A common performance killer is hull and propeller fouling. A recently published study by IMO [1] indicates that biofouling can increase the Greenhouse Gas Emissions by around 10% in case of light slime, and by up to 40-50% in case of heavy fouling. The increase in GHG emissions is an outcome of the vessel’s increased fuel consumption. A common approach, followed by many shipping companies, is to clean the vessels' hull and propeller on a regular basis, without having any information regarding the actual condition of the hull. That is a first step forward, but it is definitely not the ideal solution, since cleaning the hull when it is not needed only has a negative effect, as fouling protection will deteriorate faster. Spliethoff is going a step further and implements a condition-based approach by monitoring the actual condition of the hull. Hull condition monitoring is a complex task, due to the dynamic environment in which the vessel operates. The vessel’s fuel consumption is affected by many parameters – speed, draft, trim, weather, etc – and that adds complexity when we come to the point where a decision has to be made. This is where the vessel’s digital twin comes into play. By making use of the digital twins, the data collected from the in-house developed monitoring tool are analysed and provide us with actionable information. This way a decision can be made based on the actual condition of the hull, and thus make sure that a hull cleaning will be arranged only when it is really needed.