A practical, airflow-first blueprint for loading frozen Indonesian seafood in 40’ HC reefers. Learn the exact door gap, dunnage gate setup, pallet orientation, logger placement, and carton-count planning that prevents hotspots in tropical ports.
If you’ve ever opened a reefer at destination and found one corner soft or frosted while the rest is perfect, you know this truth. Frozen seafood quality lives or dies on airflow. Not paperwork. Not the brand of reefer. Airflow.
We ship thousands of tons of Indonesian seafood every year and the pattern is consistent. Good T-floor airflow and disciplined clearances beat most other variables. Below is the exact playbook we use in 40’ HC reefers for frozen loads, refined in tropical ports like Surabaya and Bitung.
The 12 best practices that keep frozen seafood cold and consistent
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Build the load around the reefer’s airflow, not around carton count. The unit pushes supply air along the T-floor from the machinery end to the doors. It rises at the doors and returns along the ceiling to the machinery end. Anything that blocks floor channels, the door rise, the ceiling return, or the front bulkhead grills creates hotspots. We always plan carton count after we confirm these paths are open.
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Leave a vertical door gap and use a real dunnage gate. Frozen shrimp and fish cartons need a vertical chimney at the doors so supply air can rise. We target a 10–12 cm gap measured from the last row to the closed doors, kept open by a dunnage gate. Build the gate with slats and 10 cm spacers so air passes through. Strap it to the lashing rings. Don’t rely on shrink-wrap alone. It fails when the truck hits the first pothole.
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Stay under the red load line. Give the ceiling room to breathe. Every reefer has a red line under the ceiling. Don’t touch it. For frozen cargo, we keep at least 7–10 cm of clearance below that line end to end. Stacks higher than the red line starve the ceiling return and cause the classic “top layer soft, center hard” complaint.
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Respect the front bulkhead grills and drains. At the machinery end, don’t press cartons over the return-air grills or the drain holes. We maintain 8–12 cm standoff using spacers or a sacrificial pallet. Check the front guards are intact. Crushed grills = reduced return airflow = slow pull-down on the hottest cartons.
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Use pallets that don’t choke the T-floor. Solid-bottom pallets are airflow killers. Use 1000×1200 mm or 1100×1100 mm pallets with open deck and runners that let air flow along the length of the T-floor channels. If you must use partial sheets, notch or perforate them so the T-floor isn’t bridged.
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Choose cross-stack for stability and micro-chimneys. For frozen seafood cartons, we cross-stack layers to lock the column and create small interstitial paths. Pure column stacking can work with premium cartons, but we’ve seen more leaning, which then blocks the ceiling return.
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Pallet configuration for 40’ HC reefers. Most 40’ HC reefers take 20 standard 1000×1200 pallets single-stacked in a 10×2 pattern. We keep pallet height at 2.10–2.20 m including pallet to stay under the red line and to keep the top layers cold. If weight is the limiting factor, we still cap height to preserve airflow.
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Floor-load only if your team can execute the pattern. Floor-loading increases carton count but also increases risk. If you do it, maintain straight longitudinal channels along the T-floor and a clean 10–12 cm door gap. Avoid bridging channels with cardboard or loose plastic. In our experience, poorly executed floor-loads create more hotspots than palletized loads.
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Zero fresh air for frozen. Air chutes only for chilled. Frozen seafood runs with vents fully closed. No fresh air. Air chutes are not needed for frozen loads. They’re for warm produce or chilled fish like sashimi-grade Yellowfin Saku (Sushi Grade) moving at +0 to +2°C. For frozen Mahi Mahi Portion (IQF), Grouper Fillet (IQF), or Frozen Shrimp (Black Tiger, Vannamei & Wild Caught), keep vents closed and focus on floor-to-door-to-ceiling airflow.
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Load fast in tropical heat. Power during stuffing whenever possible. At 30°C ambient, an unplugged reefer with open doors warms fast. We plan staffing so the unit is powered at the dock or by genset the entire time. If power must be cut, keep any single gap under 15 minutes and cumulative unplugged time under 30–40 minutes. Close doors between pauses. Frozen product should ship frozen, not “pulled down in transit.”
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Use data loggers where they’ll actually tell you the story. We place at least three loggers. One near front bulkhead high on the centerline. One at the doors, top third of the load, center. One mid-length, mid-height. Avoid burying them against the walls or on the floor channels. If you only use one, put it door-side top third. That’s where hotspots show up first.
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Do a final airflow walk. Don’t just sign the loading sheet. Before sealing, look from the doors and from the machinery end. Can you see the T-floor channels? Is the dunnage gate solid? Are you under the red line everywhere? Are any cartons pressed into the side walls or the front grills? This 60-second check has saved more loads than any app.
Quick answers to the questions we get every week
What is the correct door gap for return air in a reefer carrying frozen shrimp?
Leave 10–12 cm at the doors and hold it with a dunnage gate. This lets supply air rise and return along the ceiling. We’ve tested 5 cm gaps. It’s not enough when cartons settle during transit.
Do I need air chutes for frozen seafood, or only for chilled fish?
Only for chilled. Frozen cargo runs with vents closed and no air chutes. Chutes are for warm-produce or chilled fish programs where top-to-bottom airflow needs help.
How many 20 kg shrimp cartons fit in a 40’ HC reefer without blocking airflow?
You’ll be weight-limited, not space-limited. Plan for 1,250–1,350 cartons of 20 kg each (25–27 metric tons) depending on palletization, carton dimensions and the space you keep for door gap, ceiling clearance and bulkhead. If you need an exact row plan for your carton size, we can map it for you in under an hour. Need help with your specific spec? Contact us on whatsapp.
Where should I place temperature data loggers to detect hotspots?
At least three points. Front bulkhead high. Doors top third center. Mid-length, mid-height. If you run five, add door-side near floor and a centerline mid-height near the front bulkhead. Don’t tape to the wall. Log the product temperature, not the metal skin.
How far should pallets be from the reefer ceiling and side walls?
Ceiling. Keep stacks 7–10 cm below the red load line across the entire container. Side walls. Don’t hard-press cartons against the walls. We keep 3–5 cm nominal clearance so the ceiling return isn’t pinched by leaning columns. Use corner boards if cartons are soft.
What is a dunnage gate and how do I secure it at the doors?
It’s a ventilated barrier you build to hold the last row off the doors. Make a frame that stands 10–12 cm away from the doors using wood slats or plastic beams with spacers. Strap to lashing rings on both sides. The idea is simple. Hold the last row upright and let air rise. No solid sheets. No fully wrapped film across the face.
How long can I keep the reefer unplugged during loading in Indonesia?
Aim for zero. If power must be cut, keep any single interruption under 15 minutes and total unplugged time under 30–40 minutes at 30°C ambient. Close doors during pauses. You’ll see it in the curves if you go longer. Return air spikes and never quite comes back to setpoint for hours.
Practical patterns that work in Indonesia
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Frozen shrimp masters on pallets. For 20 kg shrimp masters with robust cartons, we run 20 pallets, cross-stacked, 2.10–2.20 m high, vents closed, 10–12 cm door gap, 7–10 cm below red line. Carton count usually lands 1,260–1,320.
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IQF fish portions in small cartons. For IQF portions like Mahi Mahi Portion (IQF), Grouper Bites (Portion Cut) or Kingfish Fillet (Portion Cut / IQF), small cartons settle. Use tighter wrap, edge protectors, and a firm dunnage gate. We also avoid ultra-high stacks. 2.00–2.10 m performs better through rough roads from plant to port.
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Mixed SKU loads. If you mix heavier blocks and lighter IQF cartons, place denser blocks low and forward, lighter IQF back and up. You’re balancing both weight and airflow. Never build a solid wall of block-frozen cartons at the doors.
Reading your reefer curves like a pro
For frozen cargo with closed vents, supply air should run close to setpoint. Return air will be slightly warmer. A healthy delta on a stabilized frozen load is usually 1–3°C. Signs of airflow trouble. Return air stays stubbornly high, supply is flat at setpoint, and the delta grows over time. Or you see saw-tooth spikes after stuffing that take many hours to decay. Both hint at blocked T-floor, too-high stacks, or a missing door chimney.
Final takeaway
In our experience, three things prevent 90% of frozen-seafood claims in tropical lanes. Keep the door chimney open with a proper dunnage gate. Stay below the red line everywhere. And never choke the T-floor with solid pallets or random dunnage. Get those right and your frozen shrimp, IQF fillets, and portions will arrive as specified. Questions about a tricky carton size or a mixed load? Call us.