Measurement uncertainties

Bunker disputes are frustrating, time consuming and largely avoidable. Unfortunately, they are all too frequent. One of the most common causes of fuelling disagreements is a discrepancy between the amount of fuel that is believed to have been bunkered and the amount invoiced. So what can vessel operators do to ensure they get what they pay for?

Measurement uncertainties

Even the most careful use of traditional manual tank dipping can be subject to error when measuring the quantity of fuel that has been delivered on board. Measurements can be compromised by changing weather conditions causing vessel movement, discrepancies in ship/tank geometry and inaccurate tank dips. In addition, complex calculations related to temperature, level and volumetric conversion are susceptible to human error.

The most common measurement issue, regularly reported in the media, is known as the ‘Cappuccino Effect’. This results from compressed air being injected into the fuel via the transfer pump or supply hose during the transfer. It can also occur as a result of the barge adding compressed air into its tanks to increase the apparent volume of the fuel before its transfer.

Bunkering best practice  

Fortunately, there is a way to reduce these uncertainties. An independently accredited mass flow metering system (MFMS) can help to calculate the amount of fuel delivered. This can help vessel operators to ensure they get what they pay for when bunkering.

The system uses the Coriolis-effect to constantly monitor and accurately measure the mass, not the volume, while the meters measure the density and temperature of fuel deliveries. This enables a MFMS to detect any water or air going through it and compensates accordingly.

Additional benefits  

A MFMS can save up to three hours per delivery* compared with traditional tank dipping, which can translate into significant financial and resource savings. Additionally, a MFMS can provide vessel operators with an automated process, making the system easier to use, more transparent and less susceptible to error.

In order to ensure that you gain all of these benefits it is important that you work with a supplier using an accredited MFMS, certified by a reputable, independent agency.

In ports where a MFMS is not available, there are a number of steps that can be taken to verify the correct quantity:

  • Check the sounding of the barge tanks before and after bunkering to confirm the tank quantities.
  • Check the fuel temperature prior to the transfer so that the volume can be corrected and mass calculated. Temperatures should be taken at the top, middle and bottom of the bunker barge tanks, and an average calculated for each tank.
  • Check that the density values are accurate.

ExxonMobil operates accredited MFMS’s in Hong Kong and Singapore. This technology offers vessel operators proven levels of integrity, security and efficiency for fuel quantity measurement. Bunkering has never been more consistently accurate, transparent and secure.

*Comparison versus manual tank dipping.