Bunker Survey Explained: BQS, ROB and Cappuccino Bunkers

Why Bunker Quantities Need Checking

Marine fuel is commonly purchased by mass, expressed in metric tonnes, while conventional tank measurements determine the volume of fuel inside a tank. Converting that volume into mass requires appropriate tank calibration data, temperature measurements and fuel density. Depending on the measurement method, other corrections may also be necessary.

Errors or differences in readings, tank data, temperature, density or measurement procedures can affect the calculated quantity. Even a relatively small discrepancy can have a significant financial impact when hundreds or thousands of tonnes of fuel are involved.

A bunker survey provides an independent record of the measurements and observations made during a delivery. The resulting report can help the parties compare the calculated quantity with the supplier's figures and investigate discrepancies where necessary.

Bunker Survey, BQS and ROB: What the Terms Mean

• Bunker survey: A general term for an inspection or measurement of fuel quantity delivered to a vessel or remaining on board.
• BQS (bunker quantity survey): A survey focused on the quantity of fuel delivered during a bunkering operation. Depending on the agreed scope, it may involve comparing measurements and records from the supplying barge or installation and the receiving vessel. It is also commonly called a bunker delivery survey.
• ROB (remaining on board) survey: A measurement and assessment of the fuel remaining in a vessel's tanks at a particular time. It may be carried out during vessel delivery or redelivery, for inventory purposes or when fuel records need to be checked. See our on-hire and off-hire survey service.
• BDN (bunker delivery note): The supplier's document recording prescribed information about the fuel delivered, including relevant quantity, density and fuel details. For ships subject to the applicable MARPOL Annex VI requirements, the BDN must generally be retained on board for at least three years after delivery.
• Bunker quantity investigation: A closer examination of a quantity discrepancy. Depending on the circumstances, this may involve reviewing tank readings, calibration tables, calculations, delivery records, meter data and the sequence of the operation.

How Bunker Fuel Is Delivered

Bunker fuel can be supplied through different arrangements, depending on the port, vessel and available facilities. Common methods include delivery from a bunker barge alongside the receiving vessel, delivery by road tanker, and delivery through a pipeline from a shore-based terminal.

Each method has different measurement arrangements and potential sources of discrepancy. A surveyor's duties therefore depend on the delivery method, the equipment available, the access permitted and the scope agreed with the appointing party.

How a Bunker Quantity Survey Works

The exact procedure depends on the port, delivery arrangement and agreed scope. A typical bunker quantity survey may include the following steps:

1. Before delivery, the surveyor meets the relevant ship and supplier representatives, reviews the planned delivery and checks the arrangements and access needed for the agreed inspection.
2. The surveyor measures the accessible tanks included in the survey, records the relevant readings and temperatures, and checks for free water where appropriate.
3. Where sampling is included in the agreed scope, the surveyor observes the sampling procedure and records relevant sample, label and seal details.
4. During pumping, the surveyor monitors the operation and records relevant readings, interruptions or changes to the agreed arrangements where practicable.
5. After delivery, the relevant tanks are measured again in accordance with the agreed procedure and applicable operating conditions.
6. The surveyor calculates or reviews the relevant quantities using the available measurement data and records any discrepancy identified between the figures being compared.
7. Relevant documents and calculations are reviewed, and the report records the findings, supporting measurements, observations and sample details included in the survey scope.

How Bunker Quantity Is Calculated

Tank readings are converted to volume using the relevant tank calibration tables, with corrections for factors such as vessel trim and list where applicable. The observed volume may then be corrected to the applicable reference temperature using the appropriate petroleum measurement tables and procedures.

The corrected volume and corresponding fuel density are used to calculate the fuel mass, usually expressed in metric tonnes. For many conventional petroleum fuel calculations, a reference temperature of 15°C is used, but the applicable method and tables depend on the fuel, measurement data and governing procedure. The calculation should follow the relevant contractual or industry requirements rather than assume that one method applies to every delivery.

Density is an important part of the calculation. It may be obtained from supplier documentation, available test results or an appropriate measurement of the fuel sample. The temperature reference associated with the density must be consistent with the calculation method. An incorrect or unsuitable density value can affect the calculated mass even if the tank readings are accurate.

The resulting quantity figures can then be compared with the supplier's declared quantity and other relevant delivery records. The comparison should take account of the measurement methods, available data, operating conditions and any agreed contractual requirements.

Some bunker supply arrangements use a commercial tolerance, with 0.5% cited in industry guidance as a typical figure in certain contexts. However, this is not a universal acceptance limit for every delivery. The applicable tolerance, if any, should be confirmed against the relevant supply contract and agreed measurement procedures.

Cappuccino Bunkers

A cappuccino bunker is an informal industry term for fuel containing entrained air or gas that can create a foam-like appearance. Under certain conditions, this can affect measurements or the apparent volume of fuel during delivery. As the fuel settles and entrained air escapes, tank readings may change, potentially contributing to a difference between the supplier's figures and the quantity calculated from the receiving vessel's measurements.

A surveyor can record the measurements before and after delivery, monitor relevant tank levels during pumping where practicable, and document observations that may help explain a discrepancy. The investigation may need to consider the delivery method, measurement equipment, fuel characteristics and operating conditions. The surveyor's role is to record the evidence and explain the findings within the agreed scope, rather than assume a cause without supporting evidence.

Where a significant discrepancy is suspected, the parties may need to review the measurement records, delivery procedure and other available evidence before determining the likely cause. An independent survey report can help document the facts for further investigation.

Fuel Samples and the Bunker Delivery Note

Quantity is only one aspect of a bunkering operation. Fuel quality may also need to be verified, particularly if a vessel experiences operational problems or the supplied fuel is suspected of not meeting the agreed specification.

Where the applicable MARPOL Annex VI requirements apply, the bunker delivery note is accompanied by a representative fuel oil sample collected in accordance with the relevant requirements and guidelines. The statutory MARPOL sample must be appropriately sealed and signed by the supplier's representative and the master or officer responsible for the bunkering operation, as required by the applicable provisions.

For ships subject to the relevant requirements, the BDN is generally retained on board for at least three years after delivery. The representative MARPOL sample must remain under the ship's control until the fuel has been substantially consumed and, in any event, for at least 12 months from delivery. Applicability and any relevant exceptions should be checked against the current regulations.

A surveyor may observe the agreed sampling procedure, record identifying details and seal numbers, and document the handling of samples within the survey scope. Laboratory analysis is normally required to determine whether the fuel meets specified quality characteristics. A quantity survey report alone does not establish that the fuel complies with every quality requirement.

Mass Flow Meters and Bunker Surveys

Some suppliers use mass flow meters (MFMs) to measure the mass of fuel passing through the delivery system. Unlike conventional tank gauging, which calculates mass from volume and density, a mass flow meter is designed to measure mass flow directly.

The reliability of a meter reading depends on the meter type, installation, calibration or verification status, operating conditions and applicable procedures. The equipment's records and the circumstances of the delivery should be considered when assessing the reported quantity.

Where the equipment and access permit, an independent surveyor can review the available meter records alongside relevant tank measurements, delivery documents and observations. The appropriate checks depend on the equipment, port procedures and agreed survey scope. A meter reading should not automatically be treated as conclusive evidence without considering the circumstances in which it was obtained.

When to Appoint a Bunker Surveyor

A bunker surveyor may be appointed by the buyer, shipowner, charterer or another party, depending on the commercial arrangements. MARPOL Annex VI does not, by itself, impose a general requirement for an independent bunker quantity survey at every delivery. Whether a survey is required or advisable depends on the applicable regulations, port procedures, supply contract, charter party and the parties' operational requirements.

• When the value of a fuel delivery justifies an independent quantity check, particularly where the delivery arrangements or previous experience indicate a risk of discrepancies.
• During vessel delivery or redelivery, when the remaining bunker quantity needs to be recorded or agreed under the applicable charter-party arrangements.
• When previous deliveries have resulted in differences between the vessel's figures and the supplier's declared quantity.
• When the crew needs additional independent support with recording measurements, reviewing documents or observing agreed sampling procedures.
• When a quantity dispute may arise and the parties want a documented record of the readings, calculations, observations and relevant photographs.
• When the buyer, owner or charterer requires an independent report under the supply contract, charter party or another agreed arrangement.

Choosing a Bunker Surveyor

• Relevant experience with the delivery method involved, such as barge, road tanker or shore-terminal supply, and familiarity with the port's procedures.
• Suitable and properly maintained measurement equipment, such as gauging tapes, thermometers and sampling equipment, as required for the agreed scope.
• A clear measurement and reporting method, with readings, relevant corrections, calculations and supporting observations documented in the report.
• Independence from the parties whose quantity figures are being assessed.
• Clear communication with the vessel and supplier representatives before, during and after the operation.
• Availability that matches the expected delivery schedule, subject to confirmation of attendance and access arrangements.

Becoming a Bunker Surveyor

Requirements for bunker surveyors vary by country, port, employer and the type of work undertaken. Some ports or organisations may require specific authorisations, qualifications or training, while individual survey companies may have their own competency standards.

A background in marine engineering, deck operations, petroleum measurement or a related field can be useful. Practical development may include supervised experience in tank gauging, sampling, quantity calculations, documentation and report writing. Anyone interested in this career should check the applicable requirements with the relevant port authority and prospective employers.

Bunker Surveys in Sri Lanka

Bunker survey attendance in Sri Lanka depends on the port, delivery arrangements, operational access and surveyor availability. Services may be arranged for vessels calling at Colombo, Galle, Trincomalee and Hambantota, as well as selected offshore locations, subject to confirmation.

Earndeck Shipping can assist with bunker survey arrangements and prepare reports documenting the measurements, calculations, observations and relevant sample details included in the agreed scope. To discuss a requirement, see our bunker survey service or contact us with the vessel name, port, fuel grade, estimated quantity and expected delivery date.

References and Further Reading

For regulatory requirements relating to bunker delivery notes and representative fuel oil samples, consult the International Maritime Organization's guidance on fuel oil availability and quality under MARPOL Annex VI Regulation 18.

For practical guidance on preventing bunker quantity disputes, see the International Institute of Marine Surveying's guidance on bunker quantity disputes.

Frequently Asked Questions