When cargo exceeds standard container dimensions — either too wide, too tall, too heavy, or oddly shaped — it is classified as OOG (Out of Gauge). Two specialized container types handle most OOG shipments from China: flat rack containers and open top containers. This comparison explains which equipment to use, when, and why. As a forwarder with extensive heavy lift and project cargo experience, we manage both types regularly out of Qingdao.
Equipment Specifications
| Specification | 20ft Flat Rack | 40ft Flat Rack | 20ft Open Top | 40ft Open Top |
|---|---|---|---|---|
| Internal length | 5.94 m | 12.08 m | 5.89 m | 12.03 m |
| Internal width | 2.35 m | 2.35 m | 2.35 m | 2.35 m |
| Internal height | 2.35 m (ends down) | 2.35 m (ends down) | 2.35 m (plus open top) | 2.35 m (plus open top) |
| Max payload | ~45,000 kg | ~40,000 kg | ~28,000 kg | ~26,000 kg |
| Tare weight | ~2,700 kg | ~4,850 kg | ~2,250 kg | ~3,750 kg |
| Loading access | Top, sides, ends (360°) | Top, sides, ends (360°) | Top only (crane/overhead) | Top only (crane/overhead) |
| End walls | Fixed or collapsible | Fixed or collapsible | Fixed walls; removable roof bows + tarpaulin | Fixed walls; removable roof bows + tarpaulin |
| Weather protection | None — cargo fully exposed | None — cargo fully exposed | Tarpaulin cover — basic rain/sun protection | Tarpaulin cover — basic rain/sun protection |
Cargo Type Suitability
| Cargo Type | Recommended Equipment | Reason |
|---|---|---|
| Heavy machinery (excavators, bulldozers) | Flat rack (40ft) | Machinery can be driven/loaded from side; exceeds open top weight limits |
| Steel coils / pipes | Flat rack | Loaded from top or side; heavy concentrated load distributes across flat bed |
| Wind turbine components (blades, nacelles) | Flat rack | Extreme dimensions; requires 360° lashing access and custom cradles |
| Tall machinery (presses, injection molding) | Open top | Crane-loaded from above; benefits from side-wall protection |
| Generators and transformers | Flat rack | Typically 20-40 tons single piece; exceeds open top weight limit |
| Boats / yachts | Flat rack (with cradle) | Loaded from side or top; custom cradle required |
| Tall crated equipment (2.8-3.5m height) | Open top | Over-height but not over-width; crane-loaded; tarpaulin protects crate |
| Pre-fabricated steel structures | Flat rack | Over-width and over-length; bundled on flat rack with dunnage |
Lashing and Securing Requirements
Proper lashing is the single most critical factor in OOG transport. Both flat racks and open tops require a lashing plan (securing scheme) submitted to and approved by the carrier before loading. The plan must specify:
- Type and breaking strength of lashing equipment (chains, wire ropes, webbing straps)
- Number and position of lashing points used
- Calculated G-forces the securing arrangement can withstand (typically 0.8g lateral, 1.0g longitudinal for sea transport)
- Dunnage and chocking arrangement to prevent sliding
Our heavy equipment export case study details a real flat rack operation for SANY construction machinery where the lashing plan involved 12 chain lashings per unit, each rated at 10,000 kg breaking strength.
Case Examples from Qingdao
| Project | Equipment | Cargo | Weight | Key Challenge |
|---|---|---|---|---|
| SANY excavators to Middle East | 40ft flat rack x 8 | Large excavators | ~35t each | Over-width at 3.2m; required port road closure for transport to terminal |
| Injection molding machines | 40ft open top x 3 | Tall machinery | ~18t each | Crane loading through top; tarpaulin over custom crating for sea protection |
| Wind turbine nacelle | 40ft flat rack x 2 | Nacelle units | ~42t each | Custom steel cradle; extreme OOG requiring route survey from factory to port |
Frequently Asked Questions
What is the maximum weight a flat rack container can carry?
A 20ft flat rack can typically carry up to 45 tons depending on the specific unit design; a 40ft flat rack carries up to 40-45 tons. By comparison, a 20ft open top container maxes out at approximately 28 tons, and a 40ft open top at 26 tons. For single pieces exceeding 28 tons, flat rack is the only containerized option — beyond that, breakbulk shipping may be necessary.
Do open top containers protect cargo from rain?
Open top containers come with a removable tarpaulin cover that provides basic weather protection against rain and sun. However, the tarpaulin is not fully waterproof — water can seep through seams during prolonged heavy rain or rough sea conditions. For moisture-sensitive cargo, additional waterproof wrapping inside the container is strongly recommended. Flat racks offer zero overhead protection, so cargo must be fully weatherproofed independently, often with heavy-duty shrink wrap or custom weatherproof covers.
How much does a flat rack or open top container cost compared to a standard container?
Special equipment commands a premium. A flat rack or open top container typically costs 30-80% more than a standard 40ft container on the same route. The exact premium depends on equipment availability, origin-destination pair, and season. Additionally, OOG surcharges apply based on how far the cargo exceeds standard dimensions. A freight forwarder with project cargo expertise can optimize stowage to minimize OOG surcharge brackets.