Lashing over-dimension machinery on a flat rack comes down to four decisions: where the weight sits, what you tie to, how many points you use, and whether the hardware can actually hold the load the ship will put on it. Get any one of those wrong and the cargo either doesn’t sail or doesn’t arrive intact.
This is the part of heavy cargo that separates forwarders who ship machinery from forwarders who ship cartons.
What “OOG” actually means
A flat rack is a platform with two collapsible end walls and no sides and no roof. Cargo sits on the deck and is held by lashings to the deck, not by walls.
OOG — out of gauge — means the cargo exceeds the standard container envelope. In practice that is any of:
- Width over 2.438 m
- Height over 2.591 m
- Length beyond the rack’s own platform
An OOG flat rack is not a problem in itself. It ships on deck, in a position the carrier approves, and it’s charged as OOG. What creates problems is when the dimensions, the weight and the lashing plan don’t match what the carrier was told.
Where the weight goes
This is the first thing a surveyor looks at, and the first thing that goes wrong.
The centre of gravity has to be centred, and it has to be low.
If a machine is loaded with its heavy end hanging over one end of the rack, the load is eccentric. That does two things: it concentrates weight on one part of the deck, and it makes the cargo want to rotate under the ship’s roll. Lashings can hold a load; they can’t fix a load that’s already trying to tip.
Point loads need spreaders. A flat rack deck is steel, but a 40-tonne machine resting on four small feet is not the same as 40 tonnes distributed over the deck. Timber dunnage or steel spreader beams under the feet spread the load. Without them you can deform the deck — and a deformed deck is a cargo claim.
Do not load onto the end walls. The end walls are collapsible and are not rated for cargo weight. They exist to hold the cargo from shifting longitudinally and to let the rack be stacked when empty.
Corner castings are for lifting and locking — not for lashing. This is worth stating plainly because it’s one of the most common mistakes we see: the castings at the four corners are for the crane and for the ship’s twist locks. Tying a wire rope to a corner casting is not a lashing; it’s a way of damaging the casting.
What you lash to
Lashing rings — D-rings — are set into the deck along both edges. On a 20′ flat rack they’re typically spaced around a metre apart, and the exact count and position depends on the maker.
Two things to check before you plan a single lashing:
- The rack’s lashing plan. Every flat rack should have one, showing ring positions and the rated capacity of each ring. Ring capacity is not unlimited, and it is not the same as the lashing’s capacity — the chain is only as strong as the ring it’s hooked to.
- The ring condition. Rings get bent, worn and painted over. A lashing plan assumes the rings are intact.
How many lashing points
There is no single number. But the logic is consistent:
- Four points is the floor for any flat rack cargo, not a target.
- Heavy machinery usually needs six, eight or more, and they need to work in different directions.
- A lashing at a steep angle resists very little sideways force. A wire running almost vertically down to the deck holds the cargo down; it does nothing to stop it sliding. Effective lashings sit at a moderate angle to the deck — roughly 30 to 60 degrees.
- Cross-lashing matters. Running lashings diagonally, in an X, resists lateral movement and rotation far better than parallel lashings in one direction.
The point of more lashings isn’t redundant strength. It’s that each lashing fails in a different direction, and you need coverage in every direction the ship can move.
The hardware — and the mistake that halves its strength
Steel wire rope is standard for heavy machinery. Also common: chain lashings, and turnbuckles or tensioners to take up slack.
The single most common hardware mistake is skipping the thimble.
A thimble is the teardrop-shaped insert that goes inside the eye of a wire rope where it meets a ring or a shackle. Without it, the rope bends sharply against bare metal at the attachment point — and a wire rope bent sharply around a small radius loses roughly half its breaking strength at that point. You can have a rope rated well above the load and still fail it, because the working limit at the bend is half of what the label says.
Every attachment needs a thimble, a properly rated shackle, and a turnbuckle that is locked after tensioning. Turnbuckles that work loose in transit are how lashings go slack.
Webbing straps are not for this. They’re for lighter cargo and for cargo with soft contact points. On 40 tonnes of machinery they’re decoration.
Timber blocking is part of the system. Lashings stop the cargo lifting and shifting; timber blocks and wedges stop it sliding in the first place, and they protect the machine’s feet from abrasion. A heavy cargo with perfect wire rope and no blocking is still a cargo that relies entirely on friction being enough.
The standard you’ll be measured against
The reference document is the IMO CSS Code — the Code of Safe Practice for Cargo Stowage and Securing. It sets out how securing arrangements are assessed, and it defines MSL — Maximum Securing Load — as a defined fraction of a component’s breaking load, where the fraction depends on the material.
Two practical consequences:
You don’t invent the numbers. The required MSL comes from a calculation based on the cargo’s weight, the ship’s accelerations and the lashing geometry. That’s why heavy cargo goes through a calculation rather than a rule of thumb.
The carrier’s securing manual is what actually decides. Each liner has its own approval process for flat rack and OOG cargo, and it will reject a lashing plan that doesn’t meet its manual — even if the plan looks sensible.
What the carrier will ask for
Before an OOG flat rack is accepted, expect to submit:
- Exact dimensions — length, width, height, including any protrusion
- Gross weight and the weight of the cargo alone (separate from the rack)
- Centre of gravity — longitudinal and vertical
- Lifting points
- Lashing plan — points, angles, hardware, MSL
- Photos — the cargo, the rack, the dunnage, and the lashings
Photos are not a formality. A carrier that sees a clean, well-blocked, properly lashed machine approves faster than one that gets a spreadsheet with no pictures.
Five mistakes we see on flat rack cargo
- Lashing to corner castings. They’re for lifting and locking. Use the deck rings.
- No thimbles. Halves the working strength at the attachment point.
- Too few points, all in one direction. Covers lifting, not shifting or rolling.
- No timber blocking. Everything depends on friction — and friction is not a lashing.
- Photos taken after the fact. The carrier wants to see how it was built, not the finished result from one angle.
How we do it
We’ve been loading heavy and over-dimension cargo out of China for more than a decade, including power transformers, CNC machining centres, injection moulding machines and production lines.
The process is:
- You send the machine’s dimensions, weight and any photos or drawings you have.
- We confirm the rack size and the OOG dimensions — including where it protrudes and how much.
- We plan the load — CoG position, dunnage and blocking, lashing points and angles — and submit it to the carrier for approval.
- We load and lash under supervision, and photograph every stage: bare rack, blocked and positioned, lashings tensioned.
- We send you the photos before the container moves, so you can see exactly what left the factory.
If a shipment needs an independent surveyor, we arrange one. On high-value machinery that’s usually the right call — a surveyor’s report is cheap next to a claim.
If you have a machine that doesn’t fit a standard container, send us the dimensions and we’ll tell you what it needs.
Key facts
- OOG means width over 2.438 m, height over 2.591 m, or length beyond the platform.
- Centre of gravity must be centred and low — lashings can’t fix a load that’s already trying to tip.
- Corner castings are for lifting and locking, not lashing. Lash to the deck rings.
- Every wire rope eye needs a thimble — without one the rope can lose roughly half its strength at the bend.
- Effective lashings sit at about 30–60° to the deck; near-vertical lashings resist very little sideways force.
- Timber blocking is part of the securing system, not an optional extra.
- The IMO CSS Code and the carrier’s securing manual are the standards that decide approval.