Why Reefer Loading Technique Determines Shipment Success
A refrigerated shipping container — known in the industry as a reefer — is far more than a cold box on wheels. It is a precisely engineered cargo unit designed to maintain a set temperature for weeks across thousands of nautical miles. For frozen seafood, where a single temperature excursion can compromise product safety and marketability, how the container is loaded is as important as the unit itself.
This guide walks exporters, importers, freight forwarders, and trade compliance teams through the fundamentals of reefer container loading for frozen seafood: container types, capacity, loading patterns, temperature and ventilation setpoints, pre-shipment inspections, and common mistakes to avoid.
Reefer Container Types and Capacity
Ocean carriers operate three main reefer container formats. Choosing the right unit affects cost per kilogram, transit handling, and product protection.
20ft Standard Reefer
- External dimensions: 6.06m (L) × 2.44m (W) × 2.59m (H)
- Internal volume: approximately 27–28 cubic meters
- Maximum gross weight: 30,480 kg
- Tare weight: approximately 3,100 kg
- Seafood payload: 10–14 metric tons depending on carton density
- Best for: Trial shipments, high-value low-volume products, smaller distributors, or when destination port is weight-restricted.
40ft Standard Reefer
- External dimensions: 12.19m (L) × 2.44m (W) × 2.59m (H)
- Internal volume: approximately 58–60 cubic meters
- Maximum gross weight: 32,500 kg
- Seafood payload: 22–25 metric tons
- Best for: Standard export volumes where cube utilization is moderate.
40ft High-Cube Reefer (40HC)
- External dimensions: 12.19m (L) × 2.44m (W) × 2.90m (H)
- Internal volume: approximately 67–68 cubic meters
- Maximum gross weight: 34,000 kg
- Seafood payload: 24–26 metric tons of carton-packed frozen seafood (most common), or up to 27 MT for dense block-frozen product
- Best for: Full container load (FCL) frozen seafood exports — the industry standard.
The 40HC reefer is the workhorse of frozen seafood exports. Its extra internal height allows one additional layer of cartons compared to the standard 40ft, improving cost per kilogram by 8–12%.
Estimating Metric Tons per Container
Actual tonnage depends on product type, carton size, glazing, and loading pattern. Typical figures for a 40HC reefer:
- Shrimp (IQF, 1.8 kg/carton master): 22–24 MT
- Shrimp (block frozen, 10 kg blocks): 25–26 MT
- Fish fillets (IQF, 10 kg master): 23–25 MT
- Whole round fish (IQF, 20 kg master): 24–26 MT
- Squid/cuttlefish (block frozen): 25–27 MT
- Value-added / breaded (retail packs): 18–22 MT (lower density)
Always confirm payload limits with the carrier and destination port. Some US and EU ports enforce stricter gross weight limits due to road-haul regulations.
Temperature Setpoints for Frozen Seafood
Reefer units are designed to maintain temperature, not to freeze product. Product must be loaded at the correct core temperature before the container is closed.
- Setpoint: -20°C supply air temperature is industry standard for frozen seafood. Some sensitive products (tuna for sashimi) may require -25°C or colder.
- Core product temperature at loading: -18°C or below (many exporters target -22°C to provide safety margin).
- Return air alarm: typically set at -15°C to -16°C to alert the operator if temperature drifts.
- Supply vs return differential: under normal load, 1–3°C difference is expected; larger differentials may indicate loading or airflow issues.
Ventilation Setting — Closed for Frozen
Reefer containers include adjustable fresh air vents for respiring cargo (fruits, vegetables). For frozen seafood:
- Vents must be fully closed.
- Frozen product does not respire, so no air exchange is needed.
- Open vents introduce humid, warm ambient air that increases refrigeration load, causes frost buildup on the evaporator, and raises fuel consumption during voyage.
Loading Patterns for Maximum Cold Chain Protection
How cartons are stacked inside the container determines airflow and therefore temperature uniformity. Reefer units supply cold air through the T-floor (the channeled aluminum floor) and return warm air along the ceiling.
Block Stow (Tight Pack)
Cartons are stacked tightly floor-to-ceiling, wall-to-wall with minimal gaps. Best for fully palletized or evenly sized cartons. Advantages: maximum payload, uniform block. Requires cartons to be uniform and sturdy.
Pallet Stow
Product is pre-palletized (typically 20 pallets per 40HC). Advantages: faster loading and unloading, reduced damage, simpler counting. Disadvantages: loses 1–2 MT payload to pallet weight and gaps.
Floor Loading
Cartons stacked directly on the T-floor without pallets. Common for price-sensitive commodity exports. Advantages: maximum payload. Disadvantages: slower loading/unloading, higher risk of damage.
Critical Loading Rules
- Do not block the T-floor channels — air must flow beneath the cargo the full length of the container.
- Do not load past the red load line — the ceiling of the container has a marked line showing maximum height. Cartons above this line block return airflow.
- Maintain clearance at the front bulkhead — 5–10 cm clearance between cargo and the evaporator allows proper air discharge.
- Solid wall-to-wall pack — minimize gaps between cartons. Use dunnage (cardboard or air bags) if cargo does not fill the width.
- Avoid chimneys — vertical air channels between stacks short-circuit airflow and create warm spots.
Pre-Loading Inspection — The PTI Check
Before accepting a reefer unit for loading, conduct a Pre-Trip Inspection (PTI):
- Confirm PTI has been performed by the depot (request the PTI report).
- Verify the unit holds setpoint temperature for at least 30 minutes before loading.
- Check interior is clean, dry, and odor-free.
- Inspect T-floor for debris blocking channels.
- Confirm door gaskets are intact.
- Verify evaporator fans operate in both directions (for frozen cargo, continuous single-direction airflow is used).
- Record unit serial number, setpoint, and pre-cool temperature on the loading report.
Pre-Cool the Container Before Loading
The container must be pre-cooled to at least the setpoint temperature before loading begins. Never load frozen product into a warm container expecting the reefer unit to catch up — the unit is not designed for this, and the core of your pallets will experience temperature abuse for hours or days.
Best practice:
- Connect the reefer unit to shore power at the loading facility.
- Run for 2–4 hours before loading begins.
- Confirm return air temperature reaches -18°C or colder.
- Turn off the unit briefly during the loading itself to avoid drawing ambient air through open doors.
- Restart the unit immediately after doors are closed.
Loading Environment and Speed
- Refrigerated dock — ideally, loading takes place at a 0°C to 5°C refrigerated loading dock directly from cold storage.
- Loading speed — complete loading within 2–4 hours. Prolonged loading in ambient conditions compromises product temperature.
- Product staging — keep product in cold storage until the container is ready. Do not pre-stage pallets on a warm dock.
- Tropical considerations — in Southeast Asian ports, ambient temperature often exceeds 32°C. Refrigerated docks are essential for quality exports.
Temperature Monitoring and Data Loggers
Modern reefer units record supply and return air temperatures throughout the voyage. However, best practice is to supplement this with:
- Independent data loggers — placed inside the cargo in 2–3 locations (front, middle, back). Brands include Sensitech, Emerson, DeltaTrak, and Testo.
- Real-time GPS/temp trackers — transmit data via cellular or satellite. Allow shipper and buyer to monitor the voyage live.
- Time-temperature indicators (TTIs) — irreversible color-change stickers that provide an at-a-glance check on arrival.
Documentation and Sealing
Once loading is complete:
- Restart the reefer unit and verify setpoint.
- Close and bolt both doors.
- Apply customs seal (bolt seal conforming to ISO 17712) and record the seal number.
- Record container number, seal number, product temperature, unit serial, setpoint, vent setting, and loading photos.
- Include this data on the shipping instruction and packing list.
For a full overview of shipping documentation, see our export documentation resources.
Common Mistakes That Cost Exporters Money
- Skipping pre-cooling — loading into a warm container causes rapid product thawing at the outer layers.
- Opening vents — increases fuel costs, causes frost buildup, and can thaw cargo near the ceiling.
- Overloading beyond the red load line — blocks return airflow, creates hot spots, and risks insurance claims.
- Loose pack with chimneys — cold air short-circuits back to the evaporator instead of flowing through the cargo.
- Slow loading in ambient conditions — 6–8 hour loading in tropical heat can cause irreversible quality loss.
- No independent data logger — disputes about temperature excursions become difficult to resolve.
Port Selection and Power Supply
Choose origin and destination ports with adequate reefer infrastructure. Hanuman Seafood exports through Laem Chabang, Bangkok Port, Songkhla, and Ranong — all of which have modern reefer plug capacity, monitoring, and connecting services to all major global trade lanes. Direct sailings without transshipment are preferred for frozen cargo to minimize power-off time during vessel-to-vessel transfers.
Ship Frozen Seafood with Confidence
Reefer container loading is a discipline that combines engineering, logistics planning, and quality control. Exporters who master the details — pre-cooling, airflow, vent settings, data logging — consistently deliver product that arrives in the same condition it left the freezer.
Contact our export team to discuss your shipping requirements, container planning, and cold chain monitoring options for frozen seafood exports from Thailand.
