Heavy machinery is exported on a timber skid or in a wooden crate, chosen according to the machine's mass, shape, sensitivity and route. The packaging has to do four jobs: carry the load through forklift, crane and sling handling, hold the machine against the accelerations of road, rail and sea transport, protect it from moisture and corrosion, and comply with ISPM 15 timber rules at the border. Getting the center of gravity and the securing forces right matters more than the thickness of the boards.
Open skid, framed crate or closed case
The first decision is how much enclosure the machine needs. Packers normally choose among three levels.
| Level | Construction | Typical use |
|---|---|---|
| Skid or base frame | Heavy timber runners and cross-members, goods bolted down, no walls | Rugged machines that go in a container or on a flat rack, or are wrapped in film |
| Framed or battened crate | Base plus a skeleton of battens and boards, partly open | Medium-value equipment, dry-route shipments |
| Closed case | Fully boarded or panel-sheathed base, walls and lid, often with a moisture barrier | Precision or corrosion-sensitive machinery, sea freight, long storage |
German industry practice, described in the HPE packing guideline, separates crates into types for goods up to 500 kg and over 500 kg, the heavier types using a load-bearing base frame to which the goods are fixed. The wider range of crate styles is covered in export crates, and the specific demands of ocean routes in seaworthy packaging.
Base design: runners, skids and fork access
The base carries the entire machine, so its design controls the rest. Principles that apply in almost every case:
- Runners (skids) under the load path. Place heavy timber runners under the machine's own frame or load-bearing points, so the weight does not rest on thin deck boards.
- Spread the load. Runners that are long and wide spread the weight on the container floor or deck, and prevent point loads. A 10 t machine standing on four small feet can exceed the floor rating of a vehicle or container, while the same machine on two long runners does not.
- Fork or sling access. Fork openings should allow the forks to reach beyond the center of gravity. Where lifting by crane is expected, define the sling points and mark them.
- Rounded or chamfered ends. Sloped ends on the runners make it easier to drag or tilt the skid over thresholds.
- Bolt, do not rely on friction. The machine should be bolted or clamped to the base through its own mounting holes where possible, and blocked in addition if there is risk of shifting.
Timber choice and moisture are important. Packers use sound, dry softwood or hardwood for the load members; see lumber grading and wood moisture content. Wet timber shrinks after the bolts are tightened and may grow mold in a sealed crate.
Center of gravity and stability
Every machine has a center of gravity (CG) that rarely lies at the geometric center. Motors, gearboxes and counterweights move it. The CG position governs where the forks or slings go, how the load is blocked and whether it can tip.
Mark the CG on the package. The German insurers' Container Handbook (GDV) states that where boxes can only be handled safely when the position of the center of gravity is known, it must be indicated by symbol from 1,000 kg gross weight, on at least two adjoining walls (four is safer), in accordance with ISO 780 or the destination country's rules. The symbols are explained in handling symbols and markings.
A tall, narrow machine is more likely to tip than to slide. A simple check compares the tipping moment from the horizontal acceleration, acting at the height of the CG, with the restoring moment from weight acting across half the base width. If the machine is slender, lower the CG with a wide base, or add bracing against the crate frame or the container wall.
Securing forces and friction
Inside a container or on a vehicle, the load is secured against the accelerations of the route. The Container Handbook uses design values of 1.0 g longitudinally (road and rail) and 0.8 g transversely (sea transport) in its worked example of a steel coil. Friction between the load and its support reduces the amount that lashings must provide:
| Contact | Friction coefficient | Remaining securing, longitudinal | Remaining securing, transverse (sea) |
|---|---|---|---|
| Wooden skid | 0.4 | 0.6 g | 0.4 g |
| Timber or steel beams | 0.3 | 0.7 g | 0.5 g |
As an illustration using those coefficients, a 10,000 kg machine on a wooden skid in a transverse sea load case would need lashings or blocking for about 0.4 × 10,000 kg × 9.81 m/s², or roughly 39 kN. This is a simplified example, not a design calculation: real cases also consider tipping, lashing angles and the safe working loads of the equipment. The IMO/ILO/UNECE CTU Code (2014 edition) is the reference for packing and securing in cargo transport units, and an introduction is in load securing standards. Principles from the code include preventing movement by locking, blocking or lashing, distributing heavy cargo over the floor, and keeping the CG correctly placed. For blocking methods and timber dunnage, see dunnage and blocking.
ISPM 15, moisture and corrosion
All solid wood packaging in international trade, including skids, runners and dunnage, falls under ISPM 15: debarked, heat treated or fumigated, and marked. The CTU Code states that timber used in packing must be properly treated and marked in line with ISPM 15, and should be sound and free of defects such as cross grain, dry rot, large knots or splits. Plywood and other processed wood panels are generally treated as outside the mark, but check destination requirements. The treatment is described in heat treatment.
Moisture control is as important as strength. Machines that travel by sea face temperature swings that cause condensation inside a closed case. The usual defense is a layered system: clean and preserve bare metal, wrap the machine in barrier film, add desiccant sized to the volume, and fit a humidity indicator. The HPE guideline lists polyethylene film, aluminum sandwich film and vapor-phase corrosion inhibitors (VCI) as options with protection periods of roughly 6 to 24 months depending on method.
Documentation and checks before closing
Before the crate is closed, packers typically verify the following:
- Gross mass, dimensions and CG position are recorded on the packing list and marked on the package.
- The machine is bolted to the base, with loose parts, doors and moving elements fixed.
- Fluids are drained or sealed according to the machine maker's instructions.
- Desiccant and indicators are in place, and film seams are sealed.
- ISPM 15 marks are visible on all solid wood, and the treatment certificate is filed.
- Lifting points, "this way up" and other handling symbols are applied.
Frequently asked questions
Does a machine always need a crate?
No. Rugged machines in dry routes are often shipped on a skid with film or a tarp, while precision or corrosion-sensitive machines and long sea routes justify closed cases with barrier film.
Where must the center of gravity be marked?
The Container Handbook says to mark it on boxes from 1,000 kg gross weight, on at least two adjoining walls, using the ISO 780 symbol or the destination country's required marking.
Is friction enough to hold a machine on a skid?
Not on its own. With a friction coefficient of 0.4 for wood on wood, the securing effort remaining is still 0.4 to 0.6 g in the Container Handbook example, so lashing, blocking or bolting is needed.
Do skids and runners need ISPM 15 marks?
Yes. All solid wood used in packaging for international shipment, including skids, runners and dunnage, must be treated and marked, apart from the standard's exemptions such as thin wood and processed panels.
Sources
- CTU Code: a quick guide (2020) — Cargo Integrity Group, via IPPC
- 1.4.3 Marking the center of gravity — GDV Container Handbook
- 5.1 Securing effort — GDV Container Handbook
- HPE Guideline for Packing, 2nd revised edition 2010 — HPE (hosted by Primetals Technologies)