The Cappuccino effect may be described essentially as the frothing or bubbling effect caused by compressed air blown through the delivery hose. The aerated bunkers when sounded will give the impression that the fuel is delivered as ordered. In fact, after some time when the entrapped air in suspension settles out of the fuel oil, the oil level drops and a shortfall is discovered.

Precautions against Cappuccino Bunkers
Before Fuel Transfer
• During usual gauging of bunker barge tanks, fuel oil from ullage hatches should be visually checked for any foam on the surface.
• Foam may also be detected on the ullage tape.
• If entrained air is suspected on the tape or fuel surface, obtain a sample and pour into a clean glass jar and observe carefully for signs of foam or bubbles. If the suspicion is confirmed,
the Chief Engineer should not start bunkering and should notify the Owners/Charterers immediately.
Identifying Cappuccino Bunkers
• Signs of froth/foam on the surface of the fuel in the barge tanks during opening gauge
• Excessive bubbles on the sounding tape prior to, during and after bunkering
• Bunker hose jerking or whipping around
• Slow delivery rates than those agreed
• Gurgling sound in vicinity of bunker manifold
• Fluctuations of pressure on manifold pressure gauge
• Unusual noises from the bunker barge

During and After Fuel
Transfer Air can also be introduced in the fuel during the pumping period, so it is important to continue gauging the ship’s tanks as air bubbles would be readily seen on the sounding tape. As stripping and line blowing can also introduce air, stripping should only be performed
at the end of the delivery for a short period of time and line blowing kept to a minimum. The ship’s bunker manifold valve should be checked shut before gauging of the ship’s tanks.
Source: London P&I Club