Automated in service and permanent prevention, removal and detection of vessel hull fouling using a sparse network of guided ultrasound sensors (VESSEL CLEAN)

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Hull fouling is the largest contributor to excess fuel consumption and carbon emissions by ships, which can be up to 50% over a year. In spite of a global expenditure of some £6bn pa on fouling prevention and cleaning amongst the global merchant fleet, fouling still costs £8bn pa in additional fuel costs and produces 70m tonnes of additional carbon dioxide. The project goal is to develop an in service automated system for permanent fouling prevention, detection and removal based on a distributed, sparse network of low frequency (~40kHz) active ultrasonic compressional wave sensors embedded in a ship hull. In normal operation, temporary but continuous quasi forced standing waves will be excited throughout the hull, with power sufficient for ultrasound leakage into water from surface antinodes to produce cavitation. Cavitation will remove thin biofilms (i.e. microfouling) and their adhesion surface as fast as they are formed, thus preventing fouling build-up i.e. macrofouling. The frequency will be swept and different parts of the network sequentially excited scan the antinodes through 100% of the hull. This programme will remove biofilm over 100% of the hull and propeller surface, with minimum ON/OFF time for the continuous waves i.e. minimum time averaged power. Periodically, pulsed waves will be excited to detect accidental macrofouling up caused by imperfect biofilm removal, which will then be removed by a temporary increase in the continuous ON/OFF time followed by a return to normal operation. There exists the possibility, to be researched that the intial formation of biofouling can be prevented by ultrasonic force fields at sub-cavitation levels, further reducing the average power consumption.