Introduction: Every Cubic Meter is Real Money
“Shipment weight 1,000 kg, but volume takes up 5 cubic meters. In sea freight, we charge by Revenue Ton (RT), whichever is larger. If the cargo is light, you pay for volume; if heavy, you pay for weight.” – This is the most fundamental pricing rule in international shipping.
For steel products like steel grating, weight‑based charging is usually the primary method. However, calculating ocean freight is not just about weight. In 2025, global logistics costs continue to rise: Maersk and other carriers significantly increased Peak Season Surcharges (PSS) in November, with some routes seeing increases of USD 500‑1,000 per container, and even over 300% on certain routes. The Guangdong‑Hong Kong‑Macao Greater Bay Area Container Export Freight Index shows that freight rates to the Singapore route have risen by a cumulative 31.38% over the past six weeks.
In such a market environment, how can you minimize sea freight costs through optimized loading? Based on industry practice, this article systematically explains sea freight loading techniques for steel grating exports – from the choice between flat‑stacking and vertical stacking, to packaging design, and prevention of transport deformation – helping overseas buyers (especially those in Singapore) load more product into each container and pay less freight.
Chapter 1: Sea Freight Pricing Rules and Container Selection
1.1 Revenue Ton Rule – Charge by Weight or Volume, Whichever is Higher
In international sea freight, freight is calculated based on the Revenue Ton (RT), using the larger of cargo weight (tonnes) and cargo volume (cubic metres). Typically 1 tonne = 1 cubic metre. This rule is particularly important for steel grating:
Weight‑based charging: applies to high‑density goods such as metal products, ores, etc., often charged per tonne.
Volume‑based charging: applies to light, bulky goods such as furniture, foam products.
Key criterion: whether the cargo density (tonnes/cubic metre) is greater than 1.
Measurement example:
G405/40/150 steel grating weighs about 30 kg per square metre and is about 40 mm thick. A 40‑foot container loaded with only one layer can hold about 30 tonnes, far exceeding the maximum payload of a 20GP/40GP (approx. 26‑28 tonnes). Therefore, the limiting factor is volume utilization – weight is rarely the constraint; the key is how to fill the container’s height space.
1.2 Container Types and Applicable Scenarios
According to the “2025 China Container Industry Market Research Report”, global container throughput has approached 900 million TEUs, with the Asian container depot market holding the largest share worldwide.
| Container Type | Internal Dimensions (L×W×H) | Door Height | Max Payload | Suitable Scenarios |
|---|---|---|---|---|
| 20ft GP | 5.9m × 2.35m × 2.39m | ~2.28m | ~28 tonnes | Small quantities of grating, accessories |
| 40ft GP | 12.03m × 2.35m × 2.39m | ~2.28m | ~26 tonnes | Regular bulk, cost‑effective choice |
| 40ft HQ | 12.03m × 2.35m × 2.69m | ~2.58m | ~26 tonnes | Extra height for 3‑layer stacking |
| Open Top (OT) | Similar to GP, openable top | — | ~26 tonnes | Oversize or crane‑handled special grating |
| Half‑height container | 40ft half height, octagonal pillars | — | up to 37 tonnes | Heavy long products like sections, rebar |
Selection advice:
For standard steel grating exports, the 40ft high cube (HQ) is preferred; the extra 30 cm of height allows three layers, increasing loading capacity by about 25% compared to GP.
For heavy cargo like steel grating, 40ft GP or half‑height containers may also be considered, but if product height limits stacking, HQ may not always give an absolute advantage.
In June 2025, data showed that Open Top (OT) containers on China‑Southeast Asia routes were 28% cheaper than flat racks – a cost‑effective choice for coils, rebar and other cargo suitable for top‑loading.
1.3 Economic Benefits of Load Factor Optimisation
According to Deloitte’s “Global Logistics Report 2025”, optimising container stowage can directly reduce sea freight costs by 7%‑12% on average, and increase loading efficiency by 15%‑20%.
For steel grating, the benefits are even more pronounced. One layer in a 40ft GP holds about 24 square metres; with three layers, loading capacity increases to about 72 square metres. Assuming a freight cost of USD 5 per square metre, the cost before optimisation is USD 120 per container; after optimisation, the actual loading cost drops to about USD 40 per container – a saving of over 65%. This means you do not have to pay extra to fill a container; you only pay for the space you use, provided you fill it well enough.
Chapter 2: Flat Stacking vs. Vertical Stacking – Comparison of Loading Strategies
2.1 Flat Stacking
Flat stacking is the most commonly used loading method for sea freight of steel grating: panels are stacked horizontally.
Key points:
Stack grating panels flat, placing wooden strips or separators between layers.
Use rigid spacers (e.g., wooden blocks, steel plates) between layers to distribute pressure evenly and prevent local denting.
Secure with lashing straps to the container floor D‑rings.
Fill gaps between layers with foam boards or air bags to reduce relative movement during transit.
Advantages: stable loading, uniform pressure distribution, easy lifting, good compatibility with most container types.
Disadvantages: number of layers limited by container door height; loading density lower than vertical stacking.
2.2 Vertical Stacking
Vertical stacking means placing steel grating on its side, using the container’s height direction to carry more panels.
Key points:
Arrange grating on its side; the bearing bar direction can be either vertical or parallel to the container wall, but spacers must ensure even pressure distribution.
Dimensions must match container width; long panels work well with 40ft wide containers.
Use double lashing straps at the four corners to prevent tipping during transit.
Mark packaging clearly with “VERTICAL STACKING”, “DO NOT TURN OVER” and other handling instructions.
Advantages: makes full use of container height, higher loading density – floor area per container increases by 30‑50%.
Disadvantages:
Lateral strength is relatively weak. Steel grating is not designed to bear loads in the side (bar height) direction; improper stacking can cause deformation or damage.
If stacked incorrectly or the centre of gravity is too high, the load may tip or collapse when the container turns.
Lifting requires multiple evenly spaced lifting points to prevent bending or edge damage from concentrated forces.
Requires wooden frames or rigid pallets to support and secure the panels, demanding higher packaging materials and workmanship.
In current industry practice, side‑loading is common for steel pipes, sections, and coils, but rarely for large flat panels like steel grating, mainly because of the grating’s limited lateral strength.
2.3 Comparison of Flat vs. Vertical Stacking
| Dimension | Flat Stacking | Vertical Stacking |
|---|---|---|
| Loading density | Baseline (1.0) | 30‑50% higher |
| Stability | ★★★★★ | ★★★☆☆ |
| Operational difficulty | Low | High |
| Packaging requirement | Standard | Special frames / wooden crates |
| Deformation prevention | Good | Needs extra care |
| Suitable scenario | Regular batches | Large orders, maximum loading |
| Height limit (40ft GP) | Max 2 layers | Single layer vertically |
2.4 Recommended Strategy
Small orders (100‑500 sqm): Flat stacking – simple, suitable for small quantities.
Medium orders (500‑2000 sqm): Flat stacking 2‑3 layers – stable and controllable loading.
Large orders (>2000 sqm): May consider vertical stacking, but must use custom frames and reinforcement; confirm with the supplier before bulk execution.
For elongated or special‑shaped grating, refer to the half‑height open‑top container solution: octagonal pillar design enhances stability; for long products like rebar, loading/unloading from the top saves labour and machinery costs.
Chapter 3: Detailed Packaging Methods
3.1 Bundle Packing (Uncrated)
Bundle packing is the most economical method, suitable for grating with low surface finish requirements.
Requirements:
Bind grating panels into bundles with steel or PET strapping.
Each bundle: about 5‑10 panels, depending on thickness.
Wrap the outside with waterproof paper or plastic sheeting to keep out rain.
Place anti‑slip mats or wooden frames on the container floor to prevent sliding; mark “NO PACKING” if needed.
Suitable for: large quantities where anti‑corrosion and anti‑staining requirements are not strict.
3.2 Pallet Packing
Grating is fixed onto wooden or metal pallets, allowing fork‑lift handling and stacking.
Requirements:
Single package dimensions should match the container interior to minimise voids.
Keep a buffer gap of at least 2 cm between cargo and package walls to absorb shocks.
Secure the grating to the pallet with straps.
Use anti‑skid pads under pallets.
Comply with destination country wood packaging quarantine requirements (IPPC marking for fumigation or heat treatment).
Suitable for: orders that need warehouse stacking and reduced damage.
3.3 Wooden Crating
Fully or partially enclosed crates made of solid wood or plywood, lined with shock‑absorbing material. Wood must have moisture content meeting international standards and be fumigated or heat‑treated with official IPPC markings to avoid customs clearance issues.
Advantages: highest level of protection, impact‑resistant, prevents deformation.
Disadvantages: high cost and consumes extra freight volume.
Suitable for: high‑precision or very valuable grating that must be protected against transport deformation.
3.4 Comparison of Packaging Methods
| Packaging Method | Cost Index | Protection Level | Volume Efficiency | Suitable Order |
|---|---|---|---|---|
| Bundle Packing | 1.0 | ★★☆☆☆ | ★★★★★ | Large quantity, low surface finish |
| Pallet Packing | 1.3‑1.5 | ★★★☆☆ | ★★★★☆ | General export orders |
| Wooden Crating | 2.0‑2.5 | ★★★★★ | ★★★☆☆ | Precision‑machined, high‑value grating |
| Pallet + Corrugated box | 1.2 | ★★★☆☆ | ★★★★☆ | Small e‑commerce orders |
Chapter 4: How to Avoid Transport Deformation
4.1 Root Causes of Deformation
Steel grating has high strength only in the vertical direction (perpendicular to the plane of the grating); lateral stresses can cause deformation or damage. Common causes include:
Rough lifting: using wire ropes directly on the grating, creating local stresses exceeding the yield strength, causing permanent bending.
Improper lifting points: lifting point spacing too large – exceeding the load‑carrying span – causing the panel to bend.
Uneven ground: stacking on an uneven surface leads to uneven pressure and bending.
Incorrect lashing: excessive strap tension or unbalanced weight distribution causes structural distortion.
In one petrochemical project, 15% of the grating arrived on site with bending exceeding tolerance due to incorrect lifting points.
4.2 Lifting Technical Specifications
Forbidden practices:
Using wire ropes directly on the grating (especially focusing force on outer edges, causing flange‑type bending).
Jerking from one side or lifting with unbalanced force.
Lifting point spacing exceeding 2 metres.
Correct practices:
Use nylon lifting slings or textile slings with two or more balanced lifting points to avoid permanent edge deformation.
Lifting point spacing ≤2 metres.
Lift no more than 10 panels at a time to prevent permanent bending due to excessive overhang.
Use a fork‑lift to lift the entire stack from underneath, avoiding single‑edge force.
If wire ropes must be used, place rubber pads or wooden blocks between the rope and the grating.
4.3 Stacking and Securing Specifications
Stacking requirements:
Ground must be flat and firm.
Stacking height: 40ft GP – max 2‑3 layers; HQ can do 3 layers (but check overall stability).
Align supporting timber or pads to ensure even pressure distribution.
Place wood or rubber separators between layers to reduce surface scratches.
Securing requirements:
Lay anti‑skid mats or wooden frames on the container floor to prevent movement during transit.
Use protective material between grating panels to reduce direct contact with container walls.
Use strapping (PP or steel bands) to form secure bundles, then lash the bundles to the container D‑rings.
Fill gaps between cargo and container walls with foam boards or inflatable dunnage bags (gap ≤5 cm) to prevent lateral shifting.
4.4 Pre‑Shipment Checklist
| Check Item | Standard Requirement |
|---|---|
| Packaging integrity | Strapping secure, no damage; even gaps on all four sides when loading |
| Centre of gravity | Weight evenly distributed over container structure; no excessive side load |
| Securing points | At least 4 lashing points; multiple cross lashings; dunnage tightly fitted |
| Stacking layers | Flat stacking ≤3 layers; vertical stacking requires special frames |
| Markings | Waterproof film, moisture warning, “no tipping”, “vertical stacking” clearly marked; no sharp protrusions |
| Rust prevention | Edge painting or anti‑rust paper if required |
| Documentation | Packing list, dimension list, container seal number complete |
Chapter 5: Q&A – Common Questions on Container Loading
Q1: Is freight charged by weight or volume?
A: International sea freight uses the Revenue Ton (RT): 1 cubic metre = 1 tonne. For high‑density cargo (weight > volume), charge by weight; for light, bulky cargo (volume > weight), charge by volume. Steel grating density is generally >1, so at about 30 kg/m², weight‑based charging dominates. However, each container’s total freight includes door‑to‑door trucking, terminal handling charges, customs clearance, etc. Therefore, fully filling the container helps spread fixed costs over more product – the more you load, the lower the “allocated freight” per square metre.
Q2: Will vertical stacking cause the steel grating to tip over and get damaged due to vessel rolling at sea?
A: There is some risk; improper handling can indeed cause tip‑over. Loaders must perform a systematic force analysis and fix the stack with frames on both sides at the top, middle, and bottom, plus cross bracing, straps, and bottom pallets to resist rolling forces. Given the weak lateral strength of grating, vertical stacking is recommended only for very large orders with good packaging and under supplier guidance. Otherwise, three layers of flat stacking offer a better cost‑safety balance.
Q3: What if the steel grating rusts during sea transit?
A: Hot‑dip galvanized or 304/316L stainless steel grating already has a corrosion‑resistant layer, so short sea voyages do not normally cause rust. However, edges, mating faces, and scratched areas may develop slight rust in the high‑humidity, salt‑laden environment of a long voyage. Recommendations: request hot‑dip galvanized grating with coating thickness ≥85μm; apply zinc‑rich repair paint to cut edges and damaged coating; for stainless steel, add plastic or stretch film as an outer wrap; use desiccants or vacuum packaging to greatly reduce oxidation risk.
Q4: Will stevedores pay attention to “Do not invert” or “Vertical stacking” markings?
A: Not all overseas terminal workers will notice. Solutions: specify the markings in your booking with the freight forwarder; use multilingual labelling (Chinese, English, and the destination language); use integrated rigid frames that eliminate the risk of mishandling; take photos of each individual package and send them to the consignee in advance. Standard wooden crates or well‑strapped pallets have a fixed shape and obvious centre of gravity, making them easier to handle carefully than single loose panels.
Q5: How can I estimate how much steel grating fits in a container without actually shipping?
A: A simple formula – a 20ft GP holds about 25‑28 tonnes, a 40ft GP/HQ about 25‑28 tonnes, but grating is limited by height stacking. The most accurate method is a one‑to‑one stowage simulation using CAD or logistics software. Divide the container’s internal height by the height of one stacked set (grating thickness + separator height) to obtain the number of layers.
Q6: Are there special requirements for importing steel grating into Singapore?
A: Steel products imported into Singapore generally require a certificate of origin, material test reports, commercial invoice, and packing list. Some special specifications may need PSB (Productivity and Standards Board) certification or compliance with SS 363:2014. It is advisable to confirm customs clearance document requirements with the Singapore consignee before shipment.
Chapter 6: Quick Selection Table for Steel Grating Sea Freight
| Order Size | Recommended Loading Method | Packaging Method | Estimated Load Area (40ft container) | Deformation Risk |
|---|---|---|---|---|
| <100 m² | Flat 1‑2 layers | Bundle/pallet | ~20‑25 m² | Low |
| 100‑500 m² | Flat 2 layers | Pallet + waterproof paper | ~40‑50 m² | Low |
| 500‑1500 m² | Flat 3 layers | Pallet + steel strapping | ~60‑72 m² | Medium |
| >1500 m² (with supervision) | Vertical stacking | Wooden frames + crates | ~80‑110 m² | High (professional guidance needed) |
Chapter 7: Conclusion and bangtu Company's Technical Commitment
Sea freight costs are a significant part of steel grating export expenses. By optimising loading methods – choosing the right container, deciding between flat and vertical stacking, using proper packaging, and preventing transport deformation – you can significantly reduce the freight cost per square metre and improve overall competitiveness.
Key takeaways:
Use 40ft high cube containers for extra stacking height.
Flat stacking 2‑3 layers is the most cost‑effective and safe option for most orders.
For very large orders, vertical stacking can be considered, but only with reinforced frames and supplier guidance.
Proper lifting and lashing are essential to prevent deformation.
Always follow destination country requirements (e.g., Singapore SS 363:2014, IPPC markings).
About bangtu Company
Bangtu Company has specialised in steel grating for over two decades. Our products are widely used in industrial platforms, petrochemical plants, marine engineering, and municipal facilities in Singapore and around the world. We commit to:
All products meet YB/T 4001.1-2019 and Singapore SS 363:2014 standards; third‑party load test reports and EAC certification (for Russia) are available upon request.
Professional packing for sea freight: bundle packing, pallet packing, or wooden crating according to your needs, with anti‑rust treatment and clear handling markings.
Free loading optimisation advice: Tell us your order quantity and destination, and we will recommend the best container type, loading method, and packaging to minimise your freight cost.
Deformation prevention guarantee: We follow strict lifting and strapping protocols; any deformation caused by our loading is covered by our warranty.
Bilingual documentation: Packing lists, dimension lists, and loading instructions are provided in both Chinese and English to facilitate Singapore customs clearance.
Contact us for a free freight‑saving consultation.
Appendix: Referenced Standards and Literature
Deloitte (2025). Global Logistics Report 2025 – referenced for container load factor optimisation benefits (7‑12% cost reduction, 15‑20% efficiency increase).
Maersk (2025). Peak Season Surcharge Announcement, November 2025 – referenced for rising freight costs (USD 500‑1,000 per container, some routes >300%).
Guangdong‑Hong Kong‑Macao Greater Bay Area Container Export Freight Index (2025) – referenced for Singapore route 31.38% cumulative increase.
2025 China Container Industry Market Research Report – referenced for global container throughput (900 million TEUs) and Asian depot market share.
SS 363:2014 Specification for steel gratings for roads, drains and walkways (Singapore) – referenced for Singapore import requirements.
YB/T 4001.1-2019 Steel Grating Bars and Matching Parts Part 1: Steel Grating Bars – referenced for product specifications and load data.
Industry case study: Petrochemical plant lifting accident – referenced for 15% grating bending due to improper lifting points.
