Cargo Securing Manual and CSS Code

The Cargo Securing Manual (CSM) is a ship-specific document, mandatory under SOLAS Regulation VI/5 and Regulation VII/5 since 1 January 1998, that prescribes how every category of cargo carried on a given vessel must be stowed and secured. It is developed from the IMO Code of Safe Practice for Cargo Stowage and Securing (CSS Code), originally adopted as Resolution A.714(17) in November 1991 and maintained through a series of circulars, most recently MSC.1/Circ.1352, MSC.1/Circ.1353/Rev.2 (2019), and the revised container-specific Annex 13 (MSC.1/Circ.1624, 2020). The CSM translates generic CSS Code methodology into vessel-specific tables of approved securing equipment, calculated load limits, and watch-keeping procedures. Incidents such as the loss of 342 containers from MSC Zoe in January 2019 and the structural failure of MOL Comfort in June 2013 have repeatedly demonstrated that inadequate cargo securing is a proximate cause of large-scale maritime casualties. The ShipCalculators.com calculator catalogue includes dedicated tools for lashing force, container stack weight, VGM compliance, and ro-ro trailer hold-down.

Contents

Background and history

Cargo loss and ship damage attributable to shifting or unsecured cargo have been documented throughout maritime history, but the systematic regulatory response emerged only after a series of high-profile casualties in the 1970s and 1980s. The IMO General Assembly adopted Resolution A.489(XII) in 1981, issuing the first guidance on safe stowage and securing. A decade of incident analysis prompted a comprehensive revision, culminating in Resolution A.714(17), which introduced the CSS Code on 6 November 1991.

SOLAS was amended to mandate the CSM through the 1994 Conference of Contracting Governments. The resulting Regulation VI/5 and Regulation VII/5 entered into force on 1 January 1998, requiring every cargo ship of 500 gross tons and above on international voyages to carry a Cargo Securing Manual approved by the flag Administration. The obligation applied both to general cargo, passenger, and bulk carrier operations under Chapter VI and to the carriage of dangerous goods under Chapter VII.

The CSS Code itself is a non-mandatory instrument that provides the technical underpinning for CSMs. Administrations and classification societies implementing CSM approval procedures draw directly on its methodology. Over the decades, a series of MSC circulars updated specific annexes without reissuing the full Code. MSC.1/Circ.1352 (2010) revised the Container Annex, then MSC.1/Circ.1353 and its revision MSC.1/Circ.1353/Rev.2 (2019) updated Annex 13 on container securing on non-cellular ships. Following MSC 102 (May 2020), a further revision - MSC.1/Circ.1624 - replaced Annex 13 entirely with a revised set of formulae reflecting updated acceleration data and performance-based lashing assessment.

IACS Unified Requirement S32, first issued in 2000 and periodically revised, specifies minimum structural requirements for container securing fittings and hatch-cover scantlings on cellular container vessels, providing a structural complement to the operational CSS Code.

The precursor to the modern CSM regime was the 1960 SOLAS Convention, which addressed cargo stowage in broad terms. The 1974 SOLAS Convention consolidated these provisions but still lacked a systematic method for calculating lashing forces. The shift from prescriptive rules to engineering-based calculations came with the 1991 CSS Code, which drew on research into vessel motion statistics and the resulting acceleration spectra for different ship types. The IMO Sub-Committee on Dangerous Goods, Solid Cargoes and Containers (DSC), subsequently renamed the Carriage of Cargoes and Containers Sub-Committee (CCC), has been the principal body revising the Code and its annexes. The 2014 amendment to SOLAS Chapter VI introduced explicit provisions on the exchange of cargo-related data before loading, reinforcing the CSM’s role as a pre-voyage planning document rather than merely a reference document carried on board.

Regulatory framework

SOLAS Chapter VI and Chapter VII

SOLAS Chapter VI, Regulation 5 reads that cargo, other than solid and liquid bulk cargoes, must be stowed and secured throughout the voyage in accordance with the CSM. Regulation VI/5-1, added in 2002, mandated that the CSM comply with the CSS Code. SOLAS Chapter VII, Regulation 5 mirrors this for dangerous goods, cross-referencing the IMDG Code (for packaged dangerous goods) and the IMSBC Code (for solid bulk cargoes). An amended Chapter VI entered into force in January 2011, tightening provisions for cargo information, stability data exchange, and ship-shore communication of cargo unit weights.

The flag Administration reviews and approves each ship’s CSM as part of the ship’s certification package. In practice, most Administrations delegate approval to the classification society of record. The approved CSM is then treated as a living document: it must be updated whenever new types of cargo are added to the vessel’s trading range, when securing equipment is modified, or after significant structural alterations to cargo spaces.

SOLAS Regulation VI/2, as amended in 2014, obliges shippers to declare the weight of cargo offered for loading. This obligation underpins the practical utility of lashing calculations in the CSM: a calculation based on a falsely declared cargo mass provides no real safety margin. The 2014 amendment also introduced provisions for the proper description of cargo nature, stowage requirements, and handling instructions, all of which feed into the CSM’s securing arrangements. Regulation VI/6 introduced provisions for unit loads, requiring that packages within containers or unit loads be individually secured.

Chapter VII of SOLAS, which addresses the carriage of dangerous goods, requires compliance with both the IMDG Code and the CSS Code. A container loaded with IMDG goods must simultaneously satisfy the IMDG stowage category, the IMDG segregation requirements for adjacent dangerous goods, and the CSS Code mechanical securing requirements. Where these requirements conflict - as when IMDG stowage dictates a particular deck position that produces unfavourable lashing geometry - the ship’s officer must resolve the conflict before departure.

Relationship to other instruments

The CSM does not stand alone. The CSS Code references and is supplemented by several parallel instruments. The IMO/ILO/UNECE Code of Practice for Packing of Cargo Transport Units (CTU Code), revised in 2014 as MSC.1/Circ.1497, addresses the responsibilities of the packer at the land side. The CTU Code is technically non-mandatory but has been adopted into national law by several maritime nations and is referenced in many charterparty and bill of lading forms. Under the CTU Code, the packer is responsible for selecting appropriate dunnage and internal securing within the container; the ship’s officer is responsible for the external securing of the container in the ship’s bay.

The ISM Code intersects with the CSM through the company’s Safety Management System. The SMS must include procedures for cargo securing, pre-departure checks, at-sea monitoring intervals, and responses to shifted cargo. The designated person ashore (DPA) carries corporate responsibility for ensuring that the SMS cargo securing procedures are maintained, that the CSM is kept current, and that crew are trained. ISM annual internal audits and external audits by the flag Administration or recognised organisation will examine CSM currency and crew familiarity with its contents.

CSS Code structure

The CSS Code is organised into ten sections and 14 annexes. The body sections address general principles, responsibilities of shipper and master, cargo units and handling equipment, general stowage and securing principles, specific requirements for vehicles and rolling stock, special requirements for heavy cargoes, and inspection and maintenance of securing gear. The annexes contain the detailed engineering methods, acceleration tables, and specimen forms.

Annex 1 gives formulae for the advanced calculation method. Annex 2 presents the simplified method using pre-calculated tables. Annex 3 addresses stowage on deck in open stowage. Annexes 4 through 12 cover specific cargo types including vehicles, trailers, railway wagons, coils and reels, pallets, forestry products, and steel products. Annex 13 governs containers stowed on non-cellular vessels. Annex 14 provides specimen lashing assessment forms. The 2020 Annex 13 revision (MSC.1/Circ.1624) introduced a performance-based framework that explicitly accounts for container ISO corner fitting fatigue accumulation in heavy sea conditions.

CSM structure and content

A compliant CSM contains seven mandatory chapters.

Chapter 1 - General identifies the ship by IMO number, flag, classification society, and gross tonnage. It states the scope of cargo types addressed and lists the valid edition of the CSS Code and any national supplements.

Chapter 2 - Cargo securing equipment catalogues every item of cargo securing equipment (CSE) on board: chain lashings, wire rope, polyester webbing straps, tensioners, shackles, D-rings, stanchions, container twist locks, and stacking cones. For each item the chapter records the nominal breaking load (BL) and the derived Maximum Securing Load (MSL). Equipment is identified by location so that inspectors can cross-reference stowage plans.

Chapter 3 - Standardised cargo gives tabulated securing arrangements for regular cargo types - typically unit loads, pallets, and containers - using pre-approved securing patterns from the CSS Code simplified method. The table format specifies the cargo weight range, the approved lashing arrangement, the total calculated securing capacity, and the safety margin against the design accelerations for that ship.

Chapter 4 - Non-standardised cargo requires individual lashing calculations for heavy lifts, project cargo, and any item outside the standardised tables. These calculations must follow the advanced calculation method in CSS Code Annex 1, or the alternative method in Annex 13 for containers.

Chapter 5 - Stowage and securing of containers on non-cellular ships applies specifically to vessels not designed primarily as cellular container ships - multipurpose vessels, heavy-lift ships, and bulk carriers with partial container capacity. This chapter integrates Annex 13 (MSC.1/Circ.1624) calculations.

Chapter 6 - Inspection and maintenance specifies inspection intervals, rejection criteria, and the record-keeping regime for CSE. Chain lashings are examined for elongation, wear, and corrosion; wire rope for broken wires and deformation; webbing for UV degradation, abrasion, and cut marks.

Chapter 7 - Crew responsibilities defines duty positions, pre-departure checklists, watch-keeping intervals for securing gear checks, and emergency procedures if cargo shifts at sea.

Maximum Securing Load

The Maximum Securing Load (MSL) is the threshold load below which a securing device may be used in strength calculations. It is derived from the nominal breaking load (BL) of the device by applying a standard safety factor. CSS Code Table 5 lists the approved ratios:

Chain (grade L, grade 2, grade 3): MSL = 50% of BL
Steel wire rope (IWRC): MSL = 50% of BL
Shackles, rings, deckeyes, turnbuckles: MSL = 50% of BL
Fibre rope (natural): MSL = 33% of BL
Polyester webbing: MSL = 30% of BL
Timber shores and wedges: MSL assessed individually

The 30% figure for polyester webbing reflects the material’s susceptibility to creep under sustained load and to UV-induced degradation. On a ship where webbing is the primary lashing material, the overall securing capacity per lashing is correspondingly lower, which increases the calculated number of lashings required.

In practical operation, the Calculated Strength (CS) concept is sometimes applied rather than the raw MSL. Where lashings are not perpendicular to the direction of applied force, a geometric correction factor reduces the effective CS below the catalogued MSL value. A horizontal lashing angled 30° from the transverse direction retains approximately 87% of its nominal MSL contribution; at 60° the contribution falls to 50%. Lashings angled more than 60° from the securing direction may still be credited but contribute negligibly to transverse restraint.

Acceleration forces and the lashing calculation

Design accelerations

The CSS Code Annex 1 advanced method uses a set of design accelerations that represent the worst combined dynamic loads expected during a sea voyage. The accelerations are expressed as multiples of gravitational acceleration (g = 9.81 m/s²) and depend on the ship’s length, the cargo position in the ship (forward, midships, aft), and whether the cargo is stowed on deck or below.

Longitudinal accelerations (gX) range from 0.3g to 0.8g and are governed primarily by pitching and wave-induced surge. Transverse accelerations (gY) range from 0.7g to 1.2g and represent the dominant design case for most securing calculations because beam rolling produces the largest inertial loads. Vertical accelerations (gZ) range from 0.5g to 1.0g and affect both the tipping tendency and the change in normal force at the cargo-deck interface.

Table A (Annex 1) tabulates design accelerations by ship length category (below 50 m, 50-100 m, 100-200 m, above 200 m) and by cargo location (bow, forward quarter, midships, aft quarter, stern). Longer vessels experience lower acceleration factors because their natural periods are less likely to resonate with typical swell periods. Container ships of 300 m or more typically attract transverse accelerations at the hatch-cover level of around 0.7g to 0.8g in the worst table position, whereas a 90 m feeder vessel may attract 1.1g or more.

Force on cargo

The resultant force Ft acting on a cargo unit of mass W in the transverse direction is:

Ft = gY × W

This must be balanced by friction forces from the cargo-deck interface and by the securing forces from lashings. The friction force Ff is:

Ff = μ × gZ × W

where μ is the coefficient of friction between the cargo base and the deck surface. The CSS Code Table 2 gives standard coefficients:

Steel on steel (dry): 0.1
Steel on wood: 0.3
Steel on rubber anti-slip mats: 0.5 to 0.6
Timber on timber: 0.4
Timber on steel: 0.3

The low steel-on-steel value of 0.1 is particularly important for steel coils, machinery skids, and unpacked steel products stowed directly on tank-top plating. A steel cask of 20 tonnes on a steel deck under gY of 0.8g generates a transverse inertial force of 156.96 kN, but friction provides only 0.1 × 0.8 × 20 × 9.81 = 15.7 kN of resistance, leaving more than 141 kN to be absorbed by lashings. Anti-slip mats with μ = 0.6 increase the friction contribution to 94.2 kN, reducing the lashing demand substantially.

Friction coefficients assume dry and clean surfaces. In practice, condensation, spillage, or oil contamination can reduce effective friction substantially below tabulated values. The CSS Code specifically notes that tabulated friction values should not be used where surface contamination is expected - for example, where cargo sweating is likely on a tropical voyage or where the cargo unit has a painted or coated base surface that has not been tested against the deck coating. Operators using surface treatments to increase μ (rubber mats, cork boards, friction tape) must ensure the treatment material is listed in the CSM and that the tabulated μ value has been validated.

Longitudinal and vertical force components

Securing calculations are sometimes simplified to consider only the dominant transverse direction, but the CSS Code Annex 1 method requires all three directions to be assessed. Longitudinal forces (gX × W) are particularly relevant for cargo in the forward hold or on the bow area, where pitching accelerations are largest. A 50 tonne piece of machinery in the forward hold under gX = 0.6g experiences a longitudinal inertial force of 294 kN, potentially exceeding the transverse demand of the same unit at gY = 0.8g and μ = 0.3. Forward-facing lashings or structural chocks must resist this force.

Vertical forces affect both the uplift tendency of cargo (important for deck cargo under high gZ values) and the reduction of the normal force at the cargo-deck interface. Where gZ exceeds 1.0g, the effective weight of cargo is momentarily reversed, meaning friction contributes nothing and the securing system must carry the full inertial force without any friction assistance. On deck in certain positions, the CSS Code vertical acceleration can approach 1.0g for smaller vessels, requiring all securing to be designed as if there is zero friction.

In practice, the three force components do not all reach their peak simultaneously. The CSS Code uses simultaneous combination factors to avoid over-conservatism: the full transverse force is combined with a fraction of the longitudinal force, and separately the full longitudinal force is combined with a fraction of the transverse force. The Annex 1 combined force approach models the actual physics of rolling and pitching more accurately than treating each direction independently.

Lashing count formula

The number of lashings N required to secure a cargo unit against transverse sliding is given by:

N = (gY × W − μ × gZ × W) ÷ (CS × MSL)

where CS is the calculated strength of each lashing (MSL corrected for angle), MSL is the Maximum Securing Load in kN, gY × W is the transverse inertial force in kN, and μ × gZ × W is the friction resistance in kN.

The container lashing force calculator at ShipCalculators.com applies the transverse-acceleration version of this logic to ISO containers, using CSS Code Annex 13 design accelerations. The ro-ro lashing calculator applies Annex 4 methodology to determine the minimum number of lashing points for trailers on ro-ro decks. The open-top container lashing calculator handles the additional lashing requirement for over-height loads in open-top containers.

Tipping, as distinct from sliding, is assessed separately. A cargo unit tips when the transverse moment arm of the inertial force exceeds the stabilising moment provided by the unit’s weight acting through its base. For a cargo unit of height h and base width b, the tipping safety factor is:

SFtip = (b/2) ÷ (h × gY ÷ gZ)

A unit with b = 1.2 m, h = 2.4 m, and gY/gZ = 1.0 has a tipping safety factor of 0.25, indicating it will tip unless lashings provide restraining moment. Units with a high centre of gravity relative to their base - coils stood upright, tall machinery, loaded pallets of packaged goods - almost always require tipping restraint in addition to sliding restraint.

Cargo securing equipment

Chain lashings

Steel chain is the dominant lashing material for heavy-weight cargo. CSS Code and IACS UR S32 recognise three grades relevant to cargo securing: grade L (low tensile, older stock), grade 2 (medium grade, largely superseded), and grade 8 (high tensile, the current standard). Grade 8 chain has a proof load of 2.5 times its nominal load and a breaking load of approximately 4 times the marked working load limit. A 13 mm diameter grade 8 chain typically has a BL of around 160 kN and therefore an MSL of 80 kN.

Chain tensioners (load binders) are used to apply pretension to chain lashings. The CSS Code requires that pretension be applied to all lashings before departure and checked at regular intervals at sea, particularly after the first heavy rolling or pitching period, as chain links can settle and shed pretension. Lever-type binders provide a tension of approximately 10-20% of MSL; screw-type turnbuckles allow more precise adjustment.

The breaking load of anchor and mooring chain is governed by IACS Unified Requirement W14 and is distinct from cargo chain standards. The IACS chain break load calculator computes the nominal breaking load by grade and nominal diameter for reference purposes, though cargo-grade chain follows separate tabulation in EN 818-7 (Europe) and ASME/ASTM standards.

Steel wire rope

Steel wire rope with an Independent Wire Rope Core (IWRC) is lighter than equivalent-strength chain and more flexible, making it preferred for cargo with awkward attachment points. Standard cargo wire is typically 16 mm to 22 mm diameter with 6×19 or 6×37 constructions. The MSL is 50% of BL, the same as chain. Wire lashings are more susceptible to kinking and notch damage at sharp edges; edge protectors are mandatory under the CSS Code wherever wire passes over a cargo corner.

Wire rope lashings must be inspected under the Chapter 6 regime for broken wires (rejection threshold: more than five broken wires per lay length in any strand), corrosion, kinking, bird-caging, and reduced diameter. A 16 mm wire with 10% diameter reduction should be removed from service.

Polyester webbing

Polyester flat webbing straps (typically 50 mm or 75 mm width) with ratchet tensioners are standard for unit loads, packaged cargo, and groupage stowage. The 30% MSL factor means a strap with a BL of 50 kN provides only 15 kN of MSL contribution - equivalent to securing roughly 1.5 to 2 tonnes per strap against typical transverse accelerations. Webbing is therefore limited to relatively light cargo unless used in multiples.

Webbing straps must not be loaded beyond their marked WLL at any point. Ratchet tensioners can generate over-tension if operated with a cheater bar, potentially exceeding the strap’s WLL during the tensioning process.

Container twist locks and deck fittings

Cellular container ships and multipurpose vessels with cellular bays use a system of ISO-compatible corner fittings and deck sockets that transmit forces between container corner castings and ship structure. The three main device types are:

Manual twist locks (MTL) - The stevedore or crew rotates a bayonet cone into the corner casting, then manually turns a locking lever. MTLs are fully reliable but require personnel to enter the stack for locking and unlocking operations, creating safety hazards at height.

Semi-automatic twist locks (SATL) - The lock is preset in the open position and snaps closed automatically when a container is lowered onto it. Unlocking still requires manual operation below the stack. SATLs are standard on most modern cellular ships and reduce lashing crew exposure.

Fully automatic twist locks (FAT) - Open and close automatically during lowering and lifting operations without any manual intervention. FATs allow loading and discharge to proceed without personnel on deck below suspended loads, but require precise landing geometry and more rigorous inspection regimes.

Deck fittings include lashing rings welded to hatch covers or main deck, bridge fittings between container layers, lashing bars (turnbuckle assemblies connecting from container bottom rail to deck lashing ring), and stacking cones (used to align containers without twist locks in outboard bay positions). The structural capacity of lashing bars is typically 250 kN BL, giving 125 kN MSL per bar. Each container in a standard six-high stack on a cellular ship may have four lashing bars plus four twist locks providing coupling to adjacent containers.

The container stack weight calculator checks whether a proposed stack of containers respects the maximum stack load rating (typically 90 to 150 tonnes for standard cellular bays) as well as any hatch-cover pressure limits.

Containers on non-cellular ships

Annex 13 and MSC.1/Circ.1624

Annex 13 of the CSS Code governs the stowage and securing of containers on ships not specifically designed as cellular container vessels - multipurpose general cargo ships, ro-ro vessels with partial container capacity, and heavy-lift ships. The revised 2020 Annex 13 (MSC.1/Circ.1624) adopted a fully performance-based framework built around the concept of a design acceleration set derived from the ship’s dimensions and the container position in the ship.

Under the revised Annex 13, the minimum number of lashing rods per ISO container is determined by direct calculation using the actual design accelerations and the rated capacity of the lashing gear. The simplified tables from earlier versions have been replaced by a calculation procedure that outputs required lashing forces at each corner. The results are entered on a standardised lashing assessment form (LAF) that becomes part of the cargo securing record for that voyage.

Annex 13 also addressed the post-2019 concern about container stacks on cellular ships in heavy weather, following the MSC Zoe incident. While MSC Zoe was a cellular ship and therefore technically outside Annex 13 scope, the incident prompted flag Administrations and classification societies to review whether acceleration factors in existing CSMs adequately covered North Atlantic and North Sea winter conditions.

IACS UR S32

IACS Unified Requirement S32, “Requirements for Containers”, prescribes structural requirements for container corner fittings, deck sockets, cell guides, and the structural reinforcement of hatch covers to carry container loads. UR S32 is mandatory for IACS member society classing of vessels with container capacity. It specifies minimum BL values for deck sockets (typically 850 kN in shear), hatch-cover lashing bridges (minimum 250 kN per attachment point), and the fatigue life of cellular guides under repeated container loading cycles.

UR S32 interacts with the CSM requirements by establishing the structural envelope within which CSM lashing calculations are valid. A lashing force calculation that calls for 150 kN per lashing bar is only valid if the deck socket and hatch-cover structure can transmit that force to the ship’s frames. If UR S32 minimum values have been used in design, the structural capacity will normally govern the number of lashing points rather than the lashing gear itself.

Ro-ro cargo securing

Roll-on/roll-off ships present specific challenges because the cargo - trucks, trailers, mafi trailers, cars, and rolling equipment - is driven aboard under its own power and rests on rubber tyres. Tyres provide friction coefficients of 0.5 to 0.7 on clean steel decks, but this can drop significantly when decks are wet or contaminated with oil or hydraulic fluid. The CSS Code Annex 4 addresses vehicle and trailer securing, requiring that trailers be chocked to prevent fore-and-aft movement and lashed to prevent transverse sliding and tipping.

The ro-ro lashing trailer calculator applies the Annex 4 methodology to determine the minimum number of lashing points for a trailer on a ro-ro deck, taking into account the trailer’s gross weight, the design transverse acceleration, and the rated WLL of each lashing.

Standard ro-ro lashing practice requires a minimum of two lashings per trailer axle, deployed in a cross-pattern so that at least one lashing resists transverse forces from either side. Heavy mafi trailers carrying containers or project cargo are assessed individually against the Annex 1 advanced method. The CSM of a ro-ro vessel must contain lashing patterns pre-approved for each class of vehicle regularly carried.

Bulk carriers and general cargo ships

Bulk carriers carrying packaged cargo in general cargo mode - a relatively common situation for opportunistic voyages - must secure that cargo in accordance with the CSM even though the vessel was designed primarily for bulk loading. The CSM must include securing arrangements for the cargo types actually carried, and the vessel must have appropriate CSE on board.

General cargo ships and multipurpose vessels represent the most complex CSM environment because they may carry a wide variety of cargo types on a single voyage. A typical multipurpose voyage might include steel coils on the tank top, packed forest products in the ’tween deck, project cargo on the main deck, and containers in a partial cellular bay. Each cargo type requires its own securing calculations, and the CSM must contain pre-approved patterns or require individual calculations for all non-standard cargoes.

Steel coils deserve specific attention because their cylindrical shape means they can both slide and roll. Coils stowed on their saddles (axis transverse) are liable to axial roll under longitudinal accelerations. Coils stowed on their saddles with axis longitudinal are liable to transverse rolling. The CSS Code requires wooden chocking, welded pipe stanchions, or dedicated coil racks supplemented by chain lashings for coils above 10 tonnes. The IMSBC loading density calculator is relevant where packaged cargo is mixed with bulk in the same hold, as it checks whether the loading density is within the structural constraints of the ship.

Heavy lifts and project cargo

Project cargo - oversized machinery, transformers, reactor vessels, offshore modules, wind turbine components - presents the most demanding CSM calculations. Individual item masses can reach several hundred tonnes, and dimensions frequently exceed the ISO container envelope. For such items, the advanced method in CSS Code Annex 1 is mandatory; simplified tables cannot be applied.

The key challenge for heavy lifts is that bespoke seafastening must be designed for the specific item and the specific vessel. The seafastening design must account for the item’s centre of gravity (which may be eccentric and not at the geometric centre), the interface between the item’s base and the ship’s deck (often a steel cradle or timber cribbing), and the distribution of load over multiple deck pads. Where the item is too large to be secured by portable lashings alone, the ship’s structure must be reinforced with temporary seafastening pads welded to the deck. The calculation must then show that both the lashing gear MSL and the deck pad weld strength are adequate.

Classification societies and marine warranty surveyors (MWS) play a key role in heavy lift operations. For cargo exceeding certain mass thresholds (commonly 100 tonnes, though thresholds vary by classification society), a MWS will review the seafastening calculation, inspect the securing arrangement before departure, and issue a warranty certificate to the cargo insurer. The seafastening calculation package - which becomes an addendum to the CSM for that voyage - must demonstrate that the design accelerations have been applied correctly and that appropriate MSL values have been used for all securing devices.

Forest products, paper reels, and packaged timber

CSS Code Annex 9 addresses forest products (logs, sawn timber, plywood) and Annex 10 addresses paper and wood-pulp reels. These cargo types share the characteristic that they are irregular in shape, difficult to lash symmetrically, and have variable friction properties depending on moisture content and surface treatment.

Round logs stowed on deck have a tendency to roll transversely; they must be secured with substantial stanchions or cradles. Sawn timber stowed in blocks can exert significant horizontal pressure on hatch coamings and cargo battens if the stow shifts. The CSS Code Annex 9 method specifies that timber deck cargo must be secured before departure and re-checked after the first heavy weather.

Paper reels are heavy, with individual masses of two to four tonnes, and are typically stowed upright (axis vertical). The cylindrical base provides a small contact area with the deck and therefore a lower friction force per unit weight than a flat-based cargo unit. The CSS Code Annex 10 calculation must account for this geometry, and reels are typically secured in multiple rows with substantial webbing or chain lashings running both longitudinally and transversely through the stow.

Passenger ships and vehicle ferries

SOLAS Chapter VI applies to passenger ships insofar as they carry cargo. Vehicle ferries and passenger/ro-ro ferries carrying private cars and coaches are subject to CSS Code provisions for vehicles on ro-ro decks. The ferry context differs from deep-sea ro-ro in two important ways: voyage durations are typically shorter (reducing the exposure time at sea), but the vessels may operate on more restricted waterways where turning manoeuvres generate unusual transverse accelerations.

Ferry-specific adaptations of the CSS Code are common in national regulations for short-sea trades. The Paris MOU and national maritime authorities in Scandinavia, the United Kingdom, and the Baltic states have issued supplementary guidance on vehicle securing for ferry operations, reflecting the high traffic volumes and the need for rapid turnaround between voyages. The CSM of a vehicle ferry must be sufficiently detailed to allow deck officers and stevedores to apply correct securing arrangements for each vehicle category under time pressure during port calls.

Dangerous goods and the IMDG Code

Where cargo secured under the CSM includes packaged dangerous goods, the segregation and stowage requirements of the IMDG Code apply in addition to the mechanical securing requirements of the CSS Code. The IMDG Code assigns a stowage category to each substance (Category A through E, plus SW1-SW35 special stowage), and these categories determine whether cargo may be stowed below deck or on deck, and the required separation from other dangerous goods classes. The IMDG segregation calculator and IMDG packing group tool assist in planning compliant stowage arrangements. Securing of IMDG cargo must not compromise the stowage segregation required by the Code.

A recurring problem identified in Port State Control inspections is the mis-declaration of dangerous goods content in containers, which can cause both incorrect segregation and, where the undeclared goods add significant weight, incorrect lashing calculations because the actual cargo mass exceeds the declared weight. The container mis-declared DG impact tool models the knock-on effect on lashing adequacy.

The VGM (Verified Gross Mass) requirement, introduced via SOLAS VI/2 amendment effective 1 July 2016, requires that shippers provide a certified weight of each packed container before it is loaded. The container VGM threshold calculator checks whether the VGM declared by the shipper triggers a verification obligation under flag-state VGM threshold rules, which vary from 0 to 5 tonnes above the nominal weight.

Notable incidents

MSC Napoli (January 2007)

The MSC Napoli was a 4,419 TEU container ship that suffered structural failure of the hull in heavy weather in the English Channel. The vessel was ultimately beached off Branscombe, Devon. Subsequent investigation by the Marine Accident Investigation Branch (MAIB) found that hull stress levels exceeding design values contributed to the structural failure, but that the cargo securing arrangements had not been fully compliant with the approved CSM. Containers in several bays had exceeded stack weight limits, increasing hatch-cover loading beyond the structural design values.

MOL Comfort (June 2013)

MOL Comfort, a 8,110 TEU container ship, broke in two on 17 June 2013 in the Indian Ocean approximately 200 nautical miles south-west of Yemen, during passage from Colombo to Jeddah. The ship sank completely. The Japan Transport Safety Board investigation concluded that the proximate cause was a structural failure in the bottom shell plating amidships, potentially exacerbated by hull stress exceeding the design envelope. Container weights in several bays had been recorded above the nominal design stack weights, and wave-induced bending moments in the prevailing sea state were estimated to have approached or exceeded the hogging design limit. The incident reinforced industry-wide attention to the accuracy of container weight declarations, which became a driving factor in the subsequent SOLAS VGM amendment.

MSC Zoe (January 2019)

MSC Zoe, a 19,224 TEU mega-container ship, lost 342 containers overboard on the night of 1-2 January 2019 while sailing from the Azores to Bremerhaven through the North Sea in heavy weather. The containers fell into the Wadden Sea and along the coast of Groningen province in the Netherlands. The Dutch Safety Board investigation (2019) concluded that the ship sailed at excessive speed given the forecast wave height, that roll and pitch accelerations experienced exceeded those for which the lashing system was designed, and that the weight distribution of loaded containers was suboptimal. The cargo securing equipment was itself compliant with the CSM, but the operating conditions generated forces beyond the design envelope.

The MSC Zoe incident triggered a review by the World Shipping Council (WSC), which in 2020 launched a Container Loss Initiative committing major liner operators to annual reporting of container losses and to investment in improved stowage planning software. The incident also led the Dutch government to pursue an international regulatory review at IMO, contributing to the 2020 revision of Annex 13 (MSC.1/Circ.1624).

X-Press Pearl (May 2021)

X-Press Pearl, a 1,818 TEU container ship, caught fire and sank off Colombo, Sri Lanka in May 2021. The fire originated in a container holding nitric acid that had been rejected by other ports. Although the incident was primarily a dangerous goods stowage and segregation failure under the IMDG Code rather than a pure CSM failure, the subsequent investigation noted that deck stowage of hazardous containers in positions inconsistent with the approved CSM had contributed to fire propagation, as the affected containers were not stowed in the positions for which the securing plan had been prepared.

Rena (October 2011)

MV Rena, a 3,351 TEU container ship, grounded on Ōtāiti (Astrolabe Reef) off Tauranga, New Zealand on 5 October 2011. The grounding was caused by navigational error. However, the subsequent response was complicated by the fact that containers on the stricken vessel had not been loaded in accordance with the approved stowage plan, with heavier containers placed above lighter ones in multiple bays. The resulting high centre of gravity caused the ship to list more severely than predicted after the grounding, impeding salvage and ultimately contributing to the break-up of the vessel and a significant oil spill.

Ever Ace (September 2021)

Ever Ace, a 23,992 TEU ultra-large container ship, encountered Typhoon Chanthu in September 2021 while in the East China Sea. The vessel experienced severe rolling and lost a number of containers overboard. Post-incident review noted that the wave and wind conditions exceeded the design parameters for the vessel’s lashing system, highlighting the ongoing challenge of designing cargo securing systems for extreme weather that mega-container ships may encounter in the world’s typhoon-prone sea lanes.

Simplified and advanced calculation methods

The CSS Code offers two pathways for producing the lashing calculations that populate the CSM: the simplified method (Annex 2) and the advanced method (Annex 1). The choice between them depends on the cargo type and the ship’s trading pattern.

Simplified method

The simplified method uses pre-calculated tables derived from the advanced method applied to a representative range of ship sizes and cargo positions. The tables express the maximum permissible cargo mass per securing point as a function of ship length and cargo position, for a standard set of lashing geometry assumptions. A ship of 150 m length with cargo in the midships transverse position and a standard 4-lashing arrangement might be approved for up to 25 tonnes per cargo unit without individual calculation. The simplified tables are conservative by design - they apply the worst-case acceleration for the table category and assume minimum friction.

The simplified method is appropriate for standardised cargo types - ISO containers, standard pallets, and vehicles - where the geometry is predictable and the tables have been validated against many actual voyages. It reduces the officer’s workload at the planning stage and allows CSM tables to be prepared in advance without knowledge of the exact cargo weights.

Advanced method

The advanced method follows the force-balance equations from CSS Code Annex 1 as described earlier. It requires the actual cargo mass, the actual design accelerations for the ship and cargo position, the actual friction coefficient, and the actual lashing geometry. The result is a minimum number of lashings of specified MSL and angle to achieve the required safety margin.

The safety margin implicit in the advanced method is a balance factor of 1.5, meaning the available securing capacity must exceed the calculated demand by a factor of 1.5 in each direction. This factor accommodates uncertainties in friction coefficient, variations in lashing geometry during the voyage, and the statistical spread of actual accelerations around the design values.

For cargo units that do not fit the simplified tables - items heavier than the table limit, items with unusual geometry, or non-standard cargo types - the advanced method is mandatory. Many ship operators require advanced-method calculations for all cargo units above a certain mass threshold (typically 10 to 15 tonnes) as a matter of company policy.

Port State Control inspection

Port State Control (PSC) officers from Paris MOU, Tokyo MOU, and other regional agreements can inspect a vessel’s cargo securing arrangements under SOLAS Chapter VI and Chapter VII. The inspection checklist for cargo securing includes:

Presence of a valid, approved CSM on board
Whether the CSM reflects the current vessel configuration and cargo types actually carried
Whether the cargo securing equipment inventory matches the CSM catalogue
Physical condition of CSE (chain corrosion, wire broken wires, webbing degradation, twist-lock serviceability)
Whether stowage and securing has been completed before departure and signed off by the officer of the watch
Whether lashing calculations for non-standard cargo are present in the voyage file

PSC deficiencies related to cargo securing are classified under Deficiency Code 07214 (cargo secured improperly) and 07225 (no approved cargo securing manual). A missing or unapproved CSM will typically result in a detention. Physical deficiencies in CSE - broken twist locks, corroded chain, cut webbing - may result in a rectification-before-departure requirement. The PSC targeting factor calculator models the inspection probability based on a vessel’s flag, history, and port MOU, relevant when planning arrivals in high-enforcement ports with known cargo-securing focus.

Shipper and operator responsibilities

The CSS Code assigns distinct responsibilities to shippers, ship operators, and masters. The shipper is responsible for providing accurate cargo information including weight, dimensions, and centre of gravity for non-standardised items. The IMO Guidelines on Packing of Cargo Transport Units (CTU Code, MSC.1/Circ.1497, 2014) provide detailed guidance to shippers on how to pack and mark containers for sea transport. The CTU Code is non-mandatory but referenced by the CSS Code and increasingly incorporated into liner bills of lading.

The ship operator (company in ISM Code terms) must ensure the vessel carries an approved CSM and is provided with adequate CSE for the intended trade. This includes maintaining a documented inspection and replacement programme for CSE and ensuring crew receive training in CSM procedures. The ISM Code places this in the Safety Management System (SMS) as a documented procedure, and ISM auditors will typically check CSM maintenance records as part of the SMS audit.

The master has authority and responsibility for verifying that cargo is secured before departure. Under SOLAS VI/2, the master may refuse to sail if cargo information is incomplete. The master’s authority to deviate from the approved CSM in an emergency - such as cutting lashings to allow cargo jettison - is implicitly recognised in the convention but must be documented in the vessel’s log and reported to the flag Administration.

CSM approval and amendment

Initial CSM approval follows a defined process: the ship’s owner or operator submits a draft CSM to the flag Administration or delegated classification society. The approving body checks that all cargo types in the intended trade are addressed, that equipment inventory matches the vessel’s actual outfit, and that calculations are correctly performed. Approval is recorded on the front page of the CSM with the approval authority’s stamp and signature.

Amendment is required when:

New cargo securing equipment is fitted or existing equipment is retired
New cargo types are added to the vessel’s certificate of fitness or charter trading range
Structural modifications to cargo spaces change the distribution or rating of deck fittings
An incident or near-miss reveals a deficiency in an existing securing arrangement

Amendments are submitted and re-approved following the same procedure as initial approval. Flag state requirements on turnaround time vary, but IACS member societies typically commit to a 10-working-day review for minor amendments.

Modern practice and industry developments

Lashing assessment software

Modern container shipping operations use dedicated lashing assessment software to automate the Annex 13 calculation for every bay position on the ship. These systems integrate with the cargo planning (stowage planning) software to generate a lashing plan showing the required lashing configuration for each container, flagging positions where the proposed stowage would produce lashing forces exceeding available CSE capacity. Leading platforms include MACS3, SeaCargoPlan, and NAVIS SPARCS.

The adoption of lashing software does not remove the requirement for an approved CSM. Rather, the CSM provides the engineering envelope - approved equipment MSL values, design accelerations, structural limits - within which the software operates. The master and cargo officer remain responsible for verifying that the software output is consistent with the CSM.

Lashing software has become sophisticated enough to perform real-time optimisation: rearranging the distribution of heavy containers across bays to keep lashing forces within limits while simultaneously satisfying intact stability requirements, hatch-cover pressure limits, and shear force/bending moment constraints from the hull loading computer. For a large container ship, this is a multi-variable optimisation problem with thousands of constraints, and modern software resolves it within minutes during the loading planning phase.

Polar and ice-class operations

The Polar Code (IMO MSC.385(94), MEPC.264(68)) entered into force on 1 January 2017 and imposes additional requirements on ships operating in Arctic and Antarctic waters. While the Polar Code’s principal focus is on structural ice strengthening, life-saving appliances, and environmental protection, its operational provisions include requirements on cargo securing in conditions where ice impact loads may be superimposed on the conventional wave-induced accelerations.

A ship operating in ice-covered waters may experience impulsive loads from brash ice impact or pressure ridges that are not represented in the CSS Code acceleration tables, which are derived from wave-induced motions in open water. The CSM of an ice-class vessel should address this by specifying additional securing requirements for operations in ice, either through conservative design accelerations or through specific supplementary calculations. Flag Administrations with significant Arctic trades (Norway, Russia, Canada, Finland) have developed national guidance on this interface.

Ultra-large container ships

The emergence of ultra-large container ships (ULCS) exceeding 20,000 TEU has raised questions about the adequacy of CSS Code design accelerations that were originally calibrated against smaller vessel types. ULCS have natural roll periods of 25 to 35 seconds, well outside the resonance band of most ocean swell, which tends to limit roll amplitudes. However, the sheer height of cargo stacks on ULCS - with containers stacked 10 or 11 high on deck - creates large overturning moments at the bottom of the stack that may exceed the original design assumptions for twist-lock capacity.

IACS UR S32 was revised to address ULCS geometry by specifying fatigue assessment criteria for twist locks subjected to the cycling loads of repeated port calls over a vessel’s service life. A twist lock on a ULCS may be installed and removed 500 times per year, accumulating significant cyclic loading that must be managed through planned replacement intervals specified in the CSM inspection programme.

The MSC Zoe incident in 2019 was an important data point for ULCS lashing system performance: the containers lost were not from structural failure of the twist locks themselves but from combined exceedance of the design accelerations and suboptimal weight distribution within bays. Post-Zoe analysis by the Dutch Safety Board and by several classification societies concluded that the CSS Code design accelerations for ULCS operations on the North Sea winter service needed to be revisited, contributing directly to the 2020 revision of Annex 13.

Container weight verification

The 2016 SOLAS VGM requirement has substantially improved the accuracy of container weight data available for lashing calculations. Prior to the VGM mandate, a significant proportion of containers were loaded with incorrectly declared weights, with documented cases of actual masses 20-30% higher than the declared weight. Incorrect weight data directly corrupts lashing calculations. The VGM method check calculator assists in determining which weighing method (Method 1: weighing the packed container, or Method 2: summing item weights) is applicable and whether any threshold exemption applies.

World Shipping Council container loss data

The WSC began systematic tracking of containers lost overboard in 2011. The annual Container Loss Report, updated since 2020 as part of the Container Loss Initiative following the MSC Zoe incident, shows that average losses were approximately 1,382 containers per year for the period 2008-2019 (including catastrophic incidents). Excluding catastrophic events, the average was approximately 779 per year. The data support the industry view that most losses occur in a small number of severe incidents rather than as a steady background rate, pointing to weather routing and operational decision-making as the primary intervention point. ShipCalculators.com aggregates cargo securing and lashing tools alongside vessel motion and stability calculators to support pre-voyage planning.

Integration with voyage planning

The CSS Code implicitly assumes that design accelerations represent the worst expected conditions. Where ships sail through regions with known high sea states - North Atlantic winter, North Sea autumn-winter, Kuroshio Current zone - operators are expected to use weather routing to avoid or minimise exposure to conditions that would produce accelerations exceeding the CSM design values. Following the MSC Zoe investigation, several flag Administrations issued operational guidance recommending that masters reduce speed in severe conditions even where the calculated lashing adequacy margin is positive, given that the CSS Code design accelerations do not capture all combinations of wave height, period, and heading.

Container ships operating on north European trades are now routinely issued with master’s voluntary reporting forms for any container loss or lashing failure, feeding into IMO and flag-state incident databases. This data feeds back into future revision cycles for the CSS Code.

Interaction with stability and loading

Cargo securing cannot be separated from intact stability. A heavily loaded hatch-cover with containers increases the ship’s vertical centre of gravity, reducing the metacentric height GM and slowing the natural roll period. Longer roll periods are associated with smaller roll amplitudes in irregular seas, but when resonance occurs the roll angles can be extreme. An adequate GM is a prerequisite for cargo securing: at extreme heel angles, the geometry of lashing arrangements changes and the perpendicular components of lashing forces deviate substantially from design values.

Trim and list also affect cargo securing. A listed ship imposes a static transverse component on all cargo, effectively pre-loading lashings on the low side and reducing their available capacity for dynamic loads. The CSM typically specifies a maximum list angle beyond which cargo securing cannot be guaranteed for the design accelerations, often two to three degrees.

References

IMO Resolution A.714(17), Code of Safe Practice for Cargo Stowage and Securing (CSS Code), adopted 6 November 1991.
IMO MSC.1/Circ.1352, Revised Guidance to Masters for Avoiding Dangerous Situations in Adverse Weather and Sea Conditions, 2010.
IMO MSC.1/Circ.1353/Rev.2, Revision of the CSS Code, Annex 13, 2019.
IMO MSC.1/Circ.1624, Revised Annex 13 to the CSS Code - Stowage and Securing of Containers on Non-Cellular Ships, 2020.
IMO MSC.1/Circ.1497, Revised Guidelines for Packing of Cargo Transport Units (CTU Code), 2014.
SOLAS 1974 as amended, Regulation VI/5 (Stowage and securing), Regulation VI/5-1, Regulation VI/2 (Cargo information), Regulation VII/5.
IACS Unified Requirement S32, Requirements for Containers, current edition.
Dutch Safety Board, Container Loss MV MSC Zoe, report 2019.
Marine Accident Investigation Branch (MAIB), Report on the investigation of the structural failure of MSC Napoli, 2008.
Japan Transport Safety Board, Marine Accident Investigation Report - MOL Comfort, 2015.
MAIB, Report on the grounding of MV Rena on Ōtāiti (Astrolabe Reef), New Zealand, 2014.
World Shipping Council, Container Loss Report 2023, WSC, 2023.
IMO MSC.1/Circ.1461, Guidelines for Verification of Conformity with SOLAS Chapter VI Requirements, 2012.