LNG Cargo: A Different Kind of Declaration
LNG cargo declarations bear almost no resemblance to conventional cargo declarations. Where an oil tanker declares product grade and API gravity, an LNG carrier must provide a full compositional analysis of the gas — the percentage of methane, ethane, propane, butane, and nitrogen in the cargo as determined by the load port's custody transfer laboratory. This composition determines the LNG's boiling point, calorific value, density at storage temperature, and boil-off characteristics.
The composition matters for Canal transit because different LNG grades behave differently under the thermal and mechanical stresses of lock operations. U.S. Gulf LNG (typically 95-97% methane) has a lower boiling point and higher boil-off rate than Middle Eastern LNG (which may contain 5-10% heavier hydrocarbons). The ACP reviews the composition to verify that the vessel's declared boil-off management strategy — reliquefaction, gas combustion, or dual-fuel engine consumption — is calibrated for the specific LNG grade aboard.
Required Cargo Documentation
- Certificate of Quality: Load port laboratory analysis showing the full compositional breakdown (methane, ethane, propane, butane, pentane+, nitrogen, CO2), gross calorific value, and Wobbe Index.
- Certificate of Quantity: Custody transfer quantity from the load port metering system, in cubic meters at standard conditions. This is the equivalent of the Bill of Lading for LNG.
- Tank-by-tank cargo inventory: Current liquid level, temperature, and pressure for each cargo tank. Levels must be derived from the vessel's calibrated gauging system.
- 72-hour tank pressure/temperature log: Continuous 72-hour history for each tank demonstrating stable operating conditions. Trends showing rising pressure or temperature require explanation.
- Boil-off gas management plan: Current daily BOG rate, management method, and projected tank conditions at transit time and transit completion.
- Containment system status per tank: CCS barrier condition, any noted anomalies, and interbarrier space monitoring data.
Composition drives everything. A cargo declaration that lists "LNG" without the detailed compositional analysis is immediately rejected. The ACP needs the full breakdown to verify BOG management, assess transit risk, and coordinate with emergency response capabilities. The Certificate of Quality from the load port is not optional — it is the foundation of the entire LNG cargo declaration.
Quantity Verification: Not Like Other Tankers
LNG quantity cannot be verified by draft survey (the method used for bulk carriers) or by conventional tank gauging (the method used for oil tankers at ambient temperature). LNG quantity is determined by cryogenic-rated radar or capacitance gauges that measure liquid level in each tank, combined with temperature and pressure readings to calculate the liquid density at storage conditions. The declared quantity must match the load port's custody transfer Certificate of Quantity. Any discrepancy triggers the same automatic VUMPA rejection as a B/L mismatch on any other vessel type.
Frequently Asked Questions
What must an LNG carrier declare in its cargo declaration?
Cargo composition (methane %, ethane, propane, etc.), per-tank quantities, temperatures, and pressures, 72-hour tank logs, BOG rate and management method, CCS status, Certificate of Quality from the load port, and Certificate of Quantity from custody transfer.
Why does the methane composition matter?
Different compositions have different boiling points, boil-off rates, and behavior under thermal stress. The ACP reviews composition to verify the BOG management strategy is appropriate for the specific LNG grade aboard.
What are tank pressure and temperature logs?
Continuous recordings showing each tank's internal condition over the past 72 hours. They demonstrate stable, safe operating conditions and help the ACP assess whether the gas management system can maintain safe pressures throughout the transit.
How is LNG quantity verified differently?
By cryogenic radar or capacitance gauges plus temperature/pressure calculations, not draft survey or conventional tank gauging. The declared quantity must match the load port's custody transfer Certificate of Quantity exactly.
Validate Your LNG Cargo Documentation
CanalClear cross-checks your cargo composition, tank logs, and BOG declarations against ACP LNG requirements before submission.
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