Container Stuffing Plans and Load Securing Under the CTU Code

The consignee wanted the two heavy crates nearest the doors so they could be pulled out first. The packer obliged, filled the front of the box with light pallets, and closed the doors on a container whose cargo weight sat well toward one end. The quay crane's spreader tilted on the lift, the crates slid against the door end in the first gale, and the claim surveyor's report blamed "inadequate stowage and securing".

A written stuffing plan prevents that sequence because it settles the numbers before anyone touches a forklift: the payload against the container's plate, where the combined centre of gravity will fall, what force each item must be held against in each direction, and which timber, battens, bags or lashings provide it. The IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units, known as the CTU Code, supplies the coefficients and methods.

• What this guide covers: plan contents, design accelerations, container limits, centre of gravity arithmetic, friction and blocking, lashing capacity and dunnage, all tied to the CTU Code text.
• What it works through: a 20-foot open top with two machinery crates and palletised spares, a securing calculation per direction, a claim trace, and a cost comparison in US dollars and Indian rupees.

What a stuffing plan must settle before the first crate moves

A stuffing plan is a short instruction, sketch or scale drawing that tells the packing team where each item goes and how it is held. Annex 7 of the CTU Code asks for it to be prepared early, and the result can be oral, written or drawn depending on how complex the load is.

Annex 7 section 1 lists what planning has to settle. The cargo mass must not exceed the container's maximum payload, so the gross mass on the CSC safety approval plate is not exceeded, and route limits for road, rail or handling equipment may be lower still. Heavy items with small footprints need their load spread to the bottom girders, and the centre of gravity must sit within limits in all three directions.

• Mass check: total cargo plus dunnage and securing material against the payload on the plate and against the lowest road or rail limit on the route.
• Position check: longitudinal centre of gravity near mid-length, transverse near half width, vertical below half the height of the cargo space.
• Concentrated loads: bedding beams for items whose footprint would overload the floor, designed with the container operator.
• Compatibility: no package stacked beyond its strength, no item that could damage its neighbour, and quarantine rules for any wood used.
• Restraint method: blocking, battens, bags or lashings chosen for each item and each direction, with material quantities listed.

Our page on LCL consolidation at the CFS deals with packing many shippers' cargo into one master container and auditing revenue tons. This article is narrower and more physical: one shipper's full container, the forces on each item, and the restraint that answers them.

Design accelerations for road, rail and the three sea areas

Every securing arrangement is sized against a design acceleration expressed as a fraction of gravity. CTU Code chapter 5 gives the coefficients by mode and direction, and the worst case on the planned route governs each direction separately.

Road transport demands 0.8 g forward, 0.5 g rearward and 0.5 g sideways, each combined with a vertical coefficient of 1.0. Rail combined transport uses 0.5 g longitudinally and sideways, with bracketed shock values of 1.0 g for impacts of 150 milliseconds or less, intended for packaging design. Sea transport depends on the significant wave height of the sea area the voyage crosses.

Container securing design under CTU Code chapter 5 uses road coefficients of 0.8 g forward and 0.5 g rearward and sideways, while an unrestricted ocean voyage in sea area C requires 0.8 g transverse and 0.4 g longitudinal with only 0.2 g vertical, which cuts the friction available to the packer.

The low vertical coefficient of 0.2 that accompanies longitudinal loads in sea area C catches planners out. Friction depends on how hard the cargo presses on the floor, so when the ship pitches, a crate that friction held comfortably on the road suddenly has very little grip. The US road leg uses the same three road figures: 49 CFR 393.102 sets cargo securement for 0.8 g forward deceleration and 0.5 g rearward and lateral.

Choosing the box: payload plate, floor rating and crane-loaded tops

The plan starts with the container type, because a general purpose box has wall, floor and lashing-point limits that heavy items can exceed. Items too heavy to drive in on a forklift belong in an open top, open side or platform unit loaded from above or the side.

CTU Code chapter 6 states that general purpose container side walls withstand a uniform load of 60% of the permitted payload, and the front wall and door end 40%. Bottom anchor points, where fitted, have a maximum securing load of at least 10 kN, with many newer boxes rated at 20 kN; lashing points on the top side rails have at least 5 kN. Floors need only withstand an axle load of 5,460 kg, or 2,730 kg per wheel.

• Forklift limit: chapter 7 notes that floor bearing limits may restrict items lifted in by forklift to roughly 3 to 3.5 tonnes, depending on the truck.
• Open top option: crane loading through the roof avoids driving into the box; the swinging header is part of the container's strength and must be refitted.
• Flatrack option: lashing brackets on the bottom girders have a maximum securing load of at least 30 kN, often 50 kN, for over-width items.
• Reefer caution: thermal containers generally lack anchor points, so lashing needs fittings attached to the T-section floor gratings.

Weight limits on the road leg can bind before the plate does. On the US Interstate network, 23 U.S.C. 127 caps a single axle at 20,000 pounds, a tandem at 34,000 pounds and gross vehicle weight at 80,000 pounds, so a heavy 20-foot box on a standard chassis may need a tri-axle or a lighter load. Indian lanes have their own axle and gross limits, which the haulier should confirm for the vehicle class booked.

Keeping the cargo centre of gravity within 5 percent of mid-length

For a container lifted level by a crane or spreader, the combined cargo centre of gravity should sit within 5% of the length from mid-point, and up to 10% only where advanced spreaders can compensate. The arithmetic takes a minute and prevents tilted lifts and overloaded chassis axles.

Annex 7 section 3.1.4 gives the 5% limit and a rule of thumb of 60% of the cargo mass in 50% of the container length. Appendix 4 gives the calculation: the distance of the common centre of gravity from the front equals the sum of each mass times its distance, divided by the total mass. In the worked example below, the stowage length is taken as 5.90 m for illustration, so the mid-point is 2.95 m and 5% is 0.295 m.

Longitudinal centre of gravity (CTU Code Annex 7, Appendix 4, section 3)
  d   = sum(m_n * d_n) / sum(m_n)
  e   = |d - L/2| / L          must be <= 0.05 (up to 0.10 only by agreement)

Sliding restraint needed per direction (blocking, static friction)
  F_req = m * g * (c_h - mu * c_v)            [kN, m in tonnes, g = 9.81]
Dunnage bag load, sliding (Annex 7, Appendix 4, section 4)
  F_bag = m * g * (c_h - mu * 0.75 * c_v)
Transverse batten fence capacity (Annex 7, Appendix 4, section 1)
  F_bat = n * w^2 * h / (28 * L_free)         [kN; w, h in cm; L_free in m]

Worked values, 20 ft open top, L = 5.90 m (illustrative)
  Draft plan:  spares 3.12 t at 0.70 m, crate B 4.5 t at 3.20 m, crate A 6.0 t at 4.95 m
               d = 46.284 / 13.62 = 3.398 m   e = 0.448 / 5.90 = 7.6 %   FAIL
  Final plan:  spares 3.12 t at 0.70 m, crate A 6.0 t at 2.60 m, crate B 4.5 t at 4.40 m
               d = 37.584 / 13.62 = 2.759 m   e = 0.191 / 5.90 = 3.2 %   PASS
  Crate A, mu = 0.45 (sawn timber skid on plywood floor), m*g = 58.86 kN
    Road forward   c_h 0.8, c_v 1.0 : F_req = 58.86 * (0.80 - 0.45)  = 20.6 kN
    Sea C fore-aft c_h 0.4, c_v 0.2 : F_req = 58.86 * (0.40 - 0.09)  = 18.2 kN
    Sea C sideways c_h 0.8, c_v 1.0 : F_req = 58.86 * (0.80 - 0.45)  = 20.6 kN
    Bag sideways   F_bag = 58.86 * (0.80 - 0.3375) = 27.2 kN
  Door-end fence for crates A + B pushed aft (10.5 t, sea area C)
    F_req = 103.0 * (0.40 - 0.09) = 31.9 kN
    Six battens 7.5 cm x 10 cm, free length 2.2 m: F_bat = 6 * 56.25 * 10 / 61.6 = 54.8 kN

Container weight distribution under CTU Code Annex 7 section 3.1.4 limits cargo centre of gravity eccentricity to 5% of container length for level lifting; in a 20-foot box with 5.90 m stowage length, the combined centre must fall within 0.295 m of the 2.95 m mid-point.

The draft plan in the block failed because both crates sat aft to suit the consignee. Moving crate A forward to 2.60 m and leaving a 0.70 m gap at the doors for a batten fence brought eccentricity to 3.2%. Transversely, each crate is centred across the width with equal gaps, and vertically the crates' own centres are well below half the box height, so the plan meets all three directions.

Friction, blocking and battens: sizing restraint for each direction

Blocking against the container structure or neighbouring cargo is the preferred restraint because it allows almost no movement. Friction reduces the force the blocking must carry, but only by a verified friction factor applied to the vertical coefficient for that direction.

Appendix 2 to Annex 7 lists static friction factors for clean surfaces: sawn timber or a wooden pallet on plywood or fabric base laminate 0.45, on grooved aluminium 0.4, on stainless steel sheet 0.3; plastic pallets on plywood only 0.2; painted smooth metal 0.2. Where the combination is missing or cannot be verified, the calculation must use no more than 0.3, and direct lashings use 75% of the static value.

The batten fence follows Appendix 4 section 1, which estimates the resistance of transverse battens wedged into the corner posts from their number, thickness, height and free length. Six battens of 7.5 cm by 10 cm across a 2.2 m free span give about 54.8 kN, comfortably above the 31.9 kN the two crates could exert aft in sea area C. The doors never count as restraint.

Lashing capacity, pre-tension limits and container anchor points

When blocking is impractical, lashings provide restraint, but the system is only as strong as its weakest element: the lashing's maximum securing load, the angle, and the anchor point it pulls on. In a general purpose box, the 10 kN floor anchors usually set the limit.

Annex 7 section 2.4 defines maximum securing load (MSL) as a proportion of breaking strength: 50% for mild steel shackles, rings and turnbuckles; 33% for fibre ropes; 75% for single-use web lashings and 50% for reusable ones; 80% for single-use wire rope and 30% reusable; 70% for steel band; and 50% for chains. Pre-tension in direct lashings should never exceed 50% of the MSL.

Lashing design for container stuffing under CTU Code Annex 7 sections 2.4 and 4.1 rates reusable web lashings at 50% of breaking strength and caps direct-lashing pre-tension at 50% of maximum securing load, while chapter 6 floor anchors offer at least 10 kN, so anchors often govern.

• Anchor governs: a reusable web lashing rated well above 10 kN gains nothing in a box whose floor rings are rated 10 kN; design to the ring.
• Short and straight: keep lashings as short as practicable and as close as possible to the direction of the intended restraint.
• Friction lashing tension: where no labelled standard tension is available, the Code allows 10% of breaking strength, capped at 10 kN, for calculation.
• Dynamic friction: direct lashings stretch before they restrain, so the calculation uses 75% of the static friction factor.

Dunnage, air bags and timber bearers for gaps and heavy footprints

Dunnage does three jobs: it protects cargo from condensation, it fills voids so blocking can work, and it spreads concentrated loads. Each job needs a different material, and air bags must be sized against the cargo force they will meet.

Annex 7 section 2.1 recommends timber planks on the floor against water collecting at the bottom, gunny cloth, paperboard or fibre mats against drips from the roof, and planks or plywood against sweat on the side walls. Timber sheets or pallets can equalise loads within stacks or create a temporary floor so lower packages are not crushed. Wood dunnage must meet the destination's quarantine rules.

• Air bag sizing: the bag's permissible load must exceed the sliding force from Appendix 4 section 4; for crate A sideways that is 27.2 kN before any safety margin.
• Correct mass: use only the cargo mass that can push on the bag, which for a sideways bag is the larger of the masses on its two sides.
• Bearers for crates: place longitudinal timber or steel bearers under heavy skids so the load reaches the cross-members and bottom girders, sized with the container operator.
• Rail caution: a footnote in the Code warns that air-inflated dunnage bags should not be used for dangerous goods on US railways.

A gearbox crate that shifted at sea, traced from gate-in to claim

The draft plan described earlier did go to sea on an earlier shipment, before the shipper adopted written plans. The trace shows how a 7.6% eccentricity and an unbraced door gap became a claim. Times and numbers are illustrative.

1. Day 1, 14:20, packing: the open top on booking BK-55102 is loaded with spares at the front, crate B mid-box and crate A aft, only 0.05 m from the doors with no fence. The seal is applied and the gross mass sent to the shipper.
2. Day 3, 09:05, terminal lift: the quay crane operator reports the box hanging nose-up on the spreader; the lift continues because the tilt is within the crane's adjustment range.
3. Day 11, 02:40, heavy weather: the vessel meets a gale on an unrestricted crossing; with only 0.2 g vertical in pitch, friction under the crates drops, crate B slides aft into crate A, and crate A bears on the door end.
4. Day 34, 10:15, unpacking: the consignee finds the door end bulged and crate A's skid broken; the surveyor photographs scuff marks 0.35 m long under crate B.
5. Day 36, claim response: the carrier declines liability, citing packing by the shipper; the shipper's cargo insurer reviews the packing records before deciding the claim.

Had the plan been written, the eccentricity and the missing aft restraint would both have failed review at the desk. The final plan fixes both at a material cost of a few hundred dollars. Our marine cargo insurance claim guide explains how surveyors and insurers use packing evidence when a claim like this is filed.

Plan checks a load-planning tool can fix and calls a packer keeps

Arithmetic and limits belong in software as fixed rules; judging a floor surface, a crate's real centre of gravity or a bag's fit belongs to a trained packer. A load-planning tool that blurs the two gives false confidence on exactly the items that fail.

Stuffing plan sign-off checklist, costs in dollars and rupees

Securing material and planning time cost a small fraction of one cargo claim. The comparison below uses illustrative prices for the worked container packed by a US exporter and by an Indian exporter, followed by the checklist a supervisor signs before sealing.

A one-page plan and a signed checklist make each container defensible from the quay to the consignee's dock. Heavier items, such as coils on trucks, follow different securement rules, explained in our steel coil transport guide, and more topics sit on the logistics and supply chain hub. If you need load-planning or packing-control software scoped for your sites, submit your requirements on our RFP page.