protect delicate surfaces. For electronic loads (control cabinets, switchboards), foam provides an additional layer of protection alongside mechanical fastening. We select the thickness and density of the foam based on the weight of the load and the expected accelerations – foam that is too soft will allow excessive deformation, whilst foam that is too hard will not absorb the shock.
Anti-slip pads and rubber mats. Placed between the load and the base of the box, they increase the coefficient of friction and prevent the load from shifting during transport. We use them to supplement mechanical securing – never as the sole securing element. Anti-slip mats are particularly important for loads with smooth metal surfaces (e.g. stainless steel tanks).
Protection of the load inside the container – corrosion protection and climate control
Oversized cargo is often a component worth hundreds of thousands of euros, exposed to corrosion, moisture and the climatic conditions of sea transport. The crate protects against mechanical damage, but export packaging also requires anti-corrosion and climate protection inside the crate.
For metal cargo, we use ZERUST/EXCOR VCI (Volatile Corrosion Inhibitors) film – an American product that has proven its worth in hundreds of our export projects. VCI film releases volatile inhibitors which settle on metal surfaces and form an invisible protective layer that remains effective even at humidity levels exceeding 90%. For sea transport, we additionally wrap the cargo in barrier aluminium foil (ALU) and use vacuum packaging – once the air has been pumped out, the VCI film works with maximum effectiveness in a sealed space.
We place desiccants (silica gel or bentonite) inside the packaging, in quantities appropriate to the volume of empty space and the planned duration of transport. For bulky loads – where the internal volume of the crate can be very large – the quantity of desiccants must be increased accordingly. We also use humidity indicators and shock indicators, which allow the recipient to immediately assess whether the transport conditions have been compromised.
Transport of oversized crates – loading, stowage, documentation
Loading onto a container or flatbed
Oversized crates require specialist loading equipment. Depending on the weight and dimensions, we use: forklift trucks with a lifting capacity of up to 10 tonnes (for loads that fit inside a container), gantry cranes (at our facility in Nowy Tuchom, we have a crane with a lifting capacity sufficient to handle oversized loads), mobile cranes (for loading directly at the customer’s premises) and rollers and winches for positioning the crates inside the container.
Placing a large-size crate inside a container requires particular care. The crate must be centred or positioned in accordance with the loading plan, taking into account the weight distribution across the container’s axles. We stow the container using ISPM 15-certified dunnage, Cordstrap woven straps, anti-slip mats and blocking wedges. Our staff, trained by SGS Poland and Cordstrap, secure the cargo in accordance with IMO/ILO guidelines on cargo stowage in maritime transport (SOLAS). For oversized cargo – exceeding the dimensions of the container – we carry out transport on flat rack or open-top platforms, with a dedicated securing plan.
Loading inspection – a guarantee of compliance
For high-value, bulky shipments, we routinely recommend a loading inspection. We work in partnership with SGS Poland – a licensed inspector supervises the entire packing and loading process, verifies compliance with the packing procedure, documents each stage with photographs, and issues an inspection certificate. For many customers – particularly those in the energy sector – such a certificate is a prerequisite for accepting the goods.
The inspection includes: checking the condition of the cargo prior to packing, inspecting the protective materials used (VCI film, barrier film, desiccants), checking the securing of the cargo inside the crate, inspecting the labelling (ISPM 15 stamp, handling labels, consignee details), verification of the placement of the crate within the container, and photographic documentation of each stage – from the exposed goods, through packing, to the sealed container.
The most common mistakes when transporting bulky goods
In over 30 years of manufacturing crates for bulky goods, we have seen mistakes that have cost customers hundreds of thousands of zlotys in damaged goods and delays. Here are the most common ones:
Designing a container solely for static weight. A 3-tonne load in storage weighs ‘5–6 tonnes’ during sea transport – because dynamic loads (handling, ship’s rolling) multiply the static weight by an acceleration factor. A crate designed “for 3 tonnes”, without taking dynamic loads into account, may not survive the first storm. The safety factor for sea transport should be at least 1.8–2.0.
Loose securing wedges that are not fixed to the base. Wedges that are not nailed or screwed to the base of the crate move along with the load, thereby losing their locking function. This is one of the most common mistakes made by packing companies with no experience in handling heavy loads. Each wedge must be permanently secured to the crate structure.
Failure to take account of the shift in the centre of gravity. A load with a displaced centre of gravity (e.g. an engine with an offset cylinder block) requires asymmetrical reinforcement of the base and an asymmetrical distribution of fixing points. Treating such a load as symmetrical leads to the container tipping over when lifted by a crane or tilting within the container.
No corrosion protection during sea transport. The crate protects against mechanical damage, but not against corrosion. Metal cargo in a sealed wooden crate without VCI film and moisture absorbers corrodes faster than in the open air – because the wood releases moisture, which condenses on the metal surfaces inside the closed packaging. Anti-corrosion packaging is mandatory, not optional.
A crate without documentation – rejected by the recipient. Offshore platform operators, EPC contractors and institutional customers require technical drawings of the crate, a gross weight declaration and loading inspection documentation. A crate without documentation – even if perfectly made – may be rejected at the destination port, incurring storage and re-export costs.
Exceeding the container’s maximum permissible weight. A 20-foot sea container has a maximum permissible load of approx. 21–28 tonnes (depending on the shipping line and container type), but the weight distribution on the container floor must not exceed approx. 4.5 t/m². A heavy crate placed in the centre of the container without load distribution may damage the floor. For loads exceeding 10 tonnes, we use spreader beams to distribute the load over a larger area.
Frequently Asked Questions (FAQ)
What is the maximum load capacity for which you can design a box?
There is no fixed limit. We design crates for loads ranging from a few dozen kilograms to over a dozen tonnes. For loads exceeding 10 tonnes, the crate effectively becomes an engineering structure – involving strength calculations, technical drawings and a bespoke securing plan. The largest projects we have undertaken have involved loads weighing over 15 tonnes.
How long does it take to design and manufacture a large-scale crate?
5 to 10 working days – depending on the complexity of the design, the weight of the load and documentation requirements. Design (1–3 days) and production (3–7 days) take place sequentially. For urgent orders, we offer an expedited service with parallel design and material preparation.
Do you handle the packaging of bulky goods directly at the customer’s premises?
Yes. We have mobile packing teams equipped with a full range of tools: carpentry tools, barrier film sealers, vacuum pumps and fastening materials. For loads where transport to our facility would be uneconomical or risky (due to their size), we pack on-site at the customer’s premises – throughout Poland, and for larger projects also across Europe.
How can bulky cargo be protected against corrosion during sea transport?
We use full vacuum packaging in VCI film (ZERUST/EXCOR) with an aluminium barrier foil (ALU) and moisture absorbers selected to suit the volume of the package. For bulky loads, the number of desiccants must be increased accordingly – the volume of empty space in the crate is significantly greater than for standard loads. Humidity and shock indicators allow the recipient to assess the transport conditions upon opening the crate.
Are large-size crates subject to ISPM 15 certification?
Yes – every solid wood component is subject to the requirements of ISPM 15 when exported outside the EU. This applies to the crate itself, as well as the securing wedges, washers and dunnage inside the container. All wooden components manufactured by Danpol bear the IPPC stamp. We use heat treatment with parameters that are more stringent than the minimum requirements of the standard, which ensures better mechanical properties of the wood and lower residual moisture content.
What should you do if your load doesn’t fit in a standard container?
We transport cargo that exceeds the dimensions of a standard container on flat rack trailers (open sides), in open-top containers (open roof) or on dedicated trailers. We design the load plan to suit the specific characteristics of the carrier in question – the securing points, lifting points and loading plan differ for a flat rack compared to a closed container.
Summary
Transport crates for oversized loads are not simply ‘larger versions’ of standard crates – they are bespoke engineering designs in which every structural element, fastening and anti-corrosion protection must be tailored to the specific load. The key to safe transport lies in three elements: the correct design of the base (taking dynamic loads into account), professional securing of the load inside the box (in all six directions) and appropriate corrosion protection (VCI film, ALU, vacuum packaging).
At Danpol, we handle the entire process – from analysing the cargo specifications, through the design and manufacture of the crate and anti-corrosion packaging, to the loading and stowage of the container, including an inspection by SGS Polska. Three facilities located near the ports of the Tri-City, a gantry crane for handling heavy loads, a timber drying facility and over 30 years of experience – check out Danpol’s full range of services.
Do you have a bulky load that needs packing? Send us the specifications – we’ll design a crate for you. Get in touch– we’ll provide a quote within 24–48 hours.
