Part IV — Ocean Freight
Containers & Container Types
The box that changed shipping — standard and specialised container types, their exact dimensions and capacities, the TEU, and how cargo is safely stuffed.
Most general cargo today moves in containers, and NAFL is emphatic that a forwarder must know container dimensions and characteristics cold — because advising clients and calculating how a shipment fits a box is daily work. Get the container choice or the cubic calculation wrong and cargo is left on the quay, or a second box is paid for needlessly.
The standard container and the TEU
The standard container is the twenty-foot (20’) box, and capacity across the industry is measured in multiples of it.
TEU = Twenty-foot Equivalent Unit. It is the unit used to describe container volumes and ship capacity. A 20’ container = 1 TEU; a 40’ container = 2 TEU. A large container vessel of NAFL’s era carried 2,000–6,000 TEU; today’s largest exceed 24,000 TEU (Chapter 12).
Dimensions and capacities — the numbers to know
NAFL gives the working figures for standard dry-cargo (DC) containers. These are the ones a forwarder quotes against:
| 20’ Dry | 40’ Dry | |
|---|---|---|
| Internal length | 5,898 mm | 12,031 mm |
| Internal width | 2,352 mm | 2,352 mm |
| Internal height | 2,393 mm | 2,393 mm |
| Cubic capacity | ~33.2 CBM | ~67.7 CBM |
| Max gross weight | 30,480 kg | 30,480 kg |
| Tare (empty) weight | ~2,300 kg | ~3,840 kg |
| Payload | ~28,180 kg | ~26,640 kg |
Two practical points NAFL draws from this table: a 40’ holds roughly double the volume of a 20’ but not double the weight payload (its own tare is heavier), so a 40’ is for bulky cargo, a 20’ for dense/heavy cargo. And the cubic figures (33.2 / 67.7 CBM) are exactly the numbers used in the stuffing calculations of Chapter 3.
The high cube and the 45’
The high-cube (HC) is a 40’ container about a foot taller (8’6” → 9’6” external) for extra volume — and NAFL notes that most 40’ boxes seen in the Middle East are high-cubes. The 45’ exists but is less common, as its extra length complicates stacking with standard 20’/40’ boxes.
Specialised container types
Beyond the standard dry box, NAFL covers the family of specialised units — each solving a particular cargo problem:
- Reefer (refrigerated) — carries its own electrically powered freezer unit; for perishables (meat, fish, fruit, dairy) needing temperature control throughout transit.
- Open-top — no solid roof (a tarpaulin instead); for out-of-gauge loads taller than the box, or top-loading with a crane (e.g. machinery).
- Flat rack — no roof and no sidewalls; strengthened lashing points; end-walls that fold down. For heavy, wide or awkward cargo (vehicles, aircraft engines, generators). Often preferred over open-top at 40’ for its much heavier payload. End-walls up = ISO flat rack; both down = platform flat.
- Open-side — opens along the side for oversized or awkward loading.
- Dry bulk — for grain, powder and granular cargo loaded through hatches.
- Half-height — for exceptionally heavy, dense cargo (steel tubes, pipes) where weight, not volume, fills the box.
- Tank (ISO tank) — a stainless-steel tank built into a 20’ frame for carrying liquids, chemicals and gases in bulk; reusable, robust, and the standard for hazardous and high-value liquids (insulated/heatable versions exist). The handle-like-a-container way to move a liquid in bulk (Chapter 17).
- Flexitank — a large disposable bladder fitted inside an ordinary 20’ dry box, turning it into a one-way carrier for non-hazardous bulk liquids such as edible and base oils (Chapter 17). Cheap, single-use, and never used for dangerous goods.
Container anatomy and safe stuffing
A forwarder should recognise the structural parts, because they explain how a box is lifted and loaded safely. NAFL labels them on a construction diagram; the ones that matter in practice:
- Corner castings (corner fittings) — the eight reinforced corners. Gantry-crane spreader bars and ship/chassis twistlocks lock into these to lift and secure the box. They are the only points designed to take the lifting and stacking loads.
- Corner posts — the vertical members at each corner that carry the stacking weight of the containers above (boxes are stacked many-high on deck and in the yard).
- Cross members — the transverse under-floor beams that carry the cargo’s weight. Heavy point-loads must be spread across several of them.
- Top and bottom side rails, end rails, side posts — the frame.
- Lashing points — fittings on the floor and side walls to secure (lash) the cargo inside; NAFL notes good containers provide ample lashing points on floor and sidewalls.
- Fork pockets — slots underneath so a heavy-duty fork-lift can lift the box (item 12 on NAFL’s diagram).
- Door gasket, locking bars, locking-bar handles/keepers — the weather-tight, lockable door gear.
Containers are lifted by gantry-crane spreaders engaging the top corner castings, or by fork-lift via the fork pockets. When stuffing, never place a particularly heavy weight directly on the floor without spreaders / bearers to distribute it across several under-floor cross members — a concentrated point load can punch through or distort the floor. Every box is periodically inspected and plated under the Container Safety Convention (CSC).
NAFL’s central stuffing rule:
Safe container transport depends chiefly on a correct and immovable stow and an even weight distribution. Either the cargo is stowed so tightly that no lateral or longitudinal movement is possible, or it must be effectively restrained. Heavy weights go at the bottom; load must be spread across several cross members using bearers or dunnage so it is never concentrated on one point of the floor.
All units are periodically inspected under the Container Safety Convention (CSC).
(The full set of stuffing, restraint and load-distribution techniques — shoring, lashing, wedging, locking — is covered with packing in Chapter 22.)
The container dimensions NAFL gives are still exactly correct — this is one area where 2003 needs no updating. What has changed is around the box: ships grew from ~6,000 TEU to 24,000+ TEU; the high cube is now the default 40’ worldwide; and new types are common — notably reefers with controlled/modified atmosphere for longer-life perishables, and standardised 45’ pallet-wide units in some trades. The box itself is the great constant of modern shipping.
Containers underpin WorldZone’s two biggest ocean services — FCL (a full box for one customer) and LCL (shared, see Chapter 13). The everyday judgement: match the box to the cargo. Dense, heavy goods → 20’; bulky, light goods → 40’/HC; out-of-gauge or heavy project pieces → flat rack or open-top; temperature-sensitive → reefer. Quote against the real capacities (33.2 / 67.7 CBM) and the payload limits — promising a customer a fit that exceeds the box’s weight or cube is a classic, avoidable error.
What to take from this chapter
- The 20’ box = 1 TEU; capacity and ships are measured in TEU.
- Know the numbers: 20’ ≈ 33.2 CBM, 40’ ≈ 67.7 CBM, max gross ~30.5 t; 40’ is for bulk, 20’ for weight.
- Match cargo to the right type — reefer, open-top, flat rack, dry-bulk, half-height.
- Safe stowage = immovable stow + even weight distribution; heavy low, load spread over cross members.