A machine that cannot pass through a standard container door does not automatically require a flat rack; over-height cargo is not always out of gauge; and temperature-sensitive cargo cannot be managed by simply booking a reefer and entering a set point. The wrong equipment choice may cause booking rejection, OOG surcharges, vessel-space constraints, cargo damage or a cold-chain failure. This guide explains when to use an Open Top, Flat Rack or Reefer based on actual packed dimensions, lifting and loading method, payload distribution, support points, environmental requirements and carrier acceptance.

TGIMEX · Updated 20/07/2026

QUICK FACTS

Open Top

Use when cargo must be lowered from above or exceeds door/roof clearance while side walls and end doors remain useful.

Flat Rack

Use for over-width, over-height, irregular or heavy cargo requiring side access, engineered support and lashing.

Reefer

Use when transport temperature must be maintained and, where the booked equipment or service supports it, ventilation, humidity or atmosphere must also be controlled; it is not a rapid pull-down freezer.

Do not choose by commodity name

The decision must follow packed dimensions, weight, centre of gravity, lifting method, support points, environmental settings and route.

Special bookings require approval

OOG, heavy or special-setting reefer cargo normally requires carrier/terminal confirmation of equipment, stowage and operating conditions before stuffing.

Illustration for Open Top, Flat Rack and Reefer Containers: When Is Special Equipment Required? — Illustration of the logistics topic, document or operation discussed in the article.

SCOPE

This article mainly applies to ocean container transport and intermodal legs using ISO freight containers. It focuses on equipment selection, booking data, packing/securing and cold-chain control. Dimensions, payloads, fleet availability, road restrictions and OOG approval procedures vary by carrier, terminal, country and sailing. Always verify the booking confirmation, the specification of the allocated unit and its CSC plate.

TERMS AND OPERATIONAL MEANING

Term	Operational meaning	Why it matters
Open Top (OT)	Container with removable/open roof, usually covered by tarpaulin, while retaining floor, side walls and end doors.	Allows top loading and approved over-height cargo.
Flat Rack (FR)	Platform-like unit with a deck and end walls, but no roof or side walls; some end walls are collapsible.	Suitable for over-width/height/length cargo and side loading; requires engineered support and securing.
Reefer	Insulated container with refrigeration machinery, supply/return air paths and controls.	Maintains carriage temperature; ventilation, active humidity control or controlled atmosphere applies only where the booked equipment and service support those functions.
In-gauge	Cargo remains within the carrier-defined envelope for special equipment and does not consume extra vessel space.	Special equipment may still be required even without an OOG charge.
Out of Gauge (OOG)	Cargo or securing material protrudes beyond the permitted length, width or height envelope.	Requires exact declaration, stowage/handling approval and often route restrictions or extra charges.
Payload / MGW	Payload is usable cargo capacity; MGW is maximum operating mass including tare and cargo.	Must be checked against the allocated unit, local road law and terminal limits.
VGM	Verified gross mass of the packed container.	A SOLAS condition for vessel loading; it does not replace accurate cargo weight and load-distribution data.

SELECTION LOGIC

The first decision is not the equipment name; it is the dominant cargo constraint:

Access and height: cargo cannot pass through the door, needs top lifting or exceeds roof clearance — review Open Top.
Width, length, support or heavy loading: side access, protrusion, concentrated loads or irregular geometry — review Flat Rack.
Environmental control: temperature control, or supported ventilation, humidity, controlled-atmosphere or cold-treatment functions — review the appropriate Reefer service.

One unit does not solve every constraint. Cargo that is both OOG and temperature-sensitive may require a project-specific solution; do not assume a standard reefer or open top can satisfy both.

OPEN TOP – FLAT RACK – REEFER COMPARISON

Decision factor	Open Top	Flat Rack	Reefer
Primary constraint	Door/roof access, top loading or approved over-height.	Over-width/height/length, side loading, concentrated loads or irregular geometry.	Temperature must be maintained; ventilation, humidity or atmosphere control applies only to capable equipment/services.
Protection	Side walls, doors and tarpaulin; weather exposure depends on covering and route.	Little side/roof protection; packaging, corrosion protection and covering are critical.	Insulated and environmentally controlled, but usable cube is lower than dry equipment.
Typical loading	Vertical crane loading or through doors if feasible.	Top/side loading or direct placement on deck with dunnage and lashing.	Preconditioned cargo, unobstructed airflow and compliance with load lines.
Key data	Packed dimensions, over-height, lifting points, tarpaulin and roof-closing feasibility.	L×W×H, weight, centre of gravity, support/load points, lifting and lashing plan.	Commodity, set point, cargo temperature at stuffing, ventilation; humidity/CA/cold treatment where supported; and airflow layout.
Main risk	Incorrect cover, undeclared height or protruding securing gear.	Local deck overload, unstable centre of gravity, poor lashing or inaccurate OOG data.	Hot stuffing, blocked airflow, wrong set point, power interruption or unsuitable settings.
Avoid when	Cargo is over-width or needs both sides fully open.	Cargo fits ordinary equipment and no engineered securing plan exists.	No product-based need for controlled conditions.

WHEN TO CHOOSE EACH TYPE

Choose Open Top when

Cargo cannot pass through the doors but can be lowered vertically.
Cargo exceeds dry-container height but remains within the Open Top footprint or has carrier-approved OOG protrusion.
Side walls and end doors remain useful for protection, bracing or discharge.

Choose Flat Rack when

Cargo is over-width, over-height or over-length, needs side loading or unrestricted top access.
Machinery, steel structures, pipes, vehicles or irregular equipment cannot be enclosed.
Support, dunnage and lashing can be engineered safely on the deck.

Choose Reefer when

A defined transport temperature must be maintained, or the cargo requires supported ventilation, humidity or controlled-atmosphere functions.
Cargo is preconditioned as required and the stow plan preserves airflow.
Power, genset, monitoring and off-power limits are defined end to end.

Keep standard dry equipment when

The cargo fits, can be loaded through the doors, remains within load limits and has no environmental-control requirement. Special equipment should not be selected merely as a precaution if it adds cost and complexity without resolving a real constraint.

ILLUSTRATIVE SPECIFICATIONS AND WARNING

Illustrative equipment	Maersk-published in-gauge envelope*	What must be confirmed before final approval
20′ Open Top	549 × 222 × 234 cm	Compare the complete secured and covered envelope; do not treat this as a universal door dimension.
40′ Open Top	1,181 × 219 × 234 cm	Confirm the equipment series, top opening and ability to fit the cover on the allocated unit.
40′ Open Top HC	1,181 × 219 × 265 cm	Confirm route availability and the actual unit dimensions in the booking confirmation.
40′ Flat Rack	1,163 × 244 × 194 cm	Freeze end-wall position, protrusions, dunnage, concentrated loads and the lashing plan.
40′ Flat Rack HC	1,163 × 244 × 226 cm	Verify vessel slots, clearance, terminal acceptance and inland restrictions.

*These are illustrative envelopes published by one carrier for in-gauge/OOG identification. Do not use this table to finalise payload or MGW: fleet pages may vary by equipment series, market and terminal acceptance. The allocated unit, CSC plate, booking confirmation and inland/terminal limits are the final control data.

DOCUMENTS AND DATA TO VERIFY

Data group	Fields to freeze	Recommended evidence	Decision affected
Cargo identity	Technical name, model, indicative HS, new/used status and DG status.	Datasheet and catalogue; SDS and the applicable dangerous-goods declaration/document where required.	Equipment acceptance, declarations and route restrictions.
Actual dimensions	Packed L×W×H, protrusions and transport orientation.	Scaled drawing, measured photos and packing sketch.	Dry/OT/FR, in-gauge/OOG, slot and handling.
Mass and load	Gross/net, centre of gravity, support points, contact area and local loads.	Weight certificate, COG drawing and dunnage design.	Payload, floor loading, lifting gear and inland route.
Lifting/securing	Lifting points, sling angles, lashing points/material, anti-slip and anti-tipping controls.	Lifting plan, lashing plan and post-stuffing photos.	Depot, terminal and carrier acceptance.
Reefer settings	Commodity, set point, stuffing temperature, ventilation; humidity/CA/cold treatment where supported; and inland power.	Reefer SI, product protocol and logger plan.	Reefer type, settings, genset and monitoring.
Route and delivery	POL/POD, transshipment, pickup/delivery, road limits, cranes and direct-to-truck needs.	Route survey, permits and terminal instruction.	End-to-end feasibility, permits and operational timing.

EQUIPMENT SELECTION AND APPROVAL PROCESS

Identify the dominant constraint

Is the problem access/height, width/length/support, or environmental control? Start from cargo physics, not equipment labels.

Measure the transport envelope

Include pallet, skid, frame, tarpaulin and securing material.

Freeze mass and load distribution

Confirm gross mass, centre of gravity, support points, local loads, lifting equipment and road limits.

Select OT, FR or Reefer provisionally

OT for top loading/over-height with side walls; FR for over-width/side loading/heavy irregular cargo; Reefer for controlled conditions.

Engineer securing or airflow

Prepare lifting/lashing/cover drawings for OT/FR, or airflow and stowage layout for Reefer.

Submit for carrier approval

Provide dimensions, weight, photos, drawings, commodity, DG status, route and reefer settings; wait for acceptance.

Validate depot, terminal and inland legs

Confirm cranes, direct-to-truck, road permits, genset, special cut-offs and handling restrictions.

Perform pre-gate-in verification

Check container number, CSC plate, condition, settings, seal, lashing/cover photos and VGM.

RISKS AND COMMON ERRORS

Error	Root cause	Impact	Control
Using Open Top for over-width cargo	Only height or crane access was considered.	Cargo cannot be stuffed or must be changed to Flat Rack.	Measure all packed dimensions and simulate the loading path.
Excluding lashing/cover from OOG dimensions	Only the machine body was measured.	Misdeclaration, re-stow, short shipment, extra cost and delay.	Declare the maximum secured and covered envelope.
Relying on nominal payload	Concentrated loads, CSC plate or road limits were ignored.	Deck damage, rejection or axle-weight breach.	Check local load distribution, allocated equipment and inland route.
Hot stuffing reefer cargo	Cargo has not reached transport temperature.	The unit may fail to pull down the entire load; product quality deteriorates.	Precondition cargo and record core/pulp temperature.
Blocking reefer airflow	Cargo exceeds red lines or blocks T-floor/return air.	Uneven temperature and quality claims.	Use a validated stow plan and inspect airflow paths.
No inland power plan	Genset or waiting time was omitted.	Loss of temperature control during haulage or dwell.	Define genset, plug-in points, off-power duration and monitoring responsibility.
Booking with estimates	Final packed data is unavailable.	Wrong equipment, booking amendment or terminal rejection.	Submit final measured data or approved engineering drawings.

REFERENCES AND SOURCES

Maersk – Out of Gauge cargo
OOG guidance and illustrative in-gauge data

Explains OOG declaration and published equipment envelopes for one carrier.

Maersk – Special Cargo
In-gauge, OOG and breakbulk

Supports the distinction between unitised special cargo and breakbulk.

Maersk – Reefer temperature range
Temperature ranges by reefer type

Shows that capability varies by equipment.

Hapag-Lloyd – Reefer Cargo Handling
Set point, humidity and ventilation

Operational guidance for refrigerated cargo.

Maersk Vietnam – Export Reefer procedure
Pre-cooling, load lines and hot-stuffing control

Local guidance requires correct temperature, ventilation and humidity settings, respect for load lines and proper cargo pre-cooling.

IMO/ILO/UNECE – CTU Code
Code of Practice for Packing of CTUs

Global non-mandatory code covering packing and securing.

IMO – SOLAS VGM
Verification of gross mass

Confirms shipper responsibility and VGM as a condition for loading.

IMO – Cargo Securing and Packing
Safe stowage and securing

Highlights risks from poor packing, overloading and incorrect declarations.

FAQ

Does cargo taller than a dry container always require an Open Top?

No. Check door clearance, possible disassembly/orientation and the full packed envelope. Over-width, over-length or side-loading cargo may require a Flat Rack.

Is every Open Top shipment OOG?

No. An Open Top can carry in-gauge cargo. OOG begins only when the cargo exceeds the carrier-defined envelope.

Can a Flat Rack carry any heavy machine?

No. Payload is only one limit. Local deck loading, centre of gravity, support, lifting, inland axle limits and carrier approval remain critical.

Can a reefer cool warm cargo down to the required temperature?

It should not be treated as a blast freezer. Most cargo should be at or near transport temperature before stuffing, subject to commodity protocol.

Can a non-operating reefer be used as a dry container?

Some routes may accept NOR under specific conditions, but cube, payload, ventilation and availability differ. Book and confirm the correct product.

Are website dimensions enough to finalise a booking?

No. They are fleet references. Check the allocated unit, CSC plate, booking confirmation, terminal and inland restrictions.

When should cargo move from Flat Rack/Open Top to breakbulk?

When it cannot be safely unitised, exceeds equipment/handling limits, or the carrier cannot provide suitable stowage. Assessment is case-specific.

APPLICATION NOTE: Equipment selection cannot be concluded from a commodity name alone. It depends on final packed drawings, centre of gravity, local loads, lifting/securing, product protocol, vessel route, fleet availability, terminal restrictions and inland road law. This article is operational guidance and does not replace carrier, surveyor or engineering approval for a specific shipment.

TGIMEX IMPLEMENTATION SUPPORT

TGIMEX helps businesses turn the article into a shipment-ready checklist, covering input-data review, dossier preparation, milestone control, and coordination with the relevant parties.

Convert guidance into checks

Assign an owner and deadline to every operational control point.

Reconcile shipment data

Compare booking, transport, commercial, customs, and delivery evidence.

Manage operational risk

Record discrepancies, actions, and decision evidence to prevent recurrence.

Discuss your shipment dossier

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