SeaReadyMaster's Companion

IMSBC Code 07-23 & 08-25 · International Grain Code (MSC.23(59)) · Dewpoint & 3°C Ventilation

IMSBC Bulk Cargo Liquefaction (TML), Grain Stability & Hold Ventilation Guide

Dry bulk cargo carriage is governed by two mandatory SOLAS Chapter VI instruments — the IMSBC Code (Amendment 07-23 mandatory 1 January 2025; Amendment 08-25 via IMO Res. MSC.575(110) voluntary 1 January 2026 and mandatory 1 January 2027) and the International Grain Code (IMO Res. MSC.23(59)) — alongside strict P&I and RightShip RISQ 3.2 standards for cargo hold ventilation.

Complementing our Draft Survey Calculation Guide and IMO BLU Code Ship/Shore Checklist, this guide covers Group A liquefaction (`TML` vs `MC` and the `Can Test`), Group B self-heating coal and DRI, Grain Code heeling moments (`≤ 12°`, `≥ 0.075 m·rad`, `GM₀ ≥ 0.30 m`), and the Dewpoint vs Three-Degree (`3°C`) ventilation rules.

Updated · Written by SeaReady in our own words. Not affiliated with OCIMF, RightShip, CDI, any MoU or any administration — always check the current official documents.

1. IMSBC Code Cargo Groups (A, B & C) and International Grain Code Summary

Before accepting any bulk cargo fixture or signing the BLU Code Ship/Shore Safety Checklist, the Master and Chief Officer must verify the shipper’s BCSN (Bulk Cargo Shipping Name) and cargo declaration (`SOLAS VI/2` & `IMSBC § 4.2`) against the four statutory categories:

IMSBC Code Groups A, B and C (Res. MSC.539(107) / MSC.575(110)) and International Grain Code (Res. MSC.23(59)).
Statutory Category & CodeMandatory Thresholds & CertificatesOperational & Vetting Controls
IMSBC Code Group A (Cargoes Which May Liquefy or Undergo Dynamic Separation)TML = 90% of Flow Moisture Point (FMP); shipper MC certificate ≤ 7 days old (IMSBC § 4.3.2)Includes iron ore fines (Group A), nickel ore, bauxite (Group A), mineral concentrates, and coal slurry. Actual Moisture Content (MC) must be strictly below the certified Transportable Moisture Limit (TML) unless carried on a specially constructed/fitted cargo ship (§ 7.3) or under a specially approved Bauxite/Iron Ore Fines schedule.
IMSBC Code Group B (Cargoes Possessing Chemical Hazards — MHB / IMDG Class)SOLAS VI/2 & VII/7-1 Document of Compliance for Dangerous Goods (DoC-DG)Includes Coal (Group B or Group A and B — self-heating > 55°C and methane CH₄ > 20% LEL), Direct Reduced Iron (DRI A, B & C — N₂ inerting and H₂ < 1% LEL), Seed Cake, Ammonium Nitrate Fertilizers, Wood Pellets, and Metal Sulphide Concentrates.
IMSBC Code Group C (Cargoes Which Neither Liquefy Nor Possess Chemical Hazards)Trimmed per IMSBC § 5 to prevent shifting; verify high-density tank-top load limit (t/m²)Includes Group C iron ore, lump bauxite, cement, sand, silica, and scrap metal. High-density cargoes (stowage factor ≤ 0.56 m³/t) require sheer-strake/tank-top local point-load verification and SOLAS XII/12 water-ingress alarm readiness.
International Grain Code (IMO Res. MSC.23(59) / SOLAS Ch. VI Part C)Heel ≤ 12°; Residual Dynamic Area ≥ 0.075 m·rad; Initial GM₀ ≥ 0.30 mApplies to wheat, maize (corn), oats, rye, barley, rice, pulses, and seeds in bulk. Requires an onboard Document of Authorization (§ 3), Grain Loading Stability Booklet, and volumetric heeling moment verification for filled and partly filled compartments (§ 7).

2. Group A Liquefaction Defence: TML, 7-Day Moisture Certificate & Can Test

Cargo liquefaction and dynamic separation of Group A mineral concentrates, nickel ore, iron ore fines, and bauxite remain a primary cause of sudden bulk carrier capsize:

  • Transportable Moisture Limit (`TML`) & 7-Day Sampling Rule (`IMSBC § 4.3.2`): The shipper must deliver a signed certificate stating the cargo’s TML (tested within 6 months) and actual Moisture Content (`MC`) sampled no more than 7 days prior to loading. If rain or snow falls on uncovered stockpiles or barges between sampling and loading, the Master must demand re-sampling and re-testing before loading continues.
  • Complementary Shipboard Can Test (`IMSBC § 8.4`): Deck officers should perform and log regular Can Tests on each barge or stockpile lot (tapping a half-full 0.5–1.0 L cylindrical metal can 25 times against a hard surface from a height of 10–20 cm every 1–2 seconds). If free water or a glossy fluid surface appears, suspend loading of that lot immediately, notify the P&I Club and Company DPA, and require laboratory verification.
  • Weather Precautions & Bilge Pumping During Voyage: Never load Group A cargoes during precipitation unless the cargo is already well below TML and approved in writing. Keep hatch covers closed when rain threatens, sound hold bilges daily, and pump out any free water draining to the bilge wells.

3. International Grain Code (MSC.23(59)): Heeling Moments & Stability Criteria

Under SOLAS Chapter VI Part C and the International Grain Code, free-flowing bulk grain settles by roughly 2% of volume during a sea passage, creating void spaces under the deckhead that allow grain to shift transversely (15° in filled trimmed compartments; 25° in untrimmed/partly filled surfaces):

  • Volumetric Heeling Moment (`VHM`) & Vertical Shift Factor: For every hold, look up the Volumetric Heeling Moment (m⁴) from the ship’s approved Grain Loading Stability Booklet, apply the required vertical shift factor (1.06 for filled trimmed compartments, 1.12 for filled untrimmed ends or partly filled compartments), and divide by the cargo’s Stowage Factor (`SF`, m³/t) and displacement (Δ) to obtain the grain heeling lever λ₀ = Σ(VHM × factor) / (SF × Δ) (with λ₄₀ = 0.8 × λ₀).
  • Three Mandatory Grain Stability Limits (`Section A 7`): Verify in SeaReady’s Grain Stability Calculator that across departure, intermediate, and arrival conditions: (1) Angle of Heel ≤ 12° (or deck-edge immersion if smaller); (2) Residual Dynamic Area ≥ 0.075 metre-radians up to 40°, the angle of maximum difference, or the down-flooding angle θ_f; and (3) Corrected Initial GM₀ ≥ 0.30 m.
  • Securing Partly Filled Compartments: Unless the vessel’s Grain Loading Booklet is explicitly approved for untrimmed or multiple slack holds (which most modern bulk carriers are), partly filled holds must be levelled and secured by overstowing or strapping/lashing per Part B of the Grain Code.

4. Cargo Hold Ventilation: Dewpoint Rule vs Three-Degree (3°C) Rule

Use SeaReady’s Cargo Ventilation Calculator to log ambient and hold psychrometric readings and apply the correct rule for your cargo type:

Hygroscopic vs non-hygroscopic cargo ventilation rules, IMSBC Coal ventilation and MSC.1/Circ.1264 fumigation.
Cargo Type & ExamplesPrimary Condensation RiskMandatory Ventilation & Gas-Testing Rule
Hygroscopic Bulk Cargoes (Grain, Soya Beans, Coffee, Cocoa, Timber, Bagged Agricultural Goods)Cargo Sweat Risk (Cold → Warm voyage)Retain inherent moisture; warm moist ambient air blown onto cold cargo condenses directly on the cargo. Ventilate ONLY when the outside air dewpoint is LOWER than the cargo hold dewpoint (or, if dewpoint tables/sensors are unavailable, when outside dry-bulb temperature is at least 3°C cooler than cargo temperature — the "Three-Degree Rule").
Non-Hygroscopic Cargoes (Steel Coils, Canned Goods, Machinery, Dry Minerals)Ship Sweat Risk (Warm → Cold voyage)Do not emit inherent moisture, but warm humid hold air condenses on cold hull steel and drips down from deckheads when seawater cools rapidly. Ventilate vigorously when outside air dewpoint is LOWER than hold dewpoint to purge moist air before hull plating cools.
Coal Cargoes (IMSBC Code Coal Schedule — Group B / Group A & B)Surface Ventilation First 24h Only; Then Sealed unless CH₄ > 20% LELConduct surface ventilation for the first 24 hours after departure to disperse initial methane release, then stop ventilation unless methane exceeds 20% LEL or scheduled gas sampling requires purging. Never force air into the body of a coal stow (triggers spontaneous self-heating; monitor CO > 50 ppm and hold temperature > 55°C).
In-Transit Fumigated Cargo Holds (IMO MSC.1/Circ.1264 — Phosphine PH₃)Strictly Prohibited Until Gas-Free Certificate Issued at Discharge PortSeal hold ventilators and access hatches with warning signs, test adjacent accommodation and engine-room spaces every 4–8 hours with a calibrated Phosphine (PH₃, TLV 0.3 ppm) detector, and verify respirator canisters on board.

Questions seafarers ask

What is the difference between TML, FMP, and the shipboard Can Test under the IMSBC Code?

Under the IMSBC Code (2025 Edition / Amendment 07-23 mandatory 1 Jan 2025, Amendment 08-25 MSC.575(110) voluntary 1 Jan 2026 and mandatory 1 Jan 2027), the Flow Moisture Point (FMP) is the percentage moisture content at which a Group A cargo begins to lose shear strength and flow like a liquid, while the Transportable Moisture Limit (TML) is set at 90% of the FMP. The shipper must provide a signed declaration and laboratory moisture content (MC) test certificate sampled within 7 days before loading (§ 4.3.2), and re-tested after any rain. The shipboard Can Test (§ 8.4 — tapping a half-filled 0.5–1.0 L cylindrical can 25 times from 10–20 cm onto a hard surface every 1–2 seconds) is a complementary check: if free moisture or a wet fluid surface appears, loading must stop for laboratory re-testing, but a "pass" on the can test never proves a cargo is safe if the laboratory MC exceeds TML.

What are the three mandatory stability criteria under the International Grain Code (SOLAS Chapter VI Part C)?

Under Section A 7 of the International Code for the Safe Carriage of Grain in Bulk (IMO Resolution MSC.23(59)), after accounting for free-surface effects in slack liquid tanks, the ship’s intact stability throughout the voyage must demonstrate: (1) an angle of heel due to the assumed shift of grain of not greater than 12° (or the angle of deck-edge immersion, whichever is less); (2) in the statical stability diagram, a net or residual area between the grain heeling arm curve and the righting arm (GZ) curve up to the angle of maximum difference between the ordinates of the two curves, or 40°, or the angle of flooding (whichever is least), of not less than 0.075 metre-radians; and (3) an initial metacentric height (GM0) of not less than 0.30 m.

When should deck officers use the Dewpoint Rule versus the Three-Degree Rule for cargo hold ventilation?

The Dewpoint Rule (ventilate whenever the ambient outside air dewpoint is lower than the cargo hold dewpoint) is always the primary scientific rule when both outside and inside wet-bulb and dry-bulb temperatures can be measured accurately. The Three-Degree Rule (ventilate a hygroscopic cargo when the outside dry-bulb temperature is at least 3°C below the cargo temperature recorded at loading) is used when entering holds to read inside wet/dry bulb temperatures is unsafe or impractical during the voyage.

Why do RightShip RISQ 3.2 inspectors and P&I surveyors scrutinise cargo hold ventilation and bilge logs?

Soybean, grain, and steel-coil sweat claims are among the costliest dry-bulk P&I cargo claims worldwide. Under RightShip RISQ 3.2 Chapter 8 and P&I Club loss-prevention standards, inspectors verify that the bridge keeps a continuous 4-hourly or watch-by-watch Cargo Hold Ventilation & Bilge Sounding Log recording UTC/position, ambient dry-bulb/wet-bulb/dewpoint, hold temperature/dewpoint, sea temperature, weather/spray restrictions, ventilation status (ON/OFF with reason), and daily hold bilge soundings.

Open the Grain Stability & Hold Ventilation Calculators in SeaReady

Run International Grain Code heeling-moment checks, Dewpoint / 3°C hold ventilation logs, and Draft Surveys — 100% offline in SeaReady.

  • Offline SIRE 2.0, RightShip RISQ and PSC checklists
  • AI mock inspector and orals examiner
  • AI photo review of defects and ship-work photos
  • Rest-hour planner and record-book tools
Start your 14-day free trial See plansOpen this tool in the app

Crew $39.99/mo · Officer Pro $99.99/mo · Ship licence $899/mo per ship + 5% sales tax

14-day free trial, no card needed. Works offline at sea once installed.

Related guides

All 68 guides →