SOLAS Chapter XII: Additional Safety Measures for Bulk Carriers

Background

Why Chapter XII exists

Bulk carriers carry approximately one-third of all maritime tonnage by mass: iron ore, coal, grain, bauxite, alumina, cement, fertiliser, sulphur, salt and other dry-bulk cargoes that move in vast quantities between mining and farming regions and the world’s industrial consumers. Yet bulk carriers, particularly the larger ore-carrying types, have produced one of the worst safety records of any merchant ship type:

• The 1990s alone saw approximately 200 bulk carrier losses worldwide, with cumulative crew fatalities in the thousands.
• The pattern was particularly stark for older Capesize and Panamax ore carriers in heavy weather, and for ships carrying dense cargoes (iron ore concentrate, magnetite, ilmenite, lead concentrate) at the structural limits.
• The losses repeatedly exhibited similar failure modes: rapid foundering after a hatch cover failure or transverse bulkhead failure allowed water to flood No. 1 cargo hold, with progressive flooding through subsequent holds and structural collapse before the crew could even abandon ship.

The combination of high cargo density, large cargo holds, simple hatch cover access, single-skin side construction (older ships), and exposure to severe wave loading on long ocean voyages produced a structural risk profile distinct from any other ship type. By the mid-1990s, the IMO accepted that the existing SOLAS framework (which addressed bulk carriers within general cargo ship provisions) was inadequate. Chapter XII was developed as a dedicated regulatory chapter for bulk carriers.

The 1997 adoption and successive amendments

The original Chapter XII was adopted in 1997 and entered into force on 1 July 1999. It addressed the most urgent issues:

• Damage stability for ships of 150 m and above to survive flooding of any one cargo hold.
• Structural strength of hatch covers, forward bulkheads and forecastle.
• Loading instrument to support intermediate-stress verification during loading and unloading.

Subsequent amendments progressively strengthened the regime:

• 2002 amendments (Resolution MSC.170(79), entered into force 2004) added requirements for water-level detectors in cargo holds and dry spaces, and tightened the Enhanced Survey Programme.
• 2004 amendments introduced double-side construction for new bulk carriers above 150 m carrying high-density cargoes.
• 2006 amendments introduced the alternate-hold loading restrictions to prevent overstowing of stress in adjacent holds.
• 2010 amendments (Resolution MSC.296(87)) harmonised damage stability methodology with the Chapter II-1 probabilistic regime.
• 2014 amendments harmonised hold flooding criteria, water-level detector tests, and the loading instrument standards.

The chapter is now stabilised, with continued attention to specific issues (very large ore carrier conversion, lithium-bearing cargoes) addressed through individual cycles.

Relationship to other SOLAS chapters and codes

Chapter XII is the bulk-carrier-specific layer over a stack of more general regulation:

• Chapter II-1 provides the construction and stability framework, with bulk carriers above 150 m subject to the Goal-Based Standards (GBS) and the IACS Common Structural Rules under Part A-1.
• Chapter II-2 provides fire protection, with specific cargo-hold requirements for IMSBC Group B cargoes that have chemical hazards.
• Chapter VI provides cargo carriage requirements, with the IMSBC Code imported as mandatory for solid bulk cargoes.
• The BLU Code provides operational guidance on loading and unloading.
• The IACS Unified Requirements (the UR S series for bulk carrier structure and the UR Z series for surveys) provide the engineering and inspection standards underpinning compliance.
• The Polar Code under Chapter XIV adds polar-specific requirements where relevant.

The result is a layered compliance structure that gives bulk carriers more attention than any other ship type, reflecting the historical casualty experience.

Application

Chapter XII applies to:

• Bulk carriers as defined: ships designed primarily for the carriage of dry cargoes in bulk, with single deck and (typically) transverse hatch openings on the weather deck.
• New bulk carriers of 150 metres in length and above for the principal structural and damage stability requirements.
• Existing bulk carriers of 80 metres and above for certain operational requirements (loading instrument, water-level detectors).
• Bulk carriers carrying solid bulk cargoes of density 1000 kg/m3 or above for the double-side construction requirement (introduced in 2004).

The application is a definition-based scope: a ship that meets the bulk carrier definition is covered, regardless of how the operator labels the ship in commercial documentation. Some ships at the margins (combination carriers, heavy lift vessels carrying occasional bulk cargo) require flag-state determination of applicability.

Damage stability (Regulation 4)

The damage stability requirement

Bulk carriers above 150 m must survive defined damage to the foreship without progressive flooding through cargo holds. The damage scenario is:

• Damage extent: from the forward perpendicular aft to a defined position (typically B/3 of breadth aft and a defined longitudinal extent of the hull).
• Damage depth: from the side shell inboard to a defined penetration.
• Vertical extent: from the keel up to the bulkhead deck.

After this damage, the ship must:

• Float at an equilibrium waterline that does not immerse non-watertight openings.
• Have positive metacentric height (GM > 0) corrected for free-surface effect.
• Have a residual righting arm (GZ) of at least 0.10 m at the equilibrium heel angle.
• Have a positive range of stability of at least 16 degrees beyond the equilibrium heel.
• Survive a defined wind heeling moment without breaching the heel-angle criterion.

The criterion is satisfied through:

• Strong forward bulkhead preventing progressive flooding from a damaged No. 1 hold to No. 2 hold.
• Forward forecastle providing reserve buoyancy if the bow trim becomes excessive.
• Adequate damaged-condition GM with margin against free-surface effect of partially-flooded holds.
• Watertight cross-flooding arrangements to balance asymmetric flooding.

Harmonisation with Chapter II-1

The 2010 amendments harmonised the bulk carrier damage stability with the probabilistic methodology in Chapter II-1 Part B. New bulk carriers compute the attained subdivision index A under the probabilistic methodology and demonstrate A >= R where R is the required index.

For bulk carriers, R is calibrated to give equivalent safety to the deterministic worst-case foreship damage. In practice, modern bulk carriers above 150 m comfortably exceed R.

The post-Derbyshire context

The damage stability requirement has its origins in the loss of MV Derbyshire (1980). The 26-year investigation completed in 2000 concluded that hatch cover failure on No. 1 hold allowed flooding, and that the forward bulkhead could not retain the flooded hold against the head of water generated by ship motions. The investigation also revealed that the design loadings used in the original construction had been conservative for the Pacific typhoon environment but had been progressively eroded by the size growth of bulk carriers (Derbyshire was a 91,000 DWT bulk carrier, very large for her time but routine by 1990s standards).

The post-Derbyshire amendments to Chapter XII strengthened the forward bulkhead and the forecastle, and added water-level detection that would warn of hold flooding before progressive failure became inevitable.

Structural strength (Regulation 5) and IACS CSR

Structural strength requirements

Regulation 5 requires that bulk carriers be designed and constructed to withstand the loads encountered in service. The requirement is implemented through:

• IACS Common Structural Rules (CSR) for new bulk carriers above 150 m (mandatory under GBS).
• Classification society rules for smaller bulk carriers (with class society rules underpinned by IACS Unified Requirements).
• Specific IACS Unified Requirements:
  • UR S21: hatch cover loading and strength verification (the IACS UR S21 hatch expand calculator implements the verification).
  • UR S26: hatch securing arrangements (the IACS UR S26 hatch calculator implements the strength verification).
  • UR S31: forward hold flooding scenario for bulk carriers.
  • UR S25: structural strength of bulk carrier hatch covers.

The IACS hatch load calculator provides general hatch cover load calculations for bulk carriers.

CSR architecture

The IACS CSR for bulk carriers covers:

• Hull girder strength: still-water bending moment, wave bending moment, shear forces, with a defined margin against yielding and against buckling.
• Local plating strength: scantlings of plating in cargo holds, on weather decks, on hatch covers, on transverse bulkheads, on hopper sloping plates, on topside tank plating.
• Stiffener strength: longitudinal and transverse stiffeners against local plate buckling and against compression in the upper deck and bottom plating.
• Fatigue life: spectrum fatigue analysis for high-stress structural details (hatch corner brackets, bulkhead-to-hopper junctions, longitudinals at transverse bulkheads).
• Residual strength after damage: post-grounding and post-collision survivability analysis.
• Coating performance: coating durability for ballast tanks (mandatory PSPC, Performance Standard for Protective Coatings).

The CSR replaced the previous bulk carrier structural rules of individual class societies in 2006, providing a uniform standard. The CSR is itself amended in cycles, with major updates in 2012 (Common Structural Rules Harmonisation) and 2017.

Hatch cover strength

The hatch cover is the most-cited single failure point in bulk carrier casualties. The IACS UR S21 specifies:

• Hatch cover plate scantlings sized to withstand the wave-induced load on the cover plus the static cargo load if cargo is stowed on the cover.
• Securing arrangements with deck-mounted closing devices and side-mounted compression seals.
• Drainage arrangements to prevent water accumulation on the cover.
• Inspection accessibility with crawl-through access for surveyors to verify the underside of the cover.

Modern bulk carriers use either:

• Steel hatch covers (single-piece or multi-piece pontoon design), the standard for Capesize and larger.
• Folding covers (Macgregor, Tesma) on smaller bulk carriers with deck-mounted hydraulic actuators.
• Side-rolling covers on container-bulk dual-purpose ships.

The post-Derbyshire investigations identified that older hatch covers (1970s and 1980s designs) had insufficient scantlings for severe wave loading and that the securing arrangements could fail under impact. The post-2002 amendments raised the design wave load by approximately 50 percent.

Structural and other requirements (Regulation 6)

Double-side construction

For new bulk carriers above 150 m carrying solid bulk cargoes of density 1000 kg/m3 or above, Regulation 6 requires double-side construction. The requirement was introduced in 2004 amendments after the bulk carrier loss cluster of the 1990s and 2000s.

Double-side construction provides:

• Side shell: outer plating exposed to the sea.
• Cargo hold side: inner plating bounding the cargo hold.
• Wing void space between the two: 760 mm minimum width, providing a buffer against side-shell penetration in collision or grounding.

Benefits of double-side construction:

• Collision and grounding resilience: a side-shell breach does not immediately flood the cargo hold. The wing void floods first, providing a barrier and time for damage assessment.
• Bulkhead support: the wing void provides a stronger anchor for transverse bulkheads, reducing the risk of bulkhead failure under flooded-hold loading.
• Easier ballast water management: the wing void can be used as a dedicated ballast tank.
• Easier survey access: the wing void is accessible for inspection from the deck without entering the cargo hold.

The cost of double-side construction is higher light-ship displacement, with corresponding loss of cargo capacity, plus the additional structural complexity. The trade-off was accepted as the cost of safety improvement.

Forward bulkhead and forecastle strengthening

Regulation 6 requires:

• Forward transverse bulkhead of higher strength than required by general SOLAS, designed to retain a flooded No. 1 hold against the dynamic head of water from ship motions.
• Forecastle providing reserve buoyancy in the event of bow trim by flooding. Forecastles on bulk carriers are typically extended over a substantial length to provide both seakeeping (reducing green water on deck) and reserve buoyancy.
• Forward fore-end deck plate strengthened to withstand green seas and to prevent deck flooding from contributing to forecastle integrity loss.

Bulkhead access and survey provisions

Regulation 6 requires:

• Permanent ladders and access platforms for inspection of structural details.
• Access through bulkheads via doors with positive sealing arrangements.
• Survey accessibility for the Enhanced Survey Programme.

Enhanced Survey Programme (Regulation 7)

The Enhanced Survey Programme

The Enhanced Survey Programme (ESP) is a more rigorous survey regime applicable to bulk carriers and oil tankers. Mandatory under both Chapter XII and the harmonised survey scheme:

• Annual surveys: visual survey of structure, with selected close-up examinations on rotation.
• Intermediate surveys (mid-cycle, year 2 to 3): extended close-up examination of structural details.
• Renewal (Special) surveys (every 5 years): comprehensive close-up examination of all critical structural details, with thickness measurements at defined locations.

The IACS UR Z10 series specifies the ESP scope and methodology:

• UR Z10.2: ESP for bulk carriers.
• UR Z10.5: ESP for oil tankers.
• UR Z10.7: ESP for double-hull oil tankers.

The IACS UR Z10 intervals calculator returns the survey schedule for a given ship.

Specific bulk carrier survey scope

For bulk carriers, the close-up survey covers:

• Hatch covers (each cover, including underside): condition of plating, stiffeners, securing arrangements, seals.
• Transverse bulkheads: vertical web frames, shedder plates, lower stool, upper stool, plate corrosion, weld integrity.
• Hopper sloping plates: corrosion, stiffener buckling, weld integrity.
• Topside tank plating: corrosion, stiffener buckling.
• Cross deck plating: corrosion, weld integrity.
• Cargo hold ladders and platforms: structural integrity, anchorage.
• Ballast tank plating and stiffeners: coating condition, corrosion, secondary structure.
• Forward bulkhead and forepeak: detailed survey of high-stress and high-corrosion areas.

Thickness measurement and corrosion margin

The ESP requires periodic thickness measurement of structural plating to detect corrosion before it reaches the structural reserve. The corrosion allowance built into the original scantlings is typically 1 to 2 mm per side, with end-of-life allowance for ballast tanks of 2 to 3 mm.

The ship is condemned (or the affected plating renewed) when the measured thickness falls below the original scantling minus the allowance.

Cargo declaration (Regulation 10)

Cross-reference to Chapter VI

Regulation 10 requires the shipper of solid bulk cargo to provide the master with a declaration of cargo properties, cross-referenced to Chapter VI Regulation 2. The declaration includes:

• Cargo description and IMSBC group classification.
• Stowage factor and angle of repose.
• Moisture content and TML for Group A cargoes.
• Chemical hazards and segregation requirements for Group B cargoes.
• Loading and discharge procedures.

The cross-reference avoids duplicating the detailed Chapter VI requirements while making the declaration directly applicable to bulk carriers under Chapter XII.

Specific bulk-carrier-related cargoes

Bulk carriers carry the principal Group A cargoes that have produced liquefaction casualties:

• Iron ore fines (the IMSBC iron ore fines calculator implements the moisture verification).
• Nickel ore (the IMSBC nickel ore calculator implements the moisture verification).
• Bauxite (added to Group A after the MV Bulk Jupiter casualty).
• Mineral concentrates (zinc, lead, copper).

Bulk carriers also carry the principal Group B cargoes that have chemical hazards:

• Coal (CO emission, oxygen depletion, self-heating).
• Direct reduced iron (hydrogen emission).
• Sulphide ores (SO2 and H2S emission).

Loading instrument (Regulation 11)

Mandatory loading computer

Every bulk carrier must carry a loading instrument (loading computer) capable of computing in real time:

• Hull girder bending moment at each frame.
• Hull girder shear force at each frame.
• Stability (intact and damage) at the proposed loading.
• Trim and draft at proposed loading.

The loading instrument is type-approved by the classification society or the flag state, and is validated against the ship’s stability information booklet. Loading computers are used:

• Pre-loading: to plan the loading sequence so that the cargo is distributed without exceeding strength or stability limits at any intermediate stage.
• During loading: to verify that the actual loading is following the plan and to alert the crew to deviations.
• Pre-departure: to verify that the final loading is within acceptable limits before sailing.

Bulk loading rate-arm

A specific loading-instrument application for bulk carriers is the rate-arm calculation: the maximum rate at which cargo can be loaded into each hold without exceeding intermediate-stage stress limits. The bulk loading rate-arm calculator implements the calculation, taking ship type, hull girder section modulus, and the loading sequence as inputs.

Rate-arm management is critical for Capesize and larger bulk carriers, where high loading rates (up to 12,000 tonnes per hour at major iron ore terminals) can produce significant stress concentrations if the cargo distribution is not managed.

Alternate-hold loading restrictions

The 2006 amendments introduced restrictions on alternate-hold loading (loading every other hold full while leaving intermediate holds empty). The pattern, used to optimise voyage trim or to handle dense cargoes, was identified as a contributor to several casualties because of the high stresses concentrated at the loaded-hold-to-empty-hold transition bulkheads.

Modern bulk carriers either avoid alternate-hold loading entirely, or are designed (and certified) for it with reinforced transverse bulkheads at the transition locations.

Water level detectors (Regulation 12)

Detector requirements

Regulation 12 requires water level detectors in:

• Each cargo hold: with sensors at low (about 0.5 m above the cargo hold inner bottom) and high (about 15 percent of the hold height or 2 m above the inner bottom, whichever is lesser) water levels.
• Ballast tanks (if not normally manned): with single-level high-level alarm.
• Dry spaces forward of the collision bulkhead (forepeak, fore deck void): with high-level alarm.

The alarm is presented to the bridge with audible and visible indication, supplemented by alarm in the engine control room. Detection of water in any of these spaces is treated as a serious casualty event, requiring:

• Immediate inspection of the affected space.
• Damage assessment.
• Verification of damage stability for the developing flooded condition.
• Pumping or other dewatering if practicable.
• Course alteration to refuge or to slow seas.

Detector technology

Common detector technologies:

• Conductive probes: simple bare-metal probes that conduct when wet, triggering alarm.
• Ultrasonic level sensors: non-contact sensors mounted on overhead structure, detecting water by acoustic reflection.
• Capacitive sensors: sensors detecting the dielectric change at water surface contact.
• Float-actuated sensors: mechanical floats with magnetic switches.

The detectors are tested annually for operation. Failures are common because of corrosion, mechanical damage from cargo handling, and dry-cargo dust accumulation, requiring regular maintenance.

Pumping systems (Regulation 13)

Regulation 13 requires that bulk carriers above 150 m have pumping arrangements capable of dewatering any one cargo hold from the deepest waterline within a defined time. The arrangement typically includes:

• Multiple bilge pumps with capacity for the largest hold.
• Bilge wells in each hold with strums sized for the cargo type (avoiding clogging by fine particles).
• Bilge piping system permitting selective pumping from any hold.
• Tie-in to the ballast pumping system for emergency dewatering capacity.

The pumping capability is specifically not credited in the damage stability calculation under Regulation 4 (the assumption is that flooding is irreversible), but it provides an operational margin for limited damage that can be managed.

Notable casualties

MV Derbyshire, 1980

The British-flagged bulk carrier MV Derbyshire foundered in Typhoon Orchid south of Japan on 9 September 1980 with 44 dead. The 26-year investigation completed in 2000 attributed the loss to failure of the No. 1 hatch cover, allowing flooding of No. 1 hold and progressive structural failure.

The Derbyshire investigation was foundational for Chapter XII because it:

• Identified the specific failure mode (hatch cover, forward bulkhead, progressive flooding) that recurred in subsequent bulk carrier losses.
• Provided detailed engineering analysis of the structural failure sequence.
• Established the post-incident analysis methodology that was applied to subsequent investigations.

MV Marika 7, 1990

The Greek-flagged bulk carrier MV Marika 7 sank in the North Pacific on 10 February 1990 in heavy weather with 29 dead. The investigation found similar features to Derbyshire: hatch cover failure, hold flooding, progressive structural collapse.

MV Leros Strength, 1997

The Greek-flagged bulk carrier MV Leros Strength sank off the coast of Norway on 8 February 1997 with 20 dead. The investigation found foreship structural failure, possibly initiated by side-shell damage.

MV Vinalines Queen, 2011

The Vietnam-flagged bulk carrier MV Vinalines Queen capsized in the Pacific on 25 December 2011 carrying nickel ore from Indonesia, with 22 of 23 crew lost. Liquefaction of the Group A nickel ore cargo was identified as the cause. The casualty was a direct driver of post-IMSBC Code amendments and of further attention to Group A cargoes under Chapter VI cross-references.

MV Bulk Jupiter, 2015

The bulk carrier MV Bulk Jupiter sank in the South China Sea on 2 January 2015 carrying bauxite from Malaysia, with 18 of 19 crew lost. Liquefaction of the bauxite cargo (an unusual finding because bauxite was not classed as Group A at the time) led to the addition of bauxite fines to Group A in subsequent IMSBC amendments.

MV Stellar Daisy, 2017

The Marshall Islands-flagged Very Large Ore Carrier MV Stellar Daisy split and sank in the South Atlantic on 31 March 2017 carrying iron ore fines from Brazil to China, with 22 of 24 crew lost. The casualty triggered investigation of the structural integrity of converted VLOCs (the ship had been converted from a tanker) and contributed to IACS unified requirements on VLOC structure.

The Stellar Daisy was particularly significant because it was a converted ship (tanker to ore carrier conversion in the early 2000s), highlighting the structural risk of conversion. Subsequent IACS amendments tightened the requirements for ship conversions and introduced stricter periodic survey for converted ships.

Cumulative loss pattern

Across the period 1980 to 2020, the bulk carrier loss pattern has been:

• 1980s: average approximately 8 to 12 losses per year, often with high crew fatalities.
• 1990s: peak losses in 1991-1994, with 15 to 20 losses per year and crew fatalities in the hundreds annually.
• 2000s: declining loss rate after Chapter XII implementation, but with periodic spikes (Derbyshire investigation publication 2000, Bulk Jupiter 2015).
• 2010s: continued decline, with losses now typically below 5 per year.
• 2020s: very low loss rate, with the principal residual risk being liquefaction of Group A cargoes from emerging ore-export jurisdictions.

The trend reflects the cumulative effect of Chapter XII, the IMSBC Code, IACS CSR, and the operational discipline imposed by classification societies and port-state control.

Bulk carrier classification societies and IACS coordination

The major classification societies (ABS, BV, CCS, ClassNK, DNV, KR, LR, RINA, RS, IRS, PRS, CRS) operate the bulk carrier rules under the IACS unified framework. Each society’s bulk carrier rules incorporate:

• IACS Common Structural Rules (CSR) for new bulk carriers above 150 m.
• IACS Unified Requirements (UR S series) for hatch covers, transverse bulkheads, fore-end strengthening, and other bulk carrier-specific structural elements.
• IACS Unified Requirements (UR Z series) for the Enhanced Survey Programme.
• Society-specific rules for cases not covered by IACS unified requirements (typically smaller bulk carriers below 150 m, specialty designs, or cases where the IACS unified requirements have not yet been updated).

The classification society conducts the periodic surveys, witnesses the loading instrument approval, audits the operator’s compliance with Chapter XII, and issues the Class Maintenance Certificate that is required for the SOLAS certificate to remain valid. Loss of class (suspension or withdrawal) renders the SOLAS certificate invalid and prevents the ship from sailing.

Cargo hold preparation and inspection

Each cargo hold must be prepared between cargoes to a state suitable for the next cargo. Preparation includes:

• Cleaning: removal of residue from previous cargo, with intensity scaled to the contamination tolerance of the next cargo. For grain following coal, the cleaning standard is “grain clean” (visually clean, no residual coal). For higher-purity cargoes (e.g. food-grade soybean meal, pet food ingredients), cleaning may extend to “hospital clean” requiring chemical sanitisation.
• Drying: removal of moisture from cleaning operations. Some cargoes are sensitive to residual moisture (cement, soda ash, lime).
• Coating inspection: examination of hold coating for damage, peeling or absence. Coating damage allows corrosion and contamination.
• Bilge well inspection: clearance of strums and bilge piping.
• Hold integrity test: water-hose test of hatch covers and ventilation closures, verifying weather-tight integrity.
• Pest fumigation: where required by the next cargo or by destination biosecurity rules.

The hold preparation is documented in a hold preparation log, with each cleaning step signed off and the final state verified by master, chief officer or independent surveyor. The log is required by many cargo claim defenses and is checked at PSC inspection.

Bulk carrier crew training

Bulk carrier crew training is concentrated through:

• STCW Section A-V/2: Familiarisation training for masters, officers and ratings on bulk carriers, covering bulk cargo operations, IMSBC Code, loading procedures, hatch cover operations.
• Bulk carrier-specific simulator training: many maritime training institutions operate bulk carrier loading simulators with real-time stress and stability calculation, supporting officer training in loading sequence management.
• Iron ore and coal trade-specific orientation: operators with concentrated trade in specific commodities provide cargo-specific training in addition to the general STCW requirements.

The training is documented in seafarer endorsements and is verified at PSC inspections.

Modern bulk carrier evolution

Size classes

The world bulk carrier fleet is segmented by size class, each with characteristic trades and structural design constraints:

• Handysize (10,000 to 35,000 DWT): smallest class, geared (with own cargo cranes) for terminals without shore-side cargo handling. Wide trade flexibility.
• Handymax / Supramax / Ultramax (35,000 to 65,000 DWT): mid-size geared bulk carriers, the workhorse of the global trade.
• Panamax (65,000 to 85,000 DWT): sized to fit the original Panama Canal locks (gone since the 2016 expanded canal).
• Kamsarmax (80,000 to 90,000 DWT): a Panamax variant optimised for the bauxite trade ex-Guinea.
• Post-Panamax / New Panamax (85,000 to 120,000 DWT): post-2016 expanded Panama Canal optimisations.
• Capesize (120,000 to 220,000 DWT): too large for the Panama Canal (pre-expansion) and Suez Canal (typically), routed via Cape of Good Hope or Cape Horn for ore and coal.
• Newcastlemax (180,000 to 210,000 DWT): sized to fit Newcastle (Australia) coal terminals.
• Very Large Ore Carrier (VLOC) (200,000 to 320,000 DWT): purpose-built for iron ore.
• Valemax (380,000 to 400,000 DWT): the largest class, built specifically for the Vale ore trade from Brazil.

Each size class has size-dependent regulatory implications. Chapter XII applies to all bulk carriers above 150 m, which includes all classes from Handymax up. Below 150 m (rare for new construction), the chapter’s structural and damage stability provisions do not apply, but the loading instrument and water-level detector provisions extend down to 80 m for existing ships under specific Regulation 8.

Energy efficiency and decarbonisation

Modern bulk carriers are subject to multiple energy-efficiency regulations operating alongside Chapter XII:

• EEDI (Energy Efficiency Design Index, mandatory under MARPOL Annex VI for new builds since 2013): structural design implications for hull form optimisation.
• EEXI (Energy Efficiency Existing Ship Index, mandatory since 2023): retrofit measures including engine power limitation (EPL) on existing ships.
• CII (Carbon Intensity Indicator, annual ratings since 2023): operational efficiency rating with implications for charter market.
• FuelEU Maritime (regional EU regulation, in force from 2025): well-to-wake greenhouse gas intensity reduction.

The energy-efficiency requirements interact with structural design under Chapter XII when ship modifications (slow-steaming, engine power reduction, alternative-fuel retrofitting) affect the structural design loads.

Alternative fuels

Bulk carriers are slowly adopting alternative fuels:

• LNG-fuelled bulk carriers: small but growing fleet, mainly newer Capesize and VLOCs.
• Methanol-fuelled bulk carriers: pilot vessels in operation since 2023, with a small fleet under construction.
• Ammonia-fuelled bulk carriers: commercial vessels expected from 2026 onward as the supply chain matures.
• Wind-assisted propulsion: rotor sails (Norsepower) and rigid sails on a small fleet of bulk carriers, with measured fuel savings of 5 to 15 percent depending on route.

The IGF Code (under Chapter II-1 Part G) governs these installations, with structural and machinery implications under Chapter XII.

Smart ship and digital technology

Recent bulk carrier construction increasingly incorporates digital technology:

• Hull stress monitoring: real-time strain gauges on critical structural details with continuous data logging and alarm.
• Vibration and shock monitoring: detection of unusual vibration patterns that may indicate developing structural fatigue.
• Cargo monitoring: temperature, moisture, gas concentration sensors throughout cargo holds.
• Predictive maintenance: data-driven prediction of structural and machinery component failures.
• Voyage data optimisation: integration of voyage planning with weather routing, fuel consumption, structural stress and cargo conditions.

These technologies are not yet mandatory but are being progressively adopted as cost-effective additions to the regulatory baseline.

Bulk carrier port state control practice

PSC inspections of bulk carriers focus heavily on Chapter XII compliance:

• Hatch cover condition: inspection of plating, stiffeners, securing, seals.
• Cargo information (under Regulation 10 cross-referenced to Chapter VI): verification of shipper declarations and master’s confirmation of moisture content for Group A cargoes.
• Loading instrument: verification that the loading computer is approved, tested and used for the actual voyage’s loading.
• Water level detectors: operational test of detectors with documentation of test results.
• Enhanced Survey Programme records: review of close-up survey reports.
• Hold inspection: visual inspection of cargo hold structure, with thickness measurement at randomly selected locations.
• IMSBC Code: verification that the code copy on board is current and that the schedule for the actual cargo has been reviewed.
• Forward bulkhead and bulkhead access: inspection of forward bulkhead integrity and accessibility.
• Crew training records: verification of bulk carrier-specific training and STCW certificates.

Major PSC regimes (Paris MOU, Tokyo MOU, USCG, AMSA, China MSA) maintain bulk carrier-specific inspection campaigns at intervals (typically every 3 to 5 years), with bulk carriers selected for intensive inspection based on age, casualty history, operator profile and PSC database flags.

Hatch cover engineering in detail

IACS UR S21: Hatch cover loading

The IACS Unified Requirement S21 specifies the design loads for bulk carrier weather-deck hatch covers:

• Design wave height scaled to ship size and intended trade area, with a 25-year return period.
• Hydrodynamic load from green seas: a vertical pressure on the cover combined with a horizontal racking load on the cover edges.
• Static cargo load if cargo is stowed on the cover (typical for forest products, certain steel cargoes).
• Snow and ice load for ships in cold trades.
• Personnel load for surveyors and crew working on the cover (1500 N/m² distributed plus a point load).

The cover must satisfy:

• Yield criterion: maximum stress in plating and stiffeners less than 95 percent of yield.
• Buckling criterion: plate panels and stiffeners free from buckling under the design loads.
• Deflection criterion: maximum deflection less than typically 0.0056 of the supported span (about 1/180 ratio).
• Fatigue life: 25 years under spectrum loading.

The IACS UR S21 hatch expansion calculator computes the structural verification.

IACS UR S26: Hatch securing

Securing arrangements use a combination of:

• Compression seals between cover and coaming, providing watertight integrity under static and dynamic conditions.
• Cleating mechanisms (manual or hydraulic) at each cover panel edge.
• Side-mounted retaining bars preventing horizontal slip of the cover relative to the coaming.
• End cleats at the fore and aft ends of each cover.

The IACS UR S26 specifies the strength of each securing element, with the sum of securing forces sufficient to withstand the worst-case design wave load. The IACS UR S26 hatch calculator computes compliance.

Transverse bulkhead design

The transverse bulkhead between cargo holds is a critical structural element. Specific design considerations:

• Plate scantlings sized for the head of water from the most severe damage scenario (typically full hold flooded to bulkhead deck with adjacent hold dry).
• Vertical web frames providing flexural support.
• Lower stool: triangular structure at the bottom of the bulkhead transferring loads to the double bottom and providing local stiffness.
• Upper stool: similar structure at the top.
• Cross-flooding penetrations (where used): maintained tight against accidental flooding while permitting controlled cross-flooding for damage stability.
• Inspection accessibility: permanent ladders and platforms for the Enhanced Survey Programme.

Post-Derbyshire, the IACS Unified Requirement UR S20 specifies the strength of forward transverse bulkheads on bulk carriers. UR S22 covers the bulkhead between forward holds with adjacent hopper structure.

Hopper and topside tank structure

The cargo hold of a typical bulk carrier has hopper sloping plates at the bottom corners and topside (wing) tanks above. These structures serve multiple functions:

• Hopper: sloping plates funnel cargo to the centreline of the hold for efficient discharge by grab or pneumatic. They also form ballast tanks below the cargo hold.
• Topside tanks: wing tanks at the top of each hold, used for ballast and providing structural stiffness to the upper deck.

The hopper-to-bulkhead junction is a high-stress detail subject to corrosion (cargo abrasion and salt water ballast). It is one of the principal close-up survey targets under the Enhanced Survey Programme.

VLOC conversion analysis post-Stellar Daisy

The conversion question

The MV Stellar Daisy (2017) was a Very Large Ore Carrier converted from a tanker (VLCC) in the early 2000s. The conversion involved:

• Removing the tanker’s cargo tank arrangement.
• Installing bulk carrier holds with hopper and topside tanks.
• Reinforcing the structure for ore loading.

After the casualty, the IACS reviewed the conversion methodology and concluded that:

• The structural fatigue life calculation for converted ships had been overly optimistic, not accounting for the high cyclic loading of ore-carrier service.
• The cargo hold design, although adequate for the planned cargoes, had not anticipated the load cycles induced by Cape-route trans-Atlantic voyages.
• The post-conversion survey programme had been less rigorous than for new-build ships.

The post-Stellar Daisy IACS amendments (UR Z32 and related) tightened:

• The structural analysis methodology for conversions.
• The post-conversion enhanced survey scope and frequency.
• The acceptance criteria for converted ships entering high-cycle ore service.

The future of converted ships

The bulk carrier industry has progressively moved away from large-scale tanker-to-bulker conversions, with most major operators preferring purpose-built ore carriers (Newcastlemax, Valemax, etc.) for the very large size class. Smaller-scale conversions (chemical tanker to product tanker, container ship to multipurpose) remain economic for certain markets but are subject to the same post-Stellar Daisy enhanced scrutiny.

Bulk loading terminal operations

Iron ore terminal practices

The major iron ore export terminals (Port Hedland, Dampier, Saldanha Bay, Tubarão, Ponta da Madeira, Rizhao, Qingdao) use coordinated practices that interact with Chapter XII compliance:

• Pre-arrival ship inspection: terminal staff verify the ship’s hatch covers, holds, and loading manual before berthing.
• Cargo loading sequence: developed jointly between master and terminal, with specific intermediate-stage stress checkpoints.
• Loading rate: typically 6,000 to 12,000 tonnes per hour from a single shiploader, with multiple shiploaders working in parallel on the largest ships.
• Trim and draught: managed throughout loading to keep the ship in even-keel condition (or in commercially-required pre-departure trim).
• Shipment surveys: independent draught surveys (and sometimes hold surveys) at start and end of loading to verify cargo quantity.

The high loading rate combined with the structural sensitivity of the bulk carrier makes Chapter XII’s loading-instrument requirement (Regulation 11) particularly important: the ship’s loading computer must keep up with the actual loading and alert the crew if any intermediate stage approaches stress limits.

Coal terminal practices

Coal terminals (Newcastle Australia, Richards Bay South Africa, Hampton Roads USA, multiple Indonesian terminals) operate with similar high-rate loading. Specific coal-related considerations:

• Self-heating monitoring: stockpile temperature monitoring before loading; cargo temperature monitoring during voyage.
• Methane release: cargo space ventilation arrangements during loading and immediately after to dissipate methane release.
• Hold preparation: cleanliness from previous cargo, especially if previous cargo was dangerous or reactive with coal.

Grain terminal practices

Grain terminals (USA Gulf Coast, Pacific Northwest, Argentina Rosario, Brazil Paranaguá and Santos, Ukraine Odesa, France La Rochelle) operate with much smaller loading rates (typically 500 to 2,000 tonnes per hour) due to the lower density of grain compared with ore or coal. Grain operations are governed by the Grain Code (Chapter VI Part C) and require:

• Document of Authorization verification before loading.
• Stability calculation with assumed grain shift.
• Trimming to the maximum extent practicable.
• Strapping or saucers for partially-loaded compartments where stability margin is marginal.

Insurance and P&I dimensions

Bulk carrier safety has significant insurance and P&I (Protection and Indemnity) dimensions:

• Hull and machinery insurance: covers physical damage to the ship. Bulk carrier H&M premiums are sensitive to the operator’s compliance record, age of fleet, and specific casualty experience.
• P&I clubs: cover third-party liability including cargo claims, crew injury, pollution, wreck removal. The 13 IG P&I clubs collectively insure approximately 90 percent of world ocean-going tonnage. P&I clubs have been particularly active in driving Chapter XII and IMSBC compliance because cargo liquefaction casualties produce very large claims (vessel total loss plus cargo loss plus crew injury claims).
• War risks insurance: covers ship and cargo against war and terrorism. Bulk carriers in piracy-affected regions (Gulf of Aden, West Africa) require additional war risk premium.
• Loss of hire (LoH) insurance: covers loss of charter income from defined casualty events.

The post-2015 cluster of bulk carrier liquefaction casualties led to specific P&I club initiatives:

• Intercargo Casualty Reports: annual analysis of bulk carrier losses, distributed to operators and to P&I clubs.
• P&I club guidance: detailed practical guidance on Group A cargo verification, master’s authority, and loading procedures.
• Premium differentiation: operators with poor compliance records face higher premiums or refusal of coverage.

Documentation

Every bulk carrier covered by Chapter XII carries on board:

• The Cargo Ship Safety Construction Certificate, with evidence of compliance with Chapter XII alongside Chapters II-1, II-2, VI and others.
• The bulk carrier loading manual.
• The ship’s loading computer with type-approval certificate.
• The Enhanced Survey Programme records under IACS UR Z10.
• The IMSBC Code copy on board.
• The CSS Code copy on board.
• The BLU Manual (recommended).
• Water level detector test records.
• Hatch cover inspection and certificate records under IACS UR S21 and S26.
• Cargo declaration forms for each consignment.
• For converted ships: the conversion engineering analysis and the post-conversion structural survey records.

Related Calculators

• Bulk, Shore Loading Rate Check Calculator
• Hatch Cover Deflection Limit (UR S21) Calculator
• IACS UR S26, Hatch-Cover Design Pressure Calculator
• Hatch Cover Design Pressure (IACS UR S21A) Calculator
• IMSBC, Iron Ore Fines (IOF) Calculator
• IMSBC, Nickel Ore Calculator
• Grain, Cargo Displacement Volume Calculator
• Grain Heeling, Volumetric Heeling Moment Calculator
• Thickness Measurement Intervals (IACS UR Z10) Calculator

See also

• SOLAS Convention parent article
• SOLAS Chapter II-1: Construction, Subdivision, Stability, Machinery and Electrical Installations
• SOLAS Chapter II-2: Fire Protection, Detection and Extinction
• SOLAS Chapter VI: Carriage of Cargoes and Oil Fuels
• SOLAS Chapter VII: Carriage of Dangerous Goods
• Bulk Carrier
• IMSBC Code
• IMSBC Group A Cargoes
• Cargo Securing Manual
• Hull Strength and Longitudinal Bending
• Damage Stability
• Probabilistic Damage Stability
• Classification Society
• ISM Code

References

• IMO, International Convention for the Safety of Life at Sea (SOLAS), 1974, as amended, Chapter XII.
• IMO Resolution MSC.170(79) (2004), Adoption of amendments to SOLAS Chapter XII (water level detectors).
• IMO Resolution MSC.296(87) (2010), Adoption of amendments to SOLAS Chapter XII (harmonised damage stability).
• IMO, International Maritime Solid Bulk Cargoes Code (IMSBC Code), Resolution MSC.268(85), as amended.
• IMO, Code of Practice for the Safe Loading and Unloading of Bulk Carriers (BLU Code), Resolution A.862(20).
• IACS Common Structural Rules for Bulk Carriers and Oil Tankers, current edition.
• IACS Unified Requirements UR S21, S25, S26, S31 (bulk carrier structure).
• IACS Unified Requirements UR Z10.2 (Enhanced Survey Programme for bulk carriers).
• IACS Unified Requirements UR Z10.5 and Z10.7 (Enhanced Survey Programme for oil tankers).
• INTERCARGO Bulk Carrier Casualty Report, annual editions.
• Lord Donaldson Report on the Loss of the MV Derbyshire, 2000.
• IMO Code of Practice for the Investigation of the Casualties and Incidents, Resolution A.849(20).