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Marine Cargo Securing and Lashing Systems

Marine cargo securing and lashing systems prevent cargo movement during ship motion in seaways, protecting cargo from damage, ship structure from impact, and crew from injury. The forces generated when 100,000 tonne ships roll, pitch, and heave in heavy weather can create accelerations of 1g or more on cargo, generating forces that easily exceed the structural strength of cargo packaging unless properly secured. Cargo shifting in heavy weather has been a contributing factor in numerous casualties from the loss of European Gateway (1982) through to ongoing incidents on container ships and ro-ro vessels. The integrated framework of cargo securing equipment, calculation methods, and operational procedures has progressively reduced casualty rates while accommodating increasingly diverse cargo types and operations. ShipCalculators.com hosts the relevant computational tools and a full catalogue of calculators.

Contents

Background

The regulatory framework for cargo securing is anchored in SOLAS Chapter VI (Carriage of Cargoes) and the supporting IMO MSC.1/Circ.1353 (CSS Code Revised Guidelines), with additional input from the various class societies, industry guidance from organisations like ISO and the IMO, and operational practices developed by experienced ship operators and stevedores. The detailed engineering of cargo securing equipment, from the precision-machined twistlocks of modern container ships through to the heavy chain lashings of breakbulk cargo, reflects the accumulated learning of decades of marine cargo experience. Understanding cargo securing requires knowledge of the loading forces generated by ship motion, the strength characteristics of various securing equipment, and the operational practices that translate these into reliable cargo securing in service.

Regulatory Framework

The international regulatory framework for cargo securing combines SOLAS, IMO codes and circulars, classification society rules, and industry standards.

SOLAS Chapter VI (Carriage of Cargoes) establishes the requirement that cargoes be loaded, stowed, and secured to prevent damage to the ship and personal injury, and to remain safe under all anticipated voyage conditions. Specific regulations include:

  • Regulation 5: stowage and securing
  • Regulation 5.1: cargo securing manual
  • Regulation 5.2: stowage of cargo

The Cargo Securing Manual (CSM) is required by SOLAS for every ship carrying cargo other than solid bulk cargo. The CSM documents:

  • Cargo securing equipment available
  • Securing arrangements for various cargo types
  • Stress limits and safety factors
  • Inspection and maintenance procedures

IMO Resolution MSC.1/Circ.1353 (Revised Guidelines for the Preparation of the Cargo Securing Manual), the most recent comprehensive guidance, replaced earlier MSC.1/Circ.745. The guidelines provide detailed requirements for CSM preparation, with specific provisions for different cargo types.

Code of Safe Practice for Cargo Stowage and Securing (CSS Code), originally MSC/Circ.745 and refined through subsequent amendments, provides the engineering basis for cargo securing calculations. The CSS Code includes:

  • Acceleration coefficients for various ship motions
  • Force calculation methods
  • Securing equipment selection guidance
  • Inspection and maintenance recommendations

ISO 3874 series (Series 1 freight containers - Specifications and testing) covers container construction including the corner castings that interface with twistlocks and lashings.

ISO 1496 series covers ISO container classifications and dimensions.

Class society rules (DNV, Lloyd’s Register, ABS, Bureau Veritas, ClassNK, RINA, KR) implement SOLAS and IMO guidance through detailed engineering requirements covering ship structure for cargo securing, certification of cargo securing equipment, and survey procedures.

National regulations including the UK Merchant Shipping (Carriage of Cargoes) Regulations, the Australian Marine Order 42, and similar instruments translate international requirements into binding national law.

Container manufacturer standards (ISO standards plus various national codes) cover container strength and securing point requirements.

Cargo Securing Manual

The Cargo Securing Manual (CSM) is a vessel-specific document detailing the cargo securing arrangements available and approved methods for various cargo types.

CSM contents typically include:

  • Description of all permanent and portable cargo securing equipment
  • Approved cargo arrangements for specific cargo types
  • Stress limits and safety factors for each securing type
  • Calculation procedures for non-standard cargoes
  • Inspection and maintenance requirements
  • Records of securing equipment certification

CSM development is performed by the ship’s designer (during construction) or by competent organisations (for modifications). The CSM must be approved by the flag administration or recognized organisation.

CSM use during cargo operations:

  • Loading planning to ensure approved arrangements
  • Verification of securing equipment availability
  • Documentation of cargo securing decisions
  • Reference for crew during voyages

CSM revision when cargo characteristics change, equipment is added/removed, or operational experience indicates needed changes. Class approval is required for modifications.

CSM compliance is verified during port state inspection, class survey, and major incidents.

Cargo Securing Forces

Cargo securing forces are calculated based on ship motion and cargo characteristics.

Ship motion accelerations cause cargo forces. Per CSS Code:

  • Roll acceleration: typically 0.5-0.8g amplitude
  • Pitch acceleration: typically 0.5-0.7g amplitude
  • Heave acceleration: typically 0.5-0.6g amplitude

Combined accelerations using vector summation (with phasing factors) determine peak cargo forces.

Acceleration coefficients vary with cargo position on the ship:

  • Forward, aft positions: high pitch effects
  • Side positions: high roll effects
  • Combined positions: maximum design accelerations

Cargo weight and centre of gravity determine cargo mass-induced forces. Higher weights generate higher forces requiring stronger securing.

Cargo dimensions affect:

  • Wind forces (on exposed cargo)
  • Buoyancy forces (on partially submerged cargo, like deck cargo near the waterline)
  • Aerodynamic effects in heavy weather

Friction forces between cargo and ship structure provide some resistance to sliding. Friction coefficients vary:

  • Steel on dry steel: 0.10-0.15 (low)
  • Wood on wood: 0.30-0.40 (moderate)
  • Rubber on steel: 0.50-0.80 (high)

Securing equipment must handle the difference between total force and friction-resisted force.

CSS Code calculation method:

  1. Determine cargo location and accelerations from CSS Code tables
  2. Calculate inertia forces using F = ma
  3. Subtract friction-resisted forces
  4. Sum forces in each direction
  5. Compare with available securing equipment strength
  6. Verify safety factor exceeds minimum required

Maximum Securing Load (MSL) for each securing arrangement is the breaking load of the equipment divided by the safety factor.

Calculated Securing Load (CSL) is the actual load on the equipment based on cargo and motion. CSL must be less than MSL for safe operation.

Container Securing

Container securing on container ships is a substantial engineering discipline addressing the unique characteristics of containerised cargo.

Twistlocks at container corner castings provide the principal corner-to-corner connection between containers. Modern twistlocks include:

  • Manual twistlocks: traditional rotating-cone design requiring manual lock/unlock
  • Semi-automatic twistlocks: locks automatically when containers stack, manual unlock
  • Fully automatic twistlocks: completely automatic engagement

Twistlock designs include:

  • Pin-style: vertical pin engaging the corner casting
  • Cone-style: tapered cone with ring rotation for engagement
  • Various hybrid designs

Lashing rods (also called lashing bars) connect lower containers to deck lashing points. Modern lashing rods include:

  • Solid steel rods (typical for older systems)
  • Cellular rod systems (more compact, easier handling)
  • Various lengths and capacities

Lashing rod layout typically follows specific patterns:

  • Cross lashings between containers
  • Longitudinal lashings to lashing points
  • Vertical lashings within stacks

Twistlock and lashing combination provides:

  • Twistlocks: vertical and horizontal restraint between containers
  • Lashing rods: support for the bottom of stacks against transverse motion
  • Combined: resistance to ship motion accelerations

Modern automated container ships use:

  • Push-button container handling at terminals
  • Automatic lashing engagement during stacking
  • Reduced manual operations

Container weight stack limits determine maximum container weight at each tier. Modern container ships typically allow 7-10 high stacks, with weight limits decreasing for higher tiers due to combined load implications on the lower containers.

Container code per ISO 6346 includes:

  • Owner code (3 letters)
  • Equipment category (1 letter, U for container)
  • Serial number (6 digits)
  • Check digit (1)

Container condition rating per ISO 7166 (Container Condition Code) describes container damage levels.

Container Stack Strength

Container stack strength determines the maximum weight that can be stacked safely.

Container corner casting strength per ISO 1496:

  • Rated for vertical load of 86,400 kg per stack (max stack weight)
  • Lateral load capability for ship motion forces
  • Compression strength at corner castings

Stack weight calculation considers:

  • Maximum container weight
  • Number of containers in stack
  • Combined static + dynamic loading

Stack acceleration reduces apparent stack capacity:

  • Roll: substantial reduction in lateral capacity
  • Pitch: reduction in fore-aft capacity
  • Heave: increase in vertical loading

Container stacking sequence:

  • Heaviest containers on bottom
  • Lighter containers progressively higher
  • Match center of gravity to ship stability

Damaged or weakened containers must be lower-tier. ISO 7166 condition rating indicates if container can be loaded high in stack.

Special container types have different stack characteristics:

  • Reefer containers (with refrigeration units): heavier, may have weight restrictions
  • Open top containers: lower stack strength
  • Tank containers: lower stack strength typically

Lashing Calculation

Lashing calculations verify that the proposed securing arrangement is adequate for the cargo and voyage conditions.

Standard calculation procedure:

  1. Determine cargo position on ship
  2. Calculate accelerations from CSS Code tables
  3. Calculate inertia forces (F = ma)
  4. Subtract friction forces
  5. Determine net required securing force
  6. Compare with available securing capacity (MSL × number)
  7. Verify safety factor

Practical examples for container ships:

  • Container in stack 5, position 4 in row, location: amidships
  • Cargo weight: 30 tonnes
  • Roll acceleration: 0.6g (CSS Code value)
  • Lateral force: 30 × 0.6 = 18 tonnes (180 kN)
  • Friction force: 30 × 0.15 = 4.5 tonnes (45 kN)
  • Net required securing: 18 - 4.5 = 13.5 tonnes (135 kN)
  • Available lashing capacity: per ship’s CSM

For specific cargo types, software tools and CSM tables provide pre-calculated arrangements. For unusual cargoes or arrangements, manual calculations following CSS Code are required.

Lashing software including MaCSlash, MARIN’s tools, and proprietary class society software provide automated calculation for complex cargo arrangements.

RoRo Cargo Securing

RoRo cargo (vehicles, trailers, plant equipment) requires different securing approaches than containers.

RoRo cargo types:

  • Cars and light commercial vehicles
  • Heavy trucks and trailers
  • Construction equipment and machinery
  • Project cargo on flat racks
  • Various other rolling cargoes

Securing equipment for RoRo:

  • Wheel chocks (preventing horizontal movement on parked wheels)
  • Lashing chains and tensioners
  • Wire rope lashings
  • D-rings and tie-down points on the ship’s deck

Chain lashings are common for trailers and heavy equipment:

  • Grade 80 (T) or Grade 100 (V) alloy steel chain
  • Connecting at trailer or vehicle securing points
  • Tensioned with chain tensioners (lashing chain hooks)

Wire rope lashings provide additional flexibility:

  • Steel wire rope of various diameters
  • Connected with shackles and turnbuckles
  • Used where chain might damage cargo

Lashing tension typically 50-100 kg per inch of chain or 50-150 kg per centimetre of wire rope, depending on the cargo type and motion expected.

Lashing pattern follows the cargo and motion:

  • Forward and aft lashings (preventing fore-aft movement)
  • Lateral lashings (preventing roll-induced movement)
  • Vertical lashings on tall cargo

Number of lashings depends on:

  • Cargo weight
  • Cargo characteristics (bulk vs. concentrated weight)
  • Voyage conditions expected
  • CSM specifications

Lashing inspection during voyage:

  • Daily checks of all visible lashings
  • Tension verification (re-tensioning if needed)
  • Damage inspection
  • Documentation of all checks

Breakbulk Cargo Securing

Breakbulk cargo (general cargo not in containers) covers wide variety of items each with specific securing requirements.

Breakbulk cargo types:

  • Project cargo (heavy machinery, transformers, generators)
  • Steel coils (rolls of steel sheet)
  • Bagged cargo (rice, sugar, cement)
  • Palletised cargo
  • Bulky machinery
  • Logs and timber products

Securing approaches:

  • Cargo-specific lashing arrangements per CSM
  • Steel chain or wire rope tensioned with turnbuckles
  • Ship’s gear (cargo hold tween-deck pockets, lashing points)
  • Heavy cargo: timber dunnage and chocks plus lashings
  • Light cargo: friction-reliant if mass is low and cargo well-stowed

Steel coil securing per CSS Code requires:

  • Cradle blocks supporting the coil
  • Multiple lashings per coil
  • Specific tensioning pattern
  • Inspection during voyage

Project cargo securing:

  • Engineered securing for each load
  • Multiple chains/wire ropes
  • Specialised equipment (load-spreading beams, sliding gear)
  • Documentation of complete securing arrangement

Bagged cargo securing:

  • Stowage in proper pattern (preventing avalanching)
  • Securing across bag faces (cribbing)
  • Limited movement allowed within bag piles

Palletised cargo:

  • Pallet-to-pallet stacking with stretch-wrap or banding
  • Limited stacks (typically 2-3 pallets)
  • Anti-slip mats between pallets where required
  • Securing to ship structure for high-acceleration zones

Cargo Securing Equipment

Cargo securing equipment must be certified for safe use.

Lashing chain:

  • Grade 80 (T) - 800 N/mm² minimum yield
  • Grade 100 (V) - 1000 N/mm² minimum yield
  • Manufactured to ISO 7592 or equivalent
  • Marked with grade, manufacturer, and certification

Wire rope:

  • Various constructions (6x36 IWRC, 8x36 IWRC, etc.)
  • Diameters from 16 to 38 millimetres typical
  • Manufactured to ISO 4344 or equivalent
  • Marked with manufacturer and breaking load

Lashing rods:

  • Manufacturer’s certification per ISO 8862 or equivalent
  • Marked with capacity and identification
  • Various lengths for different applications

Twistlocks:

  • Manufacturer’s certification per ISO 3874
  • Marked with capacity and identification
  • Various types (manual, semi-automatic, automatic)

Turnbuckles and tensioners:

  • Various types (frame, jaw-and-eye, eye-and-eye)
  • Capacity from 1 to 25 tonnes
  • Manufacturer’s certification

Shackles:

  • Bow shackles, D-shackles, web slings
  • Various capacities
  • Forged steel construction

Equipment marking includes:

  • Manufacturer’s identification
  • Capacity (Working Load Limit)
  • Certification reference
  • Date of manufacture

Equipment inspection at periodic intervals:

  • Daily visual inspection during cargo operations
  • Annual class surveys
  • Special inspections after incidents

Replacement intervals depend on condition. Damaged or worn equipment must be replaced before further use.

Specific Applications

Different ship types have characteristic cargo securing arrangements.

Container ships have substantial securing infrastructure:

  • Cell guides in the hold (passive securing of containers)
  • Twistlock systems on deck
  • Lashing equipment (rods, turnbuckles)
  • Specialised cellular rod systems

Modern automated container ships have substantially reduced manual lashing requirements through:

  • Cellular containers (full cell guide systems)
  • Auto-lashing systems
  • Advanced container designs

RoRo ships have:

  • Lashing rings throughout the cargo decks
  • Chain lashings and wire ropes
  • Wheel chocks for vehicle securing
  • Specialised lashings for heavy equipment

General cargo ships have:

  • Tween deck securing arrangements
  • Cargo hold lashing points
  • Various securing equipment for diverse cargoes
  • Detailed Cargo Securing Manual

Ro-pax ferries (passenger plus vehicles) require:

  • Dedicated passenger area securing
  • Vehicle deck lashings (chains, wheel chocks)
  • Particular attention to vehicle stability under ship motion

Heavy lift specialist ships:

  • Engineering for each load
  • Custom lashing arrangements
  • Multiple redundancy in critical areas
  • Marine surveyor approval for each major cargo

LNG and LPG carriers:

  • Cargo containment through tank design
  • Limited cargo movement within insulated tanks
  • Substantial structural securing of tanks

Cargo Safety Procedures

Operating cargo with proper securing requires established procedures.

Pre-loading planning:

  • CSM consultation for cargo type
  • Securing equipment availability check
  • Stowage plan development
  • Voyage condition forecasting

During loading:

  • Cargo position verification
  • Securing arrangement implementation
  • Continuous safety oversight
  • Documentation of all activities

Voyage operations:

  • Daily securing inspection
  • Tension verification on lashings
  • Cargo position monitoring
  • Heavy weather precautions

Heavy weather operations:

  • Course adjustment to reduce motion
  • Speed reduction to reduce wave-induced motions
  • Additional securing checks
  • Crew safety procedures

Cargo discharge:

  • Securing release sequence
  • Cargo extraction in safe order
  • Cargo damage assessment
  • Documentation of voyage cargo movements

Records and documentation:

  • Cargo securing operations log
  • Inspection records
  • Equipment certification
  • Cargo damage reports

Maintenance and Inspection

Cargo securing equipment maintenance combines daily attention, periodic preventive maintenance, and major overhauls.

Daily inspection:

  • Visual examination of all visible equipment
  • Damage detection
  • Operational testing of moving parts (turnbuckles, twistlocks)
  • Documentation of any defects

Weekly maintenance:

  • Detailed equipment inspection
  • Lubrication of mechanical components
  • Cleaning of equipment

Monthly comprehensive maintenance:

  • Major equipment inspection
  • Documentation of all conditions
  • Replacement of defective items

Annual maintenance:

  • Major equipment overhauls (turnbuckles, etc.)
  • Re-certification testing
  • Inventory verification
  • Class survey support

5-year major surveys involve dry-docking inspection of all permanent securing arrangements (deck rings, lashing points, structural reinforcements). Replacement of permanent equipment as needed.

Equipment storage requires:

  • Protection from weather
  • Organised storage location
  • Inventory management
  • Easy access for cargo operations

Future Developments

Cargo securing continues to evolve in response to operational requirements and technology.

Smart container monitoring with sensors providing real-time cargo position and condition data, integrated with vessel monitoring systems.

Improved lashing equipment including:

  • Higher-strength alloys
  • Lighter-weight materials
  • Easier-handling systems
  • Integrated tension monitoring

Automated securing on container ships continues to reduce manual labour while improving consistency.

Predictive lashing analysis using voyage forecasts, ship motion measurement, and cargo characteristics provides voyage-long securing planning.

Improved CSM software and tools provide better cargo planning capability.

Conclusion

Marine cargo securing and lashing systems are essential to safe ship operation, protecting cargo, ship, and crew from the consequences of cargo movement during voyage. The combination of properly designed and certified securing equipment, comprehensive Cargo Securing Manuals, careful loading procedures, and disciplined operational oversight produces the cargo safety that ships and shippers depend upon. Crew members responsible for cargo securing must understand the regulatory framework (SOLAS Chapter VI, CSS Code, CSM), engineering principles, equipment characteristics, and operational practices that together ensure safe cargo transport. As the maritime industry evolves through automation, smart monitoring, and improving cargo handling efficiency, securing systems are evolving in response, but the fundamental purpose, keeping cargo where it belongs throughout the voyage, remains a constant focus of cargo handling engineering.

Additional calculators:

Additional related wiki articles:

References

  • SOLAS Chapter VI - Carriage of Cargoes
  • IMO MSC.1/Circ.1353 - Revised Guidelines for the Preparation of the Cargo Securing Manual
  • IMO Code of Safe Practice for Cargo Stowage and Securing (CSS Code)
  • ISO 3874 - Series 1 freight containers - Specifications and testing
  • ISO 1496 - Series 1 freight containers - Specification and testing
  • DNV Rules for Classification of Ships - Pt 4 Ch 11 Cargo Handling and Stowage