During opening gauge the fuel could be transferred from high level to a low level (or empty / slack tank) by gravity.
For example a barge may have four tanks 1P/1S, 2P/2S, 3P/3S and 4P/4S.
The opening gauge starts from say aft tanks 4P/4S.
While the gauging is underway, the tank level of 4P/4S could be easily dropped under gravity to a slack or empty tank forward say 1P/1S.
Thus essentially the same fuel quantity is measured twice.
This method is still in use and if not detected the barge can claim that full quantity was delivered to the vessel but the vessel will have a substantial shortfall.
Once the bunkering has commenced it is too late to do anything and it will be virtually impossible to trace the 'missing' fuel.
A thorough investigation will be needed to determine the exact stock control quantity and full disclosure from the supplier which can take many months/years of legal action and still the matter may not be resolved.
The only effective way of dealing with this dubious practice is re-sounding the first tanks before bunkering commences
Remember whenever in doubt or have concerns always issue a letter of protest
Kaivan H. Chinoy is the Founder and Principal Marine Surveyor of AVA Marine Group, owners of Petro
Inspect and The Bunker Detectives.