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ASTM D1250 Tables 54A/54B · API MPMS Ch. 17.9 VEF · IGC Code Ch. 15 (MSC.370(93))

Tanker Ullage, Trim/List Correction, ASTM VCF & Liquefied Gas Cargo Calculation Guide

Accurate ullage-to-weight cargo calculations on oil, chemical, LPG, and LNG tankers are verified at every load and discharge port by independent cargo surveyors and audited during SIRE 2.0 Chapter 8 and CDI inspections.

Complementing our ISGOTT 6 Ship/Shore Safety Checklist Guide and Bunkering & Fuel Changeover Checklist, this guide walks step by step through trim and list ullage corrections, ASTM D1250 / API MPMS Chapter 11.1 `VCF` (`Tables 54A/54B/54C/54D`), Weight in Air vs Vacuum (`-0.0011 kg/L`), Vessel Experience Factor (`VEF`), and IGC Code Chapter 15 (`98%` filling limit & liquid + vapour mass).

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. Five-Step Oil & Chemical Tanker Ullage-to-Weight Calculation

Every oil and chemical tanker cargo calculation follows the five-step sequence from Observed Ullage to Metric Tonnes in Air and Vacuum:

Standard oil and chemical tanker cargo calculation sequence (ASTM D1250 / API MPMS Ch. 11.1 & Ch. 17.9).
Calculation StepStandard Formula & ASTM TableOperational & Vetting Verification
1. Observed Ullage & Interface Sounding (UTI)Closed restricted/vapour-lock UTI gauge (SOLAS II-2/4.5.4 & ISGOTT 6)Measure observed ullage (distance from gauge reference point to liquid surface), liquid temperature (upper, middle, lower average), and free-water dip using a calibrated, annually certified portable Ullage-Temperature-Interface (UTI) tape.
2. Trim, List & Tape Thermal CorrectionsApproved Tank Calibration Tables → True Corrected Ullage → TOV (m³)Apply trim correction (from forward/aft perpendicular marks) and list/heel correction from the ship’s class-approved calibration booklet to convert observed ullage into Total Observed Volume (TOV). For unpumpable liquid wedges at departure/completion, apply the Wedge Formula.
3. Free Water Deduction → Gross Observed Volume (GOV)GOV = TOV − Free Water Volume (m³)Subtract the calibrated volume of any free water detected at the bottom of the tank by the UTI interface sensor (or water-finding paste on non-volatile cargoes where closed gauging is not required) to obtain Gross Observed Volume (GOV).
4. Volume Correction Factor (VCF) via ASTM D1250 / API MPMS Ch. 11.1GSV (@ 15°C) = GOV × VCF (Tables 54A / 54B / 54C / 54D)Using the cargo’s Density @ 15°C in Vacuum (kg/m³ or kg/L from Table 53A/53B) and observed tank temperature (°C), enter ASTM D1250 Table 54A (Crude Oils), Table 54B (Refined Products), Table 54C (Special/Chemical Thermal Expansion Coefficient α), or Table 54D (Lubricating Oils) to find VCF and compute Gross Standard Volume (GSV @ 15°C).
5. Weight Conversion Factor (WCF) in Vacuum & Air + VEFMT (Vacuum) = GSV × Density_15°C; MT (Air) = GSV × (Density_15°C − 0.0011)Multiply GSV by standard density in vacuum to obtain Metric Tonnes in Vacuum, or subtract the standard air buoyancy factor (0.0011 kg/L / 1.1 kg/m³ per Table 56) to obtain Metric Tonnes in Air. Compare Total Calculated Volume (TCV) against the Bill of Lading via the ship’s Vessel Experience Factor (VEF per API MPMS Ch. 17.9 / EI HM 49).

2. Trim, List & Wedge Formula Corrections Explained

While the ship’s Class-Approved Tank Calibration Booklet is always the authoritative legal source for tank volumes, deck officers and CoC oral candidates must understand the underlying geometry and cross-check rules (Ullage Trim/List Calculator):

  • Longitudinal Trim Correction (`Δu_trim`): When a tank’s ullage pipe is not at the longitudinal centre of the tank (d_x metres aft or forward of tank mid-length), trim by the stern or head shifts the liquid surface at the gauge point by approximately Δu_trim = Trim × (d_x / LBP). If the gauge pipe is aft of the tank centre and the ship is trimmed by the stern, the liquid pools toward the gauge pipe, making the observed ullage smaller than the true mid-tank ullage (so the trim correction is added to observed ullage).
  • Transverse List / Heel Correction (`Δu_list`): When the ullage pipe is off the tank’s transverse centreline by d_y metres and the ship is listed by angle θ, the transverse correction is Δu_list = d_y × tan(θ) (plus a half-breadth (b/2) × (1 − cos θ) term in calibration tables). Always upright the vessel before final custody-transfer gauging.
  • OBQ / ROB Liquid Wedge Formula: When residual liquid at completion of discharge does not reach the forward bulkhead of the tank, standard full-surface trim tables overstate the volume. Apply the ship’s approved Wedge Tables or the geometric wedge formula using the corrected sounding at the aft bulkhead, trim, LBP, and tank length/breadth.

3. Liquefied Gas Carriers: IGC Code Ch. 15 Filling Limits & Vapour Mass

On LPG, Ammonia, Ethylene, LEG, and LNG carriers subject to the IGC Code (IMO Res. MSC.370(93)), cargo calculations must account for both the statutory 98% filling limit and the mass of cargo in the vapour phase (Liquefied Gas Calculator):

IGC Code Chapter 15 (IMO Res. MSC.370(93)) loading limits and liquefied gas liquid + vapour mass calculation.
Gas Cargo ParameterIGC Code / Custody FormulaChief Officer Verification
Maximum Allowable Loading Limit (LL) — IGC Code Ch. 15 § 15.1.2LL = FL × (ρ_R / ρ_L) where default FL = 98%Under IMO Resolution MSC.370(93) (2014 Revised IGC Code Ch. 15), no cargo tank may be more than 98% liquid-full at the reference temperature (the saturated vapour temperature corresponding to the set pressure of the pressure relief valves MARVS). Consequently, the maximum volume percent to which a tank may be loaded at loading temperature T_L is LL = 98% × (ρ_R / ρ_L).
Liquid Cargo Mass (V_liq × VCF × ρ_liquid)Float/radar level gauge + shrinkage/trim correction + saturated liquid densityApply tank shell thermal shrinkage factor (for cold LPG/Ethylene/LNG tanks) and trim/list corrections to liquid level to obtain liquid volume (m³), then multiply by liquid density at observed liquid temperature (or ASTM/GPA Table 54E / Francis formula VCF to 15°C).
Vapour Space Mass (V_vap × P/T Correction × ρ_vapour)V_vap = V_total_100% − V_liq; Ideal Gas / Molecular Weight DensityUnlike oil tankers, the vapour phase in an LPG, ammonia, ethylene, or LNG tank holds significant commercial mass: Vapour Mass = V_vap × [273.15 / (273.15 + T_vap °C)] × [(P_gauge_bar + P_atm_bar) / 1.01325] × (Molecular Weight / 22.414 kg/m³). Total Cargo = Liquid Mass + Vapour Mass.

4. SIRE 2.0 & CDI Cargo Calculation Inspection Traps

  • Expired UTI Tape & Thermometer Calibration Certificates: SIRE 2.0 and CDI inspectors verify that every portable UTI gauge (and fixed radar tank-gauging system) holds a valid annual shore calibration certificate and is cross-checked against manual dips/temperatures before cargo operations.
  • Unqualified Voyages Included in the VEF Log: Under API MPMS Chapter 17.9 / EI HM 49, voyages involving Ship-to-Ship (STS) transfers, partial loadings without full gauging, or ship/shore ratios outside ±0.0030 (±0.3%) must be excluded when calculating the qualifying Vessel Experience Factor (VEF).
  • High-Level (`95%`) & Overflow (`98%`) Alarms Not Tested Before Loading: Under SOLAS II-2/11.6.3.2, IBC Code Ch. 15.19, and IGC Code Ch. 13.3, independent high-level (`95%`) and high-high/overflow (`98%` ESD) tank alarms must be functionally tested and logged prior to every loading operation.

Questions seafarers ask

What is the difference between ASTM D1250 Table 54A, Table 54B, Table 54C, and Table 54D?

Under ASTM D1250 / API MPMS Chapter 11.1 (metric 15°C tables), Table 54A gives Volume Correction Factors (VCF) for Generalized Crude Oils based on Density at 15°C; Table 54B gives VCF for Generalized Refined Petroleum Products (gasoline, jet fuel, gasoil/diesel, fuel oil); Table 54C gives VCF for Individual and Special Applications (such as petrochemicals) using the cargo’s specific thermal expansion coefficient (alpha_15); and Table 54D gives VCF for Generalized Lubricating Oils. For barrels at 60°F, tankers use Tables 6A/6B (API Gravity) or Tables 24A/24B (Relative Density 60/60°F).

Why do tanker cargo calculations subtract 0.0011 kg/L (1.1 kg/m³) when converting Weight in Vacuum to Weight in Air?

Density reported by shore laboratories (or converted via Table 53A/53B) is Density at 15°C in Vacuum. When cargo is weighed or traded commercially as Weight in Air, Archimedes’ buoyancy of standard air (approximately 0.0011 kg/L or 1.1 kg/m³ in ASTM Table 56) reduces the apparent weight: WCF_air = Density_vac_15°C − 0.0011 kg/L. Always check whether the charter party and Bill of Lading specify Metric Tonnes in Air or Metric Tonnes in Vacuum.

How is the maximum loading limit (LL) calculated under Chapter 15 of the IGC Code for LPG, ammonia, and LNG carriers?

Under Chapter 15 (§ 15.1.1–15.1.2) of the IGC Code (IMO Resolution MSC.370(93)), the maximum Filling Limit (FL) at the reference temperature is 98% of tank volume (so 2% vapour space remains if the tank warms up to the MARVS relief-valve opening pressure). Because liquefied gas expands as it warms from the cold loading temperature (where liquid density is rho_L) to the warmer reference temperature (where saturated liquid density is rho_R), the maximum allowable Loading Limit at loading temperature is LL = 98% × (rho_R / rho_L). Every gas carrier carries a class-approved Loading Limit Curve for each cargo and MARVS setting.

When should a Chief Officer calculate the ROB / OBQ Wedge Formula and issue a Letter of Protest for ship/shore discrepancy?

The Wedge Formula applies only when unpumpable liquid remaining on board (ROB) or on-board quantity before loading (OBQ) does not touch all four bulkheads of the tank (i.e., the trimmed liquid surface intersects the tank bottom forward of the aft bulkhead). If ship vs. shore Bill of Lading figures (after applying the ship’s qualified Vessel Experience Factor VEF under API MPMS Ch. 17.9 / EI HM 49) differ by more than the charter-party / company SMS tolerance (typically 0.3% to 0.5%), the Master and Chief Officer must re-gauge jointly with the independent surveyor and issue a formal Letter of Protest before signing cargo documents.

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