Containers and container types

1. ISO naming rules and container codes

ISO 668 defines the dimensions and coding of dry containers (types 1AA / 1A / 1CC and so on under DIN). The shorthand below is what the freight industry actually uses:

Ocean freight is billed in TEU (Twenty-foot Equivalent Unit): one 20GP = 1 TEU, one 40GP / 40HQ = 2 TEU. LCL cargo is billed on a different rule — 1 CBM = 1 RT (revenue ton) — while FCL is priced per container type.

2. Dry container specifications

The standard dry container specifications built into LoadExpert are below (source: ISO 668 plus common carrier reference values; in practice, the specifications for the container number on the bill of lading or from the carrier govern. The app lets you set the payload limit to the figure on your own contract — internal dimensions stay as fixed reference values):

Internal dimensions are shown in centimetres with inches in grey; payload in kilograms with pounds in grey.

Where each type is used

• 20GP: first choice for heavy cargo (steel, machine parts, chemical raw materials) — the smallest volume but the highest payload (28.2 t). The same volume shipped in a 40GP would run overweight.
• 40GP: the most common standard container, balancing volume and payload; suits light and medium-density cargo.
• 40HQ: one foot (30 cm) taller than a 40GP and 8 m³ more volume, the most exported type — bulky furniture, home appliances, paper products and textiles all use it.
• 45HQ: 5 ft (1.52 m) longer than a 40HQ and another 10 m³ of volume. Some services and ports do not accept 45HQ, so confirm the route accepts it before booking.

3. Reefer containers (REEFER)

A reefer is a refrigerated container with a compressor and insulated walls, usually abbreviated RF or REEFER. Types include 20RF, 40RF and 40RHQ.

How it is built

• Insulation: the inner walls carry polyurethane foam roughly 5–8 cm thick, which makes the usable internal dimensions slightly smaller than a dry container of the same size (typically 10–15 cm less internal length and 5–8 cm less internal width).
• T-shaped air channels: aluminium T-section ducts at the floor or ceiling move cold air up from the bottom or down from the top. Space must be left under the cargo for airflow, otherwise the circulation is blocked and temperature control fails.
• Temperature range: commonly adjustable from -30 °C to +30 °C; fruit and vegetables usually run at +2 to +8 °C, frozen meat and seafood at -18 to -25 °C.
• Floor drainage: drain holes and channels in the floor let the liquid from thawing meat run off, and pallets are needed to keep the cargo clear of it.

Loading restrictions

Reference values only. They vary between carriers and container owners — the specifications for the container number on the bill of lading govern.

4. Open top containers (OT)

A container with an open top (a removable soft roof plus lashing rings for crane slings), used for over-height cargo such as machinery, steel structures and glass.

Characteristics and limits

• Open top: a gantry crane can lift the whole unit in from above, sidestepping the height limit.
• Poor weather protection: rain and salt spray get in easily, so a waterproof tarpaulin has to be fitted over the top.
• Higher freight: OT rates are usually 1.5–2× a dry container of the same size, so confirm them when booking.
• How it is loaded: lay waterproof timber flooring to protect the bottom of the cargo, then secure it with wire rope or straps to the lashing rings on the container walls.

5. Flat rack / platform containers

A platform with end walls (or with no walls at all) for out-of-gauge cargo — over-width, over-length or over-weight.

What matters when loading

• Lashing: out-of-gauge cargo must be secured to the flat rack's lashing points with wire rope and turnbuckles — rough seas will slide and topple anything left loose on the platform.
• Centre of gravity: heavy cargo should sit as low as possible; a high centre of gravity reduces vessel stability.
• Declaration: over-size units need their dimensions, weight and a centre-of-gravity diagram sent to the carrier in advance, and are handled as special heavy-lift cargo.

6. Tank containers

A sealed pressure vessel — a stainless steel tank inside an outer frame — used for liquids such as chemicals, edible oils and alcohol.

• Standard 20-tonne tank (in practice it holds 21,000–26,000 litres).
• Types: IMO dangerous-goods tanks, food-grade tanks and heated tanks (to keep products such as wax and chocolate warm).
• How loading works: the tank is sealed, so "container capacity" is a matter of volume and cargo is not stacked inside it. LoadExpert does not calculate tank containers — treat volume utilization as 100%.

7. Other common special containers

8. Protecting cargo in a dry container: vents, desiccants and lashing nets

A dry container is not a sealed vacuum. On a 10–20 day ocean voyage the day-night temperature swing makes the air inside condense into droplets over and over again (container rain), and warm damp air ruins cartons, rusts metal and moulds cargo. Vents, desiccants and lashing nets are the three basic consumables that deal with damp, condensation and shifting.

Air vents

The ventilation grilles in the front and rear corner posts (one or two per side, roughly 3–4 cm across) let air inside and outside exchange slowly and release moisture. They are not the forced-air channels of a reefer — just natural ventilation, and on an ocean voyage that is not always enough.

• What they do: ease the condensation caused by sharp temperature swings; suited to cargo with respiration heat or that suffers when it is stuffy, such as coffee beans, cocoa, onions and potatoes.
• Limits: vents let in salt spray and dust, so valuable or moisture-sensitive cargo cannot rely on them alone — they still need desiccants and a container liner.
• In practice: check before loading that the vents are clear (many owners seal them against damp by default, so ventilation has to be requested at booking); for moisture-sensitive cargo you can ask the carrier for ventilated transport.

Desiccants

Desiccant placed inside the container to absorb water vapour, and the workhorse of export cargo protection. The common forms are desiccant poles (hung from the ceiling or walls), bags and tray pads.

• How it works: calcium chloride, silica gel or mineral clay fixes water vapour from the air into a solid, bringing relative humidity down into the safe range for the cargo (usually a target of <60% RH).
• Quantity: estimate from the container's volume and the season — a standard 40HQ at normal temperatures needs several poles in the 200–400 g class; double that on wet routes, in the rainy season or where the temperature swing is large. The principle is better to over-supply than to under-supply.
• Placement: distribute them evenly, favouring the door end, the side walls and the gap above the cargo; before closing the doors, check that the poles are hanging securely and are not blocking ventilation or handling.
• Don'ts: desiccant must not touch food directly (it needs segregated packaging), and it does not replace a waterproof liner against liquid water.

Lashing nets

A flexible mesh used to catch the cargo inside the container and stop it shifting or collapsing at sea, common with palletised, bagged and oversized loads.

• What it does: once the container is full, the net is hooked onto the lashing rings inside the doors and tensioned, catching any stack that could fall toward the door; the coverage is more even than a few individual straps.
• Used with: tensioning straps or turnbuckles plus wooden wedges or inflatable dunnage — the net covers a whole face, airbags fill a local gap and wedges stop things rolling.
• Choosing one: match the net width to the container's internal width; polyester (PES) webbing is light, corrosion-resistant and reusable, and is what dry containers mostly use.

9. Dry container loading limits — quick reference

Five limits to check before loading. Exceed any one of them and you risk the container being refused, the load being re-stuffed, or an insurance claim being turned down:

1. Weight

   Total container weight ≤ the payload limit (20GP 28.2 t / 40GP 26.6 t / 40HQ 26.5 t / 45HQ 27.6 t). The driver can weigh the unit on a weighbridge; over by 100 kg and it is refused at the gate.

2. Door height

   The height of a single carton ≤ the door height (40GP 228 cm / 40HQ 258 cm), otherwise it will not go through the door. When a whole pallet is forklifted in, it is the pallet's total height that has to clear the door. LoadExpert checks both cases.

3. Volume

   Total carton dimensions ≤ the container's internal dimensions. Any buffer is yours to add — LoadExpert lays the cartons out at the sizes you enter, against the standard internal dimensions, and does not deduct anything on your behalf. As a rule of thumb leave 2–4 cm in each direction to protect the rubber door seal; if that is too much bother, simply enter slightly larger carton dimensions (e.g. 60.5×40.5×25.5).

4. Centre of gravity

   LoadExpert's criteria: the offset of the centre of gravity from the container floor centre is within ±10% both lengthwise and widthwise, and the centre of gravity height is within 60% of the internal height. An unbalanced load reduces vessel stability, and any plan that goes out of range raises a warning.

5. Lashing and securing

   Straps plus wooden wedges plus inflatable dunnage against movement at sea. LoadExpert produces the loading plan only; lashing follows real warehouse practice.