What is a reefer container? Sizes, setpoints and what fails

“Reefer” is short for refrigerated. In shipping, a reefer container is a standard-size shipping container with insulated walls and its own refrigeration unit, which holds the cargo at a set temperature for the whole journey as long as it has electrical power. It is how most fresh fruit and vegetables cross an ocean today.

This guide covers what the word means on paperwork, the sizes and their real internal dimensions, what the machine controls, and the failures that turn a good load into a claim.

What “reefer” means: containers, ships and trucks #

A reefer container is the box: a 20ft or 40ft container with a refrigeration unit built into one end. It travels on an ordinary container ship, plugged into the ship’s power, and the same box goes onto a truck or a train at each end. When a booking, a bill of lading or a tariff says “reefer”, this is nearly always what it means.

A reefer ship or reefer vessel is a ship built to carry refrigerated cargo in insulated holds, usually on pallets. These specialised ships once carried a much larger share of the perishable trade; container lines have since taken most of it from an ageing specialised fleet, a shift the analyst Drewry has tracked for years.

A reefer truck or trailer is the road version. On a container import the road leg is usually the reefer container itself on a chassis, powered by a clip-on generator set (a “genset”).

How a reefer container works #

The unit on the front wall draws air out of the cargo space, cools it and blows it back in at the floor, through the T-shaped ribs of the decking. It rises through the pallets and returns at the top. The unit removes heat rather than adding cold, and it is sized to hold a temperature, not to bring a warm load down, which is why fruit has to be pre-cooled. What a modern reefer can and cannot do goes into the machine in depth.

It needs power for every hour of the trip: a reefer point at the terminal, the ship’s sockets at sea, a genset on the road. Hapag-Lloyd’s reefers, for example, take 380 V at 50 Hz up to 460 V at 60 Hz through a 32 A plug.

Reefer container sizes and specifications #

Carriers publish specification sheets, and the first thing they say is that dimensions vary by build series. The figures below come from Maersk’s and Hapag-Lloyd’s sheets; where the carriers, or several series in one fleet, differ, we give the range.

The number that matters most for fruit is the height to the load line, the red line inside the box that marks the maximum stowage height so that air can get over the top of the cargo.

20ft reefer container #

The 20ft reefer (ISO type 22R1) has well under half the space of a 40ft high cube for a payload limit not far below it, so it suits small or dense loads.

40ft reefer container #

Neither Maersk’s nor Hapag-Lloyd’s specification sheets list a standard-height 40ft reefer. On those lines a “40ft reefer” is a high cube, so check with your own carrier before you plan a load on a standard-height box.

40ft high-cube reefer container #

The 40ft high cube (ISO type 45R1) is the standard box for most fresh produce.

For comparison, Hapag-Lloyd’s 40ft dry high cube holds 76.3 m³. The insulation and machinery cost roughly 9 m³ of space in the same external size, and you pay ocean freight on all of it. Controlled-atmosphere versions weigh more: Hapag-Lloyd’s list at 4,570–4,800 kg tare.

What a reefer controls #

Temperature. The setpoint is fixed at booking from the exporter’s protocol for the commodity. Hapag-Lloyd quotes a range from as low as -40°C up to +30°C, in outside temperatures up to 50°C. The setpoint controls the air, not the fruit, which only follows if the load went in cold.

Fresh air exchange. Respiring fruit gives off carbon dioxide and ethylene, so a vent lets in outside air at a rate in cubic metres per hour, booked like the setpoint. Humidity is controlled on units with a dehumidification option.

Atmosphere, on controlled atmosphere boxes, which lower the oxygen and raise the carbon dioxide to slow ripening. Hapag-Lloyd’s ExtraFresh measures both gases and ventilates automatically, typically for avocados, bananas and mangoes. Its EverFresh injects nitrogen and carbon dioxide during the voyage, which suits blueberries.

What goes wrong with reefer containers #

Most reefer losses are not a machine breaking down in mid-ocean. They are decisions and gaps on land.

Fruit loaded warm. The unit cannot pull down field heat. It runs flat out, the log looks perfect, and the fruit spends days above specification.

The wrong setpoint or vent setting. A figure typed wrong on the booking is carried out faithfully for the whole voyage. Setting it lower “for safety” can be as bad, because chilling-sensitive fruit is damaged well above freezing.

Blocked airflow. A pallet over the floor channels or a load above the red line, and the fruit at the far end warms while the unit reports normal temperatures.

Power gaps. Terminal moves, the lift onto the ship, a transshipment hub, a genset out of fuel. A pre-cooled, full box drifts slowly, so a short gap is usually survivable; a long wait for a socket at a congested terminal is not.

Equipment faults. Units get a pre-trip inspection (PTI) before each trip, but compressors, fans and sensors still fail, and older boxes insulate less well.

A broken cold treatment. Some destinations require fruit to be held at or below a fixed pulp temperature for a set number of consecutive days to kill fruit fly larvae. A temperature rise can mean the count starts again, or the fruit is refused.

Monitoring a reefer in transit #

Every reefer logs its own temperatures, and that log is the most important document in a quality claim, so download it before the empty is returned. Newer boxes also send readings off the ship at sea. This is cold chain monitoring as the carriers sell it, and it reports the machine rather than the fruit. How to track a reefer container end-to-end goes through what to watch at each stage.

Where tracking fits #

A reefer’s risk sits in the gaps: the transshipment, the wait for a plug, the time on the quay after discharge. Those moments also decide your costs, because reefer free time is short and demurrage starts at discharge. Trackberry follows each reefer’s milestones and vessel position from loading to empty return. It does not read the unit’s temperatures; it tells you where the box is, when it was discharged and how many free days are left, while there is still time to act.

FAQ #

What does reefer mean? #

Reefer is short for refrigerated. In shipping it usually means a reefer container: a shipping container with its own refrigeration unit. It can also mean a refrigerated ship (a reefer vessel) or a refrigerated truck trailer.

What is the difference between a reefer container and a reefer ship? #

A reefer container is a refrigerated box that travels on an ordinary container ship, plugged into its power, and goes on by road or rail. A reefer ship is a specialised vessel with refrigerated holds, usually loaded with pallets. Containers now carry most of the perishable sea trade.

How big is a 40ft reefer container inside? #

A 40ft high-cube reefer is about 11.6 m long, 2.28–2.29 m wide and 2.53–2.55 m high inside, with 66.7–67.6 m³ of capacity on Maersk and Hapag-Lloyd figures. Cargo must stay below the red load line at about 2.42 m.

Sources #

• Maersk, Reefer equipment specifications (20ft standard reefer and 40ft high-cube reefers)
• Hapag-Lloyd, Container specification (reefer dimensions, temperature range, controlled atmosphere, power plugs, dry high-cube capacity)
• Drewry, Reefer shipping remains resilient despite 2022 trade contraction (containers gaining share from specialised reefer ships)