Bunker quantity checks: how to verify what you receive

Short deliveries are among the most common bunker problems, and most can only be detected while the barge is still alongside. This guide sets out the checks a ship should make before, during and after delivery, and how to record a discrepancy properly.

Why quantity needs checking

Fuel is bought by mass but measured on board by volume. Every step between a sounding tape and a tonnage on the invoice, from tank tables to temperature and density corrections, is a chance for error or manipulation. Small errors in each step add up, and the bill is normally based on the supplier's figures unless the contract says otherwise.

Before delivery

• Sound and record the temperature of every ship's tank that will receive fuel, and of those that should not, so that any unplanned transfer shows up.
• Confirm that the ship's tank calibration tables are valid and updated after any structural change.
• Use sounding tapes and thermometers with valid calibration certificates.
• Board the barge with the barge master and measure all of its tanks, not only those declared for the delivery, including slop tanks.
• Check that the barge's calibration tables carry an official certification stamp, and note any unusual pipework.
• Where a mass flow meter is used, check that its seals are intact, record the totaliser readings and ask for evidence that its calibration is current.
• Agree with the barge master that stripping and air blowing will take place only at the end of the delivery, on the chief engineer's instruction.

Temperature, density and corrections

Observed volume at tank temperature must be converted to standard volume at 15°C using a volume correction factor, commonly from ASTM Table 54B, and then to mass using the density at 15°C and a weight correction factor, commonly from ASTM Table 56. Ship and barge should use the same tables and the same version.

Three points cause frequent disagreement:

• Temperature: an error of a few degrees in a large tank makes a noticeable difference to the corrected volume. Measure at several levels where possible.
• Density: calculations normally use the density stated on the BDN, but only a laboratory test of a properly drawn sample establishes the true density. A BDN density that is higher than the real value overstates the delivered mass.
• Trim and list: take final measurements with the ship as upright and even as practical, and apply accurate corrections where it is not.

As a cross-check, compare the change in the ship's visual draughts before and after bunkering with the mass of fuel supposedly received.

Mass flow meters

A mass flow meter measures the mass of fuel passing through the delivery line directly, which removes many of the corrections described above. Singapore has required approved mass flow metering for marine fuel oil deliveries since 1 January 2017, and for distillates since 1 July 2019. In Singapore, the delivered quantity on the BDN is based on the bunker tanker's meter. The original technical reference, TR 48, was replaced in November 2019 by Singapore Standard SS 648, which adds requirements for multi-meter installations.

A meter does not remove the need for checks. Verify the seals before and after delivery, record the totaliser readings, obtain the meter ticket, and continue manual soundings at intervals during the delivery. Manual readings help detect discrepancies and prevent overfilling.

Cappuccino bunkers and other causes of short delivery

So-called cappuccino bunkers are deliveries in which air or gas has been entrained in the fuel, making it appear to occupy more volume than it really does. When the bubbles settle out, the ship finds less fuel than the soundings suggested. Warning signs include:

• Foam on the fuel surface in barge or ship tanks.
• Bubbles on the sounding tape or bob.
• Gurgling at the manifold, or air escaping noisily from tank vents.
• Unexpected pressure fluctuations at the manifold.
• The hose vibrating, jerking or making unusual noises.

Other common causes include inaccurate or uncertified barge tables, fuel held back in undeclared tanks or pipework, wrong temperatures, an overstated density, and line contents not accounted for. In cold weather, fuel below its pour point may not settle, so soundings do not respond to changes in trim; the fuel needs heating before it can be measured reliably.

If you suspect air entrainment, take photographs or video, record the observations in the engine log book and issue a letter of protest. Once the transfer is complete, the evidence is hard to recover.

The role of an independent surveyor

An independent bunker surveyor measures barge and ship tanks before and after the delivery, witnesses meter readings and sampling, checks the documents and reports the findings to the party that appointed them. Where a discrepancy arises during the delivery, the surveyor can identify its likely cause while the evidence is still available. For shore pipeline deliveries, where the crew cannot see the shore tanks, the surveyor's attendance is especially useful.

Surveyors are most effective when appointed before the barge arrives, with clear instructions on what to measure and report.

Letters of protest and signing the BDN

1. If the chief engineer's figures do not agree with the BDN, do not sign the BDN as if they do. Record the ship's own figures.
2. Issue a letter of protest stating the discrepancy and its likely cause, and ask the barge master to acknowledge receipt.
3. Where appropriate, sign documents only for volume at observed temperature, rather than accepting a corrected mass that cannot be verified.
4. Record the discrepancy in the engine log book and oil record book, and keep official records consistent with the actual quantity on board.
5. Inform owners, operators and charterers promptly in writing, with copies of all measurements, photographs and protests.
6. Check the contract terms. The BIMCO Bunker Terms 2018, for example, require a quantity discrepancy to be noted on the BDN or in a letter of protest, and the claim to be presented to the seller within 14 days of delivery, unless the parties agree a different period.

Making quantity checks routine

These checks take time, but a standard checklist used on every delivery makes them quicker. Atlas Bunkering strongly recommends an independent bunker surveyor on every stem and can arrange one on request, alongside accredited laboratory testing of the delivered fuel.

Questions and answers

Sources

1. Britannia P&I: Bunkering precautions, quantity
2. UK P&I Club: How to reduce bunker claims
3. MPA Singapore Port Marine Circular No. 15 of 2019: mass flow metering for distillates
4. MPA Singapore: SS 648 code of practice for bunker mass flow metering (November 2019)
5. BIMCO Bunker Terms 2018

This guide is general information, not legal or technical advice. Check the current rules and your engine maker's guidance for your vessel.